Flood-induced variation and source apportionment of microplastics in Jia Bharali River of mid-Brahmaputra Valley, India

In the present time, microplastics (MPs) are a cause of growing concern in freshwater environments throughout the globe. Flood accelerates the transport of MPs from river into the marine environment. However, there is a lack of research on the impact of flood on microplastic abundance and distribution in Indian rivers. This study aims to investigate the flood-induced variation of MPs along the stretch of the Jia Bharali River, one of the major tributaries of the river Brahmaputra. The mean concentration of MPs during post-flooding was highest (27.94 ± 9.25 MPs/L in surface water and 29 ± 8.73 MPs/kg in sediments) as compared to pre-flooding period (22.35 ± 5.55 MPs/L in surface water and 19.42 ± 6.08 MPs/kg in sediments). During pre-flood, fibres account for the majority of MP particles (36.13% in surface water and 38.23% in sediments). Similar results were observed for post-flooding surface water samples as fibres were the most dominant type (35.65%), while in the case of sediments, fragments (34.10%) were the major type. Polyethylene was the dominant polymer type of MPs followed by polypropylene. Polymer hazard index (PHI) indicated high risk, while the coefficient of microplastic impact (CMPI) showed an ‘average’ to ‘minimum’ risk level in the studied area. The study identified flooding, runoff from agricultural fields and various anthropogenic activities as the potential source of MPs in the river. The present study unveiled new insights into microplastic contamination of an Indian river, its source analysis, flood-induced distribution and risk assessment which will aid in mitigating and remediating freshwater microplastic pollution in the future.