Changes in mercury content in oysters in relation to sediment and seston content in the Colombian Caribbean lagoons

Changes in mercury content in oysters in relation to sediment and seston content in the Colombian Caribbean lagoons | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Changes in mercury content in oysters in relation to sediment and seston content in the Colombian Caribbean lagoons Anubis Vélez-Mendoza, Jeimmy Paola Rico Mora, Néstor Hernando Campos-Campos, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4725392/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 8 You are reading this latest preprint version Abstract Total mercury was evaluated in the mangrove oyster Crassostrea rhizophorae , in sediments and seston from the Ciénaga Grande de Santa Marta (CGSM) and Cispatá Bay (BhC) in two climatic seasons (rainy and dry). Composite samples of sediments, seston and oysters in juvenile and adult sizes were collected at six stations (three in each ecosystem) and Hg was quantified by atomic absorption spectrophotometry (EPA method 7473 PLTX-017). BhC had the highest Hg concentrations in sediment, seston and oysters compared to CGSM, with values close to the tolerable threshold for the ecosystem and associated biota (TEL) of 0.13 µg/g Hg and with a low risk of Hg contamination in the mangrove oyster. Although at CGSM Hg was below the TEL in sediment and was considered safe in the oyster, significant bioaccumulation was evident with the metal content in the seston, indicating a potential risk to the ecosystem and humans. The variables organic matter and temperature influenced metal availability in the sediment and seston, respectively; in contrast, they had no significant relationship in the oyster. In CGSM, higher [Hg] was recorded in adult sizes, while in BhC the highest accumulation occurred in juveniles, especially during the dry season. These results emphasize the need for continuous monitoring of Hg contamination in both ecosystems. In addition, they highlight the importance of considering the size of oysters when assessing Hg contamination, as they may vary according to specific ecosystem and climatic conditions. Mercury Crassostrea rhizophorae bioconcentration factor pollution index sizes Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Mercury contamination is a global environmental challenge due to its capacity for bioaccumulation and biomagnification in food webs, and its potentially devastating effects on ecosystems [ 1 , 2 ]. Throughout history, catastrophic events linked to metal contamination have been recorded, with the Minamata disaster in Japan being the iconic example for Hg intoxication. This incident, generated by the release of Hg in toxic forms such as methylmercury (CH 3 Hg) into Minamata Bay, left catastrophic after-effects on both the human population and local marine life [ 3 ]. This grim historical episode strongly underscores the dangers of Hg to human health and the environment. Hg contamination represents a significant threat to coastal marine ecosystems. The ability of this element to bioaccumulate and biomagnify in the tissues of organisms means that it can reach dangerous concentrations as it progresses through the food web [ 4 ]. Hg in toxic forms such as CH 3 Hg affects the reproduction of aquatic organisms, with negative effects on the formation and growth of eggs and larvae. It also has serious neurological impacts, altering behaviors such as feeding and predator avoidance [ 5 ]. Bivalves, such as oysters, are vulnerable at the cellular level to Hg, affecting their reproduction, growth and quality of edible tissues for humans [ 6 ]. This phenomenon has generated global concern, prompting the use of indicator organisms, such as bivalves, to assess their presence in marine-coastal ecosystems [ 7 ]. Despite the decrease in Hg levels in bivalves due to stricter regulations, concerns persist worldwide. Colombia, unfortunately, does not escape from this problem, as it is among the countries with the highest per capita Hg contamination in the world, largely due to illegal mining and gold mining [ 8 ]. In Colombia, despite the growing interest in the problem generated by Hg contamination due to illegal mining and gold mining, research on the presence of this metal in bivalves is recent. Studies conducted in areas near Cartagena Bay, such as Brujas Island and Barú Island in Cartagena, as well as in the Marina and Taganga in Santa Marta, have revealed variations in Hg concentrations in the oyster Crassostrea rhizophorae , depending on the climatic season [ 9 ]. In addition, it has been observed that climatic conditions in tropical regions, such as the Colombian Caribbean, as well as changes in physicochemical variables in the water column such as temperature, salinity, pH and dissolved oxygen [ 10 ], and the organic matter content in fine sediments and reducing condictions [ 11 ] can influence the availability of Hg in the environment. The response of bivalves to environmental variables during their life cycle [ 12 ] complicates the understanding of Hg accumulation. In turn, the differences in Hg concentrations between sites highlight [ 9 , 10 ] the need to further understand the factors that influence Hg concentrations in marine and coastal organisms such as the oyster C. rhizophorae , determine the specific sources of contamination, and assess the impacts on local ecosystems in Colombia. This study evaluated Hg contamination in the oyster C. rhizophorae and determined whether environmental variables and oyster size can facilitate Hg bioaccumulation. The research contributes to understanding the dynamics of contamination by this metal in tropical marine and coastal systems. 2. Methods 2.1 Study area The Colombian Caribbean region is characterized by a bimodal climatic regime with a rainy and dry season influenced by the Intertropical Convergence Zone (ITCZ) that generates periodic patterns [ 13 ]. Trade winds predominate from December to April (dry season), changing direction to the southeast between April and November (rainy season) [ 14 ]. The Ciénaga Grande de Santa Marta (CGSM) has an area of 450 km 2 [ 15 ] and was declared a Ramsar Wetland and Biosphere Reserve [ 16 ]. Its body of water is made up of several interconnected lagoons and a sand bar to the northeast of the Ciénaga that separates it from the Caribbean Sea [ 17 ] (Fig. 1 ). The exchange of fresh and brackish water is conducive to the development of the red mangrove Rhizophora mangle , which is essential for the mangrove oyster because it (the mangrove root) provides a substrate for the oysters [ 18 ]. It stands out as one of the most productive tropical ecosystems in the Caribbean, with significant catches of commercial fish, crustaceans and mollusks [ 19 ]. The bay of Cispatá (BhC) was transformed into an estuary as part of the lagoon system of the Sinú River delta. This mangrove-estuarine ecosystem has fine and very fine sediments, largely influenced by the Sinú River [ 20 ]. The estuary covers an area of 130 km 2 covered predominantly by mangroves [ 21 ] (Fig. 1 ), has an average monthly rainfall of 66 mm and an average sediment discharge of 3.1 kg/day. The rainy season from May to November records an average monthly rainfall of 150 mm and a sediment discharge of 11.5 kg/day [ 22 ]. Salinity is influenced by the hydrological dynamics of the ecosystem, fluctuating between rainy seasons, drought and a mixture of fresh and brackish water [ 23 ]. 2.2 Field phase Samples were collected at three stations in CGSM and three in BhC trying to cover sites with gradients of water inflow from the sea and freshwater bodies that may carry contaminants. Sampling was conducted in the rainy season (November 2021) and in the dry season (March 2022). In situ measurements of temperature, salinity, pH and dissolved oxygen were made at a depth of 0.5 m using WTW 3110 and YSI Pro1030 multiparameter probes. Oyster individuals were collected at each of the stations and grouped into juveniles (22.0–32.0 mm) and adults (35.0-56.5 mm) [ 24 , 25 ]. Several specimens of the same category were stored in previously labeled airtight polyethylene bags and transferred preserved in cold (~ 4°C). For the determination of mercury in seston, at each station three replicates of water were collected in 2.8 L amber flasks and stored cold (~ 4°C). After homogenization, they were filtered through two Whatman GF/C glass fiber filters of 47 mm diameter per sample with a manual vacuum pump. They were stored in hermetically sealed polyethylene bags previously labeled, dried in an oven at 45°C for 24 h and weighed on an analytical balance [ 11 ]. At each station, three replicates of sediment were collected with a van Veen dredge. From each unified sample per station, 600 g of sediments were separated to determine mercury, 75 g for organic matter and 75 g for redox potential. Samples were stored in airtight polyethylene bags with silicone scoop avoiding touching the edges of the dredge and kept cold (~ 4°C) [ 11 ]. 2.3 Laboratory phase For the determination of organic matter, 5 g of dry sediment were placed in porcelain crucibles (previously weighed), subjected to calcination in a muffle at 550°C for 5 h and kept in the desiccator for 2 h. The determination of organic matter was based on the difference in dry and calcined weight [ 26 ]. For redox potential quantification, the sediment sample was dried at 40°C for 24 h. 25 g of sediment were taken and homogenized in 50 mL of deionized water using a VELP Scientifica magnetic stirrer for 30 min. Measurement was performed with a YSI Pro1030 multiparameter probe through the oxidation-reduction potential electrode, previously calibrated at a standard temperature of 25°C [ 27 ]. For the chemical analyses, all the material used was previously purged with 5% nitric acid (HNO 3 ) and deionized water for 24 h. With the precaution of not contaminating the samples, gloves and glass and plastic elements were used. The samples were transferred cold preserved (~ 4°C) to the Toxicology and Environmental Management laboratory of the University of Cordoba for Hg quantification. The collected oysters were cleaned to remove any particles adhering to the valves. The anteroposterior length APL (mm) was measured on the inner side of the ventral valve to the mark of the edge of the mantle with a Vernier caliper (precision of 0.05 mm). The soft tissue was then weighed using an analytical balance (0.1 mg accuracy). In each sample composed of organisms of similar size, all soft tissue was removed and deposited in 30 mL glass vials previously washed, labeled and weighed. The soft material was weighed by subtracting the weight of the vial and the samples were lyophilized. From each seston, sediment, and oyster tissue sample, 20 to 40 mg were weighed and subjected to calcination at 450°C with a ramp of 50°C for 8 h. Then, 1 mL of concentrated HNO 3 was added and volatized on a heating plate. Finally, the sample was subjected to microwave-assisted acid digestion at 180°C for 20 min with a volume of 25 mL of distilled water. The fraction less than or equal to 65 µm of sediments and seston was digested with 5% nitric acid (HNO 3 ) for subsequent determination of total Hg concentration by atomic absorption spectrometry [ 28 ]. Hg analysis was performed by EPA method 7473 PLTX-017, which consists of direct analysis by thermal decomposition, amalgamation, and atomic absorption spectrometry [ 29 ]. For the analytical control in sediments, seston and oysters, a triplicate analysis of a solution of Hg at different concentrations (0.02, 0.05 and 0.5 µg of Hg) was used, complying with the acceptance criteria of the Association of Official Analytical Chemists (AOAC), with determination coefficients greater than 0.995 for the calibration curve and error percentages of less than 15%. TORT-1 (lobster hepatopancreas) from the National Research Council of Canada (NRCC) was used as reference material. Recovery percentages were 100 ± 1.4% in sediments (limit of detection, LOD, = 0.00073 µg/g Hg), 100 ± 5.4% in seston (LOD = 0.000015 µg/g Hg) and 100 ± 1.4% in oysters (LOD = 0.00073 µg/g Hg) [ 12 ]. 2.4 Cabinet phase The bioconcentration factor (BCF) was calculated as the ratio of Hg concentration in oyster tissue to its presence in sediment (sd) and seston (st), expressed in parts per million (ppm, µg/g) in dry weight (d.w.). This calculation was based on Mountouris et al. [ 1 ] and Romero-Murillo et al. [ 12 ]. $$\:{BCF}_{sd}=\frac{{\left[Metal\right]}_{organism}}{{\left[Metal\right]}_{sedimento}},\:{BCF}_{st}=\frac{{\left[Metal\right]}_{organism}}{{\left[Metal\right]}_{seston}}$$ BCF was used to evaluate the efficiency of Hg accumulation in oyster soft tissue. According to Mountouris et al. [ 1 ], BCF < 1 suggests no metal accumulation, BCF ≥ 1 and < 10 indicates accumulation and BCF ≥ 10 indicates hyperaccumulation of metal. Permutation analysis of variance (PERMANOVA) was applied to compare Hg concentration in oyster tissue and its BCF between the two ecosystems (k = 2), the two climatic seasons (k = 2), the six stations (k = 6) and the two categorized size classes (k = 2). 