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Spatial heterogeneity of microplastic pollution and associated emerging contaminants in tropical estuarine environments: Novel insights into distribution, bioavailability, and ecological risk
Summary
Scientists found tiny plastic particles in water, mud, and seafood like shellfish and crabs in two river areas in India. These microplastics carry harmful chemicals and are getting into the food chain, which could affect the safety of seafood that people eat. While the current risk appears low, this research shows we need better policies to reduce plastic pollution to protect both ocean ecosystems and human food sources.
Microplastic (MP) contamination represents an emerging threat to marine ecosystems and food security in tropical coastal regions. This study provides a comprehensive assessment of microplastic distribution, characteristics, bioaccumulation patterns, background heavy metal concentration, presence of emerging contaminants and risk assessment across two river estuaries in northern Kerala, India. Water microplastic concentrations ranged from 7.1 to 23.6 particles/L while sedimentary microplastic levels exhibited more substantial contamination, 25 to 176.67 particles/kg. Biological accumulation of microplastics from surrounding environment was observed in filter-feeding bivalves (1.33 to 3 particles/g) and benthic crustaceans (2 particles/g). Raman spectroscopic analysis identified diverse polymer compositions dominated by thermoplastic polymers such as polyethylene (PE), polyamide (PA), polyethylene terephthalate (PET) and polystyrene (PS), sourced from fisheries, packaging activities and single use plastic waste. Spatial analysis revealed transportation corridors, waste dumping sites, and domestic discharge and outlets along with marine tidal input as primary contamination drivers. Presence of heavy metal such as cadmium, chromium, copper, iron, nickel, lead and zinc in sediments and biota shows minimum levels of contamination, below permissible limits. Non-target analysis identified 55 emerging organic compounds, including plastic additives, degradation byproducts/hydrocarbons, surfactants pharmaceuticals, and personal care products, establishing plastics as significant contributors of chemical contaminants. Integrated risk assessment utilizing Pollution Load Index (PLI: 2.44-3.25) showed polluted status of estuaries. Very high Polymer Hazard Index (PHI) values indicated the presence of high hazard polymers in the microplastic assembly. However, the Potential Ecological Risk Index (PERI) (138-148), which accounts for both polymer toxicity and microplastic abundance demonstrated relatively low ecological risk (>150) due to microplastics in both the estuaries. Bioaccumulation factor (BAF) scoring below 100 (14.5-46) indicated low bioaccumulation potential of microplastics from estuarine sediments into the body of living organisms. The occurrence of microplastics in edible estuarine species suggests potential implications for seafood safety and highlights the need for further exposure assessment studies. This comprehensive baseline underscores the urgent need for integrated environmental management and policy interventions to safeguard estuarine ecosystems, food safety and socioeconomic wellbeing of communities dependent on fisheries resources.