Stabilization Effect And Mechanism Of Microbial In-situ Induction Of Fe-Mn Oxides On Arsenic In Soil

With the rapid development of mining,industry and agriculture,the massive use of arsenic-containing chemicals had caused arsenic pollution in terrestrial ecosystems.At present,the problem of soil arsenic pollution in our country is relatively serious.The growth of plants and crops has accelerated the migration and transformation of arsenic in the soil-plant system.How to repair arsenic-contaminated soil and reduce its environmental risk has become one of the key issues to be solved urgently in the environmental field.Studies had shown that Fe-Mn oxides play a crucial role in the adsorption,fixation and migration and transformation of arsenic in soil.Based on this,this article used the manganese oxidizing bacteria Pseudomonas putida strain Mn B1 as the experimental strain to study the effect and mechanism of its induced biogenic Fe-Mn oxides（BFMO）on the stabilization of arsenic in water and soil.The main research content was:To explore the adsorption and fixation effect and mechanism of BFMO for arsenic in water;studied the adsorption and fixation effect of biogenic Mn oxides（BMO）,biogenic Fe oxides（BFO）and BFMO on the adsorption and fixation of arsenic in soil and phytotoxicity;analyzed the influence of environmental factors on the adsorption and fixation of arsenic in soil by BFMO.The research results can provide scientific basis and theoretical guidance for BFMO to repair arsenic polluted environment.The main conclusions were as follows:（1）The removal efficiency and mechanism of As（III）and As（V）by in-situ formed BFMO by Pseudomonas putida strain Mn B1 were investigated through adjusting the factors including initial arsenic（As）concentration,As valence,bacterial inoculation percent and Fe/Mn concentration.The results indicated that:1)In-situ formed BFMO had a strong ablitiy for removing As（III）and As（V）from water.The removal efficiencies of As（III）and As（V）were more than 62%when the initial concentration of As（III）and As（V）was 0.5～5 mg·L^-1.2)The removal efficiency of As（III）and As（V）increased with the increasing of the bacterial inoculation ratio when the bacterial inoculation ratio was 0.1%～0.5%.The removal efficiency of As（III）and As（V）did not change significantly,above 85%,when the bacterial inoculation ratio was greater than 0.5%.3)The removal rate of As（III）and As（V）increased with the increase of Mn CO₃or Fe（II）concentration in the presence of 0.2～0.8 g·L^-1Mn CO₃or 2.5～25mg·L^-1Fe（II）;the removal efficiency of As（III）and As（V）changed not significantly when the concentration of Mn CO₃or Fe（II）increased again.The microstructure analysis clearly indicated that the presence of As（V）on in-situ generated BFMO surface,and the removal of As（III）and As（V）mainly through adsorption,following by co-precipitation.（2）Biomaterials such as BMO,BFO and BFMO were synthesized and prepared.The effects of these biogenic Fe-Mn oxides and in-situ induction of biogenic Fe-Mn oxides on the stabilization of arsenic in soil were studied.Based on seed germination experiment and pot experiment,the plant toxicity and plant AS accumulation during the remediation process were analyzed,and the changes of soil microbial diversity and bacterial community structure before and after remediation were determined.The results showed that:1)The leaching experiment showed that BMO,BFO,BFMO and in-situ induced BFMO could effectively reduce the water-soluble arsenic and bioavailable arsenic content of arsenic in the soil.The water-soluble arsenic content after BMO treatment drops to 0.34 mg/kg,which was stable The biochemical efficiency was 80.69%,and the in-situ induction of BFMO could reduce the bioavailable arsenic content,and the stabilization efficiency was 76.41%;2)The phytotoxicity test results showed that BMO,BFO,BFMO,and in-situ induced BFMO stabilized cabbage The toxicity of the seeds was significantly reduced.In comparison,the root length and germination rate of the seeds were significantly improved compared to the original soil;3)The pot experiment results showed that the relative plant height of Chinese cabbage was increased compared with the original soil under the BFO stabilization treatment 67.88%,and the BMO treatment could effectively reduce the accumulation of arsenic in the pakchoi,which was 39.72%less than the original soil.The study also found that the accumulation of arsenic in the pakchoi increased when the BFMO stabilization treatment was induced in situ;4)Microbial diversity analysis showed that stabilization treatment could increase the abundance of microbial communities,but reduce the diversity of microbial communities;5)Analysis of microbial community structure showed that with the extension of the reaction time,the relative difference between Firmicutes and Acidobacteria The content gradually decreased,while the relative content of Proteobacteria and Actinomycota slowly increased.（3）The effects of different temperatures,water content and BFMO formation methods on the stabilization of arsenic in soil were studied,and the changes in soil microbial diversity and bacterial community structure during the restoration process were explored.The results showed that:1)p H and ORP did not change significantly after different treatments,EC and amorphous iron content increased with the increase of temperature,and amorphous manganese also increased compared with the original soil;2)the leaching experiment results showed that the same Under environmental conditions,the adsorption and fixation effect of in-situ induced BFMO on arsenic was significantly higher than that of ex-situ remediation.At30℃,the content of water-soluble arsenic and bioavailable arsenic in in-situ induced BFMO decreased by 51.85%and 42.98%respectively compared with the original soil;3)The morphological analysis results showed that the increase in temperature and the in-situ generation of BFMO can help fix arsenic in the soil and reduce its bioavailability and environmental risks;4)Temperature had little effect on the diversity of microbial community.The diversity of microbial community was significantly higher in ex-situ than in-situ.The contents of Proteobacteria,Bacteroidetes and Actinobacteria in the stabilized soil were significantly higher than that in the original soil,while the contents of Firmicutes and Intertrophic Bacteria were significantly decreased.