Assessing microplastic contamination and associated risks in the surface waters of the Mandovi river: Upstream-to-Sink Study from freshwater to estuarine mouth in Goa, India

Abstract

Microplastic (MP) contamination in riverine environments has garnered global attention due to its associated ecological risks. This study assesses MP contamination levels and related risks in the Mandovi River, Goa, India. The average MP abundance was 2.37 plus-minus 3.11 particles/L. MPs in the 0.1-0.3 mm size range were dominant (51.96 percent), followed by 31.64 percent in the 0.3-0.85 mm range and 16.40 percent in the 0.85-5 mm range. Fibres were dominant (91.55 percent) and colourless MPs were the most prevalent (77.87 percent). MP concentrations were highest in downstream regions, likely due to intensified anthropogenic activities. The most abundant polymers identified were polyamide (28.85 percent) and polyethylene terephthalate (27.57 percent). Risk assessments revealed considerable contamination. The Pollution Load Index (PLI) was 1.71, while Polymer Hazard Index (PHI) reflected a hazard level V. The Potential Ecological Risk Index (PERI) pointed to a high risk to aquatic ecosystems. Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopy (SEM-EDS) analysis confirmed surface degradation of MPs and the presence of heavy metal contaminants. Key pollution sources included tourism, fishing, surface runoff, sewage discharge, agriculture, and plastic waste accumulation along riverbanks. This study offers critical insights into MP pollution along the river continuum. It highlights the urgent need for effective policy interventions to mitigate contamination in riverine ecosystems.