Characteristics of microplastics ingested by zooplankton from the Bohai Sea, China

Microplastic (MP) ingestion has been recorded in 39 zooplankton species from 28 taxonomic orders, and marine zooplankton are the organisms most susceptible to MPs. However, few field studies have examined the characteristics and major influencing factors of MPs in marine zooplankton. The present study investigated the shape, color, size, chemical composition and quantity of MPs in zooplankton in the rainy and dry seasons in the Bohai Sea. Furthermore, the relationship between the MPs in zooplankton and the MPs in seawater was studied. The results showed that the MPs in zooplankton of the Bohai Sea were dominated by blue fibers. In the rainy and dry seasons, fibers accounted for 92% and 93%, respectively, of all ingested MPs, while 50% and 55%, respectively, of ingested MPs were blue. The average size of MPs in zooplankton was 1300 ± 1520 μm in the rainy season and 1040 ± 1060 μm in the dry season. Regarding the MP chemical composition, in the rainy and dry seasons, the ingested MPs were dominated by cellophane, which accounted for 53% and 68%, respectively, of MPs, followed by polyester (PET), which accounted for 18% and 20%, respectively, of MPs. The composition of MPs in zooplankton was mainly affected by the composition of MPs in seawater. No significant difference in the MP composition was observed between the two seasons or among the different zooplankton groups. The MP number was significantly higher in individual medusa than in individuals of other zooplankton groups. The mean quantity of MPs in the Bohai Sea zooplankton community in the rainy season was 2.03 ± 2.87 piece/m³, which was significantly higher than that in the dry season, 0.41 ± 0.38 piece/m³. The above results will provide a reference for marine ecological risk assessments based on the characteristics of MPs in natural seas.