Microplastics in aquaculture environments: Sources, pollution status, toxicity and potential as substrates for nitrogen-cycling microbiota

Microplastics (MPs) have emerged as a pressing global pollution issue and have drawn significant attention in the field of environmental science in recent years. Plastics are widely used in aquaculture, leading to the accumulation of MPs in aquaculture environments, referred to as aquaculture-derived MPs (AD-MPs). This review summarizes the pollution status of MPs in aquaculture environments, their adverse impacts on aquaculture, and the potential benefits of MPs serving as substrates for nitrogen-cycling microbiota to improve water quality in aquaculture. Our study underscores the severity of microplastic pollution in aquaculture, with the microplastic content reaching 362.8 items L⁻¹ in water and up to 124,884 items kg⁻¹ in sediment. However, these levels vary significantly depending on the type of aquaculture system and the specific location of aquaculture activities, with MPs being most abundant in estuary aquaculture systems. The primary sources of MPs in aquaculture environments include plastic nets, packaging and other plastic tools used in aquaculture. Consequently, most of the MPs present are white fibers composed of polypropylene and polyethylene. These MPs accumulate in aquatic products such as fish, shrimp, crabs, and shellfish, with abundances reaching 61.75 items per individual. This accumulation leads to toxic and combined effects on cultured animals and poses a risk to human health through the food chain. However, the surfaces of MPs (the plastisphere) also facilitate a series of chemical reactions, including biological nitrogen fixation, nitrification and denitrification, by serving as a substrate that attracts nitrogen-cycling microorganisms. These findings highlight the potential positive effects of MPs in aquaculture. To mitigate the ecological risks arising from MPs in aquaculture and address their potential threats to human health, it is essential to conduct long-term, sustainable assessments of MPs in aquaculture water sources. Special attention needs to be given to the effects of nitrogen-cycling biofilms on the surface of MPs and their potential benefits to aquaculture water quality.