| Neonicotinoid insecticides are most effective to control sucking pests such as aphids, whiteflies, leafhoppers and planthoppers, thrips and some miniature pests of Lepidoptera and Coleoptera. However they have also negative impact on non-target organisms which attracts more and more attention. Earthworms are considered as an important bioindicator of chemical toxicity in the soil ecosystem. In this study, we detect the influence of neonicotinoid insecticides on earthworms Eisenia foetida at levels from the individual to molecular. Results of these studies will play an important role in investigating the mechanism of neonicotinoids toxity on earthworm and establishing the evaluation system to find effective biomarkers. The main findings are as follows:(1) The acute toxicity of20kinds of pesticides to earthworms was studied by the methods of artificial soil test and filter paper contact at20℃and24℃. The results showed that neonicotinoids, except thiamethoxam, showed the highest toxicity to E. fetida. Temperatures resulted in various influences on the toxicities of pesticides to earthworms. The toxicity of imidacloprid, acetamiprid, nitenpyram, clothianidin, avermectin, carbosulfan and benfuracarb in the artificial soil and of acetamiprid, clothianidin, thiacloprid, thiamethoxam, emamectin benzoate, carbofuran, carbosulfan, benfuracarb, omethoate, phoxim and chlorpyrifos in the filter paper contact on earthworms was significantly increased with increasing temperature. The toxicity of cypermethrin and cypermethr in the artificial soilon earthworms was significantly reduced with increasing temperature.(2) The effects of imidacloprid, thiacloprid and imidaclothiz on the change in glutathione S-transferase (GST), carboxylesterase (CarE), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) was detected on earthworms. Our results indicated the activities of the enzymes GST, CarE, SOD, POD and CAT were inhibited during the treatment period and activated during the recovery period. The activity of GST and CarE was suppressed to28d, while the activity of SOD, CAT and POD was inhibited to35d. The activity of GST, CarE, SOD, POD and CAT was significantly high during the recovery period. But the activity of SOD and CAT was no significantly difference compared to the control.(3) Ultrastructure of the skin and intestinal epithelium in earthworm was examined at2,7,14-day exposure of imidacloprid, thiacloprid and imidaclothiz. The results showed that secretory vesicles of mucous cells condensed and filament secretion disappeared with increasing time. Some intestinal epithelial microvilli cells and the tight junction of the intestinal epithelium swelled with a slightly damaged branching network of sealing strands. However the intestinal epithelium was more sensitive than the skin on earthworms.(4) The neutral red retention time (NRRT) of imidacloprid, thiacloprid and imidaclothiz on earthworms was investigated by the artificial soil. The results showed there was an opposite relation between NRRT and the concentration of pollutant added to soil. Also, the more exposed to imidacloprid, thiacloprid and imidaclothiz, the lower NRRT. (5) The DNA-damaging effects of imidacloprid, thiacloprid and imidaclothiz on earthworms were evaluated by SCGE assay. The results showed that DNA damage of imidacloprid, thiacloprid and imidaclothiz was increased with increasing exposure dose and time. During the recovery period, with the extension of recovery time, DNA damage of three neonicotinoid pesticides on earthworms was decreased. DNA damage of low concentration on earthworm was no significantly difference compared to the control.In summary, neonicotinoid insecticides have negative impact on the earthworm at different levels, which indicated that all those can be used as an effective biomarker to monitor the impact of neonicotinoid insecticides on soil and soil environment. Results of this paper provide a theoretical basis for soil ecology safety evaluation system and for the safety assessment for pesticide. |
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