Occurrence of microplastic in the water of different types of aquaculture ponds in an important lakeside freshwater aquaculture area of China

Aquaculture ponds are exposed to numerous potential microplastic sources, but studies on their microplastic pollution are still limited. Various culture species may influence the occurrence of microplastic in ponds. In the present study, the occurrence of microplastics was studied in aquaculture ponds for fish, crayfish, and crab, as well as in the natural lake near the aquaculture area around the Honghu Lake, which is the principal freshwater aquaculture area of China. The microplastic abundances ranged from 87 items/m to 750 items/m in the aquaculture ponds, and 117 items/m to 533 items/m in the lake. The crab ponds contained higher abundances of microplastics than fish ponds and the nearby natural lakes. Microplastics that were between 100 and 500 μm and larger than 1000 μm in size were predominant in the ponds and nearby lakes, whereas the proportion of microplastics that were smaller than 100 μm was higher in crab ponds than those in other ponds. Fragments and fibers were the predominant shapes of microplastics in the ponds. The proportion of smaller microplastics in the ponds had a positive correlation with the proportion of fragment microplastics. The results of this study implied that differences in the use of plastics in various types of aquaculture ponds might affect their microplastic pollution characteristics. Microplastics discharged from ponds to nearby lakes through drainage processes require attention in further studies.