Occurrence and distribution of microplastics in freshwater aquaculture area with different culture modes in Yangtze River Delta of China

There are multiple sources of microplastic contamination in freshwater aquaculture areas, such as water inputs, use of plastic farming tools and weathering of discarded plastics, leading to microplastic contamination of aquaculture environments, but microplastics in freshwater aquaculture areas are still limited. In our study, we investigated the distribution of microplastics (MPs) in the aquaculture water, sediments and crabs during the growth cycle of crabs with different culture modes. The results show that from May to October, MPs in surface water first increased and then decreased, which is related to water evaporation and river water recharge caused by local hot and sunny weather. The concentration of microplastics in surface water reached a maximum of 9.25 items/L in September and 0.34 items/g-dry weight in sediment in June. The MPs in the sediments, although relatively stable, fluctuated due to river water replenishment. The number of detected MPs in male crabs was higher than that in female crabs, 17.96 ± 6.23 and 16.71 ± 4.45 items/individual, respectively. Crabs of different sexes were not selective for the color of MPs. The abundance of microplastics in different tissues of river crabs was in the order of foregut > hindgut > gill > hepatopancreas, whereas they were not detected in muscles. There were microplastic uptake and excretion behaviors during the growth culture cycle of river crabs. The microplastic amount was higher in the early stage and then showed a dynamic change of decreasing and then increasing. The number of MPs was higher in culture modes with different sex ratios, especially in male-dominated culture modes, which may be related to the more frequent activities of male crabs when the male ratio is high. This study provides useful information to understand the accumulation of microplastics in cultured hairy crabs and the source sinks and transportation of microplastics in artificial freshwater aquaculture in China.