Integrated assessment of heavy metal pollution: Bioaccumulation in the river snail Filopaludina martensi, sediment, and water from the Mae Kha Canal, Chiang Mai province, Thailand

Integrated assessment of heavy metal pollution: Bioaccumulation in the river snail Filopaludina martensi, sediment, and water from the Mae Kha Canal, Chiang Mai province, Thailand | 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 Integrated assessment of heavy metal pollution: Bioaccumulation in the river snail Filopaludina martensi, sediment, and water from the Mae Kha Canal, Chiang Mai province, Thailand Thanapit Chatchakit, Nattawadee Nantarat This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7136529/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Dec, 2025 Read the published version in Ecotoxicology → Version 1 posted 9 You are reading this latest preprint version Abstract Cadmium (Cd) and lead (Pb) tend to bioaccumulate in freshwater environments, making them major hazards to environmental health. This study aimed to determine the content of the heavy metals Cd and Pb in field sediment, water, and whole tissues of the edible river snail Filopaludina martensi , which could serve as bioindicators for these metals. Principal component analysis (PCA), Permutational multivariate analysis of variance (PERMANOVA), and Pearson correlation coefficients (r) showed that heavy metals and snail populations are greatly impacted by seasonal variations (p < 0.05). The upstream section had healthier conditions compared with the midstream section, owing to the impact of anthropogenic activities. The wet season showed the highest Cd and Pb concentrations (p < 0.05) in all samples. The sediment samples had the highest Cd and Pb concentrations, followed by the snail and water samples (p < 0.05). The heavy metal concentrations in the sediment and river snail samples showed a strong correlation (PCA; p < 0.05). Importantly, the Pb concentrations in the snail samples were higher than the recommended threshold, indicating that these snails should be consumed with extreme caution. Both Cd and Pb damaged the snail digestive glands, and which may have caused DNA damage. These findings indicate that F. martensi is a reliable bioindicator of the ecological integrity of the Mae Kha Canal. Evidence of biological degradation and ongoing metal contamination in the canal emphasizes the value of using these snails for pollution monitoring and directing pollution management efforts to maintain aquatic ecosystems and public health. Freshwater snails Heavy metals Bioindicators Histopathology Freshwater ecosystem Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction The Mae Kha Canal, located in Chiang Mai province, Thailand, has historically been crucial in supporting agriculture and transportation while also contributing to several regional sub-watersheds. It drains into the Ping River and holds significant economic potential for Chiang Mai province, particularly through its role in promoting local tourism and commerce. Moreover, the economic value of the Mae Kha Canal has been estimated at 416,366 baht per year (Supatitipong, 2011 ). However, the rapid expansion of the city, along with the improper disposal of garbage and wastewater, has led to a severe decline in the canal’s water quality (Nuanla-Or, 2016 ). About 30 years ago, heavy metal contamination (including cadmium [Cd], copper [Cu], lead [Pb], and zinc [Zn]) was reported in both water and sediment, with accumulation observed in aquatic plants such as Eichhornia crassipes and Ipomoea aquatica in the Mae Kha Canal (Yang, 1997a , 1997b ). However, studies have yet to report significant accumulation of heavy metals in aquatic animals within this area. At that time, only reports on the distribution of freshwater snails were available, with some of the dominant species being Filopaludina martensi Frauenfeld, 1864 and Filopaludina filosa Reeve, 1863 (Brandt, 1974 ; Srisuwan, 1979 ). Heavy metals are naturally occurring elements found in geological sources. However, due to increasing anthropogenic pressures, such as agriculture, industry, and waste generation, excessive heavy metal contamination has occurred in the environment, impacting both terrestrial and aquatic ecosystems (Alloway, 2013 ; Hassaan et al., 2016 ). Some reports have documented contamination by various heavy metals, including arsenic (As), Cd, chromium (Cr), Pb, mercury (Hg), nickel (Ni), Zn, and others, in marine, freshwater, and sediment environments both globally and in Thailand (Adano et al., 2023 ; Kliangklao & Ariyakanon, 2022 ; Ling et al., 2023 ; Živković et al., 2019 ). These metals are known to accumulate in aquatic plants, vertebrates, and invertebrate organisms (Januar et al., 2019 ; Kliangklao & Ariyakanon, 2022 ; Monier et al., 2023 ), adversely affecting the health of flora, fauna, and humans who may be exposed either directly or indirectly (Jaishankar et al., 2014 ). For example, Cd exposure can adversely affect health by causing mitochondrial dysfunction, oxidative stress, reproductive problems, bone loss, DNA damage, and genetic changes associated with cancer. As a biomarker for oxidative DNA damage, 8-hydroxy-2-deoxyguanosine (8-OHdG) is one of the most extensively investigated oxidized metabolites (Beckman & Ames, 1997 ; Kasai, 1997 ). Similarly, Pb exposure can damage the nervous, renal, and reproductive systems, with oxidative stress contributing to developmental problems, kidney disorders, infertility, chronic diseases, and structural abnormalities in the tissues of affected organs, ultimately leading to organ dysfunction (Duan et al., 2021 ; Flora et al., 2012 ; Genchi et al., 2020 ). Various freshwater organisms, including fish, bivalves, and especially gastropods, are frequently studied for their accumulation of heavy metals in contaminated water sources, reflecting the extensive research conducted in the field (Al-Taher et al., 2020 ; Despotović et al., 2019 ; Kocabaş et al., 2023 ; Monier et al., 2023 ). Freshwater snails inhabit all continents except Antarctica and can be found in nearly all types of water bodies, such as rivers, lakes, streams, swamps, groundwater sources, springs, temporary ponds, and drainage ditches (Strong et al., 2008 ). One of the freshwater snail species widely distributed across all regions of Thailand, including the Mae Kha Canal, is F. martensi (Nabhitabhata et al., 2009 ; Srisuwan, 1979 ). This aquatic gastropod mollusk with a gill and an operculum belongs to the family Viviparidae (Brandt, 1974 ; Hristov, 2022 ). It moves slowly on ground surfaces and exhibits strong adhesive capabilities on various substrates such as logs and stones (Jakubik, 2009 ; Pyron & Brown, 2015 ). It is edible and has been consumed by humans and used as feed for various organisms. Its abundance allows it to serve as an intermediate host for various helminths in the environment. Furthermore, it is highly adaptable to a range of habitats, making it easy to collect due to its slow-moving nature. Many viviparid species are notable for their use in studies on heavy metal bioaccumulation (Piyatiratitivorakul & Boonchamoi, 2008 ). F. martensi possesses a gill-based respiratory system and feeds on detritus and vegetation at the bottom of water bodies, enabling it to accumulate pollutants in its tissues (Aroonsrimorakot et al., 2018 ; Barker, 2001 ). The hypothesis for this study is that F. martensi can serve as a bioindicator for monitoring heavy metal (Cd and Pb) accumulation in aquatic environments, in conjunction with sediment and water assessments. It is further expected that heavy metal accumulation induces alterations in biological structures and histopathological changes in the tissues of this river snail. The findings from this study can be used to support the development of strategies for water quality management and to facilitate the monitoring of heavy metal contamination in the Mae Kha Canal. Moreover, this research will contribute to a broader understanding of potential health risks to aquatic organisms and humans associated with the use and consumption of contaminated water resources. Material and methods Specimen collection and sampling site Specimens, including adult river snails, sediment, and water, were collected over three seasons, including the wet, cool, and hot (Thai Meteorological Department, 2024 ) throughout a 1-year period at nine sampling sites representing the upstream, midstream, and downstream sections of the Mae Kha Canal, as designated by the Royal Irrigation Department (Chiang Mai Province, 2018 ) (Fig. 1 , Table 1 ). Snails were collected manually using the count-per-minute method described by Olivier and Schneiderman ( 1956 ), within a 15-m transect for 30 min. Sediment samples were obtained from a depth of 0–10 cm beneath the water surface (United States Environmental Protection Agency [U.S. EPA], 2001 ), while water samples were collected at approximately 15 cm below the surface and 15 cm from the riverbank at each site (Al-Taher et al., 2020 ). Snails were rinsed with distilled water and stored at − 20°C (Lugowski et al., 1990 ). Sediment samples were stored in polythene bags at 4°C (Batley & Gardner, 1977 ). Water samples were placed in polypropylene bottles, acidified with HNO 3 to maintain a pH below 2, and stored at 4°C (Sliwka-Kaszyńska et al., 2003 ). Table 1 Description of the sampling sites. Three parts of the canal Number in map Location GPS coordinates Description of nearby canal Upstream 1 Don Kaeo Subdistrict, Mae Rim District N 18°52'45.8" E 98°58'16.0" Rural area, Forest 2 Don Kaeo Subdistrict, Mae Rim District N 18°51'10.7" E 98°58'31.1" Rural area, Forest 3 Don Kaeo Subdistrict, Mae Rim District N 18°50'43.2" E 98°58'48.0" Rural area, Forest Midstream 4 Chiang Mai Municipality, Mueang Chiang Mai District N 18°48'59.3" E 98°59'17.5" Urban area 5 Chiang Mai Municipality, Mueang Chiang Mai District N 18°47'49.0" E 98°59'39.6" Urban area 6 Pa Daet Subdistrict, Mueang Chiang Mai District N 18°45'59.3" E 98°59'16.4" Urban area Downstream 7 Pa Daet Subdistrict, Mueang Chiang Mai District N 18°45'03.4" E 98°58'53.5" Rural area 8 Pa Daet Subdistrict, Mueang Chiang Mai District N 18°42'40.8" E 98°58'42.4" Rural area, Agriculture area 9 Sop Mae Kha Subdistrict, Hang Dong District N 18°40'59.0" E 98°58'34.3" Rural area, Agriculture area Snail identification The adult snails were measured using a vernier caliper to determine the shell height and width (Fig. 1 A). They were subsequently identified based on morphological characteristics, including shell size, shape, color band, and sculpture, following the original description (Frauenfeld, 1864 ) and by comparison with images of type specimens (Brandt, 1974 ). Physicochemical parameters detection Physical and chemical parameters of water, including water temperature (WT), pH, dissolved oxygen (DO), total dissolved solids (TDS), and electrical conductivity (EC), were measured at nine sampling sites across the upstream, midstream, and downstream sections of the canal (EPA, 2001 ). These measurements were obtained using an Extech DO700 Dissolved Oxygen Meter (EPA, 2001 ). Sample preparation and heavy metal accumulation analysis The soft tissues from three sections of adult F. martensi individuals were dissected, rinsed with distilled water, and dried in an oven at 80°C for 72 hours (Krishnan et al., 2023 ). Once fully dried, the specimens were ground to a homogeneous powder using a mortar. Sediment samples from three sections were dried similarly in an oven at 40°C for 72 h or until completely dried, then homogenized by grinding (Ferrans et al., 2021 ). For metal analysis, subsamples of the river snail tissue (2.0 g) and fine sediment (1.0 g) were prepared to assess the Cd and Pb concentrations. These were digested using an in-house method based on an AOAC method (Briscoe, 2015 ) and EPA method 3050 (U.S. EPA., 1996). The digestion process involved adding 10 mL of concentrated HNO 3 , 2 mL of concentrated H 2 O 2 , and 3 mL of concentrated HCl, followed by heating on a hotplate until the solutions became clear. After cooling, each sample was first filtered through filter paper (no. 40 or no. 1), followed by a 0.45-µm filter, and then brought to a final volume of 50 mL using ultrapure water. Water samples (100 mL) were digested by adding 5 mL of concentrated HNO 3 and heating on a hotplate until clear. The digested samples were then adjusted to a final volume of 100 mL with ultrapure water, following an in-house method adapted from the American Water Works Association (AWWA) guidelines (Baird & Bridgewater, 2017 ). The Cd and Pb concentrations in all samples were analyzed using a PerkinElmer Optima 7300 DV ICP-OES spectrometer at the Science and Technology Service Center, Faculty of Science, Chiang Mai University (STSC-CMU). Histopathological changes in tissues of F. martensi Ten soft bodies of F. martensi individuals were removed from their shells and opercula, then rinsed with distilled water and fixed in 10% buffered neutral formalin for 24 h (Amemiya et al., 2019 ). After fixation, the samples were washed with distilled water and dehydrated through a graded ethanol series (70%, 85%, 95%, and absolute ethanol), with each step lasting 1 h. The samples were cleared by using mixtures of absolute ethanol and xylene in a ratio of 2:1, 1:1, and 1:2 (20 min per step), followed by immersion in pure xylene for 20 min. The tissue was subsequently embedded in a graded xylene–paraffin series (3:1, 2:1, 1:1, 1:2, and 1:3), with each step lasting 1 h, and finally in pure paraffin wax for 24 h. After embedding, the tissue blocks were sectioned at a thickness of 10–12 µm using an American Optical Rotary Microtome (Model 820). The sections were mounted on permanent slides, stained with hematoxylin and eosin, and coverslipped using Permount (Al-Sabawy et al., 2021 ). The digestive gland tissue was observed under an Olympus CX31 biological microscope at 100× and 400× magnifications. Assessment of DNA damage DNA damage was