Influence of anthropogenic pressures on the microplastic distribution in the riverine-estuarine environment: A source-apportioning approach

In this study, the influence of anthropogenic pressures, namely fishing practices and illicit and unregulated wastewater and solid waste discharge, on the microplastic distribution in India's Kallada River – Ashtamudi riverine-estuarine environment was investigated. To better characterize microplastic pollution in the Estuary, it was subdivided into cage farming, open fishing, solid waste dumping, and other zones that receive wastewater from residential areas. A source-apportioning approach was utilized to delineate the possible sources of pollution and conducted a risk assessment attributed to exposure to microplastic pollution. The results suggest that the solid waste dumping zone exhibited the highest microplastic abundance, followed by the cage farming zone. Fiber-shaped microplastic particles were abundant in cage farming and open fishing zones, while films dominated the solid waste dumping zone. FTIR analysis revealed that polyamide and polyester, widely used for regional fishing nets, were dominant in cage farming and open fishing zones, while polyamide, polystyrene, and polyethylene were dominant in solid waste dumping zones. Other zones impacted by the unregulated discharge of domestic wastewater exhibited an abundance of polyester and polyethylene microplastics. Source apportionment studies using a modified approach incorporating morphological and chemical characteristics of microplastics revealed that fishing nets/ropes contributed to 35.48 % of microplastic pollution, followed by single-use plastics and plastic bags/covers (19.35 % each), textile fabrics (16.13 %) and personal care products (9.68 %). A risk assessment analysis considering microplastic abundance and polymer hazard revealed that the solid waste dumping zone and the cage farming zone pose a medium risk to microplastic pollution. These findings highlight the role of fishing practices and solid waste dumping on the microplastic pollution in the riverine-estuarine environment.