Occurrence,human And Ecological Risks Assessment Of Neonicotinoid Insecticides In Soils Of An Typical Aricultural Zone In South China

Neonicotinoid insecticides（NIIs）have become one of the best-selling insecticides worldwide in the last two decades,and gradually replaced some part of traditional pesticedes（i.e.,organophosphorus pesticde）.However,the widepread application of NIIs has led to their constantly release to the environment,potentially inducing adverse effects on human health and ecosystems.The occurrences of NIIs in water and sediment of the Pearl River Delta（PRD）region have been reported in several studies.But limited studies have investigated the occurrences and distribution of NIIs in agricultural soils of the PRD region so far.Soil is not only one of the largest sinks of organic pollutants,but also the main habitat for most of the terrestrial organisms.Therefore,it is urgent to understand the occurrence,human exposure risk,and ecological risks of NIIs in agricultural soils in the PRD region.Guangzhou,a rapid developing city within the PRD region,lies in the subtropical area.The humid and warm weather in Guangzhou facilitates the propagation of pests.And there are frequent agricultural activies in the area.Therefore,NIIs are widely used for both pest control and agricultural cultivation in this area.The present study aims to investigate the contamination of NIIs（i.e.,imidacloprid,clothianidin,acetamiprid,imidaclothiz,dinotefuran,and flonicamid）in vegetable farms（n=176）,rice paddies（n=123）,and fruit farms（n=52）of agricultural soils in Zengcheng,within the PRD,South China.The objectives were to determine the levels of NIIs in three types of agricultural soils;to assess the potential human health risk via food intake,soil ingestion,dermal contact,and inhalation;and to investigate the ecological risks associated with soil NIIs for non-target organisms.The present study has shown that at least one NII compound was detected in 95%of all agricultural soils samples.The levels of∑₆NII（sum of imidacloprid,clothianidin,acetamiprid,imidaclothiz,dinotefuran,and flonicamid;range（median））were 0.26-390（23）ng g^-1 d.w.,0.26-280（6.1）ng g^-1 d.w.,and 0.26-120（5.0）ng g^-1 d.w.dry weight in soil samples from vegetable farms,rice paddies,and fruit farms,respectively.Neonicotinoids were detected more commonly and at statistically higher concentrations in vegetable farms compared with rice paddies and fruit farms（ANOVA,p<0.05）.This is likely ascribed to higher application frequencies of NIIs in vegetable farms,because vegetables are planted more frequently and are more vulnerably to pests compared with paddies and fruits.In addition,the compositional prifiles of NIIs were similar among the vegetable farms,rice paddies,and fruit farms.Imidacloprid,clothianidin,and acetamiprid were the dominant compounds.Imidacloprid was the most commonly detected compound among all NIIs,maily because of the long half-life of imidacloprid（100-1230 days）in the soils.The present study evaluated the average daily dose of NIIs in the general population via food intake,soil ingestion,dermal contact,and inhalation.The results showed that the average daily dose via dietary intake was at least three orders of magnitude higher than the average daily doses of the other three exposure pathways,which indicated that dietary intake was still the main exposure pathway for NIIs.In addition,the hazard index（HI）was calculated to assess the potential human exposure risk of NIIs in the agricultural soils,and the HI values were all below 1for both adults and children,suggesting that the non-cancer risks for the general residents were neglibile.In the present study,the exposure toxicity ratio for non-target organisms(HQ_non-target)was used for ecological risk assessment.In an environmentally relevant scenario（mean concentration）in all agricultural farms,50%of the non-target organisms would be suffered from sub-lethal effect(HQ_non-target≥0.01),and 7%of the species would be suffered from detrimental effect(HQ_non-target≥0.05).In the worst-case scenario（max concentration）,the results are more worrisome because all non-target species would be suffered from sub-lethal effect,and 57%of the species would be suffered from detrimental effect.Because of the higer NII concentrations detected in the vegetable farms,the proportions of potentially affected non-taret organisms in vegetable farms were higher than those in rice paddies and fruit farms.In general,the residual levels of NIIs in the agricultural soils in the studied area are likely pose sub-lethal or acute effects to non-target organisms.