9 999 permutations were performed using Euclidean distance and type III sum of squares. The p -values was computed using Monte Carlo (MC) permutation testing only when unique permutations were less than 100 [ 30 ]. The relationship of Hg concentration between sediment and seston was examined using Pearson's (data fitted to the normal distribution) and Spearman's (data not fitted to the normal distribution) correlation analyses. These analyses were conducted to identify potential relationships between physicochemical variables on Hg availability in sediments and seston [ 31 ] The influence of environmental predictor variables on the oyster Hg concentration and Hg BCF in relation to seston was evaluated using a distance-based linear model (DistLM) with adjusted R 2 criterion and 9999 permutations [ 30 ]. To evaluate mercury contamination in bivalves, the Nemerow integral contamination index -P c - was used [ 32 ]. The calculation of P c is based on the average value of the individual pollution index (P avg ), the maximum value (P max ) and the minimum value (P min ). The individual index values were calculated using the following formula: $$\:{P}_{avg}=\frac{{C}_{avg}}{S},\:{\:\:\:\:\:\:P}_{max}=\frac{{C}_{max}}{S},\:{\:\:\:\:\:\:P}_{min}=\frac{{C}_{min}}{S}\:\:\:\:\:\:\:\:\:\:\:\left[1\right]$$ C a vg is the average concentration value recorded in the data set evaluated, C max and C min are the maximum and minimum concentration values from the same data set, and S is the maximum concentration allowed in marine organisms (mollusks) with Hg (0.5 µg/g) [ 33 ]. Once the historical values of P avg , P max and P min were obtained for each country by year, the calculation of P c was performed establishing (i) P c ≤ 0.7 considered no risk, (ii) 0.7 < P c ≤ 1 low risk, (iii) 1 < P c ≤ 2 medium risk, (iv) 2 3 very high risk of contamination [ 29 ]. It was calculated using the following equation: $$\:\frac{\sum\:{P}_{c}}{n}=\sqrt{\frac{{P}_{avg}^{2}+{P}_{max}^{2}+{P}_{min}^{2}}{3}}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left[2\right]$$ ΣP c is the sum of all P c values divided by "n", the total number of years evaluated per country published in its historical record. This ensures that the values of P max and P min do not overestimate or underestimate the calculation of the contamination index for each metal evaluated, respectively. The similarities and differences of the sites were assessed with a hierarchical clustering analysis, a multivariate technique applied to construct distance dendrograms from the classification of each site according to the level of metal contamination. The analysis was applied through the use of the squared Euclidean distance with Ward's linkage, minimizing variability and producing uniformly sized clusters [ 34 , 35 ]. 3 Results 3.1 Environmental conditions in both coastal lagoons The average water temperature in CGSM and BhC reached its highest value during the rainy season. In CGSM, the temperature during the rainy season was 31.17 ± 0.48°C (n = 3), while in dry season it was 30.53 ± 0.84°C (n = 3). In BhC, with slightly lower temperatures compared to CGSM, the temperature during the rainy season was 28.97 ± 0.43°C (n = 3), and in dry season it was 29.75 ± 0.03°C (n = 3) (Fig. 2 A, Supplementary Table S1 ). Regarding pH, during the rainy season, CGSM had a higher pH value (8.77 ± 0.12, n = 3) compared to BhC (7.84 ± 0.09, n = 3), while during the dry season, were a decrease in pH in CGSM (8.44 ± 0.16, n = 3) and an increase in BhC (8.19 ± 0.003, n = 3). The values were similar in both study areas (Fig. 2 A, Supplementary Table S1 ). The average dissolved oxygen content was higher in CGSM during both climatic seasons, with values of 7.83 ± 0.66 mg/L (n = 3) in rainy season and 7.39 ± 2.4 mg/L (n = 3) during dry season. In BhC, the contents were 4.32 ± 0.5 mg/L (n = 3) in rainy season and 5.52 ± 1.28 mg/L (n = 3) along the dry season (Fig. 2 A, Supplementary Table S1 ). Regarding salinity and organic matter, CGSM showed variations in these variables, with salinity values from 2.47 ± 1.01 (n = 3) in rainy season to 18.53 ± 6.33 (n = 3) in dry season, and organic matter content during the rainy season of 11.67 ± 3.27% (n = 3), doubling the observed values on the dry season (5.97 ± 2.4%, n = 3). In contrast, in BhC, the average salinity values (from 24.9 ± 1.01, n = 3 to 30.83 ± 0.56, n = 3) and organic matter (from 5.6 ± 0.5%, n = 3 to 6.06 ± 1.28%, n = 3) varied the less between those two climatic seasons (Fig. 2 A, Supplementary Table S1 ). In sediments the redox potential, both in CGSM and BhC, reducing conditions were recorded with a range of values from 28 to 77 mV between both study areas. Increases in redox potential were observed in BhC (52 ± 3, n = 3 to 65 ± 4, n = 3), and decreases in CGSM (50 ± 11, n = 3 to 35 ± 4, n = 3) from rainy season to dry season (Fig. 2 A, Supplementary Table S1 ). 3.2 Concentration of Hg in sediments, seston and Crassostrea rhizophorae Hg concentration in sediments and seston varied markedly between the two ecosystems. In BhC, in both sediments and seston, Hg concentrations are consistently higher than in CGSM in both climatic seasons (Fig. 2 B, Supplementary Table S2). In the rainy season, the highest concentration of Hg in sediments was found in CIS-1 (BhC) with 0.128 µg/g Hg dry weight (d.w.) which is double the highest content detected in CGSM (0.059 µg/g Hg d.w . in CGS-1). Hg content in sediments at BhC was slightly lower in the dry season but remained above 0.08 µg/g Hg d.w . indicating a possible constant source of Hg contamination. In CGSM, during the dry season, lower Hg was observed in CGS-1 and higher in CGS-2 (Fig. 2 B, Supplementary Table S2). Table 1 PERMANOVA analysis on Hg concentration and bioconcentration factor (BCF-Hg) vs. sizes (juveniles and adults), stations, ecosystem, and climatic season in the oyster Crassostrea rhizophorae . Ecosytem (EC), climatic season (CS), station (ST), size (SZ), degrees of freedom (df), sum of squares (SS), and mean square (MS). For more information, see Supplementary Table S4 Hg (µg/g d.w.) Factor df SS MS Pseudo-F Únique p -value EC 1 8.8 × 10 − 2 8.8 × 10 − 2 47.31 9 836 1 × 10 − 4 CS 1 4.6 × 10 − 5 4.6 × 10 − 5 0.03 9 837 0.876 ST (EC) 4 2.5 × 10 − 2 6.2 × 10 − 3 3.31 9 948 1.6 × 10 − 2 EC × CS 1 5.3 × 10 − 3 5.3 × 10 − 3 2.85 9 843 0.098 SZ (ST (EC)) 6 4.6 × 10 − 2 7.7 × 10 − 3 4.11 9 954 1.8 × 10 − 3 CS × ST (EC) 4 2.9 × 10 − 2 7.4 × 10 − 3 3.94 9 949 7 × 10 − 3 CS × SZ (ST (EC)) 6 2.5 × 10 − 2 4.2 × 10 − 3 2.27 9 939 0.049 Residual 47 8.8 × 10 − 2 1.87 × 10 − 3 Total 70 3.07 × 10 − 1 BCF-Hg Factor df SS MS Pseudo-F Únique p -value EC 1 747.7 747.7 72.14 9 841 1 × 10 − 4 CS 1 594.8 594.8 57.39 9 864 1 × 10 − 4 ST (EC) 4 62.78 15.7 1.514 9 954 0.219 EC × CS 1 152.9 152.9 14.76 9 837 4 × 10 − 4 SZ (ST (EC)) 6 200.8 33.5 3.23 9 949 0.011 CS × ST (EC) 4 84.1 21.03 2.03 9 951 0.107 CS × SZ (ST (EC)) 6 322.4 53.7 5.18 9 931 4 × 10 − 4 Res 47 487.1 10.3 Total 70 2 720 * p -value < 0.05 indicates significant differences among the analyzed factors. In red the significant ones. The Hg available in the seston presented similar values in the stations of each ecosystem and in the two climatic seasons. However, as in sediments, a lower concentration was detected in the dry season. In BhC, the concentration went from 0.032 ± 0.005 µg/g Hg d.w . in the rainy season to 0.022 ± 0.001 µg/g Hg d.w . in the dry season. Lower concentrations were found in CGSM, with values ranging from 0.01 ± 0.001 µg/g Hg d.w . in the rainy season to 0.004 ± 0.001 µg/g Hg d.w . in the dry season (Fig. 2 B, Supplementary Table S2). In BhC the highest Hg content in seston was positively and significantly related to temperature (Pearson, r = 0.93, p -value < 0.001) and in sediments Hg was significantly related to organic matter (Pearson, r = 0.84, p -value = 0.04) (Fig. 2 , Supplementary Table S3). Hg concentrations in oyster tissue show distinct accumulation patterns in CGSM and BhC, varying as a function of climatic seasons. However, a pattern similar to that of sediment and seston was maintained, with a higher Hg content in oyster soft tissue in BhC (Fig. 2 B). In the rainy season, Hg in the oyster was 0.083 ± 0.007 µg/g d.w . (n = 17) in CGSM and of 0.135 ± 0.015 µg/g d.w . (n = 18) in BhC showing significant differences between the two ecosystems (Permanova, p -value < 0.01). In dry season, these differences were maintained, given the decrease in oyster Hg content in CGSM (0.066 ± 0.007 µg/g Hg d.w ., n = 18) and increased in BhC (0.154 ± 0.019 µg/g Hg d.w ., n = 18) (Table 1 , Fig. 3 A, Supplementary Table S4). With respect to Hg BCF, both in sediments and seston, both ecosystems presented accumulation to hyperaccumulation of Hg in the oyster tissue, with the highest values in the dry season. In this same climatic season, at CGSM, the oyster presented an accumulation of Hg with the sediment (BCF ≥ 1) and a hyperaccumulation of the metal with the seston (BCF ≥ 10), as opposed to the accumulation condition in both matrices during the rainy season. In BhC, the oyster maintained the accumulation condition in both matrices (BCF ≥ 1) as in rainy season (Table 1 ). These results notably emphasize the capacity of the oyster to accumulate Hg in its tissues, especially in CGSM through the seston in the dry season. Significant differences in BCF were determined between CGSM and BhC ecosystems, with higher concentrations in BhC (Permanova, p -value < 0.05). However, no significant differences in concentrations were observed between climatic seasons, since the values measured at two of three stations in both CGSM (CGS-2 and CGS-3) and BhC (CIS-1 and CIS-3) were similar in both climatic seasons (Table 1 , Fig. 3 B, Supplementary Table S4). In the two ecoystems evaluated, there were significant differences in the Hg contents between stations (Permanova, p -value < 0.05; Table 1 ). In the rainy season at CGSM the differences occurred between stations CGS-1 and CGS-2 and at BhC between CIS-2 and CIS-3. In the dry season, significant differences were found between CIS-1 and CIS-2 in BhC, with the lowest concentrations in CIS-1 (Fig. 2 B, Supplementary Table S4 and S5). There were significant differences in the length of juveniles and adults (Permanova, p -value < 0.05) between stations (Table 1 ). In CGSM in the dry season, concentrations were higher in adult sizes at station CGS-3 (0.121 ± 0.016 µg/g Hg d.w .) with respect to juveniles (0.039 ± 0.009 µg/g Hg d.w .). In BhC, in both rainy and dry seasons, the highest concentration of juvenile lengths was at station CIS-2 (Fig. 3 A, Supplementary Table S4 and S5). 3.2.1 Importance of seston in the bioconcentration of Hg High Hg bioconcentration factor values reflected a significant correlation with seston content (Pearson, r = 0.72, p -value < 0.01), with conditions of accumulation (BCF ≥ 1) in BhC and hyperaccumulation in CGSM (BCF ≥ 10; Supplementary Table S4). Differences in Hg bioconcentration between CGSM and BhC were determined (Permanova, p -value < 0.05; Table 1 ). These differences were also observed as a function of climatic seasons, with an increase during the dry season in each CGSM season, and significant in the CIS-2 season in BhC compared to the rainy season. When the factors ecosystem and climatic season were combined, significant differences were still present, with higher values of Hg bioconcentration in CGSM in both climatic seasons compared to BhC (Fig. 3 B, Supplementary Table S4 and S5). These results indicate that the oyster in CGSM is accumulating higher concentrations of Hg in its tissues compared to the BhC oyster, although the accumulation is also considerably higher in the BhC oyster. Significant differences between juvenile and adult sizes were determined with the BCF-Hg, which was maintained when considering the climatic season (Table 1 ). In BhC, the highest values of BCF-Hg were observed in juvenile sizes in both climatic seasons. In CGSM, the highest BCF occurred in adult sizes during the dry season, while they were similar in both sizes during the rainy season (Spearman, r = 0.25, p -value > 0.05; Fig. 3 B, Supplementary Table S4). Table 2 Analysis of DistLM in the relationship between Hg concentration and its bioconcentration in Crassostrea rhizophorae with physicochemical variables (predictors). Stepwise model and selection criterion of adjusted R 2 were used (9999 permutations). SS: sum of squares. Juvenile size Variable SS Pseudo-F p -value Proportion of variation explained Temperature 11.2 0.41 0.54 0.039 Salinity 28.1 1.09 0.33 0.098 pH 27.8 1.07 0.33 0.097 Dissolved oxygen 22.1 0.84 0.38 0.077 Organic matter 0.61 0.02 0.89 0.021 Adult size Variable SS Pseudo-F p -value Proportion of variation explained Temperature 1.2 0.03 0.88 0.026 Salinity 4.5 0.09 0.77 0.098 pH 39.9 0.95 0.36 0.087 Dissolved oxygen 106.7 3.01 0.11 0.231 Organic matter 0.1 0.03 0.96 0.026 * p -values < 0.05 express that the variable significantly explains the variations in Hg content and its bioconcentration in Crassostrea rhizophorae . In red is the greatest variation explained. 3.3 Relationship between environmental variables and Hg bioconcentration in oysters Between the Hg concentration in the mangrove oyster tissue and its BCF by size in relation to the metal content in the seston, it was not possible to find a positive or negative relationship with the environmental variables analyzed. The relationship between physicochemical variables and size with Hg concentration and BCF in the mangrove oyster were not significant (DistLM; p -value > 0.05; Table 2 ). This suggests that environmental variables and size did not play a determining role in the differences in oyster Hg content and bioconcentration at CGSM and BhC (Fig. 3 ). Other factors, such as Hg content in the seston and local transport and sedimentation processes, may be playing a more influential role in Hg accumulation. 3.4 Hg contamination status of bivalves in a global context during the last decade Considering Hg contamination levels in global monitoring during the last 12 years in different bivalve species, both ecosystems are part of Clade 1, CGSM presents no risk of Hg contamination in oyster consumption (similar to Taganga), while BhC is close to a low risk of Hg contamination along with Isla Cayo el Pigeon (Nicaragua). However, these values exceed those reported in other areas such as China, Italy and Montenegro, which presented the lowest risk of Hg consumption by bivalves. This makes it relevant to consider the potential risk of Hg contamination in the Colombian Caribbean, which presented the highest risk of contamination by Hg in the world with bivalves during the last decade (Fig. 4 ). 