Toxic Effects Of Typical Neonicotinoid Insecticides Combined With Heavy Metals On Earthworms

Compared with the traditional insecticides,the neonicotinoid insecticides,which act on the postsynaptic nicotine acetylcholine receptor of insect central nervous system,have novel action modes,high insecticidal activity and strong root inhalation,and have been applied worldwide,resulting in an increasing number of neonicotinoid insecticides entering the soil.At the same time,with the rapid development of modern industry,livestock and poultry farming,more and more heavy metals enter the soil environment,resulting in the gradual increase of heavy metal pollution in the soil.Therefore,neonicotinoid insecticides and heavy metals can coexist in soil,and may form complex pollutants,causing potential harm to soil organisms.In order to evaluate the ecological toxicity of the combined pollution of neonicotinoid insecticides and heavy metals,the typical representatives of neonicotinoid insecticides(imidacloprid,thiamethoxam,dinotefuran)and heavy metals(cadmium,copper,zinc)were selected as soil pollutants,earthworms were used as test organisms,and artificial soil method was used to study the pollution concentration design.The multi-factor and multi-level compound pollution was studied,and the main effect and interaction of the compound pollution process were analyzed.The changes of body weight,reproductive inhibition rate,body surface and midgut structure,ultrastructure of seminal vesicle,activity of antioxidant enzymes(superoxide dismutase SOD,catalase CAT,detoxification enzyme GST),content of malondialdehyde MDA and ROS of active oxygen cluster during 28 days of exposure were measured to study the effects of compound pollution of neonicotinoid insecticides and heavy metals on earthworms.Ecotoxic effects of earthworms.The main results are as follows:(1)Compound pollution affects the growth-weight change and reproductive rate of earthworms.The main factors affecting body weight were: interaction between imidacloprid and dinotefuran > dinotefuran > interaction between imidacloprid and cadmium > interaction between imidacloprid and thiamethoxam > thiamethoxam.The reproductive rate of earthworms in the treatment group was lower than that in the control group.The interaction of imidacloprid and cadmium has significant antagonistic effect on the inhibition rate of earthworm reproduction,which also affects the inhibition rate of earthworm body weight.(2)Compound pollution caused damage to the surface,midgut and seminal vesicle of earthworms.In the treatment group,necrosis and disordered arrangement of epithelial cells in the mucosal layer were observed in the midgut of earthworms.The necrotic cells were stained or dissolved and disappeared,and the epidermis was partly absent or even exfoliated.In the treatment group,the nuclei of spermatocytes were irregular,the local nuclear envelope was depressed,the pseudo inclusion bodies appeared in the nuclei,the heterochromatin scattered in the nuclei,and some mitochondrial ridges disappeared.(3)The activities of SOD and CAT of earthworms in most treatments were lower than those in the control group during the period of exposure.Compound pollution inhibited the activities of SOD and CAT of earthworms.The activity of GST of earthworms in the treatment group showed the trend of activation and inhibition at first,and the content of ROS in the period of exposure was higher than that in the control group.The exposure of thiamethoxam significantly inhibited the activities of SOD and CAT in earthworms.The GST activity,MDA and ROS content of earthworms were affected by the interaction of imidacloprid,imidacloprid and cadmium,dinotefuran and cadmium.The interaction between imidacloprid and dinotefuran had significant antagonistic effects on CAT activity,GST activity and MDA content in earthworms.