performed by evaluating the expression level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) using DNA Damage (8-OHdG) AccuSignal™ ELISA Kit (Rockland Immunochemicals). The procedure was performed along with the manufacturer’s instruction. Statistical analysis The shell size of F. martensi and the physicochemical parameters and metal concentrations in all samples are expressed as the mean ± standard deviation (SD). Statistical significance was assessed using one-way analysis of variance (ANOVA), followed by Tukey’s honestly significant difference post hoc test in SPSS Statistics version 22.0 (IBM Corp., 2013). Bar graphs were generated using the ggplot2 and dplyr packages in RStudio (Wickham, 2016 ; Wickham et al., 2023 ). For multivariate analysis, permutational multivariate analysis of variance (PERMANOVA) was conducted to evaluate the effects of river sections and seasons on heavy metal contamination, using a Euclidean distance matrix with the vegan package (Anderson & Walsh, 2013 ; Oksanen et al., 2020 ). The relationship between the physicochemical parameters and the Cd and Pb concentrations was examined using Pearson correlation coefficients (r) and principal component analysis (PCA), employing the Hmisc and ggplot2 packages for statistical analysis and data visualization (Jolliffe, 2002; Schober et al., 2018 ). Results River snail identification and distribution A total of 515 F. martensi individuals were collected from three sections of the Mae Kha Canal and identified based on shell morphology (Fig. 1 A), following the original description by Frauenfeld ( 1864 ). The shell is characterized by a color band on the upper whorls with four pale stripes, a size typically larger than 35–40 mm, a thick periderm, and a closed umbilicus. The shell texture is generally much thicker, with distinct spiral ridges sculpting the surface, and the operculum is very thick and minimally retractable (Brandt, 1974 ; Frauenfeld, 1864 ). For adult snails, the shell width ranged from 10.88 to 14.40 mm, and the shell height ranged from 27.76 to 36.10 mm. There was no significant difference in shell size among the sites (p > 0.05). In terms of distribution, river snails were most abundant during all three seasons in the upstream section, followed by the downstream section; they were least abundant in the midstream section. The highest population (137 individuals) was recorded during the cool season at site 3 (upstream), while the lowest populations were consistently observed across all seasons at sites 5 and 6 (midstream). The physicochemical parameters The physicochemical parameter data are presented in Table 2 and Fig. 2 , which illustrate seasonal variations across the sampling sites. There were significant differences among the sites (p < 0.05). The lowest water temperature recorded during the cool season was 24.5°C, while the highest temperature (34.5°C) was observed during the hot season. The pH was slightly acidic, ranging from 6.2 to 6.6, particularly at the midstream sites (localities 5 and 6). The DO concentrations varied both seasonally and spatially, with levels ranging from 4 to 14 mg/L during the wet season, and lower levels observed during the cool and hot seasons, especially in the midstream section. Similarly, TDS and conductivity exhibited seasonal trends, with higher values detected during the hot and cool seasons, particularly at midstream site 5. Table 2 Physicochemical parameters of Mae Kha Canal. WT = water temperature, DO = Dissolved oxygen, TDS = Total dissolved solids, EC = Electrical conductivity. Physicochemical parameter Seasonal Wet Cool Hot Sep - Oct 2023 Dec 2023 – Jan 2024 Mar-Apr 2024 WT (˚C) 26.4–30.7 24.5–26.7 29.1–34.5 pH 7.5–8.7 6.2–8.6 7.6–8.5 DO (mg/L) 4.0-14.1 2.6–5.4 0.5-4.0 TDS (mg/L) 3.6–40.3 168.0-479.0 215.0-326.0 EC (µS/m) 6.4–55.1 252.0-717.0 317.0-482.0 Heavy metal determination Table 3 and Fig. 3 present the mean Cd and Pb concentrations (along with the standard deviations) in F. martensi , sediment, and water samples from the Mae Kha Canal across three seasons. Notably, the Pb concentrations in the edible snails exceeded the safety threshold, while the Cd concentrations in the sediment were slightly above the permissible limits (Table 4 ). There were significant differences (p < 0.05) in the heavy metal concentrations across the three canal sections (Fig. 3 ). Among the different sample types, the Pb concentrations in the river snails were approximately seven times higher than the Cd concentrations during the wet season, with a marked decline in both the hot and cool seasons. In the sediment, the Pb concentrations remained nearly tenfold higher than the Cd concentrations throughout the study period. The snails collected during the wet season had the highest Cd concentrations, especially in the downstream (0.692 ± 0.046 mg/L) and midstream (0.568 ± 0.029 mg/L) sections, whereas the snails collected from the upstream section exhibited the lowest concentrations (0.429 ± 0.129 mg/L). In contrast, the Cd concentrations during the cool and hot seasons were highest in the upstream section (0.331 ± 0.027 mg/L and 0.232 ± 0.027 mg/L, respectively), with relatively lower concentrations in the midstream and downstream sections. The Pb concentrations in the snails during the wet season were highest in the upstream section (3.152 ± 0.027 mg/L) and lowest in the downstream section (0.778 ± 0.052 mg/L). There was no Pb accumulation in snail tissues from any canal section during the cool season, while during the hot season, Pb was detected only in the midstream section (0.349 ± 0.018 mg/L). This survey revealed that the Cd and Pb concentrations were significantly higher in sediment than in river snails and water across all sections and seasons (Fig. 3 ). The highest Cd accumulation in sediment occurred during the wet season in the midstream (3.640 ± 0.054 mg/kg) and downstream (3.534 ± 0.063 mg/kg) sections; the concentrations in those sections surpassed the concentrations found in the upstream sections. Similarly, during the cool and hot seasons, the Cd concentrations in the sediment remained consistently lower in the upstream sections compared with the other sections. In contrast, Pb accumulation in sediment was most prominent in the midstream sections across all seasons, with concentrations of 34.362 ± 0.059 mg/kg during the wet season, 22.318 ± 0.056 mg/kg during the cool season, and 17.815 ± 0.030 mg/kg during the hot season (Table 3 ). Notably, Cd and Pb were nearly undetectable in the water throughout the study, regardless of the season or canal section. Table 3 The mean and standard deviation (SD) of heavy metal concentrations in snail soft tissues (mg/kg), sediments (mg/kg), and water samples (mg/L) across three seasons from three sections of the Mae Kha Canal. Cd Pb Seasonal Wet Cool Hot Wet Cool Hot Sample localities mean ± SD mean ± SD mean ± SD mean ± SD mean ± SD mean ± SD Snail (mg/kg) Upstream 0.429 ± 0.129 B,a 0.331 ± 0.027 A,ab 0.232 ± 0.027 A,b 3.152 ± 0.027 A,a nd nd Midstream 0.568 ± 0.029 AB,a 0.100 ± 0.018 B,b 0.150 ± 0.018 AB,b 2.647 ± 0.018 B,a nd 0.349 ± 0.018 A,b Downstream 0.692 ± 0.046 A,a 0.103 ± 0.052 B,b 0.128 ± 0.052 B,b 0.778 ± 0.052 C,a nd nd Sediment (mg/kg) Upstream 1.797 ± 0.057 B,a 1.185 ± 0.030 C,c 1.330 ± 0.030 B,b 17.815 ± 0.030 C,a 9.027 ± 0.030 C,c 10.782 ± 0.030 C,b Midstream 3.640 ± 0.054 A,a 2.413 ± 0.059 A,b 2.115 ± 0.059 A,c 34.362 ± 0.059 A,a 21.643 ± 0.059 A,b 18.865 ± 0.059 A,c Downstream 3.534 ± 0.063 A,a 2.206 ± 0.056 B,b 2.208 ± 0.056 A,b 22.318 ± 0.056 B,a 14.370 ± 0.056 B,c 15.133 ± 0.056 B,b Water (mg/L) Upstream nd nd < 0.001 0.002 ± 0.000 nd nd Midstream nd nd nd < 0.001 nd nd Downstream nd nd nd nd nd nd nd: metal element not detected. Capital letters (A, B, C) indicate significant differences (p < 0.05) among canal sections within the same season. Lowercase letters (a, b, c) indicate significant differences (p < 0.05) among seasons within the same canal section, assessed separately for each metal. The Pearson correlation coefficients between the Cd and Pb concentrations in the snail tissue, sediment, water samples, and selected water quality are presented in Fig. 4 A. There was a strong positive correlation between the Cd and Pb concentrations in the sediment (r = 0.88, p < 0.05), and between the Pb concentrations in the snails and water (r = 0.79, p < 0.05). In addition, there were moderate but significant correlations between the Cd and Pb concentrations in the snails, the Pb concentrations in the snails and sediment, and the Cd concentrations in the snails and sediment (r > 0.30, p < 0.05), indicating a potential relationship between environmental exposure and bioaccumulation patterns (Fig. 4 A). The relationship between selected physicochemical water parameters and heavy metal accumulation showed moderate to weak positive or negative correlations (–1.0 < r < 0.40) (Fig. 4 A). PERMANOVA revealed that seasonal variation significantly influenced Cd and Pb accumulation in the Mae Kha Canal (F = 74.018, p < 0.001). In contrast, spatial variation among the localities showed no significant effect. PCA showed that the first three principal components (PC1, PC2, and PC3) explained 79% of the total variance in the dataset (Fig. 4 B). The Cd and Pb concentrations in the snails were closely associated with the concentrations in the sediment, particularly during the wet season. In contrast, the Cd and Pb concentrations in the water showed weaker associations. DO exhibited a positive relationship with heavy metal accumulation in the snails. Table 4 Guidelines for the safe limits of Cd and Pb concentrations in snail, sediment, and water samples Sample Limit of Cd Limit of Pb Standards Snail (or aquatic food) mg/kg 2 0.3 Codex Alimentarius Commission, 2023 1–2 2–5 Joint FAO/WHO Expert Committee on Food Additives, 2002 2 0.3 Ministry of Public Health (Thailand), 2020 In this study 0.100-0.692 mg/kg 0.778–3.152 mg/kg Sediment (dry weight) mg/kg 1.0–3.0 50–300 European Commission, 2022 6 40–60 EPA (Onjefu et al., 2020 ) 1.0 36 Pollution Control Department (Thailand), 2022 In this study 1.185–3.640 mg/kg 9.027–34.362 mg/kg Water mg/L 0.003 0.01 World Health Organization, 2017 0.005 0.015 EPA, 2018 0.005 0.05 Pollution Control Department (Thailand), 1997 In this study < 0.001 mg/L ≤ 0.002 mg/L Histological assessment of F. martensi tissue affected by heavy metals and DNA damege The histological assessment of F. martensi tissues revealed marked differences between individuals collected from relatively uncontaminated and contaminated sections of the Mae Kha Canal (Fig. 5 A– 5 D) In snails from the uncontaminated sites (Fig. 5 A and 5 C), the digestive gland displayed normal histoarchitecture. The columnar epithelial cells contained intracellular vacuoles, indicative of lipid synthesis, located between intact cell bodies. The lumina of the digestive gland tubules were star shaped and had well-defined boundaries, and there were few basophilic cells. The connective tissue appeared loosely organized and evenly distributed around each tubule. In contrast, specimens from the contaminated sections (Fig. 5 B and 5 D) exhibited notable histopathological alterations. These included cellular disorganization, epithelial detachment and tearing, distortion of the glandular tubules with irregular luminal boundaries, and widespread vacuolar degeneration. The connective tissue structure appeared degraded, and the number of basophilic cells was notably increased. Additionally, there was evidence of necrosis. These pathological features suggest significant cellular damage and impaired physiological function of the digestive gland due to heavy metal exposure. The effects of DNA damage were examined by comparing snails from heavy metal-contaminated and uncontaminated locations by measuring the levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biological substance generated when DNA is damaged or experiences oxidative DNA damage. The snails in the heavy metal-contaminated group expressed 8-OHdG (8-OHdG > 0; 0.0024–0.0789 ng/ml), whereas the snails in the uncontaminated group did not express 8-OHdG. Discussion Physicochemical parameters and F. martinis populations The survey and analysis of physicochemical parameters of the Mae Kha Canal in Chiang Mai Province, Thailand, highlighted the influence of seasonal weather conditions, particularly variations in temperature and rainfall on water quality (Xu et al., 2019 ). Variations in rainfall during the wet season resulted in higher water volumes and dilution of dissolved minerals and substances in the canal, leading to lower TDS and electrical conductivity (Fig. 2 and Table 2 ). Conversely, the cool and hot seasons, which lower water levels and increase evaporation, contributed to elevated concentrations of these parameters (Wetzel, 2001 ). A particularly noticeable factor influencing aquatic life was the DO levels, especially at survey points located within the center of Chiang Mai (Sites 4–6 in Fig. 1 ). These points are the midstream and downstream sections (Sites 4–7 in Fig. 1 ) of water drainage from diverse sources, including residential areas, hospitals, markets, and other business sectors, contributing to the canal’s degradation (Mettes, 2014 ). These sections showed low water levels, coinciding with oxygen levels that were below the threshold for aquatic survival (DO < 4 mg/L). Additionally, these central sampling points showed a slightly acidic pH during the cool season, consistent with findings from a previous study (Manene et al., 2024 ), which indicated conditions unsuitable for living organisms, including freshwater snails. The long-term degradation of the canal may have impacted the snail populations. Due to their physiology, snails inhabiting the canal bottom rely on gills and require environments with high oxygen levels and a neutral pH. The absence of these conditions in some areas has likely contributed to their disappearance. Thus, the highest distribution was observed in upstream sections, followed