Microplastics in wetlands: contrasting fish contamination between mangroves and temporary ponds in southeastern Brazil

Microplastics in wetlands: contrasting fish contamination between mangroves and temporary ponds in southeastern Brazil | 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 Microplastics in wetlands: contrasting fish contamination between mangroves and temporary ponds in southeastern Brazil Gustavo Henrique Soares Guedes, Laryssa Cordeiro, Luís Felipe Silva Pinto Azeredo, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7861289/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract Microplastic pollution is ubiquitous in aquatic ecosystems, but comparative analyses across wetland types and fish life histories are still rare. This study compares microplastic contamination in killifishes (Cyprinodontiformes: Rivulidae) with contrasting life histories—annual (short-lived: Notholebias minimus , Leptopanchax opalecens ) vs. perennial (long-lived: Kryptolebias ocellatus ; Kryptolebias hermaphroditus )—across two wetland types (temporary ponds vs. mangroves) on the coastal plain of Rio de Janeiro (Brazil). The tested hypothesis is that small, short-lived fishes in temporary wetlands exhibit lower microplastic contamination than perennial mangrove species, due to lower hydrological connectivity and shorter exposure time. Fishes were digested (KOH solution), vacuum filtered, and analysed using microscopy and µ-FTIR. Microplastic were detected in all species and 60.5% of individuals (1.58 ± 1.84 items fish⁻¹). Most particles were small (< 1,000 µm), blue/black fragments or microfibers, with polymers dominated by polypropylene and poly(4-methyl-1-pentene). Contrary to H1, MP loads did not differ between mangroves and temporary ponds (GLMM: χ² = 0.18, p = 0.671), nor with body size ( χ² = 0.44, p = 0.507). Atmospheric deposition, precipitation, and runoff can supply rain-fed wetlands with MPs at levels sufficient to produce fish microplastic burdens comparable to those observed in tidally influenced mangroves. Convergent functional traits of rivulids—small gape, generalist foraging, and routine use of shallow microhabitats where fibers and fragments accumulate—likely equalize ingestion probabilities across life histories. Collectively, these findings show that temporary wetlands are not refuges from plastic contamination and should be explicitly included in monitoring and mitigation strategies that target diffuse, landscape-scale MP inputs. killifish mangroves Microplastic pollution Rivulidae bioaccumulation Brazil micro-FTIR Figures Figure 1 Figure 2 Figure 3 1. Introduction Microplastics are particles of synthetic polymers smaller than five millimeters that have become a ubiquitous contaminant on a planetary scale. They originate either from the degradation of larger plastic debris (“secondary sources”) or are intentionally manufactured at small sizes for use in products such as cosmetics and textiles (“primary sources”), and constitute a significant environmental threat (Hartz et al. 2025). Their persistence, coupled with efficient transport by oceanic circulation and aeolian processes, has led to their detection in the most remote ecosystems—from the deepest ocean trenches (Peng et al. 2020) to the summit of Mount Everest (Napper et al. 2020). This widespread dispersal underscores the transboundary nature of the problem, highlighting failures in global plastic-waste management and the consequent contamination of soils, water bodies, and the atmosphere (Geyer et al. 2017). The massive presence of microplastics across ecosystems entails toxicological risks arising both from their intrinsic chemical composition and from their capacity to adsorb and transport other hazardous pollutants (Wang et al. 2020; Leslie et al. 2022), consolidating them as a worldwide environmental and public-health challenge. There has been a marked global expansion of research on microplastics across environmental compartments, driven by heightened public, regulatory, and academic attention to plastic pollution and its ecological and human-health impacts. Nevertheless, important biases persist in the literature: a geographic concentration of studies in high-income regions (e.g., China, United States), a taxonomic focus skewed toward charismatic or economically important groups, and a disproportionate emphasis on marine–coastal environments (Amparo et al., 2023; Sacco et al., 2024; Hartz et al., 2025; Jolaosho et al. 2025). Within the marine literature, over 80% focuses on sandy beaches (Browne et al. 2015), whereas brackish habitats such as mangroves remain understudied (Deakin et al. 2025). In freshwater systems, this bias is even more pronounced, with most studies targeting lotic environments—particularly large rivers (Moreira et al. 2025; Semensatto et al. 2025)—while freshwater wetlands and their biota have received limited attention (Qian et al. 2021; Dalvand and Hamidian 2023; Li et al. 2024). Consequently, a critical knowledge gap persists regarding the magnitude, exposure pathways, and ecological effects of plastic contamination in wetlands, constraining cross-ecosystem comparisons and the design of effective mitigation strategies. Wetlands, as broadly defined by the Ramsar Convention (1971), encompassing areas of marsh, fen, peatland, or water, whether natural or artificial, permanent or temporary, with water that is static or flowing; fresh, brackish, or salt; and including areas of marine water whose depth at low tide does not exceed six metres. These environments function as hydrological and biogeochemical interfaces where multiple microplastic (MP) input pathways converge (rivers, tides, urban/agricultural runoff), and are therefore particularly susceptible to the contamination and retention of these emerging pollutants (Dalvand and Hamidian 2023; Elnahas et al. 2024; Qiao and Wang 2024). Wetlands receive MPs via both aquatic and atmospheric fluxes, and typical hydromorphological features—low flow velocity, high lateral connectivity, and long residence times—favor the deposition and accumulation of plastic particles (Li et al. 2024). Dense vegetation (e.g., aerial roots and canopies in mangroves) acts as a physical “sieve” that retains MPs, although high-energy events (storm surges, floods) can remobilize them, characterizing these environments as sinks and, at times, secondary sources (Paduani 2020; Qiao and Wang 2024; Deakin et al. 2025). Evidence from analogous systems (constructed wetlands) indicates high MP retention along hydraulic–vegetation gradients, reinforcing the underlying physical mechanism (Boyer et al. 2024). Neotropical inland wetlands provide habitat for a diverse fish family (Rivulidae), comprising approximately 490 valid species (Fricke et al. 2025). Rivulid fishes are commonly subdivided into two main life-history groups—annual and perennial (Furness 2018; Guedes et al. 2025). This dichotomy reflects striking evolutionary adaptations to extreme environmental pressures, including high temperatures, low oxygen concentrations, acidic waters, and extreme hydrological fluctuations that approach the limits of vertebrate tolerance (Polačik and Podrabsky 2015; Podrabsky et al. 2016). Annual species are specialized colonizers of temporary wetlands, which are ephemeral, often isolated systems with low hydrological connectivity and predominantly rain-fed hydrology (Loureiro et al. 2018; Lanés et al. 2021). To survive periodic desiccation, these fishes produce eggs that enter a dormant state known as embryonic diapause (Furness, 2016). This trait enables embryos to persist for months within dry soil, awaiting the return of rains for hatching (Abrantes et al. 2020; Guedes et al. 2023a; Costa et al. 2024; Hinncands et al. 2025). Synchrony between the life cycle and the hydrological regime yields one of the shortest lifespans among vertebrates, with individuals living only a few months, which in turn has selected for extremely rapid growth and sexual maturation (Hu et al. 2020; Žák et al. 2021). By contrast, perennial rivulid species inhabit more stable aquatic environments such as streams, permanent wetlands, and mangroves. Their development follows the typical teleost pattern, without the three obligatory phases of embryonic diapause (Furness et al., 2018). Within the perennial group, a notable case is the genus Kryptolebias Costa, 2004, three species of which are known to occur strictly in mangroves: K. ocellatus (Hensel, 1868), K. marmoratus (Poey, 1880), and K. hermaphroditus Costa, 2011. Living in the dynamic and challenging mangrove environment, these species have evolved a suite of extraordinary traits. They are capable of cutaneous respiration, which enables direct oxygen uptake from air, and they can remain out of water for extended periods, sheltering in fallen logs and crab burrows during low tide (Wright 2012; Turko and Wright 2015). In addition, the genus Kryptolebias includes the only vertebrates known to exhibit simultaneous hermaphroditism with natural self-fertilization ( K. marmoratus and K. hermaphroditus ), allowing a single individual to found new clonal populations (Avise and Tatarenkov 2015; Rhee et al. 2017). Given the diversity of species’ life histories and the heterogeneous distribution of microplastics (MPs) across wetlands, vulnerability to MP contamination among rivulid fishes is unlikely to be uniform.Therefore, the main objective of this study is to compare microplastic (MP) contamination between fish with contrasting life-history durations (annual, short-lived; vs . perennial, long-lived) across two wetland types (temporary ponds vs . mangroves) on the coastal plain of Rio de Janeiro State, southeastern Brazil. We test the hypothesis that short-lived species inhabiting temporary wetlands exhibit lower MP contamination than long-lived species inhabiting mangrove systems with higher hydrological connectivity. This hypothesis is supported by evidence that mangroves act as filters and sinks for MPs due to continuous inputs from rivers and wastewater and to tidal resuspension, which together increase environmental MP availability (Deakin et al. 2025). In addition, field data, reviews, and modeling indicate that age and body size, which serve as proxies for lifespan and exposure time, are positively associated with MP occurrence and loads in fishes (Roch et al., 2020; Yagi et al. 2022; Ding et al. 2023). 2. Material and Methods 2.1 Study area The study area encompasses temporary wetlands in the municipalities of Seropédica (T1, 22°42'19.5"S – 43°41'36.1"W) and Rio de Janeiro (T2, 22°59'23.8"S – 43°25'03.0"W), as well as mangrove forests in Magé (M1, 22°42'36.9"S – 43°13'05.9"W; M2, 22°39'44.5"S – 43°05'09.7"W), which drain into the Jacarepaguá Lagoon System, and into Sepetiba and Guanabara bays, in the state of Rio de Janeiro, southeastern Brazil (Figure 1). Rivers and the biota comprising these drainage systems exhibit high levels of microplastic contamination (Alves et al., 2023; Drabinski et al., 2023). The climate in the region ranges from tropical monsoon (Am) in Magé and Rio de Janeiro, and tropical savanna (Aw) in Seropédica, according to the Köppen classification (https://koppenbrasil.github.io/). Mean annual temperatures vary from 21.7°C to 22.6°C, and total annual rainfall ranges from 1,332 to 1,806 mm. All localities are situated within the Atlantic Forest biome, a region recognized as a global biodiversity hotspot due to its exceptional species richness and high levels of endemism (Myers et al. 2000). 2.2 Fish collection Fish were collected in June 2025 using immersion nets (oval-shaped hand nets, 50 × 40 cm, 1 mm mesh size) in water less than 50 cm deep. After capture, specimens were anesthetized with benzocaine hydrochloride (50 mg/L), euthanized, and fixed in 10% formalin in situ . In the laboratory, fish were measured to the nearest 0.01 cm, weighed to the nearest 0.001 g, and, after 48 h, preserved in 70% ethanol. A total of 200 specimens belonging to four rivulid species from four localities (Figure 1) were analyzed: 100 individuals from temporary wetlands ( Notholebias minimus- annual specie, n = 50, from the municipality of Rio de Janeiro; Leptopanchax opalescens - annual specie, n = 50, from Seropédica) and 100 individuals of the perennial species Kryptolebias ocellatus and K. hermaphroditus from two mangrove sites in Magé (n = 100). Fish were collected under permits issued by the Instituto Chico Mendes de Conservação da Biodiversidade (IBAMA/ICMBio permits #10707 and #87082) and the Ethics Council for Animal Use (CEUA/ICBS/UFRRJ; authorization #12.28.01.00.00.00.45, February 2023). 2.3 Laboratory analysis 2.3.1 Microplastic extraction Due to the small body size of the analyzed species (mean ± SD = 1.99 ± 0.6 cm TL; range: 1.1–4.0 cm), whole fish were submerged in a 10% KOH solution (10 mL per gram of tissue) to digest organic matter. Therefore, the microplastic load reported in this study corresponds to the total present in all tissues and organs of each individual. Samples were then heated on a TEC NAL hot plate at 40 °C for four hours, following the protocol adapted from NOAA (Herring et al., 2015). Subsequently, each digest was vacuum-filtered through glass-fiber membrane filters. Filters were examined under a LEICA M205 C stereomicroscope, and all visible microplastics were counted, measured (µm), and classified into four categories—microfibers, fragments, spheres (beads), or pellets—according to Dekiff et al. (2014) and Hidalgo-Ruz et al. (2012). 2.3.2 Microplastics Characterization After visual inspection, a subsample corresponding to 10 % of the total microplastics observed was randomly selected following Hanke et al. (2013) and subjected to infrared microspectroscopy using a µ-FTIR Spectrum 3 equipped with a Spotlight 200 module (PerkinElmer) for chemical polymer characterization. The material retained during filtration was transferred, under an Olympus SZX10 stereomicroscope, to a polished KBr disk cell (13 × 2 mm) for µ-FTIR analysis in transmission mode. Particle screening was performed using halogen illumination (Olympus LG-PS2-5); for occasional visual enhancement of selected particles, a UV flashlight (A.F-535A). The µ-FTIR was operated in transmittance mode with a spectral resolution of 1 cm⁻¹ over a range of 4000–600 cm⁻¹. Aperture size and shape were adjusted for each particle, with dimensions varying between 25 and 150 µm. Obtained spectra were compared against the PerkinElmer “Polymers” reference library using Spectrum IR software (v. 10.7.2), and particles were classified as microplastics when their spectral match exceeded 75 %. 2.3.3 Quality assurance and control Recovery tests were performed to assess the efficiency of the extraction procedures. Samples were spiked with two microfibers of each polymer type: PET (polyethylene terephthalate), PVC (polyvinyl chloride), PS (polystyrene), and PA (polyamide). Procedural blanks consisted of Petri dishes containing filtered distilled water, which were placed alongside the samples throughout processing to monitor potential airborne contamination; any microplastics detected in these blanks were subsequently quantified. To minimize external contamination, all equipment (Petri dishes, scissors, tweezers) was thoroughly cleaned with distilled water followed by 70 % ethanol, and laboratory personnel wore latex gloves and lab coats at all times. 2.4 Data analysis Microplastics were quantified and categorized by manually counting each particle in the samples, recording both their color and size. We then calculated the relative frequency of each morphology type (microfibers, fragments, spheres, pellets) and each color category, expressing all values as percentages to provide a comprehensive, comparative overview of microplastic distribution across the analyzed fish. To test the hypothesis (H1) that short-lived fish species inhabiting temporary wetlands exhibit lower microplastic contamination than long-lived species inhabiting wetlands (mangroves), a Generalized Linear Mixed Model (GLMM) framework was employed. The response variable—microplastic abundance per fish (MP)—showed clear overdispersion (variance/mean = 2.14), moderate positive skewness (1.30), and high kurtosis (7.39), consistent with a long-tailed, sharply peaked distribution. Zeros accounted for 39.5% of observations (79/200), nearly double the proportion expected under a Poisson process with the same mean (20.5%), indicating substantial zero inflation —a common pattern in microplastic contamination datasets (e.g., Hou et al., 2021). Given the data structure, we fitted zero-inflated negative binomial GLMMs (ZINB) with a log link using the glmmTMB package (Brooks et al., 2017). Fixed effects included wetland type (mangrove vs. temporary ponds), fish body length (proxies for lifespan and exposure time), and their interaction (wetland type × body length), with sampling localities specified as random factors. These predictors were included in both the conditional and zero-inflation components of the models. Model significance for main effects and interactions was assessed using Type II Wald χ² ANOVA via the car package, with α = 0.05. Model assumptions and adequacy were checked using the simulateResiduals function from the DHARMa package (Hartig, 2024). Diagnostic plots were used to verify distributional assumptions, check for overdispersion, and identify potential outliers. No significant violations were detected (Fig. S1 - Supplemental Material 1). All statistical analyses were performed in R version 4.3.1 (R Core Team, 2024). Data used in the analyses are available in Supplemental Material 2. 