Distribution of microplastics in seafloor sediments and their differential assimilation in nearshore benthic molluscs along the south-west coast of India.

Spatial and temporal distribution of microplastics (MPs) in the nearshore seafloor sediments along the Southwest coast of India and their patterns of accumulation in selected infaunal and epibenthic molluscs with diverse feeding strategies were investigated. Along the 300-km coastal stretch, which is one of the most productive and biodiversity rich regions of the eastern Arabian Sea, notable levels of MP contamination in both sediment (617.7 items/kg dry weight) and molluscs (5.39 items/g) was recorded. The concentration of MPs in sediments also varied seasonally, with a higher prevalence during the post-monsoon season. Among the four molluscan groups studied, the highest MP abundance was recorded among scavenging gastropod Pseudominolia biangulosa (9.13 items/g), followed by microcarnivore scaphopod Tesseracme quadrapicalis (5.96 items/g). In comparison, the suspension feeding bivalve, Anadara hankeyana and deposit feeding clam Jitlada philippinarum had lesser accumulation of MPs (2.98 items/g and 3.50 items/g respectively). The majority of MPs in sediments and within molluscs were less than 250 µm in size (89.14%) and were predominantly fibres and fragments. Chemical characterisation of MPs revealed eleven types of polymers dominated by polyethylene (PE) and polypropylene (PP). Present study identified positive correlations between ingested MP polymers and the feeding strategies of molluscs. Higher values for the ecological risk assessment indices (PHI, PLI and PERI) in most of the stations indicated the severity of plastic pollution in the region. Molluscs being a major contributor to the benthic food web is also a connecting link to higher trophic levels. Hence understanding the specificity in the MPs accumulation pattern within this group has far reaching significance in utilizing them as potential bioindicators for pollution studies in marine ecosystems.

Spatio-temporal evaluation and risk assessment of microplastics in nearshore surface waters post-2018 Kerala deluge along the southwest coast of India.

Spatial and temporal distribution of microplastics along the nearshore surface waters of Kerala after the floods of 2018 was studied. Results indicated a seven-fold increase in its mean concentration (7.14 ± 3.03 items/m3) post deluge. The average abundance was highest during pre-monsoon (8.27 ± 3.09 items/m3). Fibres were the dominant group, with blue and black being the most prevalent colours. Polyethylene and polypropylene were the most commonly found polymers, possibly gaining entry through sewage waste or land-based plastic litter. Highest abundance of microplastic was recorded off Kochi categorising it at Hazard Level I under Pollution Load Index assessment. Similarly high levels of Pollution Hazard Index and Potential Ecological Risk Index were also reported due to the presence of hazardous polymers PVC and PU that can cause concern to marine life. The differential weathering pattern and surface morphology analysis suggested microplastics to be relatively old that had undergone substantial mechanical and oxidative weathering.