The first report on the source-to-sink characterization of microplastic pollution from a riverine environment in tropical India

Microplastics are plastic pieces <5 mm in size that are more harmful than large plastic debris. The world's oceans contain large amounts of these particles, and their presence is severely affecting the marine organisms. Smaller aquatic organisms ingesting microplastics, mistaking them for food, and their subsequent entry into the food chain is of significant concern. Rivers are major carriers of these materials from the terrestrial environment to the oceans. In this study, for the first time, we have done the source-to-sink characterization of microplastics (5 mm-0.3 mm) for a tropical Indian river, namely the Netravathi River, which debouches into the Arabian Sea. Here, we present a detailed investigation made on water, sediments and soil samples collected from the river catchment. All the samples showed the presence of microplastics with a mean numerical abundance of 288 pieces/m³ (water), 96 pieces/kg (sediment) and 84.45 pieces/kg (soil). Fibres, films and fragments are the main categories obtained from the catchment. The microplastics present in the samples were mostly transparent and white coloured which are due to the decay of plastic carry bags, packing materials and fishing lines. Different coloured microplastics were also present in lesser numbers. Polyethylene (PE) and polyethylene terephthalate (PET) are the most abundant polymers present in the samples. Fragmentation of larger plastic materials which is due to mismanaged solid waste and garment washing are the primary sources of these materials in the river catchment. Moreover, the sampling sites near to important pilgrim centres like Dharmasthala and Subrahmanya, register higher concentration of fibres released due to washing of clothes. The study concludes that the Netravathi River is contaminated with microplastics from its origin to the sink. However, the spatial distribution and abundance of microplastic particles demonstrate the influence of population distribution, land use and good household practices of waste management in some areas.