Study On The Eco-toxiclogical Effects Of Single And Combined Pollution Of Cadmium And Phoximon On Earthworms And Soil

Cadmium(Cd)is a kind of common heavy metal,which is easy to migrate and transform in environment.Phoxim is a common organophosphorus pesticide that can inhibit the activity of acetylcholinesterase in the nervous system and kill insects.In this paper,the subacute toxic effects of single and combined pollution of Cd and phoxim under various concentration on earthworm and soil environment were investigated using artificial soil test.Phoxim and Cd concentration in earthworm and soil,as well as the eco-toxicological index at different aging time were measured.The effects of single and combined pollution of Cd and phoxim on physiological and biochemical indexes of earthworm,soil enzyme activities and microbial community structure were studied at the cellular and molecular level.Under Cd single pollution,the activities of superoxide dismutase(SOD)and catalase(CAT)in earthworms increased with the aging time(0-28 days)and the Cd concentrations.The activity of SOD reached the maximum in treatment group of 25mg/kg at the 21 th day and CAT activity reached the maximum in treatment group of 100mg/kg at the 14 th day.Soil urease(UE)activity increased with aging time,and the activity at the 28 th day was 1.6-10.9 times as much as that on the 7th day.Under phoxim single pollution,the activity of CAT and SOD in earthworm increased firstly and then decreased with the initial concentration of phoxim,which reached the maximum in the experimental group of 25mg/kg.The concentration of malondialdehyde(MDA)increased significantly in late period,and those in experimental group of 100mg/kg was 1.52 times as much as that in the control group.The presence of phoxim significantly increased soil acid phosphatase(ACP)activity,which was 1.06-5.78 times as much as that in the control group.Compared with single pollution,combined pollution had a synergistic effect on the activity of SOD.When Cd concentration was 25 mg/kg,the combined pollution had an antagonistic effect on the activity of CAT.When Cd concentration was 100 mg/kg,the combined pollution has a synergistic effect on CAT activity.However,combined pollution showed an antagonistic effect on the concentration of MDA.What's more,combined pollution showed a synergistic effect on soil UE activity but antagonism on soil ACP activity.The structure of soil bacterial community in soil samples under combined pollution aged for 7th day(group A)and 28 th day(group D)were analyzed.The results showed that Proteobacteria was the dominant bacteria in all experimental groups,accounting for 58%-67%.The dominant bacteria of degradation of phoxim is Massilia,Sphingomonas,while the dominant bacteria of degradation of Cd polutant is Limnobacter.The bacterial OUTs number decreased with Cd and phoxim concentration increasing at 28 th day,soil bacterial richness decreased.According to the analysis of species difference between T-test groups,there was significant difference between A group and D group at Phylum level,and the species diversity of A group was higher than that of D group.In conclution,the activity of SOD,CAT,and concentration of MDA in earthworm,as well as the UE and ACP activity,the change of microbial community structure and diversity in soil can be used as biomarkers to evaluate and characterize the toxic effect of the cadmium and phoxim.