4 Discussion The higher concentrations of Hg, in all of them sediment, seston and oyster, in BhC compared to CGSM (Fig. 2 B, Supplementary Table S1 ) raise concerns about environmental quality and ecosystem health in the region. Hg contamination in BhC is linked to the connection of the Sinú River through the Sicará stream, suggesting contamination associated with water and sediment flows from surrounding agricultural areas [ 36 ], as well as the use of fungicides containing phenylmercury (C 6 H 5 Hg) and extensive spraying of rice fields with mercury agrochemicals [ 37 ]. Other sources identified include regional gold mining, wastewater discharge, use of Hg in ship paints as an anti-corrosion compound, and air pollution [ 38 , 39 ]. In CGSM, the sources of Hg contamination are less clear; the entry of this metal into the swamp is associated with atmospheric deposits and anthropogenic activities [ 40 ], gold mining and industrial activities [ 41 , 42 ] mainly from the Magdalena River [ 43 ]. Although the levels of Hg in sediments in BhC and CGSM are lower than those reported in other regions, such as in Cartagena Bay, Colombia (0.094–10.293 µg/g Hg d.w .) [ 40 ] and in San Vicente Bay, Chile (0.37 to 0.95 µg/g Hg d.w .) [ 44 ], and considering that the Hg content was below the tolerable threshold for the ecosystem and associated biota (TEL) of 0.13 µg/g [ 45 ], the risk of Hg contamination is higher in BhC compared to CGSM. In previous assessments conducted by Feria et al. [ 46 ], Campos et al. [ 36 ] and Marrugo-Negrete et al. [ 37 ], Hg concentrations exceeding the TEL threshold have been reported in sediments along the Sinú riverbed and at the mouth of the BhC. In contrast, in CGSM, Hg concentrations reported in sediments have been less than 0.11 µg/g Hg d.w ., being similar to what was found in this study (Fig. 2 B). The slight increase in Hg content in sediment and seston during the rainy season compared to the dry season (Fig. 2 B) could be attributed to metal flushing from land-based sources, influenced by increased sediment and freshwater input [ 47 , 48 ]. These factors are especially relevant in the CGSM with significant contributions from the Magdalena River in the CGSM [ 40 ] and the Sinú River in BhC [ 37 ]. Although these variations between climatic seasons were not significant for Hg content in the mangrove oyster (Table 2 , Fig. 3 A), the importance of sediment-seston interaction and the influence of local conditions in the coastal areas of the Colombian Caribbean on Hg availability in the oyster is highlighted [ 9 ]. Variables such as temperature and organic matter may be playing an important role in the Hg content of sediments and seston. In BhC, the highest Hg contents in the seston during the rainy season were significantly correlated with the highest temperature values (Fig. 2 ), this being a variable that can affect the rate of chemical reactions, including its methylation [ 49 ]. In turn, higher Hg values in sediments were related to higher organic matter content in the rainy season, underlining the fundamental role of organic matter in the retention of metals in sediments, together with fine sediments and a sulfate-reducing environment [ 11 ], as in CGSM [ 43 ] and BhC (Fig. 2 A). Although no direct correlation was identified between pH and Hg concentrations in sediments and seston (Supplementary Table S3), slightly acidic or neutral pH conditions result in higher Hg precipitation in sediments [ 50 ], which could possibly explain why BhC, with lower pH values, had higher Hg contents in sediments compared to CGSM (Fig. 2 ). Another aspect to take into account in the precipitation of Hg in sediments is the variations from sulfates to sulfides, which possibly increase the flux of reactive phosphate and ammonium at the sediment-water interface [ 51 ]. This process favors that Hg tends to precipitate in the sediments as insoluble hydroxides, oxides, carbonates or phosphates [ 52 , 53 ]. The interaction of these processes could help to understand the variations of Hg content in sediments, taking into account the pH values in each climatic season. This pattern is particularly noticeable in BhC because of the differences in pH from rainy to dry season (Fig. 2 ). With respect to the mangrove oyster, the influence of the environmental variables analyzed on the concentration and bioconcentration factor (BCF) of Hg was not significant (Tables 2 , Fig. 3 , Material Supplementary S4). This finding responds to what has been reported in other investigations, in which the influence of variables such as temperature, salinity and pH on the uptake and accumulation of Hg is not completely understood in bivalves [ 53 ], unlike what occurs in sediments and seston in which the processes of accumulation, uptake, toxicity and speciation of Hg are known [ 54 , 55 ]. Although no significant relationship could be established between Hg BCF with environmental conditions in CGSM and BhC, it is important to consider that high concentrations of dissolved oxygen in CGSM, together with changes in the chemical composition of the sediments, may increase and/or alter the metabolic activity of bivalves [ 56 , 57 ], which could affect the capacity for Hg uptake and excretion in bivalves such as the oyster [ 55 ]. The mangrove oyster is known for its ability to filter large volumes of water during feeding [ 17 ] and particulate matter from sediments [ 58 ]; therefore, Hg concentrations in the oyster were closely related to the metal content in its environment (Fig. 2 B). Hg bioconcentration was significantly associated with seston, which was to be expected considering that collection of the organism was mainly on mangrove roots. As with seston, metal accumulation and hyperaccumulation were obtained with respect to Hg concentrations in the sediment (Table 1 ). In this regard, measurements of metals in sediments, such as with seston, provide crucial data on the availability and uptake of Hg by the bivalve, providing a comprehensive view of the interaction between these organisms and their contaminated environment. The results in BhC are consistent with previous studies. Coimbra [ 59 ] in Sepetiba Bay in Brazil in Mytela guyanensis and Díaz et al. [ 44 ] in San Vicente Bay in Chile in Tagelus dombeii , reported inverse correlations between Hg content and species size. They suggested that there are metal assimilation rates similar to the excretion rate in larger individuals, which may be generated by decreased metabolism and less water pumping with bivalve growth [ 60 ]. During the growth of bivalves, several mechanisms are involved that regulate the accumulation of toxic metals such as Hg in their tissues. The formation of mineralized granules allows storage and possibly detoxification by Hg [ 61 ]. For its release, bivalves develop a homeostatic regulation system during their growth that includes several excretion mechanisms through urine and feces, which contribute to maintain adequate Hg concentrations [ 62 ]. Another aspect is the development of new gill systems; their formation plays a key role in the filtration of particles, including metals from the aquatic environment [ 48 ]. This progressive development of gill systems contributes to the efficiency of bivalves in capturing and regulating Hg in their tissues as they develop. The emission of gametes during reproduction is another important strategy that bivalves deploy to mitigate the accumulation of toxic metals [ 60 ]. During the release of gametes from the mangrove oyster, an increase in Hg BCF could have been experienced during the rainy season, as it is associated with a decrease in organism biomass with spawning [ 63 ]. However, in both CGSM and BhC the highest values of BCF in oysters were obtained during the dry season (Table 1 , Fig. 3 B). During gamete release, which generally occurs during the rainy season and encompasses several breeding peaks in the Colombian Caribbean [ 17 ], mineralized granules stored in the lysosomes may be released along with the gametes. This process, called exocytosis, allows the contents of lysosomes, including metals such as Hg, to be released into the aquatic environment [ 61 ]. This possible release of mineralized Hg granules in lysosomes together with the expulsion of gametophytes could have contributed to the lower Hg BCF values during the rainy season. As for CGSM, slightly higher concentrations and BCF in adult lengths were observed in dry season, similar to what was reported by Costa et al. [ 64 ] and De Gregori et al. [ 65 ], and being the inverse of what was found in BhC in both climatic seasons. This result highlights the complexity of the relationship between the various environmental and organismal factors that influence Hg bioconcentration. 4.1 Hg intake risk in C. rhizophora e at CGSM and BhC Variability in contamination sources and Hg concentrations in CGSM and BhC stands out as a key factor influencing contamination risk. In particular, BhC shows values close to the permissible limit for Hg in bivalves for human consumption of 0.5 µg/g Hg d.w . [ 33 ], raising concerns about the health of the ecosystem. This situation is similar to what has been reported on Cayo el Pigeon Island in Nicaragua and Santa Marta in Colombia by Aguirre-Rubí et al. [ 9 ] (Fig. 4 ). However, both ecosystems are far from what has been reported for this species in coastal areas of the Dominican Republic, where Sbriz et al. [ 66 ] recorded one of the highest Hg contents in the mangrove oyster (7.02 µg/g Hg d.w .). When comparing Hg concentrations in mangrove oysters with other bivalve species globally over the last decade, CGSM and BhC stand out as ecosystems that maintain low to no risk of Hg contamination. This contrasts with findings in coastal areas of China [ 67 – 69 ], Italy [ 70 ] and Montenegro [ 71 ], with a lower risk of Hg contamination in the world and serves as a reference for the potential risk of contamination in CGSM and BhC (Fig. 4 ). The relevance of this study is intensified when considering the current situation of Hg contamination in Colombia. In the bay of Cartagena with C. rhizophorae its has reported the highest risk of Hg contamination in the last decade in the world [ 9 ] (Fig. 4 , Supplementary Table S6 and S7). In a historical context, the Bay had a direct discharge of Hg from the Alcalis chlorine plant [ 40 , 72 ]. Similar cases prior to 2010 have been reported in Tagelus dombeii (San Vicente Bay, Chile) [ 44 ], in Archivesica gigas (Gulf of California, United States) [ 73 ] and in Mytilus galloprovincialis (Adriatic Sea, Croatia) [ 74 ] with concentrations above 0.5 µg/g Hg d.w . These findings underscore the need for continuous monitoring at CGSM and BhC to identify specific sources of contamination and generate appropriate preventive measures. 5 Conclusions Cispatá Bay (BhC) had the highest concentrations of Hg in sediments, seston and oysters compared to Ciénaga Grande de Santa Marta (CGSM) in both climatic seasons. However, the oyster exhibited the highest values of bioconcentration factor (BCF) with the seston of the CGSM, with a higher risk of Hg contamination. Temperature in the water column and organic matter in sediments influenced Hg concentrations in seston and sediments but have a limited and insignificant impact with the other environmental variables on Hg bioconcentration by size in the oyster. Adult sizes accumulated more Hg in CGSM, while juvenile sizes accumulated more Hg in BhC. This highlights the importance of considering the size of the bivalve when assessing Hg contamination, taking into account the specific environmental conditions of each ecosystem. The CGSM exhibited contamination without risk for human consumption, similar to that reported in other areas in the Colombian Caribbean, while BhC presented near-low contamination due to its higher Hg content. Declarations Founding sources This study was done within the research program "Redes tróficas marinas del Caribe colombiano en la era del plástico y los contaminantes tóxicos” (code MINCIENCIAS 71475)”, funded by MINCIENCIAS and Universidad Jorge Tadeo Lozano, in partnership with Universidad Nacional de Colombia, sede Caribe. The funding for Hg analysis in oysters was provided of Colombia Biodiversa (I-2023) and Banco de la República with the Project 5.131 from the Foundation for the Promotion of Research and Technology (Fundación para la Promoción de la Investigación y la Tecnología). Translation funding was provided by internal grants from the Universidad Jorge Tadeo Lozano. Competing Interests The authors have no relevant financial or non-financial interests to disclose. CRediT authorship contribution statement Anubis Vélez-Mendoza : Funding Acquisition, Conceptualization, Methodology, Data Curation, Formal Analysis, Visualitation, Writing & Original draft, Writing, Review & Editing. Jeimmy Paola Rico Mora: Funding Acquisition, Data Curation, Visualitation, Supervision, Writing, Review & Editing. Néstor Hernando Campos-Campos: Funding Acquisition, Data Curation, Visualitation, Supervision, Writing, Review & Editing. Margui Lorena Almario-García: Supervision, Writing, Review & Editing. Adolfo Sanjuan-Muñoz: Project Administration & Funding Acquisition, Supervision, Writing, Review & Editing. Acknowledgement We would like to especially thank the members of the team Diana Bustos-Montes, Paulo Tigreros-Benavides, Diana Rubio-Lancheros, María Camila Castellanos Jimenez, Ana M. 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Environ Pollut 92(3): 359-368. https://doi.org/10.1016/0269-7491(95)00077-1 Sbriz L, Aquino MR, Alberto De Rodriguez NM, Fowler SW, Sericano JL (1998) Levels of chlorinated hydrocarbons and trace metals in bivalves and nearshore sediments from the Dominican Republic. Mar Pollut Bull 36(12): 971-979. https://doi.org/10.1016/S0025-326X(98)00097-6 Wang L, Wang X, Chen H, Wang Z, Jia X (2021) Oyster As, Cd, Cu, Hg, Pb and Zn levels in the Northern South China Sea: long-term spatiotemporal distributions, interacting effects, and risk assessment to human health. Research Square. https://doi.org/10.21203/rs.3.rs-478762/v1 Liu Q, Xu X, Zeng J, Shi X, Liao Y, Du P, Tang Y, Huang W, Chen Q, Shou L (2019) Heavy metal concentrations in commercial marine organisms from Xiangshan Bay, China, and the potential health risks. Mar Pollut Bull 141: 215-226. https://doi.org/10.1016/j.marpolbul.2019.02.058 Wang X-N, Gu Y-G, Wang Z-H, Ke C-L, Mo MS (2018) Biological risk assessment of heavy metals in sediments and health risk assessment in bivalve mollusks from Kaozhouyang Bay, South China. Mar Pollut Bull 133: 312-319. https://doi.org/10.1016/j.marpolbul.2018.05.059 Squadrone S, Brizio P, Stella C, Prearo M, Pastorino P, Serracca L, Ercolini C, Abete MC (2016) Presence of trace metals in aquaculture marine ecosystems of the northwestern Mediterranean Sea (Italy). Environ Pollut 215: 77-83. https://doi.org/10.1016/j.envpol.2016.04.096 Perošević A, Joksimović D, Đurović D, Milašević I, Radomirović M, Stanković S (2018) Human exposure to trace elements via consumption of mussels Mytilus galloprovincialis from Boka Kotorska Bay, Montenegro. J Trace Elem Med Biol 50: 554-559. https://doi.org/10.1016/j.jtemb.2018.03.018 Bolaños-Alvarez Y, Ruiz-Fernández AC, Sanchez-Cabeza J-A., Díaz Asencio M, Espinosa LF, Parra JP, Garay J, Delanoy R, Solares N, Montenegro K, Pena A, López F, Castillo-Navarro AC, Gómez Bastidas M, Quejido-Cabezas A, Metian M, Pérez-Bernal LH, Alonso-Hernández CM (2024) Regional assessment of the historical trends of mercury in sediment cores from Wider Caribbean coastal environments. Sci Total Environ 920: 170609. https://doi.org/10.1016/j.scitotenv.2024.170609 Ruelas-Inzunza J, Soto LA, Páez-Osuna F (2003) Heavy-metal accumulation in the hydrothermal vent clam Vesicomya gigas from Guaymas basin, Gulf of California. Deep Sea Res I: Oceanogr Res Pap 50(6): 757-761. https://doi.org/10.1016/S0967-0637(03)00054-2 Kljaković-Gašpić Z, Herceg-Romanić S, Kožul D, Veža J (2010) Biomonitoring of organochlorine compounds and trace metals along the Eastern Adriatic coast (Croatia) using Mytilus galloprovincialis . Mar Pollut Bull 60(10): 1879-1889. https://doi.org/10.1016/j.marpolbul.2010.07.019 Additional Declarations No competing interests reported. Supplementary Files BTERSupplementaryTablesVelezetal2024.