The Joint And Chronic Toxicity Of Neonicotinoid Insecticides On Earthworm (Eisenia Fetida)

As a novel chemical,neonicotinoids possess the characteristics of low toxicity for mammals but high lethal effect to insects,which have been wildly used for pest control.Due to its unique effect of acetylcholine receptor inhibition,the risk of cross-resistance with organophosphorus insecticides,carbamate insecticides or pyrethroid insecticides is much lower.However,it still has environmental effect and threat non-target organisms after field spraying.As an indicator creature,Earthworms are frequently used for the risk evaluation of ecosystem and environmental impact.In this study,toxicity of several neonicotinoids pesticides have been tested using Earthworm(Eisenia fetida),and its behavior effected by Neonicotinoids has been observed,intending to profile the joint toxicity of neonicotinoids and establish a system for its risk assessment of environmental impact.The main results are as follows:1.The acute toxicity of eight neonicotinoids were studied by methods of artificial soil test and filters paper contact.The results showed that by contact filters paper test,the 48 h half-maximal lethal concentration of acetamiprid,dinotefuram,imidacloprid,clothianidin,thiacloprid,nitenpyram,pymetrozine,thiainethoxam was 0.026?0.034?0.038?0.228?1.16?1.24?>62.92 and>629.2 ?g/cm,respectively.Pymetrozine and thiainethoxam had low toxicity to earthworm,the others present high toxicity.In artificial soil test,the 14 d half-maximal lethal concentration was 1.116?2.996?3.594?5.506?56.75?8.005?>2000 and>20000 mg/kg,respectively.Pymetrozine and thiainethoxam had negligible toxicity to earthworm,whereas others had moderate toxicity.2.A standard OECD artificial soil test technique was employed for the joint toxicity test of imidacloprid and five neonicotinoid insecticides(acetamiprid,dinotefuram,clothianidin,thiacloprid,nitenpyram).The results showed that mixing imidacloprid with individual neonicotinoid insecticide in equal proportion of toxicity unit 1:1,the toxicity(14 d-LC50)of the five neonicotinoid insecticides could be increased 6.55?7.23?5.31?9.94 and 5.66 times,respectively.Additive index of five pesticides was 2.39?2.61?1.68?3.93 and 2.22,respectively,implying the synergistic effect with imidacloprid.3.Avoidance behavior of earthworm with six neonicotinoid insecticides(acetamiprid,dinotefuram,clothianidin,thiacloprid,nitenpyram,imidacloprid)was carried out following the protocol of ISO.The results revealed that earthworm showed obvious avoidance behavior against the pesticide,and the medium concentration for avoidance behavior(ACso)of six pesticides was 0.14?0.55?0.91?7.87?1.32 and 0.77 mg/kg.In comparison with acute toxicity,avoidance behavior test could be more significant for the indication of soil contamination with pesticides.4.Chronic toxicity of above six neonicotinoids were evaluated.By exposing to the pesticide with 5%,10%,20%,50%of 14 d-LCso dosages,the weight of earthworm decreased after 28 d,the higher concentration the lower earthworm weight.Mean yield of cocoons per earthworm was significantly decreased compared with controls,even in low concentrations of the insecticides.However,mean cocoon weight was reduced only upon high concentrations of the pesticides,and cocoons were smaller and deformed.The reproduction of earthworms were significantly reduced with a 56 d half-maximal effective hatchability concentration(EC50)was 0.368?0.743?1.305?3.566?1.196?0.697mg/kg(acetamiprid,dinotefuram,clothianidin,thiacloprid,nitenpyram,imidacloprid),respectively.Meanwhile,the number of juvenile earthworm was reduced with the increasing concentrations of neonicotinoids.