Microplastic-Mediated Heavy Metal Contamination in Freshwater Ecosystems: An Emerging Contaminant Perspective
Abstract
Microplastics (MPs) coexist with heavy metals in aquatic ecosystems, influencing contaminant mobility and
ecological risks. We analyzed sediments, water, and MPs from five freshwater lakes in Coimbatore, India, for Cu, Fe, Cd, As,
Pb, Sn, Ni, Mn, and Sr using ICP–MS. All metals were detected across matrices, with sediments showing the highest
concentrations. Cd levels in MPs (0.08–0.26 mg/kg) closely reflected those in sediments and water, indicating environmental
adsorption. In contrast, As (0.11–0.34 mg/kg) and Sn (0.09–0.28 mg/kg) were enriched in MPs, consistent with their use as
plastic additives. These results suggest dual sources of metal contamination—environmental deposition and polymer
additives—shaping the metal burden of MPs. By serving as carriers of trace metals, MPs represent potential vectors for
contaminant transfer into aquatic food webs. This study provides baseline evidence of MP–metal interactions in Indian
freshwater lakes, with implications for ecological risk assessment and water resource management.
Keywords
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Introduction
Microplastics (MPs), defined as plastic particles <5 mm, are emerging contaminants of global concern in aquatic ecosystems. They originate either from the breakdown of larger plastics or direct industrial and domestic inputs. Owing to their persistence, small size, and high surface-to-volume ratio, MPs can adsorb coexisting pollutants and alter their environmental fate (Neelavannan et al., 2023). Among such pollutants, heavy metals represent a priority group, as they persist in sediments, bioaccumulate in organisms, and exert toxic effects even at trace levels (Mvovo et al., 2025).
Interactions between MPs and metals occur through surface complexation, electrostatic attraction, or physical entrapment, leading to altered contaminant mobility, trophic transfer, and potential combined toxicity (Tenea et al., 2024; Gong et al., 2025; Rezaei Kahkha et al., 2025). Evidence from marine environments shows that MPs act as carriers of metals such as Cu, Pb, and Cd, increasing their bioavailability (Ashton et al., 2010; Turner, 2016). However, freshwater ecosystems—particularly in rapidly urbanizing regions—remain understudied, despite being critical sources of drinking water, irrigation, and fisheries (Patidar et al., 2023).
The adsorption of metals onto MPs is governed by multiple factors including polymer type, particle size, surface weathering, and environmental conditions such as pH, salinity, and dissolved organic matter (Holmes et al., 2014; Brennecke et al., 2016). Weathered MPs with oxidized surfaces and enhanced roughness exhibit higher sorption capacities than pristine particles, and the presence of biofilms can further alter metal partitioning through biosorption mechanisms (Tang et al., 2020). This complex interplay of factors influences the potential of MPs to act as vectors for metal contamination in aquatic ecosystems.
Conclusion
This study presents one of the first comprehensive assessments of microplastics (MPs) and associated heavy metals in freshwater lakes of Coimbatore, India. Our results demonstrate the coexistence of MPs and trace metals in water and sediment, highlighting their dual role as environmental contaminants. Cadmium (Cd) in MPs closely mirrored concentrations in surrounding water and sediment, indicating adsorption under local geochemical conditions. In contrast, elevated levels of arsenic (As) and tin (Sn) in MPs suggest contributions from plastic additives, emphasizing the need to consider both production-related and environmentally derived metal sources.
Metal accumulation on MPs was influenced by polymer type, surface aging, and environmental factors such as pH, collectively affecting contaminant partitioning among sediments, water, and biota. Statistical analysis confirmed these patterns, with significant positive correlations (p < 0.05) observed between metal concentrations in microplastics and those in sediments and water. This indicates that the metal burden of MPs is closely linked to ambient contamination levels and supports their role as environmental indicators of trace metal pollution. The morphological characterization of MP—dominated by weathered fragments—further supports the role of MPs as active sorbents in these freshwater systems.
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