3. Results Microplastic contamination was detected in 60.5% of rivulid fish (mean ± SD = 1.58 ± 1.84 particles per individual; Figure 2). Rates were similar across habitats: 62% in mangroves (1.50 ± 1.84 MP) and 59% in temporary wetlands (1.67 ± 1.97; Table 1). Particle composition was dominated by fragments (59.3%) and microfibers (38.4%); spheres and pellets were rare (< 2%; Figure 2 and 3; Table S1 - Supplemental Material 1). In terms of color, blue (65.3%), and black (23.3%) particles predominated, together accounting for 88.6% of all items recovered (Figure 3; Table S2 - Supplemental Material 1). Regarding size, particle lengths spanned 22–4,192 µm. Smaller particles (<1,000 µm) were the most prevalent across samples from both mangroves and temporary ponds (Figure 3). µ-FTIR analysis showed that the identified particles were mainly polypropylene (PP, 39.5%) and poly(4-methyl-1-pentene, PMP/TPX, 23.3%), followed by α-cellulose (16.3%), poly(ethylene terephthalate), PET (14.0%), cellulose (2.3%), and other polymers (4.7%) (Figure 3). By environment, Mangrove was dominated by PP (43.8%), with contributions from PMP (18.8%), α-cellulose (18.8%), PET (12.5%), and cellulose (6.3%). In temporary ponds (TP), PP (37.0%) and PMP (25.9%) predominated, with PET (14.8%) and α-cellulose (14.8%) at intermediate frequencies, plus other polymers (7.4%). Table 1 . Summary of morphometrics (TL = total length - cm, Wight= wet mass - g) and microplastic load by wetland type, site, and specie on the coastal plain of the state of Rio de Janeiro, Brazil. Values are mean ± SD; sample size per species in parentheses. Wetland Local Specie (N) TL (cm) Wight (g) MP per ind. Mangrove M1 K. ocellatus (37) 1.99±0.51 0.08±0.05 1.84±1.92 K. hermaphroditus (13) 2.22±0.51 0.11±0.06 1.46±1.81 M2 K. ocellatus (39) 2.69±0.71 0.24± 0.14 1.28±1.61 K. hermaphroditus (11) 2.82±0.66 0.25±0.16 1.18±1.47 Temporary pond T1 Leptopanchax opalescens (50) 1.44±0.2 0.03± 0.02 1.7±1.93 T2 Notholebias minimus (50) 1.77±0.35 0.06± 0.04 1.64±1.98 Microplastic abundance per fish were modeled with a zero-inflated negative binomial GLMM (AIC = 697.1). The zero-inflation component indicated a significant excess of structural zeros (logit intercept = −1.09 ± 0.36, p = 0.0026), corresponding to an average structural-zero probability of ~0.25. In the count component, neither wetland type ( χ ² = 0.18, p = 0.671) nor fish total length ( χ ² = 0.44, p = 0.507), nor their interaction ( χ ² = 0.18, p = 0.669) was associated with MP abundance; therefore rejecting H1. 4. Discussion 4.1 Microplastic Profiles: Morphotype, Color, Length, Polymer Composition Fragments (60%) and microfibers (38%) dominated the particles recovered from fish in both mangroves and temporary ponds, whereas spheres and pellets contributed only marginally. This profile contrasts with the meta-analysis (Lim et al. 2022; Dalvand and Hamidian 2023), which reported fibers as the dominant morphotype (70-98%) and fragments as secondary (8-19%) in fish globally. The observed inversion may be linked to the absence of temporary wetlands in the studies reviewed and may also reflect a combination of non-exclusive mechanisms: (i) habitat-specific sources and transformations—in mangroves, tidal energy, vessel traffic, and wear of fishing gear favor the secondary fragmentation of macroplastics, while root architecture and fine sediments act as sinks that modulate the relative availability of fibers in the water column (Paduani 2020; Qiao et al. 2024); and (ii) in temporary ponds, UV radiation, elevated temperatures, and wet–dry cycles accelerate photo-oxidation and abrasion, increasing the proportion of fragments (Qian et al. 2021; Li et al. 2024), while low hydrological connectivity reduces exposure to continuous inputs of textile microfibers from domestic/industrial effluents. Blue and black microplastic particles predominated in fish from both wetland types, together accounting for 88.6% of all items recovered. This pattern aligns with scientometric and global meta-analyses in fishes showing that blue and black particles are most frequently reported in field investigations (Lim et al. 2022; Sacco et al. 2024). Ecological and methodological processes likely act in concert across brackish and freshwater habitats: (i) shared inputs from urban effluents, surface run-off, and atmospheric deposition deliver a similar “color mix,” with blue plastics incidentally ingested due to high environmental availability (Lim et al. 2022); (ii) visual selection by fish may favor blue particles that resemble zooplankton prey, while black particles commonly reflect tire-wear debris and ropes/fishing gear (Ory et al. 2017); and (iii) visual sorting can overestimate vivid/dark colors and undercount transparent particles (Lusher et al. 2020). Particles <1,000 µm were the most prevalent in this study, consistent with syntheses in fishes indicating that the 0–1 mm class is the most common among ingested items (Oza et al. 2024). Biologically, the small body size of rivulids imposes gape limitations and favors selection of proportionally small natural prey; such morphological constraints likely render smaller microplastics more susceptible to incidental ingestion during foraging (e.g., Siddique et al. 2024). The high frequency of polypropylene observed in this study is consistent with syntheses and meta-analyses reporting polyolefins (PE/PP) as the most common polymers in fishes (Lim et al., 2022). This pattern reflects their high production, low density, and persistence, which favor surface transport and stranding in physical retention zones such as mangrove roots and emergent macrophytes (Amparo et al. 2023; Oza et al 2024; ). 4.2 Effects of Wetland Type and Body Length on Microplastic Contamination Contrary to H1, microplastic (MP) burdens were similar in short-lived fishes from temporary wetlands and long-lived fishes from mangroves, despite the expectation of higher contamination in mangroves owing to stronger hydrological connectivity and longer life spans (and thus greater cumulative exposure). This finding suggests that efficient pathways of MP input and ingestion also operate in fishes from temporary wetlands, offsetting the effects of lower connectivity and shorter life cycles. Reviews show that mangrove root structure and tidal regimes promote the retention and enrichment of microplastics (MPs) in mangroves (e.g., Qiao et al. 2024; Deakin et al. 2025), and that body size—used as a proxy for lifespan and exposure time—is positively associated with MP occurrence and loads in fishes (Roch et al. 2020; Yagi et al. 2022; Ding et al. 2023), which would, a priori, justify the expectation of higher loads in mangrove fishes. A key mechanism underlying MP contamination of fishes in the temporary wetlands examined here may be atmospheric and pluvial inputs. Owing to their small size and low density, MPs become airborne and can be transported over long distances by wind before being redeposited on terrestrial and aquatic surfaces (Allen et al. 2019; Elnahas et al. 2024). Precipitation also plays a crucial role by scavenging suspended MPs from the atmosphere and depositing them in concentrated fluxes, effectively acting as a “concentration funnel” (Brahney et al. 2020; Dong et al. 2024). In addition, overland runoff from roads/highways and traffic-derived dust—particularly tire- and brake-wear particles—constitute an important MP source (e.g., Jaiswal et al. 2025). Runoff from agricultural areas can transport mixtures of pesticides into water bodies inhabited by rivulids (Zebral et al. 2018; Godoy et al. 2025), together with microplastics (MPs), creating co-exposure scenarios. This is consistent with the study’s sampling sites: the temporary pond of Leptopanchax opalescens is located in an industrial/ agricultural zone near a state highway (Guedes et al. 2020), whereas the Notholebias minimus site lies within an urban area of the city of Rio de Janeiro (Guedes et al. 2023b), one of the most densely populated regions of Brazil. The hydrological “isolation” of a temporary wetland from perennial waters is therefore illusory from the standpoint of plastic pollution. Predominantly rain-fed temporary ponds can receive intense MP pulses directly from the atmosphere during rainfall events, in addition to surface runoff from nearby roads, making MPs readily available for fish ingestion. Beyond environmental MP availability, the observed similarity in ingestion among species may stem from functional traits shared by rivulids. Small body size and reduced gape impose size-selective filtering, favoring ingestion of fine particles (<1 mm)—the fraction that tends to predominate in MP records (Siddique et al. 2024; Lim et al. 2022). In addition, a generalist trophic habit and recurrent use of shallow microhabitats (shallow benthos, periphyton/detritus, and the air–water interface)—where fibers and fragments accumulate via flotation, settling, and resuspension—create similar opportunities for incidental ingestion in both annual and perennial species. Despite shorter lifespans, annual species exhibit high growth and foraging rates to complete a rapid life cycle (Furness 2016; Žák et al. 2021), which may compensate for reduced exposure time and bring MP loads closer to those of perennial species. Taken together, (i) shared morphological traits (small body/reduced gape), (ii) convergent use of microhabitats with high MP availability, and (iii) elevated foraging rates in annuals tend to homogenize the spectrum of particle sizes ingested and, consequently, the individual MP burdens observed in this study. 