Acute And Chronic Toxicity Effects Of Azoxystrobin On Earthworms In Four Different Soils

Azoxystrobin,a broad-spectrum strobilurin fungicide,is widely used in agricultural production.With a large consumption,azoxystrobin will inevitably accumulate in soil and pose potential threaten to soil ecosystem.Earthworm is the invertebrate in soil with largest biomass.Some research has studied toxic effects of azoxystrobin on earthworm in artificial soil.However,there are a lot of differences between physical and chemical properties of artificial soil and natural soil.Therefore,effects of azoxystrobin on earthworms in real soil environment can't be evaluated objectively by cultivating earthworms in artificial soil.To assess ecological risk of azoxystrobin in real soil environment,we performed a study on effects of azoxystrobin on earthworm(Eisenia fetida)in three different natural soil(fluvo-aquic soil,black soil and red soil).Acute toxicity of azoxystrobin was determined by filter paper test and soil test on the 48^th hour and 14^th day,respectively.Accordingly,expose concentrations of chronic toxicity were set as 0,0.1,1.0 and 2.5 mg/kg.Reactive oxygen species(ROS),activity of antioxidant enzymes(superoxide dismutase,catalase and peroxidase),detoxifying enzyme(glutathione transferase),level of lipid peroxidation (malondialdehyde)and level of oxygen damage of DNA(8-hydroxy deoxyguanosine)in earthworms were determined on 7^th,14^th,21^th,28^th,42^th and 56^th days.In the present study,actue toxicity and chronic toxicity of azoxystrobin on earthworms in three natural soil and artificial soil were compared respecively.And combined with physical and chemical properties of the soils,ecological risk of azoxystrobin in different soils was evaluated.The present experiment provided scientific guidance for rational application of azoxystrobin in agricultural production.Main results of the present experiment are as follows:(1)For acute toxicity of azoxystrobin in fluvo-aquic soil,black soil,red soil and artificial soil,LD₅₀ on day 14 were 32.5,214.0,21.3 and 528.7 mg/kg.Acute toxicity order was:red soil>fluvo-aquic soil>black soil>artificial soil.The correlation coefficients between acute toxicity and amount of sand,available nitrogen,organic matter and organic carbon were higher than 90%.And the lower those indicators are,the higher acute toxicity are.(2)In three natural soil,content of ROS in earthworm exposed to azoxystrobin increased with exposure concentration and exposure time.ROS accumulated in earthworms exposed to azoxystrobin in three natural soil.Activity of antioxidant enzyme and glutathione transferase in earthworms exposed to azoxystrobin were activated,which is consistent with the chang pattern of ROS.Content of indicators of lipid peroxidation and oxygen damage of DNA increased significantly.(3)By calculating the integrated biomarker response index(IBR),chronic toxicity of azoxystrobin in different soils was:black soil>red soil>fluvo-aquic soil>artificial soil.The correlation coefficients between acute toxicity and cation exchange capacity and conductivity were higher.