A systems analysis of microplastic pollution in Laizhou Bay, China

Microplastic contamination is attracting increasing attention worldwide. In this study, the patterns of microplastic contamination in surface water and sediment from 58 sites, and living fish from 31 sites were investigated in a semi-closed bay (Laizhou Bay, China). Microplastics in Laizhou Bay were pervasively distributed, particularly in the form of fibers. Microplastic abundance exhibited no significant differences among regions in either surface waters or sediments, indicating multiple sources of microplastics pollution in the bay. Spatial hotspot (Getis-Ord Gi*) analysis demonstrated that microplastic pollution was mainly concentrated in the Laizhou-Weifang area, which in turn was mainly affected by ocean current dynamics. Although the spatial distribution of microplastics in sediments was different from surface water, it was also affected by geology, hydrogeology, and anthropogenic activities. The most common polymer in the surface waters was polyethylene terephthalate (PET), while cellophane (CP) was the most frequently observed polymer in sediment, suggesting different sinking behaviors of these microplastics. The proportion of low-density microplastics (PE and PP) in surface water was approximately 19.9%, but these microplastics accounted for only approximately 1.7% in the sediment, suggesting that low-density microplastic particles preferentially migrate to open sea. There were significant differences in shape, size and polymer type of the microplastics among surface water, sediment and biota (p < 0.05). Cluster analysis suggested that the Gudong, Yellow River Estuary and Laizhou-Weifang regions are three sources of microplastics, which might originate from river input, plastic recycling and marine raft aquaculture. Furthermore, microplastic particle diversity was greater in sediment at offshore sites, suggesting that these sites receive microplastics from multiple sources. Our results characterize the microplastic pollution pattern, clarify the possible transfer mechanisms between different environmental media, and will provide important information for risk evaluation and pollution control in this area.