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 & PLUSMN; 3.03 items/m3) post deluge. The average abundance was highest during pre-monsoon (8.27 & PLUSMN; 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.