5. Conclusions This first quantification of microplastics in Rivulidae fishes reveals widespread contamination—particles occurred in all four species and in 60.5% of individuals (1.58 ± 1.84 items fish⁻¹)—with profiles dominated by < 1,000 µm blue/black fragments and microfibers, chiefly polypropylene, poly(4-methyl-1-pentene) and PET. Contrary to H1, MP loads did not differ between mangroves and temporary ponds, nor with body size, indicating that atmospheric deposition, rainfall washout, and runoff can supply rain-fed wetlands with MPs at levels comparable to tidally influenced mangroves. Convergent functional traits of rivulids—small body and gape, generalist foraging, and routine use of shallow microhabitats where fibers and fragments accumulate—likely equalize ingestion probabilities across life histories. Collectively, these findings show that temporary wetlands are not refuges from plastic contamination, and should be explicitly included in monitoring and mitigation strategies that target diffuse, landscape-scale MP inputs. Declarations Contributions G.H.S.G. conceived the study, conducted field sampling, curated and analyzed the data, wrote the original draft, and revised and edited the manuscript. L.C. and L.F.S.P.A. performed laboratory work, curated and analyzed data, contributed to the review of the literature and methods, and revised and edited the manuscript. F.G.A. supervised the research process, contributed to the theoretical framework, and revised and edited the manuscript. All authors read and approved the final manuscript. Funding This study was funded by Fundo Brasileiro para a Biodiversidade – FUNBIO Conservando o Futuro, and Instituto HUMANIZE (Proc. # 028/2023), Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (E-26/200.897/2021, E-26/210.103/2023), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 140.512/2022-5). Declaration of competing interest The author declares no competing interests. Data availability The datasets generated during the current study are available in Supplementary material 2. Supplementary material This article includes Supplementary material 1 and 2. References Abrantes YG, Medeiros LS, Bennemann ABA, Bento DM, Teixeira FK, Rezende CF et al (2020) Geographic distribution and conservation of seasonal killifishes (Cyprinodontiformes, Rivulidae) from the Mid-Northeastern Caatinga ecoregion, northeastern Brazil. 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14:34:34","extension":"html","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":145018,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7861289/v1/aba8ef05c9efc132bba8978f.html"},{"id":94679636,"identity":"c6c26701-2d94-4dc9-855e-5398eb3d41cb","added_by":"auto","created_at":"2025-10-29 14:34:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":772922,"visible":true,"origin":"","legend":"\u003cp\u003eMap showing the sampling sites of rivulid fishes on the coastal plain of the state of Rio de Janeiro, Brazil. Black circle: \u003cem\u003eLeptopanchax opalescens – \u003c/em\u003etemporary wetland (T1); triangle: \u003cem\u003eNotholebias minimus – \u003c/em\u003etemporary wetland (T2); squares\u003cem\u003e: Kryptolebias ocellatus and Kryptolebias hermaphroditus – \u003c/em\u003emangroves (M1 and M2).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7861289/v1/b6b9398ffae5dd742cdaeb99.png"},{"id":94679642,"identity":"4b78df9b-337d-4ef6-add3-2b46a2dc50c0","added_by":"auto","created_at":"2025-10-29 14:34:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":787643,"visible":true,"origin":"","legend":"\u003cp\u003ePhotographs of microplastics detected in rivulid fishes. Fragments (a–b); microfibers (c); spheres (d).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7861289/v1/376dadf52a45e173f223d379.png"},{"id":94728307,"identity":"61ee7b0f-746b-4120-be9d-e5628637038d","added_by":"auto","created_at":"2025-10-30 07:03:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":230026,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of microplastic contamination in rivulid fishes between two wetland types (Mangroves and temporary ponds) in southeastern Brazil—by (i) morphology (ring/donut charts), (ii) color (bars proportional to frequency), (iii) size (horizontal histograms of length distribution, in µm), and polymer composition (bars proportional to frequency).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7861289/v1/5731c453f2b4c4e8ddf1186f.png"},{"id":94731179,"identity":"14d500ea-13d8-49cb-9675-b42b039e0c6a","added_by":"auto","created_at":"2025-10-30 07:07:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2395489,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7861289/v1/783b8a3b-8feb-4cb3-adaa-eedfc06a833d.pdf"},{"id":94728672,"identity":"5cb28f39-1fc2-4ac8-b767-87bf0e1234da","added_by":"auto","created_at":"2025-10-30 07:04:09","extension":"xlsx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":37836,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementalMaterial2DataMPrivulidae.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7861289/v1/afd93dce2072006000945cc1.xlsx"},{"id":94679643,"identity":"84d4b3a8-77c1-4d3c-819b-fcfee2b9a795","added_by":"auto","created_at":"2025-10-29 14:34:34","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":189028,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarymaterial1.docx","url":"https://assets-eu.researchsquare.com/files/rs-7861289/v1/47972cc08ad216ef330f8b76.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Microplastics in wetlands: contrasting fish contamination between mangroves and temporary ponds in southeastern Brazil","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMicroplastics are particles of synthetic polymers smaller than five millimeters that have become a ubiquitous contaminant on a planetary scale. They originate either from the degradation of larger plastic debris (\u0026ldquo;secondary sources\u0026rdquo;) or are intentionally manufactured at small sizes for use in products such as cosmetics and textiles (\u0026ldquo;primary sources\u0026rdquo;), and constitute a significant environmental threat (Hartz et al. 2025). Their persistence, coupled with efficient transport by oceanic circulation and aeolian processes, has led to their detection in the most remote ecosystems\u0026mdash;from the deepest ocean trenches (Peng et al. 2020) to the summit of Mount Everest (Napper et al. 2020). This widespread dispersal underscores the transboundary nature of the problem, highlighting failures in global plastic-waste management and the consequent contamination of soils, water bodies, and the atmosphere (Geyer et al. 2017). The massive presence of microplastics across ecosystems entails toxicological risks arising both from their intrinsic chemical composition and from their capacity to adsorb and transport other hazardous pollutants (Wang et al. 2020; Leslie et al. 2022), consolidating them as a worldwide environmental and public-health challenge.\u003c/p\u003e\n\u003cp\u003eThere has been a marked global expansion of research on microplastics across environmental compartments, driven by heightened public, regulatory, and academic attention to plastic pollution and its ecological and human-health impacts. Nevertheless, important biases persist in the literature: a geographic concentration of studies in high-income regions (e.g., China, United States), a taxonomic focus skewed toward charismatic or economically important groups, and a disproportionate emphasis on marine\u0026ndash;coastal environments (Amparo et al., 2023; Sacco et al., 2024; Hartz et al., 2025; Jolaosho et al. 2025). Within the marine literature, over 80% focuses on sandy beaches (Browne et al. 2015), whereas brackish habitats such as mangroves remain understudied (Deakin et al. 2025). In freshwater systems, this bias is even more pronounced, with most studies targeting lotic environments\u0026mdash;particularly large rivers (Moreira et al. 2025; Semensatto et al. 2025)\u0026mdash;while freshwater wetlands and their biota have received limited attention (Qian et al. 2021; Dalvand and Hamidian 2023; Li et al. 2024). Consequently, a critical knowledge gap persists regarding the magnitude, exposure pathways, and ecological effects of plastic contamination in wetlands, constraining cross-ecosystem comparisons and the design of effective mitigation strategies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWetlands, as broadly defined by the Ramsar Convention (1971), encompassing areas of marsh, fen, peatland, or water, whether natural or artificial, permanent or temporary, with water that is static or flowing; fresh, brackish, or salt; and including areas of marine water whose depth at low tide does not exceed six metres. These environments function as hydrological and biogeochemical interfaces where multiple microplastic (MP) input pathways converge (rivers, tides, urban/agricultural runoff), and are therefore particularly susceptible to the contamination and retention of these emerging pollutants (Dalvand and Hamidian 2023; Elnahas et al. 2024; Qiao and Wang 2024). Wetlands receive MPs via both aquatic and atmospheric fluxes, and typical hydromorphological features\u0026mdash;low flow velocity, high lateral connectivity, and long residence times\u0026mdash;favor the deposition and accumulation of plastic particles (Li et al. 2024). Dense vegetation (e.g., aerial roots and canopies in mangroves) acts as a physical \u0026ldquo;sieve\u0026rdquo; that retains MPs, although high-energy events (storm surges, floods) can remobilize them, characterizing these environments as sinks and, at times, secondary sources (Paduani 2020; Qiao and Wang 2024; Deakin et al. 2025). Evidence from analogous systems (constructed wetlands) indicates high MP retention along hydraulic\u0026ndash;vegetation gradients, reinforcing the underlying physical mechanism (Boyer et al. 2024).