Neonicotinoid pollution in marine sediments of the East China Sea

Neonicotinoid insecticides are widely and exceedingly applied in farmlands worldwide and are ubiquitous in various environments, including surface water, soil, river sediments, etc. However, few studies reported neonicotinoid residues in the marine environment. Considering the large application of neonicotinoids in China, here, we collected marine sediments in offshore and far sea areas of the East China Sea, including the Hangzhou Bay and the area along the Zhejiang Province coast, and measured the concentrations of nine commercialized neonicotinoids. The total concentration of neonicotinoids was 11.9 ± 6.22 ng/g (dry weight) (range: 4.77-29.9 ng/g), which was higher than other regions reported in previous studies. Neonicotinoid residues found in far sea areas were statistically lower than those in offshore areas. Nitenpyram and dinotefuran were the dominant compounds, contributing to >75 % of the total residue. It is thought that the flux of the Yangtze River is the main source of the neonicotinoid pollution in the East China Sea and the sediment is the sink of neonicotinoid residue from mainland China. Neonicotinoid residues were found to be negatively correlated with sediment pH, and positively correlated with microbial diversity and nitrate content. Based on structural equation modeling, we also illustrated the associations between neonicotinoid residues and different factors, suggesting that the change in sediment pH and microbial diversity were related to the degradation of neonicotinoid residues. Actinobacteriota, Chloroflexi, and Nitrospirota were found to be the key bacterial community at the phylum level on the degradation of neonicotinoids. Our findings provide new insights into the understanding of spatial distribution, source, and migration of neonicotinoids and their impacts on marine microorganisms.