Microplastics in freshwater environment: the first evaluation in sediment of the Vaal River, South Africa

Abstract

Microplastic pollution has become an environmental concern worldwide. In this study, the occurrence, abundance, and composition of microplastics (MPs) in sediment of the Vaal River, South Africa were assessed. Twenty-five sediment samples were collected from the Vaal River using a Van Veen grab sampler, samples underwent digestion, density separation, and filtration prior to physical and chemical analysis. Following the extraction, potential MPs were visually identified under a Nikon stereomicroscope, aided by chemical characterization using Raman spectroscopy. The results revealed 100% prevalence in sediment samples, with an average abundance of 463.28 ± 284.08 particles/kg_dw. Small-sized MPs of 2 mm and less were the most abundant, representing more than 82% of the total particles. Fragments and coloured MPs were the most dominant compared to other shapes and transparent particles, accounting for 63% and 60%, respectively. Microplastics were identified as polyethylene (PE) (both high and low density), polypropylene (PP), and polyethylene co-vinyl acetate (PEVA), polyester (PES), polyurethane foam (PU), and polyethylene/hexene-1-copolymer (PEH). These findings reveal elevated levels of MP contamination within the Vaal from secondary sources. Potential sources include wastewater effluent, anthropogenic activities, surface run-off from urban centres, inflow from tributaries, and recreational activities.