Toxicological Effects On Escherichia Coli And Shewanella Putrefaciens After Adsorption Of Lead Ions By Artificial Carbon-Based Materials

Heavy metal pollution poses a significant threat to the soil ecological environment in China and around the world.To address this issue,various remediation methods have been developed.Among these methods,the use of biochar（BC）and artificial humic substances（A-HS）for remediation of soil heavy metal pollution,which are artificial carbon-based materials,has become one of the key chemical remediation techniques.Previous research has pri marily focused on the heavy metal adsorption capabilities of these materials,overlooking the potential impact on soil microorganisms after adsorption.The purpose of this study was to investigate the anti-degradation and toxicity effects of BC and A-HS adsorbing varying concentrations of lead ions(Pb²⁺)on Escherichia coli（aerobic bacteria）and Shewanella putrefaciens（anaerobic bacteria）.This study will provide feedback into the feasibility of using artificial carbon-based materials remediating soil heavy metal pollution,laying a crucial foundation for it broader application in agriculture.The research results are as follows:（1）Firstly,the Pb²⁺adsorption performance of BC prepared at different carbonization temperatures is investigated.Secondly,the toxic effects of BC on E.coli after adsorbing Pb²⁺is explored.The results showed that Pb²⁺adsorption capacity of BC increased with the increas e in preparation temperature,and highest adsorption capacity（129.5 mg/g）was achieved when temperature reaches 700°C（A700B）.Moreover,the toxic effects of BC on E.coli after Pb²⁺adsorption also increased with the rise of preparation temperature,and A700B shows the most obvious toxic effects.The specific toxicological effects and mechanisms of ABC on E.coli are as follows:1)1)A300B can only release low dosage of Pb²⁺and have a slight toxicological effect on E.coli,while E.coli adsorbs the Pb²⁺released by A300B can reduce Pb²⁺concentration in the environment.2)In contrast,A500B released a large amount of Pb²⁺and had a strong toxic effect on E.coli.E.coli responded to Pb²⁺stress by regulating its own morphology and polarizing its cytoplasm.3)Regardless of the dose of A700B used,the amount of Pb²⁺released exceeded the threshold for E.coli’s tolerance to Pb²⁺stress,resulting in severe toxic effects on E.coli.Moreover,E.coli released citric acid to protonate the surface of A700B,which was not conducive to the retention of Pb²⁺on A700B,leading to a raise Pb²⁺concentration in the experimental environment.（2）In this study,artificial humic substances（A-HS）were first prepared and added it to the synthesis of hematite to prepare hematite-artificial humic substances（Fe-HS）.Then,the Pb²⁺adsorption performance of Fe-HS artificial carbon-based materials was investigated,and denote as（Fe-HS-Pb）.Finally,the toxic effects of Fe-HS on S.putrefaciens before and after Pb²⁺adsorption under anaerobic conditions was explored.The results showed that with the increase in the amount of A-HS used in the material preparation,Fe-HS could adsorb more Pb²⁺（240 mg/g）,leading to the strongest toxic effects on S.putrefaciens.The specific toxic effects and mechanisms of Fe-HS and Fe-HS-Pb on S.putrefaciens were as follows:1)Fe-HS did not have a toxic effect on S.putrefaciens but increased its cell activity.In addition,it promoted dissimilatory iron reduction（DIR）effect.The stronger DIR effect,the higher the amount of A-HS used in the material preparation;2)In contrast,Fe-HS-Pb caused obvious toxic effects on S.putrefaciens due to the presence of Pb²⁺.Moreover,Fe-HS-Pb prepared with low dosage A-HS released Pb²⁺,which inhibited S.putrefaciens’DIR ability,while Fe-HS-Pb prepared with high amounts of A-HS released sufficient soluble organic carbon（1100 mg/L）to provide a carbon source for S.putrefaciens to resist Pb²⁺stress.The additional electron transfer agents released also helped S.putrefaciens perform DIR,promoted the degradation of Fe-HS-Pb by S.putrefaciens,and led to an increase in the Pb²⁺concentration in the experimental environment.