Spatial distribution of microplastics in the riverine waters of southwest India

, Amrutha K., Kumar Warrier Anish.

Plastic pieces ¡ 5 mm in size are termed as microplastics and is an emerging pollutant. Microplastics were reported from all types of environments. The ingestion of microplastics by the smaller aquatic organisms mistaking them as food, and their subsequent transfer to higher trophic level organisms through food chain and their ability to adsorb heavy metals and pollutants, make them a global urgent socio-economic problem. River act as an important carrier of microplastics from the continents to the oceans. In this study, we have investigated the levels of microplastic pollution (5mm – 0.3mm) for an Indian river, namely the Netravathi River. Surface water samples were collected from 14 locations right from its highland to its estuary during the monsoon season (June 2019). The extracted microplastics were visually identified, quantified and categorized using a stereo-zoom microscope, which is further validated by FTIR-ATR analysis. The study reveals the presence of microplastics in all the samples with a mean numerical abundance of 282 particles/m3. The high abundance of microplastics were obtained from the estuary region (NW14; 2328 particles/m3) and low abundance from the highland (NW1; 56 particles/m3). The downstream of the Netravathi River flows through relatively higher populated urban areas, and hence, a relatively higher abundance of microplastics is observed in the downstream sites. Fibres (51.59%) were the most abundant category of microplastics present in the samples followed by films (34.92%), fragments (8.13%), foams (5.16%) and pellets (0.20%). Polyethylene dominated the polymer composition in the samples followed polyethylene terephthalate, polypropylene and polyvinylchloride. Mismanaged solid waste and lack of effective wastewater treatment facilities are the main reasons for the presence of microplastic materials in the river. Source-to-sink characterization of microplastics from the river concludes that population density and anthropogenic activities play a major role in the distribution and abundance of microplastics.

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