by the downstream sections; the midstream sections showed the lowest abundance of snails (Fig. 2 ). Heavy metal determination A previous study conducted nearly 30 years ago reported trace amounts of two heavy metals, Cd and Pb, in the sediment and water of the Mae Kha Canal (Yang, 1997b ). However, the accumulation of heavy metals in water remains inconsistent, which is a result of efforts to promote and improve wastewater treatment in the Mae Kha Canal (Nuanla-Or, 2016 ). Moreover, this study provides the first report that F. martensi , an invertebrate representative of the Mae Kha Canal, is contaminated with heavy metals. The findings highlight the possible ecological influence on aquatic life by showing that these heavy metals have also accumulated in the species. The Cd concentrations in the snail samples are within the permissible limits of the standard criteria (Codex Alimentarius Commission, 2023 ; Ministry of Public Health, 2020 ). However, the Pb concentrations exceed the recommended level (Table 4 ). This raises serious concerns about the safety of eating snails or other aquatic animals that may accumulate heavy metals, as well as the health of aquatic animals in these water sources. Although the Cd and Pb concentrations in the sediment remain within tolerable limits, they are believed to have accumulated substantially compared with the water. Although statistical tests showed that location did not directly influence Cd and Pb contamination of river snails, sediment, and water in the Mae Kha Canal, it is important to note that human activities such as waste disposal from households, agriculture, and businesses contributed to contamination differences between the three regions (Mettes, 2014 ; Nuanla-Or, 2016 ). Water flow and sediment transport also play key roles in metal distribution (Allan & Castillo, 2007 ). The lower canal sections act as accumulation zones, leading to the highest Cd and Pb concentrations in the midstream (urban) and downstream (waste-receiving) sections (Fig. 1 ). This reflects the ongoing accumulation of metals (Cd, Pb, Zn, and Cu) in the Mae Kha Canal (Yang, 1997b , 1997a ). The necessity for immediate monitoring and action is highlighted by the notable discovery of Cd and Pb in river snails, even in the upstream region (the canal’s origin), which is supposed to have lower contamination. Below is a discussion of the variables and outcomes that affect heavy metal concentrations. Seasonal influence on heavy metal contamination This survey showed that seasonal factors had a considerable impact on Cd and Pb contamination, particularly during the wet season across all the canal sections, as evidenced by the PCA, PERMANOVA, and Pearson correlation coefficients (Fig. 4 and Table 3 ). Similarly, the accumulation of heavy metals in F. martensi also increased during the wet season. The Mae Kha Canal is bordered by communities, businesses, hospitals, and agricultural areas, all of which contribute to environmental heavy metal contamination. During the wet season, increased surface runoff transports heavy metal–contaminated sediment from these areas into the canal (Li et al., 2023 ). In addition, the increased water volume enhances erosion and facilitates the mobilization of sediment-bound heavy metals, allowing them to settle and accumulate more extensively in aquatic organisms than during the cool and hot seasons (Chiba et al., 2011 ). Consistent with our findings, Yang ( 1997b ) also observed higher Cd concentrations in soil and water from the Mae Kha Canal during the rainy season compared with the dry season. According to Najamuddin et al. (2016), sediment from Indonesia’s Jeneberang River also showed elevated Pb and Zn concentrations during the wet season. In another study, Cd and Pb were detectable in snails and other aquatic animals, such as fish, even during the dry season, despite the increased concentrations during the wet season (Ali et al., 2022 ). These results suggest that river snails could serve as effective bioindicators for heavy metal contamination. Consistently, the F. martensi individuals collected from the Mae Kha Canal accumulated Cd and Pb, underscoring their potential use as bioindicators of heavy metal contamination, similarly to other freshwater Prosobranchia snails (Mahmoud & Abu Taleb, 2013 ). The Cd and Pb concentrations in the soft tissues of snails in all sections of the canal correlated strongly with the sediment concentrations (Fig. 4 B and Table 3 ). These results are likely attributable to bioaccumulation factors such as feeding behavior, diet composition, the growth rate, and organism age, as reported in previous studies (Amusan et al., 2002 ; Cain & Luoma, 1986 ; Despotović et al., 2019 ). Comparative studies on the accumulation of Cd and Pb in snails suggest that Pb concentrations often increase when environmental Cd concentrations are sufficiently high. In this study, Pb accumulation significantly decreased during the hot and cool seasons, although Cd accumulation persisted (Fig. 3 ). This difference between the heavy metals may be influenced by multiple factors, including water quality parameters, such as temperature, DO, hardness, pH, and acid-volatile sulfide, which affect metal solubility and bioavailability (Besser et al., 1996 ; Bighiu et al., 2017 ; Das et al., 2014 ; Verma et al., 1978 ), as shown in the correlation coefficient graphs (Fig. 4 A). Metal accumulation is also influenced by the exposure duration and the high affinity of Cd for carbonate, which is a key component in snail shell formation (Barclay et al., 2020; Stipp et al., 1993 ). This affinity can facilitate its absorption even at low environmental concentrations. Moreover, organic debris, industrial or agricultural runoff, and suspended particulate matter from natural erosion also contribute to the transport and bioavailability of heavy metals to snails that feed on detritus or filter particles (Bibby & Webster-Brown, 2006 ; Li et al., 2022 ). Effect of heavy metals on the pathophysiological changes of F. martensi and DNA damage The digestive gland, or hepatopancreas, is a critical organ for assessing the impacts of pollution at the tissue level. It plays a central role in food and energy metabolism, acting as the main source of digestive enzymes and participating in nutrient absorption, storage, and excretion (Wang et al., 2014 ). Due to these functions, it is more susceptible to the accumulation of pollutants and plays a significant role in the detoxification of substances entering the organism compared with other tissues. This study highlighted the pathological effects of environmental heavy metal contamination, particularly Cd and Pb, as evidenced by tissue abnormalities observed in F. martensi tissue collected from the Mae Kha Canal (Fig. 5 ). The Cd and Pb concentrations accumulated in the digestive gland were sufficient to induce significant histopathological alterations (Fig. 5 B and 5 D) (Abdallah & Moustafa, 2002 ; Karakaş & Otludil, 2020 ; Otitoloju et al., 2009). These alterations included changes in cell shape and tubular structure, cellular degeneration and necrosis, and increased infiltration of white blood cells, indicating inflammation in the tissue (Dummee et al., 2015 ; El-Khayat et al., 2018 ). Heavy metals induce oxidative stress through the generation of reactive oxygen species, which can damage cellular structures. In addition, they inhibit antioxidant defense enzymes such as catalase and glutathione peroxidase, thereby reducing the organism’s ability to neutralize oxidative stress (Jomova et al., 2024 ; Kalinin et al., 2021 ). This disruption ultimately results in extensive cellular damage and cell death, as illustrated in Fig. 5 D. Furthermore, the toxicity of heavy metals can lead to the destruction of biomolecules and potentially induce genetic mutations at the molecular level (Fol et al., 2024 ). Utilizing freshwater snails including F. martensi as bioindicators of heavy metal contamination provides an effective approach to assess environmental toxicity. This method enhances the understanding of contamination severity and potential ecological and health risks associated with heavy metal exposure in the Mae Kha Canal. Moreover, our data showed an elevated of 8-OHdG in snails from heavy metal-contaminated areas, indicating that oxidative damage to DNA (Kataoka et al., 2016 ). The snails may accumulate heavy metals in their tissues and are susceptible to heavy metal contamination. This finding has indicated a correlation between the amount of environmental pollution with DNA and snail tissues (Fol et al., 2024 ; Radwan et al., 2020 ). This study supports the use of freshwater snails as reliable bioindicators for monitoring heavy metal pollution. Conclusion This study has confirmed that freshwater snails, particularly F. martensi , are effective bioindicators for assessing the ecological integrity of the Mae Kha Canal. Seasonal variation, site-specific characteristics, and anthropogenic activities significantly influenced water quality, which in turn affected snail populations. The upstream section supported higher snail densities due to more favorable environmental conditions, while the midstream section, heavily impacted by urbanization and pollution, exhibited lower population levels. Analysis of the Cd and Pb concentrations in the snail soft tissue, sediment, and water samples revealed critical trends. The Cd concentrations in snails and sediment were significantly elevated during the wet season across all canal segments, likely due to increased surface runoff. Notably, the Pb concentrations in the snails exceeded the recommended safety limits, indicating potential health risks and warranting cautious consumption. Furthermore, Cd and Pb accumulation in the snails was associated with pathological alterations in the digestive gland and DNA damage, reflecting adverse health effects at the tissue and DNA level. These findings underscore the declining water quality in the Mae Kha Canal and the continued contamination of the sediment and aquatic biota with heavy metals. Overall, this study supports the use of freshwater snails as reliable bioindicators for monitoring heavy metal pollution. The results provide critical insights for environmental managers and policymakers: They could be used to guide pollution-control strategies aimed at safeguarding aquatic ecosystems and public health while promoting the sustainable rehabilitation of the Mae Kha Canal. Declarations Acknowledgment This study is partially supported by Chiang Mai University. I would like to extend my heartfelt thanks to the members at Applied Parasitology Research Laboratory, Chiang Mai University, who provided support, assistance, and inspiration during this research. Authors’ contributions TC drafted the original manuscript, conducted the survey, collected samples, analyzed physical and chemical properties, prepared samples for heavy metal analysis, and performed histological laboratory work. NN contributed to the survey, collected samples, drafted and edited the manuscript, reviewed the content, provided suggestions, and collaborated with TC to organize the project. All authors have read and approved the final manuscript. Funding No funding was received to assist with the preparation of this manuscript. Ethics approval All experimental procedures involving river snails were conducted following the guidelines of the Institute of Animals for Scientific Purpose Development (IAD), National Research Council of Thailand (Permit No. U1-03304-2559) and approved by the Ethics Committee of the Faculty of Science, Chiang Mai University (Protocol No. RE008/25). The study adhered to national regulations and institutional policies to ensure ethical treatment of animals. Competing Interests The authors declare no competing interests. References Abdallah, A. T., & Moustafa, M. A. (2002). Accumulation of lead and cadmium in the marine prosobranch Nerita saxtilis , chemical analysis, light and electron microscopy. Environmental Pollution, 116, 185–191 Adano, A. J., Marcus, N. D., Magaji, J. I., & Opaluwa, O. D. (2023). Assessment of seasonal variation in heavy metal status of a lotic ecosystem in Federal Capital Territory, Abuja, North Central Nigeria. 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PLoS ONE, 9(1). https://doi.org/10.1371/journal.pone.0084921 Wetzel, R. G. (2001). Limnology : lake and river ecosystems (3rd ed., Vol. 3). Academic Press. San Diego, US Wickham, H. (2016). ggplot2: Elegant graphics for data analysis. Springer-Verlag. New York, US Wickham, H., François, R., Henry, L., Müller, K., & Vaughan, D. (2023). dplyr: A Grammar of Data Manipulation. Retrieved April 25, 2024, from https://dplyr.tidyverse.org World Health Organization. (2017). Guidelines for drinking-water quality: First addendum to the fourth edition. World Health Organization. Retrieved January 25, 2025 https://apps.who.int/iris/bitstream/handle/ 10665/254636/9789241550017-eng.pdf Xu, G., Li, P., Lu, K., Tantai, Z., Zhang, J., Ren, Z., Wang, X., Yu, K., Shi, P., & Cheng, Y. (2019). Seasonal changes in water quality and its main influencing factors in the Dan River basin. Catena, 173, 131–140. https://doi.org/10.1016/j.catena.2018.10.014 Yang, Z. (1997a). The potential of using Eichhornia crassipes and Ipomoea aquatica as biomonitors in assessing heavy metal pollution in the Mae Kha Canal and the Mae Ping River In Chiang Mai, Northern Thailand. ScienceAsia, 23, 371–380. Yang, Z. (1997b). Trace metals in the Mae Kha canal and the Mae Ping river in Chiang Mai, Northern Thailand. Journal of The Science Society of Thailand, 23, 123–134. Živković, N., Takić, L., Djordjević, L., Djordjević, A., Mladenović-Ranisavljević, I., Golubović, T., & Božilov, A. (2019). Concentrations of heavy metal cations and a health risk assessment of sediments and river surface water: A case study from a serbian mine. Polish Journal of Environmental Studies, 28(3), 2009–2020. https://doi.org/10.15244/pjoes/89986 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 09 Dec, 2025 Read the published version in Ecotoxicology → Version 1 posted Editorial decision: Revision requested 15 Oct, 2025 Reviews received at journal 07 Oct, 2025 Reviews received at journal 04 Oct, 2025 Reviewers agreed at journal 12 Sep, 2025 Reviewers agreed at journal 10 Sep, 2025 Reviewers invited by journal 10 Sep, 2025 Editor assigned by journal 17 Jul, 2025 Submission checks completed at journal 17 Jul, 2025 First submitted to journal 16 Jul, 2025 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. We do this by developing innovative software and high quality services for the global research community. 