Seasonal shifts in microplastics: Uncovering Goa's marine pollution patterns

Abstract

This study systematically examines the spatiotemporal distribution of microplastic particles across Goa's 160 km coastal ecosystem during the pre-monsoon, monsoon, and post-monsoon seasons. It delivers the first dataset on pollution levels and indices in Goa's coastal and estuarine areas across these three seasons, addressing a critical knowledge gap in understanding seasonal variations in the region. Estuaries and coastal areas were subjected to both quantitative and qualitative assessments of microplastic particles, focusing on the foraging of microplastics by Mugil cephalus and Rastrelliger kangurta. Microplastic concentrations varied between 25 plus-minus 4.76 and 273.5 plus-minus 11.26 per liter or kilogram of the water and sediment samples. During the monsoon season, the microplastics were found higher in estuarine and coastal water compared to sediment, likely due to increased turbulence. In contrast, post-monsoon sediment in coastal areas had a higher count than water, suggesting settling after turbulent periods. Analysis showed that fibers were the most prevalent, followed by fragments, pellets, and microbeads, with the Coefficient of Microplastic Impact values reaching 0.7 in estuaries like Chapora and Sal water during the post-monsoon season. During this season, the Pollution Hazard Index indicated high risk (Category 4) at coastal areas such as Baga, Colva, and estuaries like Mandovi, and Sal. The Pollution Load Index ranged from 1.00 in Sal water post-monsoon to 3.30 in Mandovi sediment. Dark-colored particles, mainly black, blue, and green nylon fiber, constituted the majority of microplastic particles in the gut contents of Rastrelliger kangurta and Mugil cephalus. Fourier transform infrared and Raman spectroscopy identified essential polymers, including polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and nylon. Initiated during the COVID-19 lockdown, this study holds a unique significance in assessing microplastic prevalence in the marine ecosystem of Goa.