Occurrence Characteristics and Ecological Risk Assessment of Microplastics in Zooplankton Communities in Jiaozhou Bay, China

To investigate the occurrence characteristics and ecological risks of microplastics in zooplankton communities of Jiaozhou Bay, a seasonal survey on the abundance and characteristics of microplastics in zooplankton communities was conducted in February, May, August, and November. The results showed that the median number of microplastics per individual zooplankton was 0.25 MP/ind., and the median abundance of microplastics within zooplankton was 2.70 MPs/m³, ranging from 0 to 62.38 MPs/m³. The abundances in May and August were significantly higher than those in February and November (P<0.05). The total retention of microplastic within zooplankton in Jiaozhou Bay was estimated to be 3.19 × 10¹⁰ MPs, with the highest level in August. Fibers were the dominant shape of microplastics found in zooplankton (89%). Most microplastics were smaller than 500 μm, with an average length of 491 ± 454 μm, and those found in August were the longest (P<0.05). The main chemical compositions were polyester fibers and cellophane, accounting for 37% and 19%, respectively. The monthly average values of the Pollution Load Index (PLI) and Polymer Hazard Index (PHI) of microplastics in zooplankton in Jiaozhou Bay were 3.49 ± 2.94 and 4.33 ± 1.31, respectively, both corresponding to the lowest risk level, while the annual average value of the Bioaccumulation Factor (BAF) was 55.59 ± 56.84. The overall risk in May and August was higher than in February and November, posing potential threats to higher trophic-level consumers. Temperature, suspended particle concentration, and chlorophyll-a concentration significantly affected the assessment indices and showed correlations or synergistic effects with pollution load, toxicity risk, and bioaccumulation.