The Temporal And Spatial Distribution,Source And Ecological Risks Of Neonicotinoid Insecticides In The Major Rivers Of China

Neonicotinoids were a novel class of systemic insecticides.Owing to the high solubility,neonicotinoids were easily transferred into the aquatic environment by runoff and results in the ecological risks to nontarget insects,mammals and birds.However,none of the studies have reported neonicotinoid pollution in any large-scale aquatic environment in China,and none of them have focused on the source identification of neonicotinoids.In this paper,nine commercial and widely used neonicotinoids in recent years,including imidacloprid?IMI?,acetamiprid?ACE?,thiamethoxam?THIA?,clothianidin?CLO?,thiacloprid?THI?,flonicamid?FLO?,nitenpyram?NIT?,imidaclothiz?IMID?and dinotefuran?DIN?,were analyzed as research objects.The concentrations of neonicotinoids in Yangtze River Basin and rivers along the east coast of China were detected during the dry season and wet season in 2016.The temporal and spatial distribution of nine neonicotinoids was determined.And the load into the adjacent sea was estimated.The nonpoint sources and contaminant fluxes in Yangtze River Basin were identified based on a modified mass balance approach.Using the species sensitive distribution?SSD?method,the regulatory thresholds were detected and the ecological risks for aquatic animals were evaluated.The main results are divided into the following two parts:?1?Spatial distribution and source analysis of nine neonicotinoid insecticides residues in the Yangtze River Basin:the total concentrations of neonicotinoids were990 ng/L and 390 ng/L in the Yangtze River Basin during the dry season and wet season,respectively.Dinotefuran concentrations were the highest,and the second highest level was found for nitenpyram.The concentrations of dinotefuran and nitenpyram during the two seasons were 470 ng/L,430 ng/L and 190 ng/L,150 ng/L,respectively.There were obvious seasonal differences in the residues of neonicotinoids,and the concentrations in dry season were significantly higher than that in wet season.The total concentrations of neonicotinoids in the sites of mainstream were higher than those in tributaries.The main source of neonicotinoids in the Yangtze River Basin is the input of nonpoint discharge from agricultural activities,followed by the input of upstream rivers and tributaries or lakes.The input of nonpoint source in the middle-lower section of Yangtze River was higher than that in the upper section.Annual,the neonicotinoids discharge into the adjacent sea?East China Sea?was 1190 tons,of which 91.3%was input of nonpoint sources.Dinotefuran was the top contributor,with the discharges of412 tons during the dry season and 176 tons during the wet season,respectively.The annual discharge of nitenpyram was 458 tons,as the second largest.The consumption pattern of neonicotinoids in agricultural activities in the Yangtze River Basin has changed in recent years,with a trend from old type?imidacloprid and acetamiprid?to new type?dinotefuran and nitenpyram?.?2?Spatial distribution and ecological risks of neonicotinoids in the rivers of eastern China:the total mean concentrations of nine neonicotinoids were 343 ng/L and174 ng/L during the dry and wet season,respectively.Nitenpyram contributed the highest in two seasons,with the concentrations 105 ng/L for dry season and 55ng/L for wet season.The concentrations of imidacloprid during dry and wet seasons were 40ng/L and 34 ng/L,respectively.Dinotefuran?48.6%?and nitenpyram?38.2%?dominated the total neonicotinoid pollution,with a combined total of over 85%.In the Yellow River Basin,the southeast region,and Hainan island,agricultural activities result in high concentrations of tranditional neonicotinoids,such as imidacloprid and acetamiprid.While the new neonicotinoids,including nitenpyram,imidaclothiz and dinotefuran,have started to be widely used in the northeast,the Pearl Basin and the Yangtze River Basin,which indicated the differences of neonicotinoid insecticides consumption patterns in different regions.The total load of neonicotinoid discharges into the adjacent seas reaches 1256 tons per year.The neonicotinoid pollution in the Yangtze River was the most serious,with 1190 tons discharges into the East China Sea.The average level of HC₅?regulatory thresholds?were 0.362?g/L and 0.058?g/L for acute and chronic ecological risks for aquatic animals,respectively.Compared to these thresholds,the concentrations detected in 27%of the water samples exceeded the threshold of acute toxicity,and 84%of them exceeded the threshold of chronic toxicity.As for different regions,the neonicotinoid pollution in the Yangtze River and Nandu River exceeded the thresholds of acute toxicity.For the chronic toxicity assessment,neonicotinoid pollution in all the regions of China exceeded the threshold in this study.At present,the ecological risks of neonicotinoid pollution to aquatic animals is ubiquitous in the rivers along the east coast of China.The authorities should pay more attention to the current situations of neonicotinoid pollution in river waters.In conclusion,this study indicated the relatively high concentrations of neonicotinoids in the major rivers of China.The nonpoint discharge of agricultural activities contributed the neonicotinoid pollution in Yangtze River Basin and the chronic toxicity to some aquatic animals was determined.This study can provide a scientific basis for the future evaluation,consumption and risk management of neonicotinoid insecticides in China.