Characterization and risk assessment of microplastics accumulated in sediments and benthic molluscs in the mangrove wetlands along the south-west coast of India

In the present study, occurrence and characteristics of microplastics in mangrove sediments and benthic molluscs viz., black clam (Villorita cyprinoides), yellow clam (Meretrix casta), mangrove horn snail (Telescopium telescopium) and brackish water snail (Neripteron violaceum) were studied from mangrove habitats of Vembanad Lake, the largest estuary and a Ramsar site on the south-west coast of India. The average microplastic abundance in mangrove sediments varied between 235 ± 49.5 and 1414 ± 182 items/kg dry weight, with an average concentration of 673.45 ± 365.05 items/kg dry weight, which was at a relatively higher level compared to other mangrove regions of India. The highest abundance was recorded for gastropod T. telescopium (38.5 ± 11.48 items/individual). The predominant shape, colour and size of microplastic in mangrove sediment and molluscs were fragments, black and < 500 μm, respectively. The major polymers identified were polyethylene and polypropylene in sediments and molluscs. Higher values of ecological risk indices (Microplastic index and Microplastics diversity integrated index) indicated a severe microplastic pollution risk for the molluscs in the mangroves. The high bio-accumulation factor also highlights the possibility of using these species as bioindicators of plastic pollution in mangrove habitats. The results of the present study could be useful to prepare effective management strategy to minimize plastic pollution load in mangrove habitats.