Characteristics and risks of microplastic contamination in aquaculture ponds near the Yangtze Estuary, China

Microplastic pollution has been frequently reported in natural water environments, but studies on the occurrence and characteristics of microplastic in aquaculture environments especially in pond production system are relatively scarce. Herein, we investigated the abundance and characteristics of microplastic pollution in aquaculture ponds that farm different species (fish, prawn and crab) near the Yangtze Estuary, China. The average abundance of microplastic in pond water and sediment was 36.25 ± 6.79 items/L and 271.65 ± 164.83 items/kg, respectively. Compared to fish ponds (208.43 ± 57.82 items/kg), microplastic abundance was significantly higher in sediment of crab and prawn ponds (312.02 ± 38.76 and 248.87 ± 36.51 items/kg respectively). Across all ponds, transparent, white and black microplastic were the common colors. Fiber was the most common type, accounting for 40.9% and 58.6% in pond water and sediment, respectively. The size of microplastic was mainly distributed between 300 and 1000 μm. For microplastic polymer composition, polyethylene (PE) was predominant in pond water, accounting for 55%, followed by polyamide with 15%. The predominant polymer in sediment was PE with 34%, followed by polypropylene with 18%. As for the ecological risk assessment of microplastic, the pollution load index was 7.6 (risk level I) and 8.9 (risk level I) for pond water and sediment, respectively. The polymer hazard index was 85.3 (risk level II) and 12.1 (risk level II) for pond water and sediment, respectively. Taken together, the pollution risk index was rated as high and very high for pond sediment and water, respectively. These results provide a basis for the comprehensive evaluation and developing practical approaches to deal with microplastic in aquaculture pond, which is of great significance to the healthy development of pond aquaculture.