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNeotropical inland wetlands provide habitat for a diverse fish family (Rivulidae), comprising approximately 490 valid species (Fricke et al. 2025). Rivulid fishes are commonly subdivided into two main life-history groups\u0026mdash;annual and perennial (Furness 2018; Guedes et al. 2025). This dichotomy reflects striking evolutionary adaptations to extreme environmental pressures, including high temperatures, low oxygen concentrations, acidic waters, and extreme hydrological fluctuations that approach the limits of vertebrate tolerance (Polačik and Podrabsky 2015; Podrabsky et al. 2016). Annual species are specialized colonizers of temporary wetlands, which are ephemeral, often isolated systems with low hydrological connectivity and predominantly rain-fed hydrology (Loureiro et al. 2018; Lan\u0026eacute;s et al. 2021). To survive periodic desiccation, these fishes produce eggs that enter a dormant state known as embryonic diapause (Furness, 2016). This trait enables embryos to persist for months within dry soil, awaiting the return of rains for hatching (Abrantes et al. 2020; Guedes et al. 2023a; Costa et al. 2024;\u0026nbsp;Hinncands et al. 2025). Synchrony between the life cycle and the hydrological regime yields one of the shortest lifespans among vertebrates, with individuals living only a few months, which in turn has selected for extremely rapid growth and sexual maturation (Hu et al. 2020; Ž\u0026aacute;k et al. 2021).\u003c/p\u003e\n\u003cp\u003eBy contrast, perennial rivulid species inhabit more stable aquatic environments such as streams, permanent wetlands, and mangroves. Their development follows the typical teleost pattern, without the three obligatory phases of embryonic diapause (Furness et al., 2018). Within the perennial group, a notable case is the genus \u003cem\u003eKryptolebias\u003c/em\u003e Costa, 2004, three species of which are known to occur strictly in mangroves: \u003cem\u003eK. ocellatus\u003c/em\u003e (Hensel, 1868), \u003cem\u003eK. marmoratus\u003c/em\u003e (Poey, 1880), and \u003cem\u003eK. hermaphroditus\u003c/em\u003e Costa, 2011. Living in the dynamic and challenging mangrove environment, these species have evolved a suite of extraordinary traits. They are capable of cutaneous respiration, which enables direct oxygen uptake from air, and they can remain out of water for extended periods, sheltering in fallen logs and crab burrows during low tide (Wright 2012; Turko and Wright 2015). In addition, the genus \u003cem\u003eKryptolebias\u003c/em\u003e includes the only vertebrates known to exhibit simultaneous hermaphroditism with natural self-fertilization (\u003cem\u003eK. marmoratus\u003c/em\u003e and \u003cem\u003eK. hermaphroditus\u003c/em\u003e), allowing a single individual to found new clonal populations (Avise and Tatarenkov 2015; Rhee et al. 2017).\u003c/p\u003e\n\u003cp\u003eGiven the diversity of species\u0026rsquo; life histories and the heterogeneous distribution of microplastics (MPs) across wetlands, vulnerability to MP contamination among rivulid fishes is unlikely to be uniform.Therefore, the main objective of this study is to compare microplastic (MP) contamination between fish with contrasting life-history durations (annual, short-lived; \u003cem\u003evs\u003c/em\u003e. perennial, long-lived) across two wetland types (temporary ponds \u003cem\u003evs\u003c/em\u003e. mangroves) on the coastal plain of Rio de Janeiro State, southeastern Brazil. We test the hypothesis that short-lived species inhabiting temporary wetlands exhibit lower MP contamination than long-lived species inhabiting mangrove systems with higher hydrological connectivity. This hypothesis is supported by evidence that mangroves act as filters and sinks for MPs due to continuous inputs from rivers and wastewater and to tidal resuspension, which together increase environmental MP availability (Deakin et al. 2025). In addition, field data, reviews, and modeling indicate that age and body size, which serve as proxies for lifespan and exposure time, are positively associated with MP occurrence and loads in fishes (Roch et al., 2020; Yagi et al. 2022; Ding et al. 2023).\u0026nbsp;\u003c/p\u003e"},{"header":"2. Material and Methods","content":"\u003cp\u003e\u003cem\u003e2.1 Study area\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe study area encompasses temporary wetlands in the municipalities of Serop\u0026eacute;dica (T1, 22\u0026deg;42\u0026apos;19.5\u0026quot;S \u003cem\u003e\u0026ndash;\u0026nbsp;\u003c/em\u003e43\u0026deg;41\u0026apos;36.1\u0026quot;W) and Rio de Janeiro (T2, 22\u0026deg;59\u0026apos;23.8\u0026quot;S \u003cem\u003e\u0026ndash;\u0026nbsp;\u003c/em\u003e43\u0026deg;25\u0026apos;03.0\u0026quot;W), as well as mangrove forests in Mag\u0026eacute; (M1, 22\u0026deg;42\u0026apos;36.9\u0026quot;S \u003cem\u003e\u0026ndash;\u0026nbsp;\u003c/em\u003e43\u0026deg;13\u0026apos;05.9\u0026quot;W; M2, 22\u0026deg;39\u0026apos;44.5\u0026quot;S \u003cem\u003e\u0026ndash;\u0026nbsp;\u003c/em\u003e43\u0026deg;05\u0026apos;09.7\u0026quot;W), which drain into the Jacarepagu\u0026aacute; Lagoon System, and into Sepetiba and Guanabara bays, in the state of Rio de Janeiro, southeastern Brazil (Figure 1). Rivers and the biota comprising these drainage systems exhibit high levels of microplastic contamination (Alves et al., 2023; Drabinski et al., 2023). The climate in the region ranges from tropical monsoon (Am) in Mag\u0026eacute; and Rio de Janeiro, and tropical savanna (Aw) in Serop\u0026eacute;dica, according to the K\u0026ouml;ppen classification (https://koppenbrasil.github.io/). Mean annual temperatures vary from 21.7\u0026deg;C to 22.6\u0026deg;C, and total annual rainfall ranges from 1,332 to 1,806 mm. All localities are situated within the Atlantic Forest biome, a region recognized as a global biodiversity hotspot due to its exceptional species richness and high levels of endemism (Myers et al. 2000).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.2 Fish collection\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFish were collected in June 2025 using immersion nets (oval-shaped hand nets, 50 \u0026times; 40 cm, 1 mm mesh size) in water less than 50 cm deep. After capture, specimens were anesthetized with benzocaine hydrochloride (50 mg/L), euthanized, and fixed in 10% formalin \u003cem\u003ein situ\u003c/em\u003e. In the laboratory, fish were measured to the nearest 0.01 cm, weighed to the nearest 0.001 g, and, after 48 h, preserved in 70% ethanol. A total of 200 specimens belonging to four rivulid species from four localities (Figure 1) were analyzed: 100 individuals from temporary wetlands (\u003cem\u003eNotholebias minimus-\u0026nbsp;\u003c/em\u003eannual specie, n = 50, from the municipality of Rio de Janeiro; \u003cem\u003eLeptopanchax opalescens -\u0026nbsp;\u003c/em\u003eannual specie, n = 50, from Serop\u0026eacute;dica) and 100 individuals of the perennial species \u003cem\u003eKryptolebias ocellatus\u003c/em\u003e and \u003cem\u003eK. hermaphroditus\u003c/em\u003e from two mangrove sites in Mag\u0026eacute; (n = 100). Fish were collected under permits issued by the Instituto Chico Mendes de Conserva\u0026ccedil;\u0026atilde;o da Biodiversidade (IBAMA/ICMBio permits #10707 and #87082) and the Ethics Council for Animal Use (CEUA/ICBS/UFRRJ; authorization #12.28.01.00.00.00.45, February 2023).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.3 Laboratory analysis\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.3.1 Microplastic extraction\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eDue to the small body size of the analyzed species (mean \u0026plusmn; SD = 1.99 \u0026plusmn; 0.6 cm TL; range: 1.1\u0026ndash;4.0 cm), whole fish were submerged in a 10% KOH solution (10 mL per gram of tissue) to digest organic matter. Therefore, the microplastic load reported in this study corresponds to the total present in all tissues and organs of each individual. Samples were then heated on a TEC NAL hot plate at 40 \u0026deg;C for four hours, following the protocol adapted from NOAA (Herring et al., 2015). Subsequently, each digest was vacuum-filtered through glass-fiber membrane filters. Filters were examined under a LEICA M205 C stereomicroscope, and all visible microplastics were counted, measured (\u0026micro;m), and classified into four categories\u0026mdash;microfibers, fragments, spheres (beads), or pellets\u0026mdash;according to Dekiff et al. (2014) and Hidalgo-Ruz et al. (2012).