Microplastics in sediment of the tropical (Mandovi) estuary, India: Physical pollutant and vectors of metals

Abstract

Microplastics have emerged as pervasive pollutants in marine environments, originating from the degradation of larger plastic debris and direct inputs from anthropogenic sources. Their small size, persistent nature and low density enable wide dispersion via coastal currents, leading to accumulation in estuarine sediments through hydrodynamic processes. The present study investigated abundance, spatial distribution, and pollution levels of microplastics in surface sediment of the Mandovi Estuary, Goa, with particular emphasis on their role in metal adsorption. Fiber-type was the predominant shape ranging from 53.02 percent - 94.61 percent of microplastics in sediment contributed mainly from fishing activities and cloth cleaning waste. Among polymer types, polyethylene (PE) was consistently dominant and present across all sampling stations (M1-M8), whereas polypropylene (PP) was restricted to station M5, indicating localized input sources. The prevalence and severity of fiber pollution were validated through the Coefficient of Microplastic Impact (CMPI), revealing maximum to extreme levels of pollution. The Pollution Load Index (PLI) further confirmed significant microplastic pollution in intertidal sediment across lower to middle regions of the Mandovi Estuary. The metals such as Zn and Fe displayed strong affinity for microplastic surfaces, as inferred from their elevated concentrations on isolated microplastic particles. It underscored the complex interactions between microplastic pollution and metal dynamics in the estuarine environment. The study highlighted the dual ecological threat posed by microplastics as both physical pollutants and vectors of metals.