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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-7136529","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":514451720,"identity":"69a31338-b060-4c5a-a1d8-a8e4878467f0","order_by":0,"name":"Thanapit Chatchakit","email":"","orcid":"","institution":"Chiang Mai University","correspondingAuthor":false,"prefix":"","firstName":"Thanapit","middleName":"","lastName":"Chatchakit","suffix":""},{"id":514451721,"identity":"a6442899-b5b1-4a58-af78-59c6bebab862","order_by":1,"name":"Nattawadee Nantarat","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzklEQVRIiWNgGAWjYHAD5gMMjA1Eq04AYja2BJK18BgQp8Wcgffg58Ifdvn883u+SfzcYSPHwH746AZ8Wiwb+JKlZyQkW844xrtNsvdMmjEDT1raDXxaDA7wGEjzJDAbMAC1SPC2HU5skOAxI6TF+DdPQr2B/DGeZ5J/idRiBrTlsIHBMR42aWJtMbPmSTtuYHgszdhati3NmI0Ivxjf5rGpNpA7fPjhzbdtNnL87IeP4dXCIP8AzmSRAJFseJWjAeYPpKgeBaNgFIyCkQMAvNZDBgkkrrsAAAAASUVORK5CYII=","orcid":"","institution":"Chiang Mai University","correspondingAuthor":true,"prefix":"","firstName":"Nattawadee","middleName":"","lastName":"Nantarat","suffix":""}],"badges":[],"createdAt":"2025-07-16 06:38:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7136529/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7136529/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10646-025-03005-4","type":"published","date":"2025-12-09T15:58:06+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":91613821,"identity":"0ba808d3-51da-46f8-9790-77724ef72675","added_by":"auto","created_at":"2025-09-18 10:18:54","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":518873,"visible":true,"origin":"","legend":"\u003cp\u003eThe morphology of \u003cem\u003eF. martensi\u003c/em\u003e\u003cstrong\u003e \u003c/strong\u003eand the sampling sites along Mae Kha Canal. (A) Shell terminology and operculum structure of\u003cem\u003e F. martensi\u003c/em\u003e: SH = Shell High, SW = Shell Wide. (B) Location of Chiang Mai province, Thailand. (C) Nine sampling sites: Sites 1–3 represent the upstream sections, 4–6 the midstream sections, and 7–9 the downstream sections.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7136529/v1/b4a43cfe6e83e602347b8595.png"},{"id":91613802,"identity":"6dbbc4bd-3777-45af-a744-cb4544aea4df","added_by":"auto","created_at":"2025-09-18 10:18:53","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":373390,"visible":true,"origin":"","legend":"\u003cp\u003eThe physicochemical parameters levels at nine sampling sites during three seasons. * statistically significant differences (p \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7136529/v1/82f200c04364a52deb37fe5f.png"},{"id":91615259,"identity":"5a6cc9b9-e662-408e-9488-bb73587a4334","added_by":"auto","created_at":"2025-09-18 10:26:53","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":295933,"visible":true,"origin":"","legend":"\u003cp\u003eLevels of Cd and Pb contamination in \u003cem\u003eF. martensi\u003c/em\u003e, sediment, and water from the Mae Kha Canal, Chiang Mai Province, Thailand. (A \u0026amp; D) Cd and Pb concentrations in river snails; (B \u0026amp; E) Cd and Pb concentrations in sediment; (C \u0026amp; F) Cd and Pb concentrations in water. * indicate statistically significant differences (p \u0026lt; 0.05) among canal sections within the same season.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7136529/v1/867c95b59ca25d02c7da9315.png"},{"id":91613806,"identity":"b0c62da1-3b24-4dfa-b2ce-7be825ef21b6","added_by":"auto","created_at":"2025-09-18 10:18:53","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":222756,"visible":true,"origin":"","legend":"\u003cp\u003eMultivariate analyses of heavy metal accumulation and environmental factors in the Mae Kha Canal. (A) Pearson correlation matrix illustrating relationships between Cd and Pb concentrations in \u003cem\u003eF. martensi\u003c/em\u003e, sediment, water, and selected physicochemical parameters. (B) PCA-tripod showing the distribution and association of Cd and Pb concentrations in river snails, sediment, and water with physicochemical parameters across three seasons and three canal sections.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7136529/v1/a5c8d6e2304ec43c2226f42e.png"},{"id":91613814,"identity":"ee9415d1-dfe4-4eb5-8d78-f011fc12b90d","added_by":"auto","created_at":"2025-09-18 10:18:53","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":734090,"visible":true,"origin":"","legend":"\u003cp\u003eHistological tissue of \u003cem\u003eF. martensi\u003c/em\u003e, the digestive gland. (A \u0026amp; C) Digestive gland from relatively uncontaminated sections. (A) Overall morphology of the digestive gland (black arrows), (C) The normal structure of the digestive tube (blue arrows), (B \u0026amp; D) Digestive gland from contaminated sections. (B) Overall morphology of the digestive gland (black arrows), (D) The abnormal structure of the digestive tube (red arrows), BC: Basophilic cell, CEC: Columnar epithelial cells, CT: Connective tissue, DGC: Digestive cell, DGT: Digestive gland tube, L: Lumen, N: Necrosis, V: Vacuole, Scale bars: 200 µm (A and B); 50 mm (C and D).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7136529/v1/bbfb1c9e1a4bd30b67ff9eb7.png"},{"id":98243810,"identity":"e5dbc590-5b8b-4b80-813c-dcd33f884a65","added_by":"auto","created_at":"2025-12-15 16:10:34","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3238104,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7136529/v1/51fe5e0a-99c8-4c61-b5d6-fe5c890f2875.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Integrated assessment of heavy metal pollution: Bioaccumulation in the river snail Filopaludina martensi, sediment, and water from the Mae Kha Canal, Chiang Mai province, Thailand","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe Mae Kha Canal, located in Chiang Mai province, Thailand, has historically been crucial in supporting agriculture and transportation while also contributing to several regional sub-watersheds. It drains into the Ping River and holds significant economic potential for Chiang Mai province, particularly through its role in promoting local tourism and commerce. Moreover, the economic value of the Mae Kha Canal has been estimated at 416,366 baht per year (Supatitipong, \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). However, the rapid expansion of the city, along with the improper disposal of garbage and wastewater, has led to a severe decline in the canal\u0026rsquo;s water quality (Nuanla-Or, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). About 30 years ago, heavy metal contamination (including cadmium [Cd], copper [Cu], lead [Pb], and zinc [Zn]) was reported in both water and sediment, with accumulation observed in aquatic plants such as \u003cem\u003eEichhornia crassipes\u003c/em\u003e and \u003cem\u003eIpomoea aquatica\u003c/em\u003e in the Mae Kha Canal (Yang, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e1997a\u003c/span\u003e, \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1997b\u003c/span\u003e). However, studies have yet to report significant accumulation of heavy metals in aquatic animals within this area. At that time, only reports on the distribution of freshwater snails were available, with some of the dominant species being \u003cem\u003eFilopaludina martensi\u003c/em\u003e Frauenfeld, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1864\u003c/span\u003e and \u003cem\u003eFilopaludina filosa\u003c/em\u003e Reeve, 1863 (Brandt, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1974\u003c/span\u003e; Srisuwan, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e1979\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eHeavy metals are naturally occurring elements found in geological sources. However, due to increasing anthropogenic pressures, such as agriculture, industry, and waste generation, excessive heavy metal contamination has occurred in the environment, impacting both terrestrial and aquatic ecosystems (Alloway, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Hassaan et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Some reports have documented contamination by various heavy metals, including arsenic (As), Cd, chromium (Cr), Pb, mercury (Hg), nickel (Ni), Zn, and others, in marine, freshwater, and sediment environments both globally and in Thailand (Adano et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Kliangklao \u0026amp; Ariyakanon, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Ling et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Živković et al., \u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These metals are known to accumulate in aquatic plants, vertebrates, and invertebrate organisms (Januar et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kliangklao \u0026amp; Ariyakanon, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Monier et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), adversely affecting the health of flora, fauna, and humans who may be exposed either directly or indirectly (Jaishankar et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). For example, Cd exposure can adversely affect health by causing mitochondrial dysfunction, oxidative stress, reproductive problems, bone loss, DNA damage, and genetic changes associated with cancer. As a biomarker for oxidative DNA damage, 8-hydroxy-2-deoxyguanosine (8-OHdG) is one of the most extensively investigated oxidized metabolites (Beckman \u0026amp; Ames, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Kasai, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). Similarly, Pb exposure can damage the nervous, renal, and reproductive systems, with oxidative stress contributing to developmental problems, kidney disorders, infertility, chronic diseases, and structural abnormalities in the tissues of affected organs, ultimately leading to organ dysfunction (Duan et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Flora et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Genchi et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Various freshwater organisms, including fish, bivalves, and especially gastropods, are frequently studied for their accumulation of heavy metals in contaminated water sources, reflecting the extensive research conducted in the field (Al-Taher et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Despotović et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kocabaş et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Monier et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eFreshwater snails inhabit all continents except Antarctica and can be found in nearly all types of water bodies, such as rivers, lakes, streams, swamps, groundwater sources, springs, temporary ponds, and drainage ditches (Strong et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). One of the freshwater snail species widely distributed across all regions of Thailand, including the Mae Kha Canal, is \u003cem\u003eF. martensi\u003c/em\u003e (Nabhitabhata et al., \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Srisuwan, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e1979\u003c/span\u003e). This aquatic gastropod mollusk with a gill and an operculum belongs to the family Viviparidae (Brandt, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1974\u003c/span\u003e; Hristov, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). It moves slowly on ground surfaces and exhibits strong adhesive capabilities on various substrates such as logs and stones (Jakubik, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Pyron \u0026amp; Brown, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). It is edible and has been consumed by humans and used as feed for various organisms. Its abundance allows it to serve as an intermediate host for various helminths in the environment. Furthermore, it is highly adaptable to a range of habitats, making it easy to collect due to its slow-moving nature. Many viviparid species are notable for their use in studies on heavy metal bioaccumulation (Piyatiratitivorakul \u0026amp; Boonchamoi, \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). \u003cem\u003eF. martensi\u003c/em\u003e possesses a gill-based respiratory system and feeds on detritus and vegetation at the bottom of water bodies, enabling it to accumulate pollutants in its tissues (Aroonsrimorakot et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Barker, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2001\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe hypothesis for this study is that \u003cem\u003eF. martensi\u003c/em\u003e can serve as a bioindicator for monitoring heavy metal (Cd and Pb) accumulation in aquatic environments, in conjunction with sediment and water assessments. It is further expected that heavy metal accumulation induces alterations in biological structures and histopathological changes in the tissues of this river snail. The findings from this study can be used to support the development of strategies for water quality management and to facilitate the monitoring of heavy metal contamination in the Mae Kha Canal. Moreover, this research will contribute to a broader understanding of potential health risks to aquatic organisms and humans associated with the use and consumption of contaminated water resources.