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.3.2 Microplastics Characterization\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAfter visual inspection, a subsample corresponding to 10 % of the total microplastics observed was randomly selected following Hanke et al. (2013) and subjected to infrared microspectroscopy using a \u0026micro;-FTIR Spectrum 3 equipped with a Spotlight 200 module (PerkinElmer) for chemical polymer characterization. The material retained during filtration was transferred, under an Olympus SZX10 stereomicroscope, to a polished KBr disk cell (13 \u0026times; 2 mm) for \u0026micro;-FTIR analysis in transmission mode. Particle screening was performed using halogen illumination (Olympus LG-PS2-5); for occasional visual enhancement of selected particles, a UV flashlight (A.F-535A). The \u0026micro;-FTIR was operated in transmittance mode with a spectral resolution of 1 cm⁻\u0026sup1; over a range of 4000\u0026ndash;600 cm⁻\u0026sup1;. Aperture size and shape were adjusted for each particle, with dimensions varying between 25 and 150 \u0026micro;m. Obtained spectra were compared against the PerkinElmer \u0026ldquo;Polymers\u0026rdquo; reference library using Spectrum IR software (v. 10.7.2), and particles were classified as microplastics when their spectral match exceeded 75 %.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.3.3 Quality assurance and control\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eRecovery tests were performed to assess the efficiency of the extraction procedures. Samples were spiked with two microfibers of each polymer type: PET (polyethylene terephthalate), PVC (polyvinyl chloride), PS (polystyrene), and PA (polyamide). Procedural blanks consisted of Petri dishes containing filtered distilled water, which were placed alongside the samples throughout processing to monitor potential airborne contamination; any microplastics detected in these blanks were subsequently quantified. To minimize external contamination, all equipment (Petri dishes, scissors, tweezers) was thoroughly cleaned with distilled water followed by 70 % ethanol, and laboratory personnel wore latex gloves and lab coats at all times.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.4 Data analysis\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eMicroplastics were quantified and categorized by manually counting each particle in the samples, recording both their color and size. We then calculated the relative frequency of each morphology type (microfibers, fragments, spheres, pellets) and each color category, expressing all values as percentages to provide a comprehensive, comparative overview of microplastic distribution across the analyzed fish.\u003c/p\u003e\n\u003cp\u003eTo test the hypothesis (H1) that short-lived fish species inhabiting temporary wetlands exhibit lower microplastic contamination than long-lived species inhabiting wetlands (mangroves), a Generalized Linear Mixed Model (GLMM) framework was employed. The response variable\u0026mdash;microplastic abundance per fish (MP)\u0026mdash;showed clear overdispersion (variance/mean = 2.14), moderate positive skewness (1.30), and high kurtosis (7.39), consistent with a long-tailed, sharply peaked distribution. Zeros accounted for 39.5% of observations (79/200), nearly double the proportion expected under a Poisson process with the same mean (20.5%), indicating substantial zero inflation \u0026mdash;a common pattern in microplastic contamination datasets (e.g., Hou et al., 2021).\u003c/p\u003e\n\u003cp\u003eGiven the data structure, we fitted zero-inflated negative binomial GLMMs (ZINB) with a log link using the \u003cem\u003eglmmTMB\u003c/em\u003e package (Brooks et al., 2017). Fixed effects included wetland type (mangrove vs. temporary ponds), fish body length (proxies for lifespan and exposure time), and their interaction (wetland type \u0026times; body length), with sampling localities specified as random factors. These predictors were included in both the conditional and zero-inflation components of the models. Model significance for main effects and interactions was assessed using Type II Wald \u0026chi;\u0026sup2; ANOVA via the \u003cem\u003ecar\u003c/em\u003e package, with \u0026alpha; = 0.05. Model assumptions and adequacy were checked using the simulateResiduals function from the \u003cem\u003eDHARMa\u003c/em\u003e package (Hartig, 2024). Diagnostic plots were used to verify distributional assumptions, check for overdispersion, and identify potential outliers. No significant violations were detected (Fig. S1 - Supplemental Material 1). All statistical analyses were performed in R version 4.3.1 (R Core Team, 2024). Data used in the analyses are available in Supplemental Material 2.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003eMicroplastic contamination was detected in 60.5% of rivulid fish (mean \u0026plusmn; SD = 1.58 \u0026plusmn; 1.84 particles per individual; Figure 2). Rates were similar across habitats: 62% in mangroves (1.50 \u0026plusmn; 1.84 MP) and 59% in temporary wetlands (1.67 \u0026plusmn; 1.97; Table 1). Particle composition was dominated by fragments (59.3%) and microfibers (38.4%); spheres and pellets were rare \u0026nbsp;(\u0026lt; 2%; Figure 2 and 3; Table S1 - Supplemental Material 1). In terms of color, blue (65.3%), and black (23.3%) particles predominated, together accounting for 88.6% of all items recovered (Figure 3; Table S2 - Supplemental Material 1). Regarding size, particle lengths spanned 22\u0026ndash;4,192 \u0026micro;m. Smaller particles (\u0026lt;1,000 \u0026micro;m) were the most prevalent across samples from both mangroves and temporary ponds (Figure 3).\u003c/p\u003e\n\u003cp\u003e\u0026micro;-FTIR analysis showed that the identified particles were mainly polypropylene (PP, 39.5%) and poly(4-methyl-1-pentene, PMP/TPX, 23.3%), followed by \u0026alpha;-cellulose (16.3%), poly(ethylene terephthalate), PET (14.0%), cellulose (2.3%), and other polymers (4.7%) (Figure 3). By environment, Mangrove was dominated by PP (43.8%), with contributions from PMP (18.8%), \u0026alpha;-cellulose (18.8%), PET (12.5%), and cellulose (6.3%). In temporary ponds (TP), PP (37.0%) and PMP (25.9%) predominated, with PET (14.8%) and \u0026alpha;-cellulose (14.8%) at intermediate frequencies, plus other polymers (7.4%).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e. Summary of morphometrics (TL = total length - cm, Wight= wet mass - g) and microplastic load by wetland type, site, and specie on the coastal plain of the state of Rio de Janeiro, Brazil. Values are mean \u0026plusmn; SD; sample size per species in parentheses.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"619\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003eWetland\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eLocal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 210px;\"\u003e\n \u003cp\u003eSpecie (N)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eTL (cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003eWight (g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003eMP per ind.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003eMangrove\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eM1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 210px;\"\u003e\n \u003cp\u003e\u003cem\u003eK. ocellatus\u0026nbsp;\u003c/em\u003e(37)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1.99\u0026plusmn;0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.08\u0026plusmn;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e1.84\u0026plusmn;1.92\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 80px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 210px;\"\u003e\n \u003cp\u003e\u003cem\u003eK. hermaphroditus\u0026nbsp;\u003c/em\u003e(13)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e2.22\u0026plusmn;0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.11\u0026plusmn;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e1.46\u0026plusmn;1.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 80px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eM2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 210px;\"\u003e\n \u003cp\u003e\u003cem\u003eK. ocellatus\u0026nbsp;\u003c/em\u003e(39)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e2.69\u0026plusmn;0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.24\u0026plusmn; 0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e1.28\u0026plusmn;1.61\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 80px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 210px;\"\u003e\n \u003cp\u003e\u003cem\u003eK. hermaphroditus\u0026nbsp;\u003c/em\u003e(11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e2.82\u0026plusmn;0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.25\u0026plusmn;0.