Ecotoxicological Effects Of Soil Antimony And Cadmium On Earthworm (Eisenia Fetida)

Reserves and mining volumes of antimony(Sb)and cadmium(Cd)in China rank first in the world.Due to the discharge of textile printing and dyeing wastewater,antimony and cadmium coexisted in urban contaminated soil in East China.Antimony and cadmium in soil and water environment have been preliminarily studied,but the ecotoxicological effects of Sb and Cd combined pollution on earthworm have been rarely reported.This article took soil Sb and Cd as the research object,choosing Eisenia fetida as the test organism and adopting soil test,and studied the ecotoxicological effects of Sb and Cd on earthworms,who were the reliable indicator of soil quality.The main findings were as follows:(1)This chapter quantified soil antimony acute toxic on Eisenia fetida before and after the aging process,providing key toxicological parameters and risk assessment based on animal effect.The results showed that,the aging process could significantly reduce the earthworm mortality(93.33%to 66.67%),net avoidance response(36.67%to 13.33%)and escape rate(100%decreased to 53.33%)taking the treatment level of 800 mg/kg for 15 days as an example,,and median lethal content(LC₅₀)of 72 h,7 d and 15 d respectively increased from 355.27 mg/kg,322.19 mg/kg and 282.74 mg/kg to 2234.55 mg/kg,1743.19 mg/kg and 745.94 mg/kg,indicating that the aging process reduced Sb toxicity to earthworms.On the other hand,the average proportion of mild acid-soluble Sb decreased from 23.09%to 14.00%,and the 24 h mortality rate decreased accordingly.(2)This chapter used biomarker response index and addition effect index to characterize the health status of earthworms and joint effects after they were exposured to soils treated with single Sb and Cd and their mixture for 7 days,14 days,21 days,and 28 days.Firstly,earthworms could not accumulate soil Sb obviously,which was presumably related to the the high proportion of residual fraction.Secondly,under the combined and single stress of Sb and Cd,the protein content dropped by 13.86%to 58.87%,the content of malondialdehyde and metallothionein increased to 1.23 nmol/mg Pr and 40.82?g/mg Pr,respectively,and the overall activities of superoxide dismutase,peroxidase and catalase all increased by37.10%?708.11%,9.38%?150.54%and 18.94%?184.80%,respectively.Furthermore,the BRI and EAI were in the range of 1.32 to 3.35 and?0.1549 to?0.7561,respectively,indicating that Sb and Cd was antagonistic.(3)This chapter quantified the effects of earthworm on the speciation,bioavailability,bioaccessibility and soil enzyme activities in soil treated with Sb and Cd and their mixture.The results showed that earthworms could promote the activities of soil invertase,urease and neutral phosphatase,increasing by up to56.68%,114.56%and 118.97%,but earthworm had no effect on proteases and inhibited catalase activity up to 65.59%.However,the geometric mean index increased overall and indicated that earthworms had ecological benefits.Earthworms could increase the content of mild acid-soluble Sb by 4.02%to 28.39%,as well as the bioavailability and bioaccessibility of antimony,but decrease the bioavailability and bioaccessibility of Cd.(4)This chapter used microbial community diversity composition spectrum analysis to evaluate the positive effect of earthworm on soil bacteria.The results showed that the indexes of Chao1,Pielou and Shannon after earthworm treatment were 3701.51?4165.40,0.815699?0.849948 and 9.6081?10.0925,respectively,indicating that earthworm were beneficial to increase biacteria diversity,richness and evenness,as well as effecting the abundance and dominance of the biacteria composition.For example,Sphingomonas,Lactobacillus reuteri,etc.were relatively superior in the presence of earthworm,while Lactobacillus and Sphingomonas jaspsi were dominant in the case of no earthworm treatment.Overall,earthworm was generally beneficial to soil biacteria.This thesis studied the combined toxicological effects and interaction mechanism of soil Sb and Cd on earthworms,providing important support for the treatment of soil polluted by Sb and Cd,as well as having scientific significance for the hazard and risk assessment of Sb in soil environment.