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 18 Aug, 2024 Reviewers agreed at journal 12 Aug, 2024 Reviews received at journal 07 Aug, 2024 Reviewers agreed at journal 29 Jul, 2024 Reviewers invited by journal 11 Jul, 2024 Editor assigned by journal 11 Jul, 2024 Submission checks completed at journal 11 Jul, 2024 First submitted to journal 11 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4725392","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":335562565,"identity":"ee6c79ae-92d5-475c-9df6-c4fa56e73281","order_by":0,"name":"Anubis Vélez-Mendoza","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6UlEQVRIiWNgGAWjYLCCByCCvQFIFADxAWK0JIAIHpBSA5K0SCQQqYV/do/hg4SKumh+yTdmD34YMMjx3Uhg/PABjxaJO2eMDRLOsOXOnJ1jbthjwGAseSOBWXIGPmtupKVJJLbx5G64nWMmwWPAkLjhRgIbMw8eHfI30tJ/JP6TyN1/84yZ5B8DhnqCWgxuJB9jSGwwyN0gwWMmDbQlwYCQFsMbyYclEo4l5M44k1YmLWMgYTjzzMNmvH6Ru5HY+OFDTV1uf/vhbZJvKmzk+Y4nH8QbYuhAAogZG0jQMApGwSgYBaMAGwAAO3lMSH71kxgAAAAASUVORK5CYII=","orcid":"","institution":"Universidad Nacional de Colombia Sede Caribe","correspondingAuthor":true,"prefix":"","firstName":"Anubis","middleName":"","lastName":"Vélez-Mendoza","suffix":""},{"id":335562566,"identity":"0733c07c-b9b7-4ce0-ad95-ac08c43a57f0","order_by":1,"name":"Jeimmy Paola Rico Mora","email":"","orcid":"","institution":"Universidad Nacional de Colombia Sede Caribe","correspondingAuthor":false,"prefix":"","firstName":"Jeimmy","middleName":"Paola Rico","lastName":"Mora","suffix":""},{"id":335562567,"identity":"bd06cb58-e4d0-49d4-9ef5-0ebeb0401ac1","order_by":2,"name":"Néstor Hernando Campos-Campos","email":"","orcid":"","institution":"Universidad Nacional de Colombia Sede Caribe","correspondingAuthor":false,"prefix":"","firstName":"Néstor","middleName":"Hernando","lastName":"Campos-Campos","suffix":""},{"id":335562568,"identity":"052597b3-df8c-4fe8-863d-5fbaaa95d2af","order_by":3,"name":"Margui Lorena Almario-García","email":"","orcid":"","institution":"Universidad de Bogotá Jorge Tadeo Lozano","correspondingAuthor":false,"prefix":"","firstName":"Margui","middleName":"Lorena","lastName":"Almario-García","suffix":""},{"id":335562569,"identity":"ea5c9a85-9508-456b-b5cb-4405952a9f2e","order_by":4,"name":"Adolfo Sanjuan-Muñoz","email":"","orcid":"","institution":"Universidad de Bogotá Jorge Tadeo Lozano","correspondingAuthor":false,"prefix":"","firstName":"Adolfo","middleName":"","lastName":"Sanjuan-Muñoz","suffix":""}],"badges":[],"createdAt":"2024-07-11 16:08:50","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4725392/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4725392/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":61832362,"identity":"deaafe55-b763-4472-b124-9b1b079754ca","added_by":"auto","created_at":"2024-08-06 04:51:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":7279360,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of the study sites on the Colombian Caribbean Coast.\u003c/p\u003e","description":"","filename":"Figure1.CGSMandBhC.png","url":"https://assets-eu.researchsquare.com/files/rs-4725392/v1/b552f84fe3e4d546f2f1b03a.png"},{"id":61832787,"identity":"7bbbe6ee-5a13-4ef9-ab1d-f7734d21796c","added_by":"auto","created_at":"2024-08-06 04:59:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":215224,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4725392/v1/4ce44ad083aa7262c81eb3eb.png"},{"id":61832363,"identity":"9bd3ff00-2cac-408d-bd69-5890fda86988","added_by":"auto","created_at":"2024-08-06 04:51:58","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1461500,"visible":true,"origin":"","legend":"\u003cp\u003eComparative analysis of concentrations (A) and bioconcentration factor (B) of Hg in the oyster \u003cem\u003eCrassostrea rhizophorae\u003c/em\u003e between Ciénaga Grande de Santa Marta (CGSM) and Cispatá Bay (BhC): effects of organism size and climatic season. Above the green line, Hg accumulation condition in the oyster is considered (FBC≥1), and above the red line, hyperaccumulation of the metal is considered (FBC≥10).\u003c/p\u003e","description":"","filename":"Figure3.BoxplotHgBCFHg.png","url":"https://assets-eu.researchsquare.com/files/rs-4725392/v1/770858e058e972d73099564c.png"},{"id":61832359,"identity":"a445a1a5-7376-4124-bff1-5c831ec138d8","added_by":"auto","created_at":"2024-08-06 04:51:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":4339793,"visible":true,"origin":"","legend":"\u003cp\u003eHierarchical clustering analysis was conducted to evaluate the Nemerow contamination index (Pc) due to Hg in marine and coastal ecosystems measured in bivalves from the season 2010 to 2022. Colombia (COL), Nicaragua (NIC), China (CHN), Italy (ITA), and Montenegro (MNE). Clade 1: sites with close to low contamination, Clade 2 and 3: sites with low contamination. The arrow refers to the sites evaluated in the present study. For more information, see Supplementary Table S6 and S7.\u003c/p\u003e","description":"","filename":"Figure4.NemerowIndexHgbivalves.png","url":"https://assets-eu.researchsquare.com/files/rs-4725392/v1/83e1929746115229d78292bb.png"},{"id":61834598,"identity":"141a7bb7-9306-4680-bba3-3ad820184c18","added_by":"auto","created_at":"2024-08-06 05:24:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":16261045,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4725392/v1/4c2ebb3c-0d42-473a-b761-36ca312c5fbe.pdf"},{"id":61832360,"identity":"bf861bd1-9cde-470c-b073-8786331c1074","added_by":"auto","created_at":"2024-08-06 04:51:58","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":48759,"visible":true,"origin":"","legend":"","description":"","filename":"BTERSupplementaryTablesVelezetal2024.docx","url":"https://assets-eu.researchsquare.com/files/rs-4725392/v1/e31db30f022b014b575be1e5.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Changes in mercury content in oysters in relation to sediment and seston content in the Colombian Caribbean lagoons","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMercury contamination is a global environmental challenge due to its capacity for bioaccumulation and biomagnification in food webs, and its potentially devastating effects on ecosystems [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Throughout history, catastrophic events linked to metal contamination have been recorded, with the Minamata disaster in Japan being the iconic example for Hg intoxication. This incident, generated by the release of Hg in toxic forms such as methylmercury (CH\u003csub\u003e3\u003c/sub\u003eHg) into Minamata Bay, left catastrophic after-effects on both the human population and local marine life [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. This grim historical episode strongly underscores the dangers of Hg to human health and the environment.\u003c/p\u003e \u003cp\u003eHg contamination represents a significant threat to coastal marine ecosystems. The ability of this element to bioaccumulate and biomagnify in the tissues of organisms means that it can reach dangerous concentrations as it progresses through the food web [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Hg in toxic forms such as CH\u003csub\u003e3\u003c/sub\u003eHg affects the reproduction of aquatic organisms, with negative effects on the formation and growth of eggs and larvae. It also has serious neurological impacts, altering behaviors such as feeding and predator avoidance [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Bivalves, such as oysters, are vulnerable at the cellular level to Hg, affecting their reproduction, growth and quality of edible tissues for humans [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. This phenomenon has generated global concern, prompting the use of indicator organisms, such as bivalves, to assess their presence in marine-coastal ecosystems [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite the decrease in Hg levels in bivalves due to stricter regulations, concerns persist worldwide. Colombia, unfortunately, does not escape from this problem, as it is among the countries with the highest per capita Hg contamination in the world, largely due to illegal mining and gold mining [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn Colombia, despite the growing interest in the problem generated by Hg contamination due to illegal mining and gold mining, research on the presence of this metal in bivalves is recent. Studies conducted in areas near Cartagena Bay, such as Brujas Island and Bar\u0026uacute; Island in Cartagena, as well as in the Marina and Taganga in Santa Marta, have revealed variations in Hg concentrations in the oyster \u003cem\u003eCrassostrea rhizophorae\u003c/em\u003e, depending on the climatic season [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In addition, it has been observed that climatic conditions in tropical regions, such as the Colombian Caribbean, as well as changes in physicochemical variables in the water column such as temperature, salinity, pH and dissolved oxygen [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], and the organic matter content in fine sediments and reducing condictions [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] can influence the availability of Hg in the environment.\u003c/p\u003e \u003cp\u003eThe response of bivalves to environmental variables during their life cycle [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] complicates the understanding of Hg accumulation. In turn, the differences in Hg concentrations between sites highlight [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] the need to further understand the factors that influence Hg concentrations in marine and coastal organisms such as the oyster \u003cem\u003eC. rhizophorae\u003c/em\u003e, determine the specific sources of contamination, and assess the impacts on local ecosystems in Colombia.\u003c/p\u003e \u003cp\u003eThis study evaluated Hg contamination in the oyster \u003cem\u003eC. rhizophorae\u003c/em\u003e and determined whether environmental variables and oyster size can facilitate Hg bioaccumulation. The research contributes to understanding the dynamics of contamination by this metal in tropical marine and coastal systems.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study area\u003c/h2\u003e \u003cp\u003eThe Colombian Caribbean region is characterized by a bimodal climatic regime with a rainy and dry season influenced by the Intertropical Convergence Zone (ITCZ) that generates periodic patterns [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Trade winds predominate from December to April (dry season), changing direction to the southeast between April and November (rainy season) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe Ci\u0026eacute;naga Grande de Santa Marta (CGSM) has an area of 450 km\u003csup\u003e2\u003c/sup\u003e [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] and was declared a Ramsar Wetland and Biosphere Reserve [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Its body of water is made up of several interconnected lagoons and a sand bar to the northeast of the Ci\u0026eacute;naga that separates it from the Caribbean Sea [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The exchange of fresh and brackish water is conducive to the development of the red mangrove \u003cem\u003eRhizophora mangle\u003c/em\u003e, which is essential for the mangrove oyster because it (the mangrove root) provides a substrate for the oysters [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. It stands out as one of the most productive tropical ecosystems in the Caribbean, with significant catches of commercial fish, crustaceans and mollusks [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe bay of Cispat\u0026aacute; (BhC) was transformed into an estuary as part of the lagoon system of the Sin\u0026uacute; River delta. This mangrove-estuarine ecosystem has fine and very fine sediments, largely influenced by the Sin\u0026uacute; River [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The estuary covers an area of 130 km\u003csup\u003e2\u003c/sup\u003e covered predominantly by mangroves [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), has an average monthly rainfall of 66 mm and an average sediment discharge of 3.1 kg/day. The rainy season from May to November records an average monthly rainfall of 150 mm and a sediment discharge of 11.5 kg/day [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Salinity is influenced by the hydrological dynamics of the ecosystem, fluctuating between rainy seasons, drought and a mixture of fresh and brackish water [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Field phase\u003c/h2\u003e \u003cp\u003eSamples were collected at three stations in CGSM and three in BhC trying to cover sites with gradients of water inflow from the sea and freshwater bodies that may carry contaminants. Sampling was conducted in the rainy season (November 2021) and in the dry season (March 2022). In situ measurements of temperature, salinity, pH and dissolved oxygen were made at a depth of 0.5 m using WTW 3110 and YSI Pro1030 multiparameter probes.\u003c/p\u003e \u003cp\u003eOyster individuals were collected at each of the stations and grouped into juveniles (22.0\u0026ndash;32.0 mm) and adults (35.0-56.5 mm) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Several specimens of the same category were stored in previously labeled airtight polyethylene bags and transferred preserved in cold (~\u0026thinsp;4\u0026deg;C).