\u003c/p\u003e"},{"header":"Material and methods","content":"\u003cp\u003e\u003cb\u003eSpecimen collection and sampling site\u003c/b\u003e\u003c/p\u003e\u003cp\u003eSpecimens, including adult river snails, sediment, and water, were collected over three seasons, including the wet, cool, and hot (Thai Meteorological Department, \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) throughout a 1-year period at nine sampling sites representing the upstream, midstream, and downstream sections of the Mae Kha Canal, as designated by the Royal Irrigation Department (Chiang Mai Province, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Snails were collected manually using the count-per-minute method described by Olivier and Schneiderman (\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e1956\u003c/span\u003e), within a 15-m transect for 30 min. Sediment samples were obtained from a depth of 0\u0026ndash;10 cm beneath the water surface (United States Environmental Protection Agency [U.S. EPA], \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), while water samples were collected at approximately 15 cm below the surface and 15 cm from the riverbank at each site (Al-Taher et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Snails were rinsed with distilled water and stored at \u0026minus;\u0026thinsp;20\u0026deg;C (Lugowski et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). Sediment samples were stored in polythene bags at 4\u0026deg;C (Batley \u0026amp; Gardner, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1977\u003c/span\u003e). Water samples were placed in polypropylene bottles, acidified with HNO\u003csub\u003e3\u003c/sub\u003e to maintain a pH below 2, and stored at 4\u0026deg;C (Sliwka-Kaszyńska et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDescription of the sampling sites.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eThree parts of the canal\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNumber in map\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eLocation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eGPS coordinates\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eDescription of nearby canal\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eUpstream\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDon Kaeo Subdistrict, Mae Rim District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;52'45.8\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;58'16.0\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRural area, Forest\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDon Kaeo Subdistrict, Mae Rim District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;51'10.7\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;58'31.1\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRural area, Forest\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDon Kaeo Subdistrict, Mae Rim District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;50'43.2\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;58'48.0\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRural area, Forest\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eMidstream\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eChiang Mai Municipality, Mueang Chiang Mai District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;48'59.3\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;59'17.5\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eUrban area\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eChiang Mai Municipality, Mueang Chiang Mai District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;47'49.0\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;59'39.6\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eUrban area\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePa Daet Subdistrict, Mueang Chiang Mai District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;45'59.3\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;59'16.4\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eUrban area\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eDownstream\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePa Daet Subdistrict, Mueang Chiang Mai District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;45'03.4\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;58'53.5\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRural area\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePa Daet Subdistrict, Mueang Chiang Mai District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;42'40.8\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;58'42.4\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRural area, Agriculture area\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSop Mae Kha Subdistrict, Hang Dong District\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eN 18\u0026deg;40'59.0\"\u003c/p\u003e\u003cp\u003eE 98\u0026deg;58'34.3\"\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRural area, Agriculture area\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eSnail identification\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe adult snails were measured using a vernier caliper to determine the shell height and width (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). They were subsequently identified based on morphological characteristics, including shell size, shape, color band, and sculpture, following the original description (Frauenfeld, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1864\u003c/span\u003e) and by comparison with images of type specimens (Brandt, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1974\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003ePhysicochemical parameters detection\u003c/b\u003e\u003c/p\u003e\u003cp\u003ePhysical and chemical parameters of water, including water temperature (WT), pH, dissolved oxygen (DO), total dissolved solids (TDS), and electrical conductivity (EC), were measured at nine sampling sites across the upstream, midstream, and downstream sections of the canal (EPA, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). These measurements were obtained using an Extech DO700 Dissolved Oxygen Meter (EPA, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2001\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cb\u003eSample preparation and heavy metal accumulation analysis\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe soft tissues from three sections of adult \u003cem\u003eF. martensi\u003c/em\u003e individuals were dissected, rinsed with distilled water, and dried in an oven at 80\u0026deg;C for 72 hours (Krishnan et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Once fully dried, the specimens were ground to a homogeneous powder using a mortar. Sediment samples from three sections were dried similarly in an oven at 40\u0026deg;C for 72 h or until completely dried, then homogenized by grinding (Ferrans et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). For metal analysis, subsamples of the river snail tissue (2.0 g) and fine sediment (1.0 g) were prepared to assess the Cd and Pb concentrations. These were digested using an in-house method based on an AOAC method (Briscoe, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) and EPA method 3050 (U.S. EPA., 1996). The digestion process involved adding 10 mL of concentrated HNO\u003csub\u003e3\u003c/sub\u003e, 2 mL of concentrated H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, and 3 mL of concentrated HCl, followed by heating on a hotplate until the solutions became clear. After cooling, each sample was first filtered through filter paper (no. 40 or no. 1), followed by a 0.45-\u0026micro;m filter, and then brought to a final volume of 50 mL using ultrapure water. Water samples (100 mL) were digested by adding 5 mL of concentrated HNO\u003csub\u003e3\u003c/sub\u003e and heating on a hotplate until clear. The digested samples were then adjusted to a final volume of 100 mL with ultrapure water, following an in-house method adapted from the American Water Works Association (AWWA) guidelines (Baird \u0026amp; Bridgewater, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The Cd and Pb concentrations in all samples were analyzed using a PerkinElmer Optima 7300 DV ICP-OES spectrometer at the Science and Technology Service Center, Faculty of Science, Chiang Mai University (STSC-CMU).\u003c/p\u003e\u003cp\u003e\u003cb\u003eHistopathological changes in tissues of\u003c/b\u003e \u003cb\u003eF. martensi\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTen soft bodies of \u003cem\u003eF. martensi\u003c/em\u003e individuals were removed from their shells and opercula, then rinsed with distilled water and fixed in 10% buffered neutral formalin for 24 h (Amemiya et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). After fixation, the samples were washed with distilled water and dehydrated through a graded ethanol series (70%, 85%, 95%, and absolute ethanol), with each step lasting 1 h. The samples were cleared by using mixtures of absolute ethanol and xylene in a ratio of 2:1, 1:1, and 1:2 (20 min per step), followed by immersion in pure xylene for 20 min. The tissue was subsequently embedded in a graded xylene\u0026ndash;paraffin series (3:1, 2:1, 1:1, 1:2, and 1:3), with each step lasting 1 h, and finally in pure paraffin wax for 24 h. After embedding, the tissue blocks were sectioned at a thickness of 10\u0026ndash;12 \u0026micro;m using an American Optical Rotary Microtome (Model 820). The sections were mounted on permanent slides, stained with hematoxylin and eosin, and coverslipped using Permount (Al-Sabawy et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The digestive gland tissue was observed under an Olympus CX31 biological microscope at 100\u0026times; and 400\u0026times; magnifications.\u003c/p\u003e\u003cp\u003e\u003cb\u003eAssessment of DNA damage\u003c/b\u003e\u003c/p\u003e\u003cp\u003eDNA damage was performed by evaluating the expression level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) using DNA Damage (8-OHdG) AccuSignal\u0026trade; ELISA Kit (Rockland Immunochemicals). The procedure was performed along with the manufacturer\u0026rsquo;s instruction.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eThe shell size of \u003cem\u003eF. martensi\u003c/em\u003e and the physicochemical parameters and metal concentrations in all samples are expressed as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD). Statistical significance was assessed using one-way analysis of variance (ANOVA), followed by Tukey\u0026rsquo;s honestly significant difference post hoc test in SPSS Statistics version 22.0 (IBM Corp., 2013). Bar graphs were generated using the ggplot2 and dplyr packages in RStudio (Wickham, \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Wickham et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). For multivariate analysis, permutational multivariate analysis of variance (PERMANOVA) was conducted to evaluate the effects of river sections and seasons on heavy metal contamination, using a Euclidean distance matrix with the vegan package (Anderson \u0026amp; Walsh, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Oksanen et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The relationship between the physicochemical parameters and the Cd and Pb concentrations was examined using Pearson correlation coefficients (r) and principal component analysis (PCA), employing the Hmisc and ggplot2 packages for statistical analysis and data visualization (Jolliffe, 2002; Schober et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cb\u003eRiver snail identification and distribution\u003c/b\u003e\u003c/p\u003e\u003cp\u003eA total of 515 \u003cem\u003eF. martensi\u003c/em\u003e individuals were collected from three sections of the Mae Kha Canal and identified based on shell morphology (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA), following the original description by Frauenfeld (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1864\u003c/span\u003e). The shell is characterized by a color band on the upper whorls with four pale stripes, a size typically larger than 35\u0026ndash;40 mm, a thick periderm, and a closed umbilicus. The shell texture is generally much thicker, with distinct spiral ridges sculpting the surface, and the operculum is very thick and minimally retractable (Brandt, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1974\u003c/span\u003e; Frauenfeld, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1864\u003c/span\u003e). For adult snails, the shell width ranged from 10.88 to 14.40 mm, and the shell height ranged from 27.76 to 36.10 mm. There was no significant difference in shell size among the sites (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). In terms of distribution, river snails were most abundant during all three seasons in the upstream section, followed by the downstream section; they were least abundant in the midstream section. The highest population (137 individuals) was recorded during the cool season at site 3 (upstream), while the lowest populations were consistently observed across all seasons at sites 5 and 6 (midstream).\u003c/p\u003e\u003cp\u003e\u003cb\u003eThe physicochemical parameters\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe physicochemical parameter data are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, which illustrate seasonal variations across the sampling sites. There were significant differences among the sites (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The lowest water temperature recorded during the cool season was 24.5\u0026deg;C, while the highest temperature (34.5\u0026deg;C) was observed during the hot season. The pH was slightly acidic, ranging from 6.2 to 6.6, particularly at the midstream sites (localities 5 and 6). The DO concentrations varied both seasonally and spatially, with levels ranging from 4 to 14 mg/L during the wet season, and lower levels observed during the cool and hot seasons, especially in the midstream section. Similarly, TDS and conductivity exhibited seasonal trends, with higher values detected during the hot and cool seasons, particularly at midstream site 5.