Occurrence, sources and potential human health risk of microplastics in seafood species

Microplastics (MPs) pollution has become a global environmental concern, and the ocean is a known sink for MPs. The marine environment provides the necessary living space and suitable environmental conditions for the growth and reproduction of seafood species. Meanwhile, MPs in the marine environment would be inevitably ingested by seafood species. Seafood species are of major importance to human beings, which are considered an important source of high-quality proteins and provide a wide range of healthful micronutrients. However, the growth, development and nutritional quality of seafood species are necessarily affected by MPs pollution, thus resulting in potential threats to seafood species and human health. Therefore, MPs pollution in seafood species has become an important and non-negligible issue in MPs pollution. This review summarizes the occurrence and distribution of MPs in global seafood species (e.g., crustaceans, bivalves, and fishes). The results indicate that MPs have been widely detected in seafood species all over the world, and the abundance range of MPs in the seafood species is 0–140 particles/individual, with the highest MPs concentration detected in American oysters (Crassostrea virginica, 140 items/individual). The ingestion behavior (e.g., swallowing-, filtering- and sucking-feeding) of the MPs for seafood species and the MPs contamination levels within the habitat of the seafood species are the main factors that affect the level of MPs pollution in their bodies. Besides, the particle size of MPs in seafood species ranges from 0.006–5 mm, which is mainly restricted by the detection limit of the instrument. The results also show that fiber-shaped MPs are the most frequently detected shape in seafood species, as fibers are more likely to be trapped or entangled in the gill of seafood species compared to other shapes (such as fragment, particle and film). In order to effectively regulate the contamination of MPs in seafood species at source, the sources of MPs in seafood species are elucidated in depth, including terrigenous input, shipping emission, atmospheric deposition, and fishery activities. Notably, there is a special emphasis on the significant contribution of fishery activities to MPs pollution in the marine environment and seafood species. The results show that plastic fishing gears used in fishery activities, such as nets, ropes and buoys, release a large amount of MPs under photodegradation, wind and wave abrasion, and biological erosion, which are widely identified in seafood species. What is more, the results indicate that high levels of MPs are released due to intensive farming activities, which results in higher levels of MPs in farmed seafood species than in wild seafood species. Subsequently, due to a large amount of MPs accumulated in seafood species, the toxic effects of MPs on the growth and development, oxidative stress, immune response, and reproduction of seafood species are discussed, as well as the negative impact on the nutritional quality of seafood species. Humans, as the highest trophic level of the food chain, consume seafoods contaminated with MPs, which will be transferred to the human body through the trophic transfer. Therefore, the potential risks of MPs contamination (including its plastic additives and co-existing contaminants) of seafood species to human health are further summarized. Finally, this review also provides suggestions and prospects for future research directions on the prevention strategy and ecological risks of MPs in seafood species. This research contributes to better assessing the food safety of seafood species and their potential risks to human health.