\u003c/p\u003e \u003cp\u003eFor the determination of mercury in seston, at each station three replicates of water were collected in 2.8 L amber flasks and stored cold (~\u0026thinsp;4\u0026deg;C). After homogenization, they were filtered through two Whatman GF/C glass fiber filters of 47 mm diameter per sample with a manual vacuum pump. They were stored in hermetically sealed polyethylene bags previously labeled, dried in an oven at 45\u0026deg;C for 24 h and weighed on an analytical balance [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAt each station, three replicates of sediment were collected with a van Veen dredge. From each unified sample per station, 600 g of sediments were separated to determine mercury, 75 g for organic matter and 75 g for redox potential. Samples were stored in airtight polyethylene bags with silicone scoop avoiding touching the edges of the dredge and kept cold (~\u0026thinsp;4\u0026deg;C) [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Laboratory phase\u003c/h2\u003e \u003cp\u003eFor the determination of organic matter, 5 g of dry sediment were placed in porcelain crucibles (previously weighed), subjected to calcination in a muffle at 550\u0026deg;C for 5 h and kept in the desiccator for 2 h. The determination of organic matter was based on the difference in dry and calcined weight [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFor redox potential quantification, the sediment sample was dried at 40\u0026deg;C for 24 h. 25 g of sediment were taken and homogenized in 50 mL of deionized water using a VELP Scientifica magnetic stirrer for 30 min. Measurement was performed with a YSI Pro1030 multiparameter probe through the oxidation-reduction potential electrode, previously calibrated at a standard temperature of 25\u0026deg;C [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFor the chemical analyses, all the material used was previously purged with 5% nitric acid (HNO\u003csub\u003e3\u003c/sub\u003e) and deionized water for 24 h. With the precaution of not contaminating the samples, gloves and glass and plastic elements were used. The samples were transferred cold preserved (~\u0026thinsp;4\u0026deg;C) to the Toxicology and Environmental Management laboratory of the University of Cordoba for Hg quantification.\u003c/p\u003e \u003cp\u003eThe collected oysters were cleaned to remove any particles adhering to the valves. The anteroposterior length APL (mm) was measured on the inner side of the ventral valve to the mark of the edge of the mantle with a Vernier caliper (precision of 0.05 mm). The soft tissue was then weighed using an analytical balance (0.1 mg accuracy). In each sample composed of organisms of similar size, all soft tissue was removed and deposited in 30 mL glass vials previously washed, labeled and weighed. The soft material was weighed by subtracting the weight of the vial and the samples were lyophilized.\u003c/p\u003e \u003cp\u003eFrom each seston, sediment, and oyster tissue sample, 20 to 40 mg were weighed and subjected to calcination at 450\u0026deg;C with a ramp of 50\u0026deg;C for 8 h. Then, 1 mL of concentrated HNO\u003csub\u003e3\u003c/sub\u003e was added and volatized on a heating plate. Finally, the sample was subjected to microwave-assisted acid digestion at 180\u0026deg;C for 20 min with a volume of 25 mL of distilled water.\u003c/p\u003e \u003cp\u003eThe fraction less than or equal to 65 \u0026micro;m of sediments and seston was digested with 5% nitric acid (HNO\u003csub\u003e3\u003c/sub\u003e) for subsequent determination of total Hg concentration by atomic absorption spectrometry [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Hg analysis was performed by EPA method 7473 PLTX-017, which consists of direct analysis by thermal decomposition, amalgamation, and atomic absorption spectrometry [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFor the analytical control in sediments, seston and oysters, a triplicate analysis of a solution of Hg at different concentrations (0.02, 0.05 and 0.5 \u0026micro;g of Hg) was used, complying with the acceptance criteria of the Association of Official Analytical Chemists (AOAC), with determination coefficients greater than 0.995 for the calibration curve and error percentages of less than 15%. TORT-1 (lobster hepatopancreas) from the National Research Council of Canada (NRCC) was used as reference material. Recovery percentages were 100\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4% in sediments (limit of detection, LOD, = 0.00073 \u0026micro;g/g Hg), 100\u0026thinsp;\u0026plusmn;\u0026thinsp;5.4% in seston (LOD\u0026thinsp;=\u0026thinsp;0.000015 \u0026micro;g/g Hg) and 100\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4% in oysters (LOD\u0026thinsp;=\u0026thinsp;0.00073 \u0026micro;g/g Hg) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Cabinet phase\u003c/h2\u003e \u003cp\u003eThe bioconcentration factor (BCF) was calculated as the ratio of Hg concentration in oyster tissue to its presence in sediment (sd) and seston (st), expressed in parts per million (ppm, \u0026micro;g/g) in dry weight (d.w.). This calculation was based on Mountouris et al. [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] and Romero-Murillo et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:{BCF}_{sd}=\\frac{{\\left[Metal\\right]}_{organism}}{{\\left[Metal\\right]}_{sedimento}},\\:{BCF}_{st}=\\frac{{\\left[Metal\\right]}_{organism}}{{\\left[Metal\\right]}_{seston}}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eBCF was used to evaluate the efficiency of Hg accumulation in oyster soft tissue. According to Mountouris et al. [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], BCF\u0026thinsp;\u0026lt;\u0026thinsp;1 suggests no metal accumulation, BCF\u0026thinsp;\u0026ge;\u0026thinsp;1 and \u0026lt;\u0026thinsp;10 indicates accumulation and BCF\u0026thinsp;\u0026ge;\u0026thinsp;10 indicates hyperaccumulation of metal.\u003c/p\u003e \u003cp\u003ePermutation analysis of variance (PERMANOVA) was applied to compare Hg concentration in oyster tissue and its BCF between the two ecosystems (k\u0026thinsp;=\u0026thinsp;2), the two climatic seasons (k\u0026thinsp;=\u0026thinsp;2), the six stations (k\u0026thinsp;=\u0026thinsp;6) and the two categorized size classes (k\u0026thinsp;=\u0026thinsp;2). 9 999 permutations were performed using Euclidean distance and type III sum of squares. The \u003cem\u003ep\u003c/em\u003e-values was computed using Monte Carlo (MC) permutation testing only when unique permutations were less than 100 [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe relationship of Hg concentration between sediment and seston was examined using Pearson's (data fitted to the normal distribution) and Spearman's (data not fitted to the normal distribution) correlation analyses. These analyses were conducted to identify potential relationships between physicochemical variables on Hg availability in sediments and seston [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eThe influence of environmental predictor variables on the oyster Hg concentration and Hg BCF in relation to seston was evaluated using a distance-based linear model (DistLM) with adjusted R\u003csup\u003e2\u003c/sup\u003e criterion and 9999 permutations [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo evaluate mercury contamination in bivalves, the Nemerow integral contamination index -P\u003csub\u003ec\u003c/sub\u003e- was used [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The calculation of P\u003csub\u003ec\u003c/sub\u003e is based on the average value of the individual pollution index (P\u003csub\u003eavg\u003c/sub\u003e), the maximum value (P\u003csub\u003emax\u003c/sub\u003e) and the minimum value (P\u003csub\u003emin\u003c/sub\u003e). The individual index values were calculated using the following formula:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{P}_{avg}=\\frac{{C}_{avg}}{S},\\:{\\:\\:\\:\\:\\:\\:P}_{max}=\\frac{{C}_{max}}{S},\\:{\\:\\:\\:\\:\\:\\:P}_{min}=\\frac{{C}_{min}}{S}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left[1\\right]$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cem\u003eC\u003c/em\u003e \u003csub\u003e \u003cem\u003ea\u003c/em\u003evg\u003c/sub\u003e is the average concentration value recorded in the data set evaluated, C\u003csub\u003emax\u003c/sub\u003e and C\u003csub\u003emin\u003c/sub\u003e are the maximum and minimum concentration values from the same data set, and S is the maximum concentration allowed in marine organisms (mollusks) with Hg (0.5 \u0026micro;g/g) [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOnce the historical values of P\u003csub\u003eavg\u003c/sub\u003e, P\u003csub\u003emax\u003c/sub\u003e and P\u003csub\u003emin\u003c/sub\u003e were obtained for each country by year, the calculation of P\u003csub\u003ec\u003c/sub\u003e was performed establishing (i) P\u003csub\u003ec\u003c/sub\u003e \u0026le; 0.7 considered no risk, (ii) 0.7\u0026thinsp;\u0026lt;\u0026thinsp;P\u003csub\u003ec\u003c/sub\u003e \u0026le; 1 low risk, (iii) 1\u0026thinsp;\u0026lt;\u0026thinsp;P\u003csub\u003ec\u003c/sub\u003e \u0026le; 2 medium risk, (iv) 2\u0026thinsp;\u0026lt;\u0026thinsp;P\u003csub\u003ec\u003c/sub\u003e \u0026le; 3 high risk and (v) P\u003csub\u003ec\u003c/sub\u003e \u0026gt; 3 very high risk of contamination [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. It was calculated using the following equation:\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:\\frac{\\sum\\:{P}_{c}}{n}=\\sqrt{\\frac{{P}_{avg}^{2}+{P}_{max}^{2}+{P}_{min}^{2}}{3}}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left[2\\right]$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eΣP\u003csub\u003ec\u003c/sub\u003e is the sum of all P\u003csub\u003ec\u003c/sub\u003e values divided by \"n\", the total number of years evaluated per country published in its historical record. This ensures that the values of P\u003csub\u003emax\u003c/sub\u003e and P\u003csub\u003emin\u003c/sub\u003e do not overestimate or underestimate the calculation of the contamination index for each metal evaluated, respectively.\u003c/p\u003e \u003cp\u003eThe similarities and differences of the sites were assessed with a hierarchical clustering analysis, a multivariate technique applied to construct distance dendrograms from the classification of each site according to the level of metal contamination. The analysis was applied through the use of the squared Euclidean distance with Ward's linkage, minimizing variability and producing uniformly sized clusters [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Environmental conditions in both coastal lagoons\u003c/h2\u003e\n \u003cp\u003eThe average water temperature in CGSM and BhC reached its highest value during the rainy season. In CGSM, the temperature during the rainy season was 31.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48\u0026deg;C (n\u0026thinsp;=\u0026thinsp;3), while in dry season it was 30.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.84\u0026deg;C (n\u0026thinsp;=\u0026thinsp;3). In BhC, with slightly lower temperatures compared to CGSM, the temperature during the rainy season was 28.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43\u0026deg;C (n\u0026thinsp;=\u0026thinsp;3), and in dry season it was 29.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u0026deg;C (n\u0026thinsp;=\u0026thinsp;3) (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA, Supplementary Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eRegarding pH, during the rainy season, CGSM had a higher pH value (8.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12, n\u0026thinsp;=\u0026thinsp;3) compared to BhC (7.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09, n\u0026thinsp;=\u0026thinsp;3), while during the dry season, were a decrease in pH in CGSM (8.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16, n\u0026thinsp;=\u0026thinsp;3) and an increase in BhC (8.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003, n\u0026thinsp;=\u0026thinsp;3). The values were similar in both study areas (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA, Supplementary Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe average dissolved oxygen content was higher in CGSM during both climatic seasons, with values of 7.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66 mg/L (n\u0026thinsp;=\u0026thinsp;3) in rainy season and 7.39\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4 mg/L (n\u0026thinsp;=\u0026thinsp;3) during dry season. In BhC, the contents were 4.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 mg/L (n\u0026thinsp;=\u0026thinsp;3) in rainy season and 5.52\u0026thinsp;\u0026plusmn;\u0026thinsp;1.28 mg/L (n\u0026thinsp;=\u0026thinsp;3) along the dry season (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA, Supplementary Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eRegarding salinity and organic matter, CGSM showed variations in these variables, with salinity values from 2.47\u0026thinsp;\u0026plusmn;\u0026thinsp;1.01 (n\u0026thinsp;=\u0026thinsp;3) in rainy season to 18.53\u0026thinsp;\u0026plusmn;\u0026thinsp;6.33 (n\u0026thinsp;=\u0026thinsp;3) in dry season, and organic matter content during the rainy season of 11.67\u0026thinsp;\u0026plusmn;\u0026thinsp;3.27% (n\u0026thinsp;=\u0026thinsp;3), doubling the observed values on the dry season (5.97\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4%, n\u0026thinsp;=\u0026thinsp;3). In contrast, in BhC, the average salinity values (from 24.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.01, n\u0026thinsp;=\u0026thinsp;3 to 30.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56, n\u0026thinsp;=\u0026thinsp;3) and organic matter (from 5.