Microplastics in sediment of the Three Gorges Reservoir: abundance and characteristics under different environmental conditions

Freshwater microplastic pollution is an urgent issue of global concern, and research on the distribution in reservoirs is lacking. We investigated the microplastic pollution levels in wet sediments collected from the Three Gorges Reservoir, the largest reservoir of China. Results show that microplastics were ubiquitous in the sediments of the Three Gorges Reservoir, and their abundance ranged from 59 to 276 pp/kg (plastic particles per kg, dry weight). Economic development and total population were important factors affecting the spatial heterogeneity of microplastic abundance, and the contribution of large cities along the reservoir to microplastic pollution should be paid with more attention. Fibrous microplastics were the most abundant type of microplastic particles in reservoir sediments, whereas polystyrene, polypropylene, and polyamide were the main types of polymers. The apparent spatial heterogeneity in morphology and color of microplastics is attributed to different anthropogenic or land-based pollution sources. Moreover, the accumulation of microplastics near the inlet of tributaries reflects the role of potential contributors of tributaries. More importantly, multiple bisphenols (BPs) and heavy metals detected at the microplastic surfaces indicate that microplastics can act as carriers of these pollutants in the environment in the same way as sediments did, which may alter the environmental fate and toxicity of these pollutants. Therefore, we conclude that the Three Gorges Reservoir had been contaminated with microplastics, which posed a stress risk for organisms who ingest them along with their associated pollutants (BPs, heavy metals).