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePhysicochemical parameters of Mae Kha Canal. WT\u0026thinsp;=\u0026thinsp;water temperature, DO\u0026thinsp;=\u0026thinsp;Dissolved oxygen, TDS\u0026thinsp;=\u0026thinsp;Total dissolved solids, EC\u0026thinsp;=\u0026thinsp;Electrical conductivity.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003ePhysicochemical parameter\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eSeasonal\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eWet\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCool\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eHot\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSep - Oct 2023\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDec 2023 \u0026ndash; Jan 2024\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMar-Apr 2024\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eWT (˚C)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e26.4\u0026ndash;30.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e24.5\u0026ndash;26.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e29.1\u0026ndash;34.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003epH\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7.5\u0026ndash;8.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e6.2\u0026ndash;8.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7.6\u0026ndash;8.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eDO (mg/L)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.0-14.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.6\u0026ndash;5.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.5-4.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eTDS (mg/L)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3.6\u0026ndash;40.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e168.0-479.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e215.0-326.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eEC (\u0026micro;S/m)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e6.4\u0026ndash;55.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e252.0-717.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e317.0-482.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eHeavy metal determination\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e present the mean Cd and Pb concentrations (along with the standard deviations) in \u003cem\u003eF. martensi\u003c/em\u003e, sediment, and water samples from the Mae Kha Canal across three seasons. Notably, the Pb concentrations in the edible snails exceeded the safety threshold, while the Cd concentrations in the sediment were slightly above the permissible limits (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). There were significant differences (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) in the heavy metal concentrations across the three canal sections (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Among the different sample types, the Pb concentrations in the river snails were approximately seven times higher than the Cd concentrations during the wet season, with a marked decline in both the hot and cool seasons. In the sediment, the Pb concentrations remained nearly tenfold higher than the Cd concentrations throughout the study period. The snails collected during the wet season had the highest Cd concentrations, especially in the downstream (0.692\u0026thinsp;\u0026plusmn;\u0026thinsp;0.046 mg/L) and midstream (0.568\u0026thinsp;\u0026plusmn;\u0026thinsp;0.029 mg/L) sections, whereas the snails collected from the upstream section exhibited the lowest concentrations (0.429\u0026thinsp;\u0026plusmn;\u0026thinsp;0.129 mg/L). In contrast, the Cd concentrations during the cool and hot seasons were highest in the upstream section (0.331\u0026thinsp;\u0026plusmn;\u0026thinsp;0.027 mg/L and 0.232\u0026thinsp;\u0026plusmn;\u0026thinsp;0.027 mg/L, respectively), with relatively lower concentrations in the midstream and downstream sections. The Pb concentrations in the snails during the wet season were highest in the upstream section (3.152\u0026thinsp;\u0026plusmn;\u0026thinsp;0.027 mg/L) and lowest in the downstream section (0.778\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052 mg/L). There was no Pb accumulation in snail tissues from any canal section during the cool season, while during the hot season, Pb was detected only in the midstream section (0.349\u0026thinsp;\u0026plusmn;\u0026thinsp;0.018 mg/L). This survey revealed that the Cd and Pb concentrations were significantly higher in sediment than in river snails and water across all sections and seasons (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The highest Cd accumulation in sediment occurred during the wet season in the midstream (3.640\u0026thinsp;\u0026plusmn;\u0026thinsp;0.054 mg/kg) and downstream (3.534\u0026thinsp;\u0026plusmn;\u0026thinsp;0.063 mg/kg) sections; the concentrations in those sections surpassed the concentrations found in the upstream sections. Similarly, during the cool and hot seasons, the Cd concentrations in the sediment remained consistently lower in the upstream sections compared with the other sections. In contrast, Pb accumulation in sediment was most prominent in the midstream sections across all seasons, with concentrations of 34.362\u0026thinsp;\u0026plusmn;\u0026thinsp;0.059 mg/kg during the wet season, 22.318\u0026thinsp;\u0026plusmn;\u0026thinsp;0.056 mg/kg during the cool season, and 17.815\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030 mg/kg during the hot season (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Notably, Cd and Pb were nearly undetectable in the water throughout the study, regardless of the season or canal section.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe mean and standard deviation (SD) of heavy metal concentrations in snail soft tissues (mg/kg), sediments (mg/kg), and water samples (mg/L) across three seasons from three sections of the Mae Kha Canal.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e\u003cp\u003eCd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e\u003cp\u003ePb\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eSeasonal\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eWet\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCool\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eHot\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eWet\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eCool\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eHot\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eSample\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003elocalities\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003emean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003emean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003emean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003emean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003emean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003e\u003cb\u003eSnail (mg/kg)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eUpstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.429\u0026thinsp;\u0026plusmn;\u0026thinsp;0.129\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.331\u0026thinsp;\u0026plusmn;\u0026thinsp;0.027\u003csup\u003eA,ab\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.232\u0026thinsp;\u0026plusmn;\u0026thinsp;0.027\u003csup\u003eA,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3.152\u0026thinsp;\u0026plusmn;\u0026thinsp;0.027\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eMidstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.568\u0026thinsp;\u0026plusmn;\u0026thinsp;0.029\u003csup\u003eAB,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.100\u0026thinsp;\u0026plusmn;\u0026thinsp;0.018\u003csup\u003eB,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.150\u0026thinsp;\u0026plusmn;\u0026thinsp;0.018\u003csup\u003eAB,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2.647\u0026thinsp;\u0026plusmn;\u0026thinsp;0.018\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.349\u0026thinsp;\u0026plusmn;\u0026thinsp;0.018\u003csup\u003eA,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eDownstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.692\u0026thinsp;\u0026plusmn;\u0026thinsp;0.046\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.103\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052\u003csup\u003eB,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.128\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052\u003csup\u003eB,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.778\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052\u003csup\u003eC,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003e\u003cb\u003eSediment (mg/kg)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eUpstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.797\u0026thinsp;\u0026plusmn;\u0026thinsp;0.057\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.185\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030\u003csup\u003eC,c\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.330\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030\u003csup\u003eB,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e17.815\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030\u003csup\u003eC,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e9.027\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030\u003csup\u003eC,c\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e10.782\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030\u003csup\u003eC,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eMidstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.640\u0026thinsp;\u0026plusmn;\u0026thinsp;0.054\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.413\u0026thinsp;\u0026plusmn;\u0026thinsp;0.059\u003csup\u003eA,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.115\u0026thinsp;\u0026plusmn;\u0026thinsp;0.059\u003csup\u003eA,c\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e34.362\u0026thinsp;\u0026plusmn;\u0026thinsp;0.059\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e21.643\u0026thinsp;\u0026plusmn;\u0026thinsp;0.059\u003csup\u003eA,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e18.865\u0026thinsp;\u0026plusmn;\u0026thinsp;0.059\u003csup\u003eA,c\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eDownstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.534\u0026thinsp;\u0026plusmn;\u0026thinsp;0.063\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.206\u0026thinsp;\u0026plusmn;\u0026thinsp;0.056\u003csup\u003eB,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.208\u0026thinsp;\u0026plusmn;\u0026thinsp;0.056\u003csup\u003eA,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e22.318\u0026thinsp;\u0026plusmn;\u0026thinsp;0.056\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e14.370\u0026thinsp;\u0026plusmn;\u0026thinsp;0.056\u003csup\u003eB,c\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e15.133\u0026thinsp;\u0026plusmn;\u0026thinsp;0.056\u003csup\u003eB,b\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003e\u003cb\u003eWater (mg/L)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eUpstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.002\u0026thinsp;\u0026plusmn;\u0026thinsp;0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eMidstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eDownstream\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003end\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003end: metal element not detected.\u003c/p\u003e\u003cp\u003eCapital letters (A, B, C) indicate significant differences (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) among canal sections within the same season.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eLowercase letters (a, b, c) indicate significant differences (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) among seasons within the same canal section, assessed separately for each metal.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe Pearson correlation coefficients between the Cd and Pb concentrations in the snail tissue, sediment, water samples, and selected water quality are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA. There was a strong positive correlation between the Cd and Pb concentrations in the sediment (r\u0026thinsp;=\u0026thinsp;0.88, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), and between the Pb concentrations in the snails and water (r\u0026thinsp;=\u0026thinsp;0.79, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In addition, there were moderate but significant correlations between the Cd and Pb concentrations in the snails, the Pb concentrations in the snails and sediment, and the Cd concentrations in the snails and sediment (r\u0026thinsp;\u0026gt;\u0026thinsp;0.30, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), indicating a potential relationship between environmental exposure and bioaccumulation patterns (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). The relationship between selected physicochemical water parameters and heavy metal accumulation showed moderate to weak positive or negative correlations (\u0026ndash;1.0\u0026thinsp;\u0026lt;\u0026thinsp;r\u0026thinsp;\u0026lt;\u0026thinsp;0.40) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). PERMANOVA revealed that seasonal variation significantly influenced Cd and Pb accumulation in the Mae Kha Canal (F\u0026thinsp;=\u0026thinsp;74.018, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In contrast, spatial variation among the localities showed no significant effect. PCA showed that the first three principal components (PC1, PC2, and PC3) explained 79% of the total variance in the dataset (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). The Cd and Pb concentrations in the snails were closely associated with the concentrations in the sediment, particularly during the wet season. In contrast, the Cd and Pb concentrations in the water showed weaker associations. DO exhibited a positive relationship with heavy metal accumulation in the snails.