| Neonicotinoid insecticides,one of the most widely used insecticides worldwide,with high water solubility,under the action of rainfall and surface runoff,neonicotinoids can migrate to water bodies,causing serious ecological risks to human and aquatic organisms.At the same time,the residual neonicotinoid in the water will be formed through hydrolysis,photolysis and microbial degradation of the corresponding metabolites,and there are significant differences in the toxicity of different metabolites.As the first freshwater lake in China,Poyang Lake is an important water source in the lower reaches of the Yangtze River,which plays a key role in nourishing water,regulating climate,protecting biodiversity and maintaining the ecological balance of Yangtze River basin.However,the residues of neonicotinoid insecticides and their metabolites in Poyang Lake are still unclear,and the factors affecting the differences in the spatiotemporal distribution of neonicotinoid pesticides and their metabolites as well as the ecological risks arising from the cooccurrence of neonicotinoid pesticides and their metabolites need to be further studied.In this paper,ten neonicotinoid insecticides registered in China,including imidacloprid(IMI),thiamethoxam(THM),clothianidin(CLO),thiacloprid(THC),dinotefuran(DIN),acetamiprid(ACE),nitenpyram(NIT),flonicamid(FLO),imidaclothiz(IMIT),sulfoxaflor(SUL)and seven typical metabolites,including ndesmethyl-thiamethoxam(ND-THM),n-desmethyl-acetamiprid(ND-ACE),desnitro imidacloprid hydrochloride(DH-IMI),imidacloprid-olefin(IMI-Olefin),imidaclopridurea(IMI-urea),5-hydroxy-imidacloprid(5-OH-IMI),dinotefuran-urea(UF),were used as research objects.Water samples were collected from Poyang Lake,Jiangxi Province in the wet and dry seasons of 2021,and the residue levels of neonicotinoid insecticides and their metabolites were determined in the water.Accordingly,combined with the hydrological data,the mass balance equation was used to calculate the emission and transport fluxes of neonicotinoid insecticides and their metabolites in the river-lake system of Poyang Lake.With each sampling point as the center,the buffer zone with different radii was established,and the land use type and proportion within the buffer zone were calculated,combined with the water quality parameter data of each point,the effects of water quality parameters and land use on the residues of neonicotinoids and their metabolites were analyzed.To evaluate the health risks of neonicotinoid insecticides and their metabolites to humans by using the relative toxicity factor and human intake calculation system,the ecological risk of aquatic organisms was assessed by using ecological risk entropy and priority index,and the key pollutants of Poyang Lake were screened.The main results are as follows:(1)Neonicotinoid compounds are widely presented in the water of Poyang Lake with significant spatiotemporal variability.The concentrations of neonicotinoid insecticides and their metabolites in the dry season ranged from 57.50 to 1868.06 ng/L,and the residual concentration in wet season ranges from 21.61 to 150.04 ng/L.Xinjiang and Fuhe confluence into the lake and Ganjiang River into the lake at the residual concentration of neonicotinoid insecticides and their metabolites is relatively high,while the concentrations at the outlet were relatively low.DIN,UF,IMI,IMI-Olefin,IMI-urea,ACE,THM and CLO are the main neonicotinoids remaining in Poyang Lake.The total annual input of neonicotinoid insecticides and their metabolites in Poyang Lake is 16.13 tons,among which the main source is the input from five major rivers and the surrounding areas,accounting for 82.32% of the total input and the input from non-point source discharge is 2.85 tons,accounting for 17.68% of the total input,meanwhile,the input flux from non-point source in dry season is higher than that in wet season.In terms of output flux,14.61 tons of neonicotinoid insecticides and their metabolites were exported from Poyang Lake to the Yangtze River.In addition,the daily water consumption of residents caused 1.12 tons of neonicotinoid insecticides and their metabolites output,which was the second largest output pathway of neonicotinoid pesticides in Poyang Lake.(2)The spatial and temporal distribution of neonicotinoid insecticides and their metabolites in Poyang Lake are influenced by the surrounding land use and water quality.The main land use around Poyang Lake are water,wetland,farm Land,forest land,grassland and residential land,and there are significant differences in water quality data at different periods.Neonicotinoids insecticides and their metabolites were significantly correlated with different land use areas and water quality in different buffers in Poyang Lake(p<0.05).In the wet season,the 10 km buffer zone has the highest explanatory degree(59.25%)for neonicotinoid insecticides and metabolite residues,the important explanatory variables are the percentage of farm Land area,the percentage of residential land area,dissolved oxygen,chlorophyll and electrical conductivity.In the dry season,the interpretation of 500 m buffer zone was the highest(61.81%),and the important explanatory variables included the proportion of forest land area,the proportion of farm Land area and phycocyanin.(3)Neonicotinoid insecticides and their metabolites in Poyang Lake have potential ecological risks to aquatic organisms.Neonicotinoid insecticides and their metabolites pose serious ecological risk to crustaceans and lesser ecological risk to fish,mollusks,plants,and algae.In addition,the greater ecological risk presented by neonicotinoid insecticides and their metabolites in the dry season than in the wet season.THC,IMI-olefin,DH-IMI and IMI are the priority pollutants in Poyang Lake.In summary,neonicotinoid insecticides and their metabolites are widely present in the water of Poyang Lake,and their residual concentrations and species are influenced by surrounding land use and water quality.Neonicotinoid insecticides and their metabolites pose serious ecological risks to aquatic organisms and endanger aquatic ecosystems.Therefore,it is necessary to strengthen the supervision of priority pollutants such as THC.The research results provide the theoretical basis for controlling pollutants and protecting aquatic ecological environment in Poyang Lake. |
