Ecotoxic Effects Of Deltamethrin With Different Application Methods On Earthworms

In this paper,deltamethrin,a typical representative of pyrethroid pesticides,was taken as the test pollutant to study the reproductive toxicity and molecular toxicity at low concentrations with one-time application or multiple application on earthworms(Eisenia fetida),as a representative soil model macroinvertebrate,under the conditions of artificial soil and the real brown soil.The ecotoxic effects of deltamethrin and its metabolites during the cultivation period on earthworms were assessed so as to provide a theoretical basis of the ecotoxicology of deltamethrin.The results showed that the death rate of parent adults increased with the increase of the deltamethrin concentration in the one-time application or the multiple application treatment groups with the deltamethrin exposure concentrations of 0.004 mg/kg,0.020mg/kg,0.100 mg/kg,0.500 mg/kg and 2.500 mg/kg in the 56 d experimental period.There was a significant dose-effect relationship between the death rate of parent adult earthworms and the deltamethrin concentration.Compared with the multiple application treatment,the death rate of earthworms in the one-time application was significantly higher(p<0.05).There was a significant negative correlation between the reduction rate of the number of offspring earthworms with the deltamethrin concentration in the one-time and the multiple application treatment group in the artificial soil(p<0.01).Compared with the deltamethrin multiple application treatment in artificial soil,the soil organic matter content of the tested brown soil was higher,which was more conducive to the increase of the number of offspring earthworms.There were no obvious difference in the number of cocoons in the three soils,and there was no significant effect of deltamethrin at the experimental concentrations on the number of cocoons(p>0.05).The activities of superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD)in earthworms were not obvious in the first 3 days of exposure to deltamethrin in three soil conditions.It may be that earthworms are less toxic because of the low concentration in the experiment.On the 5th day,the activities of the three enzymes were significantly activated with the increase of deltamethrin concentration and time.This was because more deltamethrin was absorbed over time,which stimulated the change of enzyme activity to counter the change and stress of deltamethrin.The activity of SOD,CAT and POD enzymes was lower than that of 5-14 d after exposure to deltamethrin for14 days,and the enzyme activity was inhibited.The activity of acetylcholinesterase(AChE)in earthworms was almost the same in the three soils,that is,it showed a significant inhibitory effect with the increase of exposure time and concentration of deltamethrin.Compared with different application treatment,the one-time application treatment of deltamethrin in artificial soil was more significant than the multiple application of earthworms SOD and CAT enzyme activity.The CAT activity was more obvious in the case of multiple application in the first 3 days.However,one-time application from the 5th day is more significant than multiple application,and CAT activity may induce an enzyme activity under the stimulation of a low concentration of deltamethrin.The POD activity of the artificial soil treatment was significantly different than that of the brown soil treatment,that is,the brown soil had less influence on the POD,which may be related to the organic matter contained in the brown soil.The half-life of deltamethrin accords with the first-order kinetic equation.The half-lives of the one-time application treatment are 12.1 d,12.9 d,13.8 d,16.3 d and18.7 d,and the half-life becomes longer as the concentration increases.The average values of deltamethrin concentration in the multiple application treatments on the 28 th day were 0.0008 mg/kg,0.0011 mg/kg,0.0026 mg/kg,0.1703 mg/kg and 0.8419 mg/kg,while in the one-time application treatments were 0.0014 mg/kg,0.0019 mg/kg,0.0037mg/kg,0.2086 mg/kg,1.0695 mg/kg.The multiple application of deltamethrin can effectively reduce the deltamethrin residues in the soil.The multiple application treatment of artificial soil has a longer deltamethrin half-life than that in the facility soil.The organic matter content and the maximum water holding capacity of the facility soil are 5.76 g/kg and 31.3%,respectively,while the organic matter content and the maximum water holding capacity of the artificial soil are 2.55-2.78 g/kg and26.2-26.4%,respectively,soil organic matter content and maximum water holding capacity will affect the degradation of deltamethrin.