Detection And Distribution Of Neonicotinoids And Fipronil Insecticides In Typical Bay And Estuary Water Environment

In the previous decade,neonicotinoids（NEOs）and fipronil（FIP）have been widely used and also received increasing attention as environmental pollutants,because the high toxicity of these insecticides to bee,butterfly and some non-target arthropods has been recognized.Recent studies indicate that NEOs and FIP have been detected in aqueous environment of different lakes and rivers worldwide,as well as in soils and farm products.Estuaries and bays are typical areas of land-sea material exchange.With the development of coastal economy,especially for the aqueous environment of these areas is continuously polluted by land-sourced pesticides and persistent organic pollutants,etc.However,there are few reports on the pollution status of NEOs,FIP and its metabolites（FIPs）in coastal waters,and no international standard test method is available for the simultaneous determination of NEOs and FIPs in seawater and river water.In view of the above problems,a series of studies have been carried out in order to establish a new method for the detection of NEOs and FIPs in different environmental waters.Moreover,the distribution characteristics of these two kinds of pesticides in aqueous environment from typical bays and estuaries of China are also investigated.The details are as follows:The aim of this part is to develop a new method for the determination of eight NEOs（dinotefuran,nitenpyram,thiamethoxam,clothianidin,imidacloprid,imidaclothiz,acetamiprid,thiacloprid）,FIP,and its metabolites（fipronil desulfinyl,fipronil sulfide,fipronil sulfone）in seawater and river water samples.Disk-based solid-phase extraction（SPE）of styrene divinyl benzene（SDB-RPS）as adsorbent and high-performance liquid chromatography-tandem mass spectrometry（HPLC–MS/MS）were applied to enrich and detect the target insecticides in water samples.Compared with SPE cartridges,the sample loading procedure of the SPE disk is faster and more time-saving,thereby greatly reducing the extraction time of large-volume water samples.Completing the seawater sample extraction by disk-based SPE on the boat is feasible.Under the optimal conditions,the low limits of detection（LODs）of 12 target analytes in actual water samples ranged from 0.02 ng L^-1 to 0.10 ng L^-1,and the limits of quantitation（LOQs）ranged from 0.05 ng L^-1 to 0.50 ng L^-1.Satisfactory absolute recoveries（58.9%-106.5%）,precision（relative standard deviations,RSD≤16.8%）,and linearity（R²≥0.992）were also achieved,thereby indicating that the developed method would be suitable to determine the target NEOs and FIPs in seawater and river water.In this study,a typical bay located on the coast of the Yellow Sea was selected as the study area.Surface seawater,river water and sewage water samples from wastewater treatment plants were collected in different seasons.The composition,levels and temporal and spatial variations of NEOs and FIPs were investigated.Eleven target insecticides were detected in the river water and sewage water samples,mainly thiamethoxam,imidacloprid and acetamiprid.The total concentration of NEOs ranged from<LOQ to183.41 ng L^-1(mean concentration,12.99 ng L^-1).The total concentration of FIPs ranged from<LOQ to 9.59 ng L^-1(mean concentration,1.10 ng L^-1).The results showed seasonal variations of high concentration in summer and low concentration in spring and winter.It also shows the characteristics of high concentration in Northwest rivers such as Dagu River and Moshui River,and low concentration in eastern rivers flowing through cities.Twelve target insecticides were detected in the surface seawater samples collected from Jiaozhou Bay,mainly imidacloprid and acetamiprid,which is consistent with the composition of river water and sewage water.The total concentration range of NEOs in surface seawater was<LOQ-4.21 ng L^-1,and that of FIPs was<LOQ-0.44 ng L^-1.In summer and autumn,the concentrations of NEOs and FIPs in the surface water of Jiaozhou Bay were higher than those in spring and winter.Spatially,concentrations of NEOs and FIPs in the coastal seawater samples were higher in summer and autumn,and lower in bay mouth and bay center.The spatial distribution of NEOs and FIPs in surface water of Jiaozhou Bay was more uniform in winter and spring.The concentration,composition and spatial distribution of NEOs and FIPs in surface water of the Yangtze Estuary and its adjacent sea areas are still unknown.These two types of pesticides in surface water of the Yangtze Estuary were investigated in the summer of 2017 and 2018,respectively.The results showed that imidacloprid,thiamethoxam and dinotefuran had higher detection rate and concentration in surface water of the Yangtze Estuary and its adjacent sea areas.In summer 2017,the total concentration of NEOs in surface water ranged from ND to 12.45 ng L^-1,with an average total concentration of 3.37 ng L^-1.In summer 2018,the total concentration of NEOs in surface water ranged from ND to 99.33 ng L^-1,with an average total concentration of 32.83 ng L^-1.The detection rate of fipronil and its three metabolites were 100%,but the concentration was low,which was not the main component of the endogenous insecticides in surface waters of the Yangtze Estuary and its adjacent sea areas.It is not difficult to find that NEOs and FIPs in surface water of the Yangtze Estuary and its adjacent sea areas all exhibited spatial distribution characteristics of high near-shore concentration and low far-shore concentration.From the Yangtze Estuary to the East China Sea,the concentration decreases to below the detection limit.