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e1.18\u0026plusmn;1.47\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003eTemporary pond\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eT1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 210px;\"\u003e\n \u003cp\u003e\u003cem\u003eLeptopanchax opalescens\u0026nbsp;\u003c/em\u003e(50)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1.44\u0026plusmn;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.03\u0026plusmn; 0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e1.7\u0026plusmn;1.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 80px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eT2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 210px;\"\u003e\n \u003cp\u003e\u003cem\u003eNotholebias minimus\u0026nbsp;\u003c/em\u003e(50)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1.77\u0026plusmn;0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.06\u0026plusmn; 0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 86px;\"\u003e\n \u003cp\u003e1.64\u0026plusmn;1.98\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eMicroplastic abundance per fish were modeled with a zero-inflated negative binomial GLMM (AIC = 697.1). The zero-inflation component indicated a significant excess of structural zeros (logit intercept = \u0026minus;1.09 \u0026plusmn; 0.36, \u003cem\u003ep\u003c/em\u003e = 0.0026), corresponding to an average structural-zero probability of ~0.25. In the count component, neither wetland type (\u003cem\u003e\u0026chi;\u003c/em\u003e\u003cem\u003e\u0026sup2;\u003c/em\u003e = 0.18, \u003cem\u003ep\u003c/em\u003e = 0.671) nor fish total length (\u003cem\u003e\u0026chi;\u003c/em\u003e\u003cem\u003e\u0026sup2;\u003c/em\u003e = 0.44, \u003cem\u003ep\u003c/em\u003e = 0.507), nor their interaction (\u003cem\u003e\u0026chi;\u003c/em\u003e\u003cem\u003e\u0026sup2;\u003c/em\u003e = 0.18, \u003cem\u003ep\u003c/em\u003e = 0.669) was associated with MP abundance; therefore rejecting H1.\u0026nbsp;\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003e\u003cem\u003e4.1 Microplastic Profiles: Morphotype, Color, Length, Polymer Composition\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFragments (60%) and microfibers (38%) dominated the particles recovered from fish in both mangroves and temporary ponds, whereas spheres and pellets contributed only marginally. This profile contrasts with the meta-analysis (Lim et al. 2022; Dalvand and Hamidian 2023), which reported fibers as the dominant morphotype (70-98%) and fragments as secondary (8-19%) in fish globally. The observed inversion may be linked to the absence of temporary wetlands in the studies reviewed and may also reflect a combination of non-exclusive mechanisms: (i) habitat-specific sources and transformations\u0026mdash;in mangroves, tidal energy, vessel traffic, and wear of fishing gear favor the secondary fragmentation of macroplastics, while root architecture and fine sediments act as sinks that modulate the relative availability of fibers in the water column (Paduani 2020; Qiao et al. 2024); and (ii) in temporary ponds, UV radiation, elevated temperatures, and wet\u0026ndash;dry cycles accelerate photo-oxidation and abrasion, increasing the proportion of fragments (Qian et al. 2021; Li et al. 2024), while low hydrological connectivity reduces exposure to continuous inputs of textile microfibers from domestic/industrial effluents.\u003c/p\u003e\n\u003cp\u003eBlue and black microplastic particles predominated in fish from both wetland types, together accounting for 88.6% of all items recovered. This pattern aligns with scientometric and global meta-analyses in fishes showing that blue and black particles are most frequently reported in field investigations (Lim et al. 2022; Sacco et al. 2024). Ecological and methodological processes likely act in concert across brackish and freshwater habitats: (i) shared inputs from urban effluents, surface run-off, and atmospheric deposition deliver a similar \u0026ldquo;color mix,\u0026rdquo; with blue plastics incidentally ingested due to high environmental availability (Lim et al. 2022); (ii) visual selection by fish may favor blue particles that resemble zooplankton prey, while black particles commonly reflect tire-wear debris and ropes/fishing gear (Ory et al. 2017); and (iii) visual sorting can overestimate vivid/dark colors and undercount transparent particles (Lusher et al. 2020).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eParticles \u0026lt;1,000 \u0026micro;m were the most prevalent in this study, consistent with syntheses in fishes indicating that the 0\u0026ndash;1 mm class is the most common among ingested items (Oza et al. 2024). Biologically, the small body size of rivulids imposes gape limitations and favors selection of proportionally small natural prey; such morphological constraints likely render smaller microplastics more susceptible to incidental ingestion during foraging (e.g., Siddique et al. 2024). The high frequency of polypropylene observed in this study is consistent with syntheses and meta-analyses reporting polyolefins (PE/PP) as the most common polymers in fishes (Lim et al., 2022). This pattern reflects their high production, low density, and persistence, which favor surface transport and stranding in physical retention zones such as mangrove roots and emergent macrophytes (Amparo et al. 2023; Oza et al 2024; ).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.2 Effects of Wetland Type and Body Length on Microplastic Contamination\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eContrary to H1, microplastic (MP) burdens were similar in short-lived fishes from temporary wetlands and long-lived fishes from mangroves, despite the expectation of higher contamination in mangroves owing to stronger hydrological connectivity and longer life spans (and thus greater cumulative exposure). This finding suggests that efficient pathways of MP input and ingestion also operate in fishes from temporary wetlands, offsetting the effects of lower connectivity and shorter life cycles.\u003c/p\u003e\n\u003cp\u003eReviews show that mangrove root structure and tidal regimes promote the retention and enrichment of microplastics (MPs) in mangroves (e.g., Qiao et al. 2024; Deakin et al. 2025), and that body size\u0026mdash;used as a proxy for lifespan and exposure time\u0026mdash;is positively associated with MP occurrence and loads in fishes (Roch et al. 2020; Yagi et al. 2022; Ding et al. 2023), which would, a priori, justify the expectation of higher loads in mangrove fishes. A key mechanism underlying MP contamination of fishes in the temporary wetlands examined here may be atmospheric and pluvial inputs. Owing to their small size and low density, MPs become airborne and can be transported over long distances by wind before being redeposited on terrestrial and aquatic surfaces (Allen et al. 2019; Elnahas et al. 2024). Precipitation also plays a crucial role by scavenging suspended MPs from the atmosphere and depositing them in concentrated fluxes, effectively acting as a \u0026ldquo;concentration funnel\u0026rdquo; (Brahney et al. 2020; Dong et al. 2024). In addition, overland runoff from roads/highways and traffic-derived dust\u0026mdash;particularly tire- and brake-wear particles\u0026mdash;constitute an important MP source (e.g., Jaiswal et al. 2025). Runoff from agricultural areas can transport mixtures of pesticides into water bodies inhabited by rivulids (Zebral et al. 2018; Godoy et al. 2025), together with microplastics (MPs), creating co-exposure scenarios. This is consistent with the study\u0026rsquo;s sampling sites: the temporary pond of \u003cem\u003eLeptopanchax opalescens\u003c/em\u003e is located in an industrial/ agricultural zone near a state highway (Guedes et al. 2020), whereas the \u003cem\u003eNotholebias minimus\u003c/em\u003e site lies within an urban area of the city of Rio de Janeiro (Guedes et al. 2023b), one of the most densely populated regions of Brazil. The hydrological \u0026ldquo;isolation\u0026rdquo; of a temporary wetland from perennial waters is therefore illusory from the standpoint of plastic pollution. Predominantly rain-fed temporary ponds can receive intense MP pulses directly from the atmosphere during rainfall events, in addition to surface runoff from nearby roads, making MPs readily available for fish ingestion.