A New Analytical Method For Neonicotinoid Insecticides In Water And Its Application In Assessing Neonicotinoid Toxicity In Guangzhou Urban Waterways

Ecological consequence of extensive use of systematic neonicotinoid insecticides has raised great concerns in recent years as studies showed that they might be one of the reasons for the declines of the population of bees,butterflies and other invertebrates.Owing to their high solubility,soil–bound neonicotinoids tend to move into surface waters,posing a threat to non–target aquatic invertebrates.Therefore,it is important to understand the fate and risk of neonicotinoids in freshwater ecosystems and an effective analytical method is a premise.The present work was to use Box–Behnken design to optimize solid phase extraction(SPE)method of neonicotinoids in water and an analytical method coupling SPE and HPLC/MS was established and validated.The newly developed method was then applied to analyze neonicotinoids in water samples which were collected from a typical urban stream in Guangzhou and the potential risk of neonicotinoids in the study area was evaluated by combining chemical and toxicological data.Based on the BBD,three–level–four–factor was used to optimize the analytical method of neonicotinoids in water.The SPE conditions were optimized using multivariant nonlinear regression analyses,including the type and amount of absorbents and the type and volume of elution solvents.Two optimized methods were selected for analyzing neonicotinoids in different types of water samples.The optimized analytical conditions were using 100 mg HLB as the absorbent and 10 mL methanol as the elution solvent M(1)and the sorbents of 200 mg HLB: GCB(w: w,8: 2)and the eluent of acetonitrile(ACN): acetone(ACE)(v: v,8: 2)(M2),respectively.The method detection limits(MDLs)of M(1)and M(2)for target compounds were ranged 0.9 to 2.8 ng/L and 1.8 to 6.8 ng/L,respectively.To validate the accuracy of the methods,neonicotinoids were analyzed in spiked water at different concentrations and with different amounts of interfering substances.The results of M(1)showed that the recoveries of neonicotinoids ranged from 73.2 ± 4.17% to 122 ± 1.69% except dinotefuran which was not detected.When M(2)was applied,a recovery of 57.2 ± 3.11% was achieved for dinotefuran at low concentrations,but the recovery started to decrease when its concentrations in water increased.The lowest recovery of dinotefuran was approaching to 40% using the method M(2).In addition,the recovery of clothianidin relatively low at low spiking level,but it increased when the matix contents increased.The recoveries of other neonicotinoids were all close to 80% except dinotefuran and clothianidin.Eventually,both methods were successfully applied to determine neonicotinoids in three field water samples and imidacloprid and acetamiprid were the two most dominant neonicotinoids.The concentrations of imidacloprid and acetamiprid were from 27.5 to 193 ng/L and 17.5 to 24.3 ng/L,respectively.Using the newly developed analytical method,we studied the 96 h acute toxicity of acetamiprid(a representative of neonicotinoid insecticides)to aquatic invertebrate Hyallela azteca and the mortality was selected as the toxic endpoint.The median lethal concentration(LC50)of acetamiprid was 33.5(22.7-49.2)ng/mL.Moreover,the delay toxicity of acetamiprid to Hyallela azteca was assessed at the spiked concentration of LC50.The preliminary result confirmed the delayed toxicity of acetamiprid in H.azteca,but more studies are required to understand the mechanism.At last,an urban stream in Guangzhou(Chebei Creek)was chosen as the study area for evaluting the potential risk of neonicotinoids in urban waterways.Along the creek,24 samples were collected and additional 9 samples were collected in the outlet to the creek.The water samples were analyzed for neonicotinioids as well as theiracute toxicity to Hyallela azteca and Chironomus dilutus.In addition,chronic risk from neonicotinoids to aquatic species in this creek was also evaluated using risk quotions calcuated from the chronic toxicity benchmark from the literature.The results showed that the neonicotinoids were ubiqutious in these samples,but their contribution to the acute mortality to H.azteca and C.dilutus was minimal.Conversely,the chronic risk quotients of neonicotinoids in the study area were all greater than 0.01 and the highest value reached 3.56.Acetamiprid and imidacloprid dominated the risk contribution with the risk quotients higher than 0.1 in 81.8% and 66.7% samples,respectively.The results suggested that the neonicotinoids have posed arisk to the aquatic ecosystems in Guangzhou urban waterways.