Microplastics in surface waters and sediments of the Three Gorges Reservoir, China

Highlights: • Microplastics were studied in the largest reservoir from China. • Residential and sewage treatment plants affected microplastic concentrations. • There was no significant correlation between microplastic concentrations in each sampling site. • The high-densitiy microplastics were more likely to deposit in the sediment. We investigated microplastic pollution levels in surface waters and sediments from the Three Gorges Reservoir (TGR). The TGR is the largest reservoir in China and is located across the Chongqing municipality and Hubei Province. Microplastic abundance in the surface water ranged from 1597 to 12,611 n/m³ and in the sediments was 25 to 300 n/kg wet weight (ww). In the surface waters, the contamination was more serious in urban areas, and in the sediments, countrysides were the most heavily polluted areas. Fibers were the most abundant microplastics, the dominant color was transparent, and small-sized particles were predominant. Of all the microplastics identified by micro-Raman spectroscopy, polystyrene was the most common type (38.5%) followed by polypropylene (29.4%) and polyethylene (21%). Compared with low-density microplastics, the high-density ones were more likely to be deposited from the water into the sediment. Several contaminants adsorbed by microplastics, such as organic solvents and pharmaceutical intermediates, were observed and qualitatively analyzed by Raman spectroscopy. The results of this study could provide valuable background information for microplastic pollution in the TGR.