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5%, n\u0026thinsp;=\u0026thinsp;3 to 6.06\u0026thinsp;\u0026plusmn;\u0026thinsp;1.28%, n\u0026thinsp;=\u0026thinsp;3) varied the less between those two climatic seasons (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA, Supplementary Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eIn sediments the redox potential, both in CGSM and BhC, reducing conditions were recorded with a range of values from 28 to 77 mV between both study areas. Increases in redox potential were observed in BhC (52\u0026thinsp;\u0026plusmn;\u0026thinsp;3, n\u0026thinsp;=\u0026thinsp;3 to 65\u0026thinsp;\u0026plusmn;\u0026thinsp;4, n\u0026thinsp;=\u0026thinsp;3), and decreases in CGSM (50\u0026thinsp;\u0026plusmn;\u0026thinsp;11, n\u0026thinsp;=\u0026thinsp;3 to 35\u0026thinsp;\u0026plusmn;\u0026thinsp;4, n\u0026thinsp;=\u0026thinsp;3) from rainy season to dry season (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA, Supplementary Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Concentration of Hg in sediments, seston and \u003cem\u003eCrassostrea rhizophorae\u003c/em\u003e\u003c/h2\u003e\n \u003cp\u003eHg concentration in sediments and seston varied markedly between the two ecosystems. In BhC, in both sediments and seston, Hg concentrations are consistently higher than in CGSM in both climatic seasons (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB, Supplementary Table S2).\u003c/p\u003e\n \u003cp\u003eIn the rainy season, the highest concentration of Hg in sediments was found in CIS-1 (BhC) with 0.128 \u0026micro;g/g Hg dry weight (d.w.) which is double the highest content detected in CGSM (0.059 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e. in CGS-1). Hg content in sediments at BhC was slightly lower in the dry season but remained above 0.08 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e. indicating a possible constant source of Hg contamination. In CGSM, during the dry season, lower Hg was observed in CGS-1 and higher in CGS-2 (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB, Supplementary Table S2).\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePERMANOVA analysis on Hg concentration and bioconcentration factor (BCF-Hg) vs. sizes (juveniles and adults), stations, ecosystem, and climatic season in the oyster \u003cem\u003eCrassostrea rhizophorae\u003c/em\u003e. Ecosytem (EC), climatic season (CS), station (ST), size (SZ), degrees of freedom (df), sum of squares (SS), and mean square (MS). For more information, see Supplementary Table S4\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colspan=\"7\"\u003e\n \u003cp\u003eHg (\u0026micro;g/g d.w.)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFactor\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003edf\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePseudo-F\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026Uacute;nique\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e47.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;836\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e1 \u0026times; 10\u003c/strong\u003e\u003c/span\u003e\u003csup\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;4\u003c/strong\u003e\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.6 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.6 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;837\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.876\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eST (EC)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.2 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;948\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e1.6 \u0026times; 10\u003c/span\u003e\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u0026minus;\u0026thinsp;2\u003c/span\u003e\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEC \u0026times; CS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.3 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.3 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;843\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.098\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSZ (ST (EC))\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.6 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.7 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;954\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e1.8 \u0026times; 10\u003c/strong\u003e\u003c/span\u003e\u003csup\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;3\u003c/strong\u003e\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCS \u0026times; ST (EC)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.9 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.4 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;949\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e7 \u0026times; 10\u003c/span\u003e\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u0026minus;\u0026thinsp;3\u003c/span\u003e\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCS \u0026times; SZ (ST (EC))\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.2 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;939\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e0.049\u003c/span\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eResidual\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.87 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.07 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"7\"\u003e\n \u003cp\u003e\u003cstrong\u003eBCF-Hg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eFactor\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003edf\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eMS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003ePseudo-F\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026Uacute;nique\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003ep\u003c/strong\u003e\u003cstrong\u003e-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e747.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e747.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e72.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;841\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e1 \u0026times; 10\u003c/strong\u003e\u003c/span\u003e\u003csup\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;4\u003c/strong\u003e\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e594.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e594.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e57.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;864\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e1 \u0026times; 10\u003c/span\u003e\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u0026minus;\u0026thinsp;4\u003c/span\u003e\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eST (EC)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e62.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.514\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;954\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.219\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEC \u0026times; CS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e152.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e152.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;837\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e4 \u0026times; 10\u003c/strong\u003e\u003c/span\u003e\u003csup\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;4\u003c/strong\u003e\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSZ (ST (EC))\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e200.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;949\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e0.011\u003c/strong\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCS \u0026times; ST (EC)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e84.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;951\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.107\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCS \u0026times; SZ (ST (EC))\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e322.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e53.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u0026nbsp;931\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e4 \u0026times; 10\u003c/strong\u003e\u003c/span\u003e\u003csup\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e\u0026minus;\u0026thinsp;4\u003c/strong\u003e\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e487.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u0026nbsp;720\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e* \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 indicates significant differences among the analyzed factors. In red the significant ones.\u003c/p\u003e\n \u003cp\u003eThe Hg available in the seston presented similar values in the stations of each ecosystem and in the two climatic seasons. However, as in sediments, a lower concentration was detected in the dry season. In BhC, the concentration went from 0.032\u0026thinsp;\u0026plusmn;\u0026thinsp;0.005 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e. in the rainy season to 0.022\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e. in the dry season. Lower concentrations were found in CGSM, with values ranging from 0.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e. in the rainy season to 0.004\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e. in the dry season (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB, Supplementary Table S2).\u003c/p\u003e\n \u003cp\u003eIn BhC the highest Hg content in seston was positively and significantly related to temperature (Pearson, r\u0026thinsp;=\u0026thinsp;0.93, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and in sediments Hg was significantly related to organic matter (Pearson, r\u0026thinsp;=\u0026thinsp;0.84, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;=\u0026thinsp;0.04) (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, Supplementary Table S3).\u003c/p\u003e\n \u003cp\u003eHg concentrations in oyster tissue show distinct accumulation patterns in CGSM and BhC, varying as a function of climatic seasons. However, a pattern similar to that of sediment and seston was maintained, with a higher Hg content in oyster soft tissue in BhC (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB). In the rainy season, Hg in the oyster was 0.083\u0026thinsp;\u0026plusmn;\u0026thinsp;0.007 \u0026micro;g/g \u003csub\u003ed.w\u003c/sub\u003e. (n\u0026thinsp;=\u0026thinsp;17) in CGSM and of 0.135\u0026thinsp;\u0026plusmn;\u0026thinsp;0.015 \u0026micro;g/g \u003csub\u003ed.w\u003c/sub\u003e. (n\u0026thinsp;=\u0026thinsp;18) in BhC showing significant differences between the two ecosystems (Permanova, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.01). In dry season, these differences were maintained, given the decrease in oyster Hg content in CGSM (0.066\u0026thinsp;\u0026plusmn;\u0026thinsp;0.007 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e., n\u0026thinsp;=\u0026thinsp;18) and increased in BhC (0.154\u0026thinsp;\u0026plusmn;\u0026thinsp;0.019 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e., n\u0026thinsp;=\u0026thinsp;18) (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA, Supplementary Table S4).\u003c/p\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eWith respect to Hg BCF, both in sediments and seston, both ecosystems presented accumulation to hyperaccumulation of Hg in the oyster tissue, with the highest values in the dry season. In this same climatic season, at CGSM, the oyster presented an accumulation of Hg with the sediment (BCF\u0026thinsp;\u0026ge;\u0026thinsp;1) and a hyperaccumulation of the metal with the seston (BCF\u0026thinsp;\u0026ge;\u0026thinsp;10), as opposed to the accumulation condition in both matrices during the rainy season. In BhC, the oyster maintained the accumulation condition in both matrices (BCF\u0026thinsp;\u0026ge;\u0026thinsp;1) as in rainy season (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). These results notably emphasize the capacity of the oyster to accumulate Hg in its tissues, especially in CGSM through the seston in the dry season. Significant differences in BCF were determined between CGSM and BhC ecosystems, with higher concentrations in BhC (Permanova, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05). However, no significant differences in concentrations were observed between climatic seasons, since the values measured at two of three stations in both CGSM (CGS-2 and CGS-3) and BhC (CIS-1 and CIS-3) were similar in both climatic seasons (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB, Supplementary Table S4).\u003c/p\u003e\n \u003c/div\u003e\n \u003cp\u003eIn the two ecoystems evaluated, there were significant differences in the Hg contents between stations (Permanova, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). In the rainy season at CGSM the differences occurred between stations CGS-1 and CGS-2 and at BhC between CIS-2 and CIS-3. In the dry season, significant differences were found between CIS-1 and CIS-2 in BhC, with the lowest concentrations in CIS-1 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB, Supplementary Table S4 and S5).\u003c/p\u003e\n \u003cp\u003eThere were significant differences in the length of juveniles and adults (Permanova, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between stations (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). In CGSM in the dry season, concentrations were higher in adult sizes at station CGS-3 (0.121\u0026thinsp;\u0026plusmn;\u0026thinsp;0.016 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e.) with respect to juveniles (0.039\u0026thinsp;\u0026plusmn;\u0026thinsp;0.009 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e.). In BhC, in both rainy and dry seasons, the highest concentration of juvenile lengths was at station CIS-2 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA, Supplementary Table S4 and S5).\u003c/p\u003e\n \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.1 Importance of seston in the bioconcentration of Hg\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eHigh Hg bioconcentration factor values reflected a significant correlation with seston content (Pearson, r\u0026thinsp;=\u0026thinsp;0.72, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.01), with conditions of accumulation (BCF\u0026thinsp;\u0026ge;\u0026thinsp;1) in BhC and hyperaccumulation in CGSM (BCF\u0026thinsp;\u0026ge;\u0026thinsp;10; Supplementary Table S4).\u003c/p\u003e\n \u003cp\u003eDifferences in Hg bioconcentration between CGSM and BhC were determined (Permanova, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). These differences were also observed as a function of climatic seasons, with an increase during the dry season in each CGSM season, and significant in the CIS-2 season in BhC compared to the rainy season. When the factors ecosystem and climatic season were combined, significant differences were still present, with higher values of Hg bioconcentration in CGSM in both climatic seasons compared to BhC (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB, Supplementary Table S4 and S5). These results indicate that the oyster in CGSM is accumulating higher concentrations of Hg in its tissues compared to the BhC oyster, although the accumulation is also considerably higher in the BhC oyster.