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eGuidelines for the safe limits of Cd and Pb concentrations in snail, sediment, and water samples\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLimit of Cd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eLimit of Pb\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eStandards\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003e\u003cb\u003eSnail\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003e(or aquatic food)\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003emg/kg\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCodex Alimentarius Commission, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u0026ndash;2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2\u0026ndash;5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eJoint FAO/WHO Expert Committee on Food Additives, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2002\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMinistry of Public Health (Thailand), 2020\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eIn this study\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.100-0.692 mg/kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.778\u0026ndash;3.152 mg/kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003e\u003cb\u003eSediment\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003e(dry weight)\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003emg/kg\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.0\u0026ndash;3.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e50\u0026ndash;300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eEuropean Commission, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2022\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e40\u0026ndash;60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eEPA (Onjefu et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePollution Control Department (Thailand), 2022\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eIn this study\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.185\u0026ndash;3.640 mg/kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e9.027\u0026ndash;34.362 mg/kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003e\u003cb\u003eWater\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003emg/L\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eWorld Health Organization, \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2017\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.005\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.015\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eEPA, 2018\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.005\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePollution Control Department (Thailand), 1997\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eIn this study\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001 mg/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u0026le;\u0026thinsp;0.002 mg/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eHistological assessment of\u003c/b\u003e \u003cb\u003eF. martensi\u003c/b\u003e \u003cb\u003etissue affected by heavy metals and DNA damege\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe histological assessment of \u003cem\u003eF. martensi\u003c/em\u003e tissues revealed marked differences between individuals collected from relatively uncontaminated and contaminated sections of the Mae Kha Canal (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA\u0026ndash;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD) In snails from the uncontaminated sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC), the digestive gland displayed normal histoarchitecture. The columnar epithelial cells contained intracellular vacuoles, indicative of lipid synthesis, located between intact cell bodies. The lumina of the digestive gland tubules were star shaped and had well-defined boundaries, and there were few basophilic cells. The connective tissue appeared loosely organized and evenly distributed around each tubule. In contrast, specimens from the contaminated sections (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD) exhibited notable histopathological alterations. These included cellular disorganization, epithelial detachment and tearing, distortion of the glandular tubules with irregular luminal boundaries, and widespread vacuolar degeneration. The connective tissue structure appeared degraded, and the number of basophilic cells was notably increased. Additionally, there was evidence of necrosis. These pathological features suggest significant cellular damage and impaired physiological function of the digestive gland due to heavy metal exposure.\u003c/p\u003e\u003cp\u003eThe effects of DNA damage were examined by comparing snails from heavy metal-contaminated and uncontaminated locations by measuring the levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biological substance generated when DNA is damaged or experiences oxidative DNA damage. The snails in the heavy metal-contaminated group expressed 8-OHdG (8-OHdG\u0026thinsp;\u0026gt;\u0026thinsp;0; 0.0024\u0026ndash;0.0789 ng/ml), whereas the snails in the uncontaminated group did not express 8-OHdG.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003e\u003cb\u003ePhysicochemical parameters and\u003c/b\u003e \u003cb\u003eF. martinis\u003c/b\u003e \u003cb\u003epopulations\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe survey and analysis of physicochemical parameters of the Mae Kha Canal in Chiang Mai Province, Thailand, highlighted the influence of seasonal weather conditions, particularly variations in temperature and rainfall on water quality (Xu et al., \u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Variations in rainfall during the wet season resulted in higher water volumes and dilution of dissolved minerals and substances in the canal, leading to lower TDS and electrical conductivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Conversely, the cool and hot seasons, which lower water levels and increase evaporation, contributed to elevated concentrations of these parameters (Wetzel, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). A particularly noticeable factor influencing aquatic life was the DO levels, especially at survey points located within the center of Chiang Mai (Sites 4\u0026ndash;6 in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These points are the midstream and downstream sections (Sites 4\u0026ndash;7 in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) of water drainage from diverse sources, including residential areas, hospitals, markets, and other business sectors, contributing to the canal\u0026rsquo;s degradation (Mettes, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). These sections showed low water levels, coinciding with oxygen levels that were below the threshold for aquatic survival (DO\u0026thinsp;\u0026lt;\u0026thinsp;4 mg/L). Additionally, these central sampling points showed a slightly acidic pH during the cool season, consistent with findings from a previous study (Manene et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), which indicated conditions unsuitable for living organisms, including freshwater snails. The long-term degradation of the canal may have impacted the snail populations. Due to their physiology, snails inhabiting the canal bottom rely on gills and require environments with high oxygen levels and a neutral pH. The absence of these conditions in some areas has likely contributed to their disappearance. Thus, the highest distribution was observed in upstream sections, followed by the downstream sections; the midstream sections showed the lowest abundance of snails (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cb\u003eHeavy metal determination\u003c/b\u003e\u003c/p\u003e\u003cp\u003eA previous study conducted nearly 30 years ago reported trace amounts of two heavy metals, Cd and Pb, in the sediment and water of the Mae Kha Canal (Yang, \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1997b\u003c/span\u003e). However, the accumulation of heavy metals in water remains inconsistent, which is a result of efforts to promote and improve wastewater treatment in the Mae Kha Canal (Nuanla-Or, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Moreover, this study provides the first report that \u003cem\u003eF. martensi\u003c/em\u003e, an invertebrate representative of the Mae Kha Canal, is contaminated with heavy metals. The findings highlight the possible ecological influence on aquatic life by showing that these heavy metals have also accumulated in the species. The Cd concentrations in the snail samples are within the permissible limits of the standard criteria (Codex Alimentarius Commission, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ministry of Public Health, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, the Pb concentrations exceed the recommended level (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This raises serious concerns about the safety of eating snails or other aquatic animals that may accumulate heavy metals, as well as the health of aquatic animals in these water sources. Although the Cd and Pb concentrations in the sediment remain within tolerable limits, they are believed to have accumulated substantially compared with the water. Although statistical tests showed that location did not directly influence Cd and Pb contamination of river snails, sediment, and water in the Mae Kha Canal, it is important to note that human activities such as waste disposal from households, agriculture, and businesses contributed to contamination differences between the three regions (Mettes, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Nuanla-Or, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Water flow and sediment transport also play key roles in metal distribution (Allan \u0026amp; Castillo, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The lower canal sections act as accumulation zones, leading to the highest Cd and Pb concentrations in the midstream (urban) and downstream (waste-receiving) sections (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This reflects the ongoing accumulation of metals (Cd, Pb, Zn, and Cu) in the Mae Kha Canal (Yang, \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1997b\u003c/span\u003e, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e1997a\u003c/span\u003e). The necessity for immediate monitoring and action is highlighted by the notable discovery of Cd and Pb in river snails, even in the upstream region (the canal\u0026rsquo;s origin), which is supposed to have lower contamination. Below is a discussion of the variables and outcomes that affect heavy metal concentrations.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSeasonal influence on heavy metal contamination\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThis survey showed that seasonal factors had a considerable impact on Cd and Pb contamination, particularly during the wet season across all the canal sections, as evidenced by the PCA, PERMANOVA, and Pearson correlation coefficients (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Similarly, the accumulation of heavy metals in \u003cem\u003eF. martensi\u003c/em\u003e also increased during the wet season. The Mae Kha Canal is bordered by communities, businesses, hospitals, and agricultural areas, all of which contribute to environmental heavy metal contamination. During the wet season, increased surface runoff transports heavy metal\u0026ndash;contaminated sediment from these areas into the canal (Li et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In addition, the increased water volume enhances erosion and facilitates the mobilization of sediment-bound heavy metals, allowing them to settle and accumulate more extensively in aquatic organisms than during the cool and hot seasons (Chiba et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Consistent with our findings, Yang (\u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e1997b\u003c/span\u003e) also observed higher Cd concentrations in soil and water from the Mae Kha Canal during the rainy season compared with the dry season. According to Najamuddin et al. (2016), sediment from Indonesia\u0026rsquo;s Jeneberang River also showed elevated Pb and Zn concentrations during the wet season. In another study, Cd and Pb were detectable in snails and other aquatic animals, such as fish, even during the dry season, despite the increased concentrations during the wet season (Ali et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These results suggest that river snails could serve as effective bioindicators for heavy metal contamination. Consistently, the \u003cem\u003eF. martensi\u003c/em\u003e individuals collected from the Mae Kha Canal accumulated Cd and Pb, underscoring their potential use as bioindicators of heavy metal contamination, similarly to other freshwater Prosobranchia snails (Mahmoud \u0026amp; Abu Taleb, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe Cd and Pb concentrations in the soft tissues of snails in all sections of the canal correlated strongly with the sediment concentrations (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). These results are likely attributable to bioaccumulation factors such as feeding behavior, diet composition, the growth rate, and organism age, as reported in previous studies (Amusan et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Cain \u0026amp; Luoma, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Despotović et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Comparative studies