Occurrence, variations, and risk assessment of neonicotinoid insecticides in Harbin section of the Songhua River, northeast China

Neonicotinoid insecticides(NNIs)have been intensively used and exploited,resulting in their presence and accumulation in multiple environmental media.We herein investigated the current levels of eight major NNIs in the Harbin section of the Songhua River in northeast China,providing the first systematic report on NNIs in this region.At least four NNIs in water and three in sediment were detected,with total concentrations ranging from 30.8 to 135 ng L^(-1) and from 0.61 to 14.7 ng g^(-1) dw,respectively.Larger spatial variations in surface water NNIs concentrations were observed in tributary than mainstream(p<0.05)due to the intensive human activities(e.g.,horticulture,urban landscaping,and household pet flea control)and the discharge of wastewater from many treatment plants.There was a significant positive correlation(p<0.05)between the concentrations of residual imidacloprid(IMI),clothianidin(CLO),and S4NNIs in the sediment and total organic carbon(TOC).Due to its high solubility and low octanol-water partition coefficient(Kow),the sediment-water exchange behavior shows that NNIs in sediments can re-enter into the water body.Human exposure risk was assessed using the relative potency factor(RPF),which showed that infants have the highest exposure risk(estimated daily intake(SIMIeq EDI):31.9 ng kg^(-1) bw$d^(-1)).The concentration thresholds of NNIs for aquatic organisms in the Harbin section of the Songhua River were determined using the species sensitivity distribution(SSD)approach,resulting in a value of 355 ng L^(-1) for acute hazardous concentration for 5%of species(HC5)and 165 ng L^(-1) for chronic HC5.Aquatic organisms at low trophic levels were more vulnerable to potential harm from NNIs.