Biochar Passivation Remediation Of Lead-contaminated Soil And Its Impact And Toxic Effects On Earthworm Gut Microbes

With the rapid development of modern industry,agriculture and social economy,soil pollution caused by the heavy metal of lead has posed severe threat to the health of humans and ecosystems.The treatment and remediation technology of soil contaminated by the heavy metal of lead has become hot topics in the field of environmental protection.Among them,chemical passivation remediation technology using biochar as passivation materials has been used broadly in the remediation of soil polluted by heavy metals because of its advantages,such as strong practicability,low cost and quick effect.Adding biochar to the soil contaminated by heavy metals has an impact on the effectiveness of heavy metals and soil organisms.Existing researches on remediation of polluted soil by biochar mainly focused on the influence of biochar passivation remediation on soil physical and chemical properties,soil enzymes and speciation distribution of heavy metals,while the research on the effect of biochar passivation remediation on the toxicity and intestinal microbes of earthworm is relatively limited in amount.In this paper,the maize strawderived biochar was used as a passivation restoration material,and Eisenia fetida was acted as an indicator organism to evaluate the passivation restoration influence of the biochar.The content of heavy metals in the soil and earthworms in different groups were measured to investigating the effect of biochar passivation remediation on soil physical and chemical properties,soil enzymes,the leaching toxicity concentration and speciation distribution of lead,and toxicity and intestinal microbes of earthworm,providing underlying data and theoretical basis for the bio-effectiveness assessment of biochar passivation restoration.The main findings are as follows:1.The soil p H value,the cation exchange capacity(CEC)and the content of organic matter increased with the raising application rates of biochar.After the soil culture experiment and in soils with different concentrations of heavy metals,under the conditions of 0%?1%?3% and 5% biochar fertilization,the soil CEC increased by 0.982 ? 2.676 cmol/kg?0.259 ? 3.004 cmol/kg?0.499 ?1.768 cmol/kg and 0.996 ? 4.541 cmol/kg,and the content of soil organic matter increased by 1.83%? 7.42%?0.54% ? 11.66%?2.03% ? 7.44% and 1.81% ? 9.95%,respectively compared with the control group,but the increase of soil p H value was not noticeable.Simultaneously,the incorporation of biochar decreased the leaching toxicity concentration of lead in soil,and the effect increased with raising addition of biochar.2.With raising rate of the added quantity of biochar,the sucrase,urease and alkaline phosphatase activity in the soil presented a trend of increasing in the beginning and then decreasing.And with biochar additions of 3%,the soil enzyme activity was the highest.In soils with different contents of heavy metals,the soil sucrase activity enhanced by 14.04%?13.33%?9.95% and10.65%,the soil urease activity increased by 1.32%?4.97%?11.74% and 1.38%,the soil alkaline phosphatase activity elevated by 13.54%?19.06%?15.86% and 7.37%,respectively compared to the contrast.3.Biochar passivation remediation exerted impact on the speciation distribution of lead in soil.After the soil contaminated by heavy metal was passivated,the fractionation of lead made great transition from the exchangeable state and the carbonate bound state to the iron-manganese oxide bound state,the organic bound state and the residual state that were stable.And in soils with different contents of heavy metals,the best application mass percentages was 5%.4.Incorporation of biochar into the soil decreased the mortality,weight loss and accumulation amount of lead in earthworms,and this impact dropped along with the increase of biochar addition amounts,the content of lead decreased by 30.16% ? 38.25%?45.77% ? 68.75%?30.62% ? 63.46%and 19.05% ? 53.27% than control,respectively.With the prolonging cultivation time,the content of lead in the earthworms demonstrated an increasing tendency,and there was an extremely significant positive correlation with the mortality of the earthworms.5.At the level of the bacterial phylum,the core flora of intestinal microbes of the earthworms were Proteobacteria(50.82%)?Actinobacteriota(32.37%)?Firmicutes(4.83%)and Bacteroidota(1.88%),etc.;and the level of family were Comamonadaceae(33.47%)?Microbacteriaceae(30.83%)?Burkholderiaceae(9.40%)and Microscillaceae(3.44%),etc.The addition of biochar contributed to the increase of the diversity of the intestinal microbial community in the earthworms in the soil without adding any exogenous heavy metals,the most obvious application mass percentages was 5%;conversely,in the soil with the addition of exogenous heavy metals with content of 300 mg/kg and 1000 mg/kg,the intestinal microbial community diversity of the earthworms increased first and then decreased with the increasing application rate of biochar,and the most optimal application mass percentages was 3%.