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBeyond environmental MP availability, the observed similarity in ingestion among species may stem from functional traits shared by rivulids. Small body size and reduced gape impose size-selective filtering, favoring ingestion of fine particles (\u0026lt;1 mm)\u0026mdash;the fraction that tends to predominate in MP records (Siddique et al. 2024; Lim et al. 2022). In addition, a generalist trophic habit and recurrent use of shallow microhabitats (shallow benthos, periphyton/detritus, and the air\u0026ndash;water interface)\u0026mdash;where fibers and fragments accumulate via flotation, settling, and resuspension\u0026mdash;create similar opportunities for incidental ingestion in both annual and perennial species. Despite shorter lifespans, annual species exhibit high growth and foraging rates to complete a rapid life cycle (Furness 2016; Ž\u0026aacute;k et al. 2021), which may compensate for reduced exposure time and bring MP loads closer to those of perennial species. Taken together, (i) shared morphological traits (small body/reduced gape), (ii) convergent use of microhabitats with high MP availability, and (iii) elevated foraging rates in annuals tend to homogenize the spectrum of particle sizes ingested and, consequently, the individual MP burdens observed in this study.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThis first quantification of microplastics in Rivulidae fishes reveals widespread contamination\u0026mdash;particles occurred in all four species and in 60.5% of individuals (1.58\u0026thinsp;\u0026plusmn;\u0026thinsp;1.84 items fish⁻\u0026sup1;)\u0026mdash;with profiles dominated by \u0026lt;\u0026thinsp;1,000 \u0026micro;m blue/black fragments and microfibers, chiefly polypropylene, poly(4-methyl-1-pentene) and PET. Contrary to H1, MP loads did not differ between mangroves and temporary ponds, nor with body size, indicating that atmospheric deposition, rainfall washout, and runoff can supply rain-fed wetlands with MPs at levels comparable to tidally influenced mangroves. Convergent functional traits of rivulids\u0026mdash;small body and gape, generalist foraging, and routine use of shallow microhabitats where fibers and fragments accumulate\u0026mdash;likely equalize ingestion probabilities across life histories. Collectively, these findings show that temporary wetlands are not refuges from plastic contamination, and should be explicitly included in monitoring and mitigation strategies that target diffuse, landscape-scale MP inputs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eG.H.S.G. conceived the study, conducted field sampling, curated and analyzed the data, wrote the original draft, and revised and edited the manuscript. L.C. and L.F.S.P.A. performed laboratory work, curated and analyzed data, contributed to the review of the literature and methods, and revised and edited the manuscript. F.G.A. supervised the research process, contributed to the theoretical framework, and revised and edited the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by Fundo Brasileiro para a Biodiversidade \u0026ndash; FUNBIO Conservando o Futuro, and Instituto HUMANIZE (Proc. # 028/2023), Funda\u0026ccedil;\u0026atilde;o Carlos Chagas Filho de Amparo \u0026agrave; Pesquisa do Estado do Rio de Janeiro (E-26/200.897/2021, E-26/210.103/2023), and Conselho Nacional de Desenvolvimento Cient\u0026iacute;fico e Tecnol\u0026oacute;gico (CNPq 140.512/2022-5).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;The author declares no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during the current study are available in Supplementary material\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary material\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis article includes Supplementary material 1 and 2.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbrantes YG, Medeiros LS, Bennemann ABA, Bento DM, Teixeira FK, Rezende CF et al (2020) Geographic distribution and conservation of seasonal killifishes (Cyprinodontiformes, Rivulidae) from the Mid-Northeastern Caatinga ecoregion, northeastern Brazil. 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A glyphosate-based herbicide reduces fertility, embryonic upper thermal tolerance and alters embryonic diapause of the threatened annual fish \u003cem\u003eAustrolebias nigrofasciatus\u003c/em\u003e. Chemosphere 196: 260-269. https://doi.org/10.1016/j.chemosphere.2017.12.196 \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":"wetlands-ecology-and-management","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wetl","sideBox":"Learn more about [Wetlands Ecology and Management](https://www.springer.com/journal/11273)","snPcode":"11273","submissionUrl":"https://submission.nature.com/new-submission/11273/3","title":"Wetlands Ecology and Management","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"killifish, mangroves, Microplastic pollution; Rivulidae, bioaccumulation, Brazil, micro-FTIR","lastPublishedDoi":"10.21203/rs.3.rs-7861289/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7861289/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMicroplastic pollution is ubiquitous in aquatic ecosystems, but comparative analyses across wetland types and fish life histories are still rare. This study compares microplastic contamination in killifishes (Cyprinodontiformes: Rivulidae) with contrasting life histories\u0026mdash;annual (short-lived: \u003cem\u003eNotholebias minimus\u003c/em\u003e, \u003cem\u003eLeptopanchax opalecens\u003c/em\u003e) vs. perennial (long-lived: \u003cem\u003eKryptolebias ocellatus\u003c/em\u003e; \u003cem\u003eKryptolebias hermaphroditus\u003c/em\u003e)\u0026mdash;across two wetland types (temporary ponds vs. mangroves) on the coastal plain of Rio de Janeiro (Brazil). The tested hypothesis is that small, short-lived fishes in temporary wetlands exhibit lower microplastic contamination than perennial mangrove species, due to lower hydrological connectivity and shorter exposure time. Fishes were digested (KOH solution), vacuum filtered, and analysed using microscopy and \u0026micro;-FTIR. Microplastic were detected in all species and 60.5% of individuals (1.58\u0026thinsp;\u0026plusmn;\u0026thinsp;1.84 items fish⁻\u0026sup1;). Most particles were small (\u0026lt;\u0026thinsp;1,000 \u0026micro;m), blue/black fragments or microfibers, with polymers dominated by polypropylene and poly(4-methyl-1-pentene). Contrary to H1, MP loads did not differ between mangroves and temporary ponds (GLMM: \u003cem\u003eχ\u0026sup2;\u003c/em\u003e = 0.18, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.671), nor with body size (\u003cem\u003eχ\u0026sup2;\u003c/em\u003e = 0.44, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.507). Atmospheric deposition, precipitation, and runoff can supply rain-fed wetlands with MPs at levels sufficient to produce fish microplastic burdens comparable to those observed in tidally influenced mangroves. Convergent functional traits of rivulids\u0026mdash;small gape, generalist foraging, and routine use of shallow microhabitats where fibers and fragments accumulate\u0026mdash;likely equalize ingestion probabilities across life histories. Collectively, these findings show that temporary wetlands are not refuges from plastic contamination and should be explicitly included in monitoring and mitigation strategies that target diffuse, landscape-scale MP inputs.\u003c/p\u003e","manuscriptTitle":"Microplastics in wetlands: contrasting fish contamination between mangroves and temporary ponds in southeastern Brazil","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-29 14:34:29","doi":"10.21203/rs.3.rs-7861289/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-17T07:11:50+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-15T20:55:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"6158619401417599579307719621951984491","date":"2026-03-26T12:28:14+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-19T15:21:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"25605448055336500214282342588870608784","date":"2025-10-29T09:02:21+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"332364367055087239089895984763276774192","date":"2025-10-21T13:13:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-15T12:37:29+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-15T12:20:22+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-10-15T12:12:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Wetlands Ecology and Management","date":"2025-10-14T18:20:14+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"wetlands-ecology-and-management","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wetl","sideBox":"Learn more about [Wetlands Ecology and Management](https://www.springer.com/journal/11273)","snPcode":"11273","submissionUrl":"https://submission.nature.com/new-submission/11273/3","title":"Wetlands Ecology and Management","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3e062126-be84-430d-91a4-0c6a615e8b8a","owner":[],"postedDate":"October 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-09T13:10:25+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-29 14:34:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7861289","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7861289","identity":"rs-7861289","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}