\u003c/p\u003e\n \u003c/div\u003e\n \u003cp\u003eSignificant differences between juvenile and adult sizes were determined with the BCF-Hg, which was maintained when considering the climatic season (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). In BhC, the highest values of BCF-Hg were observed in juvenile sizes in both climatic seasons. In CGSM, the highest BCF occurred in adult sizes during the dry season, while they were similar in both sizes during the rainy season (Spearman, r\u0026thinsp;=\u0026thinsp;0.25, \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB, Supplementary Table S4).\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAnalysis of DistLM in the relationship between Hg concentration and its bioconcentration in \u003cem\u003eCrassostrea rhizophorae\u003c/em\u003e with physicochemical variables (predictors). Stepwise model and selection criterion of adjusted R\u003csup\u003e2\u003c/sup\u003e were used (9999 permutations). SS: sum of squares.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colspan=\"5\"\u003e\n \u003cp\u003eJuvenile size\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVariable\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePseudo-F\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eProportion of variation explained\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTemperature\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.039\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSalinity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.098\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.097\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDissolved oxygen\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.077\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOrganic matter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.021\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"5\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdult size\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003ePseudo-F\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003ep\u003c/strong\u003e\u003cstrong\u003e-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eProportion of variation explained\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTemperature\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.026\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSalinity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.098\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e39.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.087\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDissolved oxygen\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e106.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan style=\"color: rgb(226, 80, 65);\"\u003e\u003cstrong\u003e0.231\u003c/strong\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOrganic matter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.026\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e*\u003cem\u003ep\u003c/em\u003e-values\u0026thinsp;\u0026lt;\u0026thinsp;0.05 express that the variable significantly explains the variations in Hg content and its bioconcentration in \u003cem\u003eCrassostrea rhizophorae\u003c/em\u003e. In red is the greatest variation explained.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Relationship between environmental variables and Hg bioconcentration in oysters\u003c/h2\u003e\n \u003cp\u003eBetween the Hg concentration in the mangrove oyster tissue and its BCF by size in relation to the metal content in the seston, it was not possible to find a positive or negative relationship with the environmental variables analyzed. The relationship between physicochemical variables and size with Hg concentration and BCF in the mangrove oyster were not significant (DistLM; \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). This suggests that environmental variables and size did not play a determining role in the differences in oyster Hg content and bioconcentration at CGSM and BhC (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). Other factors, such as Hg content in the seston and local transport and sedimentation processes, may be playing a more influential role in Hg accumulation.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Hg contamination status of bivalves in a global context during the last decade\u003c/h2\u003e\n \u003cp\u003eConsidering Hg contamination levels in global monitoring during the last 12 years in different bivalve species, both ecosystems are part of Clade 1, CGSM presents no risk of Hg contamination in oyster consumption (similar to Taganga), while BhC is close to a low risk of Hg contamination along with Isla Cayo el Pigeon (Nicaragua). However, these values exceed those reported in other areas such as China, Italy and Montenegro, which presented the lowest risk of Hg consumption by bivalves. This makes it relevant to consider the potential risk of Hg contamination in the Colombian Caribbean, which presented the highest risk of contamination by Hg in the world with bivalves during the last decade (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Discussion","content":"\u003cp\u003eThe higher concentrations of Hg, in all of them sediment, seston and oyster, in BhC compared to CGSM (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB, Supplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) raise concerns about environmental quality and ecosystem health in the region. Hg contamination in BhC is linked to the connection of the Sin\u0026uacute; River through the Sicar\u0026aacute; stream, suggesting contamination associated with water and sediment flows from surrounding agricultural areas [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], as well as the use of fungicides containing phenylmercury (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eHg) and extensive spraying of rice fields with mercury agrochemicals [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Other sources identified include regional gold mining, wastewater discharge, use of Hg in ship paints as an anti-corrosion compound, and air pollution [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn CGSM, the sources of Hg contamination are less clear; the entry of this metal into the swamp is associated with atmospheric deposits and anthropogenic activities [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], gold mining and industrial activities [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] mainly from the Magdalena River [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlthough the levels of Hg in sediments in BhC and CGSM are lower than those reported in other regions, such as in Cartagena Bay, Colombia (0.094\u0026ndash;10.293 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e.) [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] and in San Vicente Bay, Chile (0.37 to 0.95 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e.) [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], and considering that the Hg content was below the tolerable threshold for the ecosystem and associated biota (TEL) of 0.13 \u0026micro;g/g [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], the risk of Hg contamination is higher in BhC compared to CGSM. In previous assessments conducted by Feria et al. [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], Campos et al. [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] and Marrugo-Negrete et al. [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], Hg concentrations exceeding the TEL threshold have been reported in sediments along the Sin\u0026uacute; riverbed and at the mouth of the BhC. In contrast, in CGSM, Hg concentrations reported in sediments have been less than 0.11 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e., being similar to what was found in this study (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eThe slight increase in Hg content in sediment and seston during the rainy season compared to the dry season (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB) could be attributed to metal flushing from land-based sources, influenced by increased sediment and freshwater input [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. These factors are especially relevant in the CGSM with significant contributions from the Magdalena River in the CGSM [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] and the Sin\u0026uacute; River in BhC [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Although these variations between climatic seasons were not significant for Hg content in the mangrove oyster (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA), the importance of sediment-seston interaction and the influence of local conditions in the coastal areas of the Colombian Caribbean on Hg availability in the oyster is highlighted [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eVariables such as temperature and organic matter may be playing an important role in the Hg content of sediments and seston. In BhC, the highest Hg contents in the seston during the rainy season were significantly correlated with the highest temperature values (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), this being a variable that can affect the rate of chemical reactions, including its methylation [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. In turn, higher Hg values in sediments were related to higher organic matter content in the rainy season, underlining the fundamental role of organic matter in the retention of metals in sediments, together with fine sediments and a sulfate-reducing environment [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], as in CGSM [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] and BhC (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003eAlthough no direct correlation was identified between pH and Hg concentrations in sediments and seston (Supplementary Table S3), slightly acidic or neutral pH conditions result in higher Hg precipitation in sediments [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e], which could possibly explain why BhC, with lower pH values, had higher Hg contents in sediments compared to CGSM (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAnother aspect to take into account in the precipitation of Hg in sediments is the variations from sulfates to sulfides, which possibly increase the flux of reactive phosphate and ammonium at the sediment-water interface [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. This process favors that Hg tends to precipitate in the sediments as insoluble hydroxides, oxides, carbonates or phosphates [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. The interaction of these processes could help to understand the variations of Hg content in sediments, taking into account the pH values in each climatic season. This pattern is particularly noticeable in BhC because of the differences in pH from rainy to dry season (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWith respect to the mangrove oyster, the influence of the environmental variables analyzed on the concentration and bioconcentration factor (BCF) of Hg was not significant (Tables\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Material Supplementary S4). This finding responds to what has been reported in other investigations, in which the influence of variables such as temperature, salinity and pH on the uptake and accumulation of Hg is not completely understood in bivalves [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e], unlike what occurs in sediments and seston in which the processes of accumulation, uptake, toxicity and speciation of Hg are known [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlthough no significant relationship could be established between Hg BCF with environmental conditions in CGSM and BhC, it is important to consider that high concentrations of dissolved oxygen in CGSM, together with changes in the chemical composition of the sediments, may increase and/or alter the metabolic activity of bivalves [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e], which could affect the capacity for Hg uptake and excretion in bivalves such as the oyster [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe mangrove oyster is known for its ability to filter large volumes of water during feeding [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] and particulate matter from sediments [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]; therefore, Hg concentrations in the oyster were closely related to the metal content in its environment (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). Hg bioconcentration was significantly associated with seston, which was to be expected considering that collection of the organism was mainly on mangrove roots. As with seston, metal accumulation and hyperaccumulation were obtained with respect to Hg concentrations in the sediment (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In this regard, measurements of metals in sediments, such as with seston, provide crucial data on the availability and uptake of Hg by the bivalve, providing a comprehensive view of the interaction between these organisms and their contaminated environment.