on the accumulation of Cd and Pb in snails suggest that Pb concentrations often increase when environmental Cd concentrations are sufficiently high. In this study, Pb accumulation significantly decreased during the hot and cool seasons, although Cd accumulation persisted (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This difference between the heavy metals may be influenced by multiple factors, including water quality parameters, such as temperature, DO, hardness, pH, and acid-volatile sulfide, which affect metal solubility and bioavailability (Besser et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Bighiu et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Das et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Verma et al., \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e1978\u003c/span\u003e), as shown in the correlation coefficient graphs (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Metal accumulation is also influenced by the exposure duration and the high affinity of Cd for carbonate, which is a key component in snail shell formation (Barclay et al., 2020; Stipp et al., \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e1993\u003c/span\u003e). This affinity can facilitate its absorption even at low environmental concentrations. Moreover, organic debris, industrial or agricultural runoff, and suspended particulate matter from natural erosion also contribute to the transport and bioavailability of heavy metals to snails that feed on detritus or filter particles (Bibby \u0026amp; Webster-Brown, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cb\u003eEffect of heavy metals on the pathophysiological changes of\u003c/b\u003e \u003cb\u003eF. martensi\u003c/b\u003e \u003cb\u003eand DNA damage\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe digestive gland, or hepatopancreas, is a critical organ for assessing the impacts of pollution at the tissue level. It plays a central role in food and energy metabolism, acting as the main source of digestive enzymes and participating in nutrient absorption, storage, and excretion (Wang et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Due to these functions, it is more susceptible to the accumulation of pollutants and plays a significant role in the detoxification of substances entering the organism compared with other tissues. This study highlighted the pathological effects of environmental heavy metal contamination, particularly Cd and Pb, as evidenced by tissue abnormalities observed in \u003cem\u003eF. martensi\u003c/em\u003e tissue collected from the Mae Kha Canal (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The Cd and Pb concentrations accumulated in the digestive gland were sufficient to induce significant histopathological alterations (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD) (Abdallah \u0026amp; Moustafa, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Karakaş \u0026amp; Otludil, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Otitoloju et al., 2009). These alterations included changes in cell shape and tubular structure, cellular degeneration and necrosis, and increased infiltration of white blood cells, indicating inflammation in the tissue (Dummee et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; El-Khayat et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Heavy metals induce oxidative stress through the generation of reactive oxygen species, which can damage cellular structures. In addition, they inhibit antioxidant defense enzymes such as catalase and glutathione peroxidase, thereby reducing the organism\u0026rsquo;s ability to neutralize oxidative stress (Jomova et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Kalinin et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This disruption ultimately results in extensive cellular damage and cell death, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD. Furthermore, the toxicity of heavy metals can lead to the destruction of biomolecules and potentially induce genetic mutations at the molecular level (Fol et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Utilizing freshwater snails including \u003cem\u003eF. martensi\u003c/em\u003e as bioindicators of heavy metal contamination provides an effective approach to assess environmental toxicity. This method enhances the understanding of contamination severity and potential ecological and health risks associated with heavy metal exposure in the Mae Kha Canal. Moreover, our data showed an elevated of 8-OHdG in snails from heavy metal-contaminated areas, indicating that oxidative damage to DNA (Kataoka et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The snails may accumulate heavy metals in their tissues and are susceptible to heavy metal contamination. This finding has indicated a correlation between the amount of environmental pollution with DNA and snail tissues (Fol et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Radwan et al., \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This study supports the use of freshwater snails as reliable bioindicators for monitoring heavy metal pollution.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study has confirmed that freshwater snails, particularly \u003cem\u003eF. martensi\u003c/em\u003e, are effective bioindicators for assessing the ecological integrity of the Mae Kha Canal. Seasonal variation, site-specific characteristics, and anthropogenic activities significantly influenced water quality, which in turn affected snail populations. The upstream section supported higher snail densities due to more favorable environmental conditions, while the midstream section, heavily impacted by urbanization and pollution, exhibited lower population levels. Analysis of the Cd and Pb concentrations in the snail soft tissue, sediment, and water samples revealed critical trends. The Cd concentrations in snails and sediment were significantly elevated during the wet season across all canal segments, likely due to increased surface runoff. Notably, the Pb concentrations in the snails exceeded the recommended safety limits, indicating potential health risks and warranting cautious consumption. Furthermore, Cd and Pb accumulation in the snails was associated with pathological alterations in the digestive gland and DNA damage, reflecting adverse health effects at the tissue and DNA level. These findings underscore the declining water quality in the Mae Kha Canal and the continued contamination of the sediment and aquatic biota with heavy metals. Overall, this study supports the use of freshwater snails as reliable bioindicators for monitoring heavy metal pollution. The results provide critical insights for environmental managers and policymakers: They could be used to guide pollution-control strategies aimed at safeguarding aquatic ecosystems and public health while promoting the sustainable rehabilitation of the Mae Kha Canal.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study is partially supported by Chiang Mai University. I would like to extend my heartfelt thanks to the members at Applied Parasitology Research Laboratory, Chiang Mai University, who provided support, assistance, and inspiration during this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTC drafted the original manuscript, conducted the survey, collected samples, analyzed physical and chemical properties, prepared samples for heavy metal analysis, and performed histological laboratory work. NN contributed to the survey, collected samples, drafted and edited the manuscript, reviewed the content, provided suggestions, and collaborated with TC to organize the project. All authors have read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding was received to assist with the preparation of this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll experimental procedures involving river snails were conducted following the guidelines of the Institute of Animals for Scientific Purpose Development (IAD), National Research Council of Thailand (Permit No. U1-03304-2559) and approved by the Ethics Committee of the Faculty of Science, Chiang Mai University (Protocol No. RE008/25). The study adhered to national regulations and institutional policies to ensure ethical treatment of animals.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbdallah, A. T., \u0026amp; Moustafa, M. A. (2002). Accumulation of lead and cadmium in the marine prosobranch \u003cem\u003eNerita saxtilis\u003c/em\u003e, chemical analysis, light and electron microscopy. Environmental Pollution, 116, 185\u0026ndash;191\u003c/li\u003e\n\u003cli\u003eAdano, A. J., Marcus, N. D., Magaji, J. I., \u0026amp; Opaluwa, O. D. (2023). Assessment of seasonal variation in heavy metal status of a lotic ecosystem in Federal Capital Territory, Abuja, North Central Nigeria. Makara Journal of Science, 27(4), 264\u0026ndash;272. https://doi.org/10.7454/mss.v27i4.1407\u003c/li\u003e\n\u003cli\u003eAli, M. M., Ali, M. 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Journal of The Science Society of Thailand, 23, 123\u0026ndash;134.\u003c/li\u003e\n\u003cli\u003eŽivković, N., Takić, L., Djordjević, L., Djordjević, A., Mladenović-Ranisavljević, I., Golubović, T., \u0026amp; Božilov, A. (2019). Concentrations of heavy metal cations and a health risk assessment of sediments and river surface water: A case study from a serbian mine. Polish Journal of Environmental Studies, 28(3), 2009\u0026ndash;2020. https://doi.org/10.15244/pjoes/89986\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ecotoxicology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ectx","sideBox":"Learn more about [Ecotoxicology](https://www.springer.com/journal/10646)","snPcode":"10646","submissionUrl":"https://submission.nature.com/new-submission/10646/3","title":"Ecotoxicology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Freshwater snails, Heavy metals, Bioindicators, Histopathology, Freshwater ecosystem","lastPublishedDoi":"10.21203/rs.3.rs-7136529/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7136529/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCadmium (Cd) and lead (Pb) tend to bioaccumulate in freshwater environments, making them major hazards to environmental health. This study aimed to determine the content of the heavy metals Cd and Pb in field sediment, water, and whole tissues of the edible river snail \u003cem\u003eFilopaludina martensi\u003c/em\u003e, which could serve as bioindicators for these metals. Principal component analysis (PCA), Permutational multivariate analysis of variance (PERMANOVA), and Pearson correlation coefficients (r) showed that heavy metals and snail populations are greatly impacted by seasonal variations (p \u0026lt; 0.05). The upstream section had healthier conditions compared with the midstream section, owing to the impact of anthropogenic activities. The wet season showed the highest Cd and Pb concentrations (p \u0026lt; 0.05) in all samples. The sediment samples had the highest Cd and Pb concentrations, followed by the snail and water samples (p \u0026lt; 0.05). The heavy metal concentrations in the sediment and river snail samples showed a strong correlation (PCA; p \u0026lt; 0.05). Importantly, the Pb concentrations in the snail samples were higher than the recommended threshold, indicating that these snails should be consumed with extreme caution. Both Cd and Pb damaged the snail digestive glands, and which may have caused DNA damage. These findings indicate that \u003cem\u003eF. martensi\u003c/em\u003e is a reliable bioindicator of the ecological integrity of the Mae Kha Canal. Evidence of biological degradation and ongoing metal contamination in the canal emphasizes the value of using these snails for pollution monitoring and directing pollution management efforts to maintain aquatic ecosystems and public health.\u003c/p\u003e","manuscriptTitle":"Integrated assessment of heavy metal pollution: Bioaccumulation in the river snail Filopaludina martensi, sediment, and water from the Mae Kha Canal, Chiang Mai province, Thailand","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-18 10:18:48","doi":"10.21203/rs.3.rs-7136529/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-15T16:08:43+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-07T08:06:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-04T06:21:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"203001451855985016194696786383491937266","date":"2025-09-13T01:45:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"68916069924328907316193979840106500421","date":"2025-09-11T03:43:24+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-10T21:25:13+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-17T05:39:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-17T05:38:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ecotoxicology","date":"2025-07-16T06:29:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ecotoxicology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ectx","sideBox":"Learn more about [Ecotoxicology](https://www.springer.com/journal/10646)","snPcode":"10646","submissionUrl":"https://submission.nature.com/new-submission/10646/3","title":"Ecotoxicology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"885b18af-e373-411f-9f2f-7cb201cd042c","owner":[],"postedDate":"September 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-15T16:02:45+00:00","versionOfRecord":{"articleIdentity":"rs-7136529","link":"https://doi.org/10.1007/s10646-025-03005-4","journal":{"identity":"ecotoxicology","isVorOnly":false,"title":"Ecotoxicology"},"publishedOn":"2025-12-09 15:58:06","publishedOnDateReadable":"December 9th, 2025"},"versionCreatedAt":"2025-09-18 10:18:48","video":"","vorDoi":"10.1007/s10646-025-03005-4","vorDoiUrl":"https://doi.org/10.1007/s10646-025-03005-4","workflowStages":[]},"version":"v1","identity":"rs-7136529","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7136529","identity":"rs-7136529","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}