Study On A New Method For Detection Of Neoicotinoids And Fipronil In Sediments,and Their Photodegradation In Seawater

Neonicotinoids and fipronil are the two most commonly used insecticides in agriculture and hygiene,which aggravates the risk of environmental pollution and exposure to non-target organisms,and will have varying degrees of impact on the survival,development and reproduction of non-target organisms such as bees,fish and aquatic invertebrates.In recent years,research on the pollution status,toxic effects and environmental fate of these two new types of pollutants in the environment has gradually become an international hot spot.However,the current detection technology for neonicotinoids and fipronil insecticides in different marine environmental media is still immature,and there is very limited understanding of the degradation laws of these two types of insecticides in offshore marine environments.Establishing a method for simultaneous analysis of neonicotinoids and fipronil insecticides in sediments,and ascertaining the photodegradation rules and its influencing factors of these two insecticides in seawater are the main objectives of this study.The specific research contents are as follows:A new method to simultaneously detect eight neonicotinoids and fipronil and its three transformation products in sediments was developed using high-performance liquid chromatography-tandem mass spectrometry?HPLC-MS/MS?based on a combined pretreatment of methanol-methanol-water continuous solvent extraction?CSE?and solid phase extraction?SPE?in order to overcome the problem of determination of neonicotinoids and fipronil insecticides in sediments.Firstly,the optimization of extraction and cleanup conditions,chromatographic and mass spectrometric parameters were peformed,and then the method was validation under the optimum conditions.The results show that the established method is sensitive,linear,accurate and precise,the limits of detection?LOD?of target compounds were0.012?g/kg-0.055?g/kg d.w.Good linearity?R²>0.990?was observed between4.0×10^-2?g/kg-20.0?g/kg d.w.The recovery rates of all target compounds were between 75.5%and 98.5%,and the relative standard deviations?RSD?were all less than 15.0%at the low,medium,and high spiked levels.Finally,the optimized method was applied to analyze target compounds in the sediments obtained from Jiaozhou Bay of China and its main inflow rivers.Acetamiprid,thiamethoxam,fipronil sulfide,and fipronil sulfone were detected in the river sediment samples at the concentration from<LOQ to 0.197?g/kg d.w,which shows that the rivers around Jiaozhou Bay have been contaminated by neonicotinoids and fipronil insecticides,and it further indicates that this method is effective for the detection of these two types of insecticides in sediments.The photodegradation rules and influencing factors of eight neonicotinoids and fipronil and its three transformation products in seawater were studied through photodegradation simulation experiments to ascertain neonicotinoids and fipronil insecticides attenuation characteristics in offshore aquatic environment.A light avoidance control experiment was also performed to clarify whether other factors have effects.Firstly,the photodegradation of eight neonicotinoids and fipronil and its three transformation products was studied under outdoor sunlight.There was no significantly loss of twelve target compounds in the dark control experiment.The six neonicotinoid insecticides with the exception of acetamiprid and thiacloprid were almost completely photodegraded within 0.25 d-10 d under light conditions,almost no obvious changes were found for the concentration of acetamiprid and thiacloprid after 10 d of light exposure.The removal rate of fipronil was 97.4%after 5 d of outdoor exposure,the elimination rates of fipronil desulfinyl,fipronil sulfone and fipronil sulfide by natural light were 21.5%,37.8%and 92.9%after 10 d,respectively.Which indicates that fipronil was more prone to photochemical reactions than its transformation products in seawater.Then the effects of environmental factors such as the pH of seawater,humic acid and dissolved oxygen content,metal ion strength on the photodegradation of twelve target compounds in seawater were investigated under simulated light conditions in the laboratory.The first-order kinetic equation describe the photodegradation of all target compounds in seawater well under the irradiation of xenon light.Ultraviolet light determines the photodegradation of the target compounds rather than visible light.Most target compounds were eliminated faster by light when the pH of seawater is relatively low in the selected range.The increase of dissolved oxygen content in seawater will increase the photodegradation rate of all target compounds,Fe³⁺and Cu²⁺can promote the photodegradation of most target compounds to some extent.The photodegradation rates of the target compounds gradually decreases with the increasing concentration of humic acid in seawater.Overall,the subtractive cycle of neonicotinoids and fipronil insecticides in seawater were affected by various environmental parameters of seawater.