\u003c/p\u003e \u003cp\u003eThe results in BhC are consistent with previous studies. Coimbra [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e] in Sepetiba Bay in Brazil in \u003cem\u003eMytela guyanensis\u003c/em\u003e and D\u0026iacute;az et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] in San Vicente Bay in Chile in \u003cem\u003eTagelus dombeii\u003c/em\u003e, reported inverse correlations between Hg content and species size. They suggested that there are metal assimilation rates similar to the excretion rate in larger individuals, which may be generated by decreased metabolism and less water pumping with bivalve growth [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDuring the growth of bivalves, several mechanisms are involved that regulate the accumulation of toxic metals such as Hg in their tissues. The formation of mineralized granules allows storage and possibly detoxification by Hg [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. For its release, bivalves develop a homeostatic regulation system during their growth that includes several excretion mechanisms through urine and feces, which contribute to maintain adequate Hg concentrations [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAnother aspect is the development of new gill systems; their formation plays a key role in the filtration of particles, including metals from the aquatic environment [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. This progressive development of gill systems contributes to the efficiency of bivalves in capturing and regulating Hg in their tissues as they develop.\u003c/p\u003e \u003cp\u003eThe emission of gametes during reproduction is another important strategy that bivalves deploy to mitigate the accumulation of toxic metals [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]. During the release of gametes from the mangrove oyster, an increase in Hg BCF could have been experienced during the rainy season, as it is associated with a decrease in organism biomass with spawning [\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]. However, in both CGSM and BhC the highest values of BCF in oysters were obtained during the dry season (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). During gamete release, which generally occurs during the rainy season and encompasses several breeding peaks in the Colombian Caribbean [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], mineralized granules stored in the lysosomes may be released along with the gametes. This process, called exocytosis, allows the contents of lysosomes, including metals such as Hg, to be released into the aquatic environment [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. This possible release of mineralized Hg granules in lysosomes together with the expulsion of gametophytes could have contributed to the lower Hg BCF values during the rainy season.\u003c/p\u003e \u003cp\u003eAs for CGSM, slightly higher concentrations and BCF in adult lengths were observed in dry season, similar to what was reported by Costa et al. [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e] and De Gregori et al. [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e], and being the inverse of what was found in BhC in both climatic seasons. This result highlights the complexity of the relationship between the various environmental and organismal factors that influence Hg bioconcentration.\u003c/p\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Hg intake risk in \u003cem\u003eC. rhizophora\u003c/em\u003ee at CGSM and BhC\u003c/h2\u003e \u003cp\u003eVariability in contamination sources and Hg concentrations in CGSM and BhC stands out as a key factor influencing contamination risk. In particular, BhC shows values close to the permissible limit for Hg in bivalves for human consumption of 0.5 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e. [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], raising concerns about the health of the ecosystem. This situation is similar to what has been reported on Cayo el Pigeon Island in Nicaragua and Santa Marta in Colombia by Aguirre-Rub\u0026iacute; et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). However, both ecosystems are far from what has been reported for this species in coastal areas of the Dominican Republic, where Sbriz et al. [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e] recorded one of the highest Hg contents in the mangrove oyster (7.02 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e.).\u003c/p\u003e \u003cp\u003eWhen comparing Hg concentrations in mangrove oysters with other bivalve species globally over the last decade, CGSM and BhC stand out as ecosystems that maintain low to no risk of Hg contamination. This contrasts with findings in coastal areas of China [\u003cspan additionalcitationids=\"CR68\" citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e], Italy [\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e] and Montenegro [\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e], with a lower risk of Hg contamination in the world and serves as a reference for the potential risk of contamination in CGSM and BhC (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe relevance of this study is intensified when considering the current situation of Hg contamination in Colombia. In the bay of Cartagena with \u003cem\u003eC. rhizophorae\u003c/em\u003e its has reported the highest risk of Hg contamination in the last decade in the world [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Supplementary Table S6 and S7). In a historical context, the Bay had a direct discharge of Hg from the Alcalis chlorine plant [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e]. Similar cases prior to 2010 have been reported in \u003cem\u003eTagelus dombeii\u003c/em\u003e (San Vicente Bay, Chile) [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], in \u003cem\u003eArchivesica gigas\u003c/em\u003e (Gulf of California, United States) [\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e] and in \u003cem\u003eMytilus galloprovincialis\u003c/em\u003e (Adriatic Sea, Croatia) [\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e] with concentrations above 0.5 \u0026micro;g/g Hg \u003csub\u003ed.w\u003c/sub\u003e. These findings underscore the need for continuous monitoring at CGSM and BhC to identify specific sources of contamination and generate appropriate preventive measures.\u003c/p\u003e \u003c/div\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eCispat\u0026aacute; Bay (BhC) had the highest concentrations of Hg in sediments, seston and oysters compared to Ci\u0026eacute;naga Grande de Santa Marta (CGSM) in both climatic seasons. However, the oyster exhibited the highest values of bioconcentration factor (BCF) with the seston of the CGSM, with a higher risk of Hg contamination. Temperature in the water column and organic matter in sediments influenced Hg concentrations in seston and sediments but have a limited and insignificant impact with the other environmental variables on Hg bioconcentration by size in the oyster. Adult sizes accumulated more Hg in CGSM, while juvenile sizes accumulated more Hg in BhC. This highlights the importance of considering the size of the bivalve when assessing Hg contamination, taking into account the specific environmental conditions of each ecosystem. The CGSM exhibited contamination without risk for human consumption, similar to that reported in other areas in the Colombian Caribbean, while BhC presented near-low contamination due to its higher Hg content.\u003c/p\u003e"},{"header":"Declarations","content":"\n\u003ch2\u003eFounding sources\u003c/h2\u003e\n\u003cp\u003eThis study was done within the research program \u0026quot;Redes tr\u0026oacute;ficas marinas del Caribe colombiano en la era del pl\u0026aacute;stico y los contaminantes t\u0026oacute;xicos\u0026rdquo; (code MINCIENCIAS 71475)\u0026rdquo;, funded by MINCIENCIAS and Universidad Jorge Tadeo Lozano, in partnership with Universidad Nacional de Colombia, sede Caribe. The funding for Hg analysis in oysters was provided of Colombia Biodiversa (I-2023) and Banco de la Rep\u0026uacute;blica with the Project 5.131 from the Foundation for the Promotion of Research and Technology (Fundaci\u0026oacute;n para la Promoci\u0026oacute;n de la Investigaci\u0026oacute;n y la Tecnolog\u0026iacute;a). Translation funding was provided by internal grants from the Universidad Jorge Tadeo Lozano.\u003c/p\u003e\n\u003ch2\u003eCompeting Interests\u003c/h2\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003ch2\u003eCRediT authorship contribution statement\u003c/h2\u003e\n\u003cp\u003e\u003cstrong\u003eAnubis V\u0026eacute;lez-Mendoza\u003c/strong\u003e: Funding Acquisition, Conceptualization, Methodology, Data Curation, Formal Analysis, Visualitation, Writing \u0026amp; Original draft, Writing, Review \u0026amp; Editing. \u003cstrong\u003eJeimmy Paola Rico Mora:\u003c/strong\u003e Funding Acquisition, Data Curation, Visualitation, Supervision, Writing, Review \u0026amp; Editing. \u003cstrong\u003eN\u0026eacute;stor Hernando Campos-Campos:\u003c/strong\u003e Funding Acquisition, Data Curation, Visualitation, Supervision, Writing, Review \u0026amp; Editing. \u003cstrong\u003eMargui Lorena\u003c/strong\u003e \u003cstrong\u003eAlmario-Garc\u0026iacute;a:\u003c/strong\u003e Supervision, Writing, Review \u0026amp; Editing. \u003cstrong\u003eAdolfo Sanjuan-Mu\u0026ntilde;oz:\u003c/strong\u003e Project Administration \u0026amp; Funding Acquisition, Supervision, Writing, Review \u0026amp; Editing. \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eAcknowledgement\u003c/h2\u003e\n\u003cp\u003eWe would like to especially thank the members of the team Diana Bustos-Montes, Paulo Tigreros-Benavides, Diana Rubio-Lancheros, Mar\u0026iacute;a Camila Castellanos Jimenez, Ana M. Hern\u0026aacute;ndez-Chamorro, Nic\u0026oacute;las Santos-V\u0026aacute;squez, Andr\u0026eacute;s Navarro-Mart\u0026iacute;nez, Nelson Rafael Camargo Tibamoso, Laura Daniela Garc\u0026iacute;a Mel\u0026eacute;ndez and the students of the Marine Ecology and Biodiversity (ECOBIOMAR-UTADEO) research incubator, for their support in taking samples and laboratory analysis. Special thanks to CECIMAR of the Caribbean headquarters of the National University of Colombia for providing their spaces for sample processing. To INVEMAR for the support provided for the treatment of samples.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eMountouris A, Voutsas E, Tassios D (2002) Bioconcentration of heavy metals in aquatic environments: The importance of bioavailability. 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Deep Sea Res I: Oceanogr Res Pap 50(6): 757-761. https://doi.org/10.1016/S0967-0637(03)00054-2\u003c/li\u003e\n \u003cli\u003eKljaković-Ga\u0026scaron;pić Z, Herceg-Romanić S, Kožul D, Veža J (2010) Biomonitoring of organochlorine compounds and trace metals along the Eastern Adriatic coast (Croatia) using \u003cem\u003eMytilus galloprovincialis\u003c/em\u003e. Mar Pollut Bull 60(10): 1879-1889. https://doi.org/10.1016/j.marpolbul.2010.07.019\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"biological-trace-element-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bter","sideBox":"Learn more about [Biological Trace Element Research](https://www.springer.com/journal/12011)","snPcode":"12011","submissionUrl":"https://submission.nature.com/new-submission/12011/3","title":"Biological Trace Element Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Mercury, Crassostrea rhizophorae, bioconcentration factor, pollution index, sizes","lastPublishedDoi":"10.21203/rs.3.rs-4725392/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4725392/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTotal mercury was evaluated in the mangrove oyster \u003cem\u003eCrassostrea rhizophorae\u003c/em\u003e, in sediments and seston from the Ci\u0026eacute;naga Grande de Santa Marta (CGSM) and Cispat\u0026aacute; Bay (BhC) in two climatic seasons (rainy and dry). Composite samples of sediments, seston and oysters in juvenile and adult sizes were collected at six stations (three in each ecosystem) and Hg was quantified by atomic absorption spectrophotometry (EPA method 7473 PLTX-017). BhC had the highest Hg concentrations in sediment, seston and oysters compared to CGSM, with values close to the tolerable threshold for the ecosystem and associated biota (TEL) of 0.13 \u0026micro;g/g Hg and with a low risk of Hg contamination in the mangrove oyster. Although at CGSM Hg was below the TEL in sediment and was considered safe in the oyster, significant bioaccumulation was evident with the metal content in the seston, indicating a potential risk to the ecosystem and humans. The variables organic matter and temperature influenced metal availability in the sediment and seston, respectively; in contrast, they had no significant relationship in the oyster. In CGSM, higher [Hg] was recorded in adult sizes, while in BhC the highest accumulation occurred in juveniles, especially during the dry season. These results emphasize the need for continuous monitoring of Hg contamination in both ecosystems. In addition, they highlight the importance of considering the size of oysters when assessing Hg contamination, as they may vary according to specific ecosystem and climatic conditions.\u003c/p\u003e","manuscriptTitle":"Changes in mercury content in oysters in relation to sediment and seston content in the Colombian Caribbean lagoons","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-06 04:51:53","doi":"10.21203/rs.3.rs-4725392/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2024-08-18T21:36:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"138934638055224563281474123361728471970","date":"2024-08-12T18:24:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-07T11:18:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"174650675360044474823571378880694632008","date":"2024-07-29T13:27:06+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-12T02:55:05+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-12T02:54:18+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-12T00:43:31+00:00","index":"","fulltext":""},{"type":"submitted","content":"Biological Trace Element Research","date":"2024-07-11T15:57:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"biological-trace-element-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bter","sideBox":"Learn more about [Biological Trace Element Research](https://www.springer.com/journal/12011)","snPcode":"12011","submissionUrl":"https://submission.nature.com/new-submission/12011/3","title":"Biological Trace Element Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3b49c8ba-61b2-42fd-b54a-fa230f869e51","owner":[],"postedDate":"August 6th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-08-06T04:51:53+00:00","versionOfRecord":[],"versionCreatedAt":"2024-08-06 04:51:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4725392","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4725392","identity":"rs-4725392","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}