Microplastics in specific tissues of wild sea urchins along the coastal areas of northern China

Sea urchins serve as an essential niche for benthic ecosystems and are valuable seafood for humans. However, little is known about the microplastics (MPs) accumulation in sea urchins. Here, we investigated the abundances and characteristics of MPs in specific tissues of wild sea urchins for 12 sites across 2, 900 km of coastlines in northern China. Sea urchins from all sites were detected to have MPs, with a total detection rate of 89.52%. The MPs abundance in sea urchins from all sites ranged from 2.20 ± 1.50 to 10.04 ± 8.46 items/individual or 0.16 ± 0.09 to 2.25 ± 1.68 items/g wet weight. The samples from Dalian were found to have the highest value by individual, and samples from Lianyungang had the highest value by gram. Furthermore, MPs were found in different tissues of sea urchins, i.e., gut, coelomic fluid and gonads. The highest abundance of MPs was found in the gut of sea urchins, followed by coelomic fluid and gonads. The size of MPs ranged from 27 to 4742 μm, and the mean size found in gut was bigger than coelomic fluid and gonads. More interestingly, the MPs abundance increased with the decrease of anus size, shell diameter and gonad index (the wet weight ratio of gonad to total soft tissues). The MPs were dominated by fiber in shape, blue-green in colour and cellophane in composition. The high MPs abundance in sea urchins indicates the potential risks to human as they are consumed in many parts of the world, particularly in Asia and Europe.