Biological Effects Of Carbon Nanomaterials On Soil Microorganisms Under Different Exposure Scenario

With the industrialization of carbon nanomaterials（CNMs）,various forms of CNMs have entered our lives through different ways.A large number of CNMs enter the soil environment through various ways during their production,use and treatment.Current studies on the effects of CNMs on soil microorganisms mainly focus on the effects of single exposure to high concentration of CNMs on soil microorganisms.However,repeated exposure to low concentrations of CNMs in natural environments or combined exposure to other environmental pollutants are more likely to occur.Biological effects of CNMs on soil microorganisms under these exposure modes are limited and need to be further studied.In this study,we used Biolog-Eco plates and high-throughput sequencing technology to investigate the effects of multi-walled carbon nanotubes（MWCNT）,graphene（GR）and fullerene(C₆₀)on the carbon metabolism and structure of soil microorganisms under single and repeated exposures.In addition,we used saturated soil columns to study the effects of multi-walled carbon nanotubes（MWCNT-COOH,MWCNT-OH and MWCNT-NH₂）modified with different ligand on the migration and transformation of sulfathiazloe（STZ）in soil and the effects of their combined exposure on the metabolism of soil microbial communities.The main research contents and results are as follows:（1）The Biolog-Eco plate was used to determine the metabolic status of soil microorganisms on 31 carbon sources under single,two and three times CNMs exposure.The heat map,PCA and similarity analysis showed that compared with the type of CNMs,the carbon metabolic activity of soil microbial community was more affected by the type of CNMs exposure.The two times and three times exposures of CNMs made soil microorganisms gradually form an adaptive mechanism to reduce the stress intensity caused by pollution,and the impact of CNMs on the carbon metabolism capacity of soil microorganisms was lower than that of single exposure.Compared with C₆₀ and MWCNT,GR had a stronger inhibitory effect on soil microbial carbon metabolism.（2）High-throughput sequencing of single and multiple CNMs exposed soils summarized the relative abundance of system types at the gate level.Acidobacteria,Proteobacteria,Actinobacteria,Chloroflexi,Bacteroidota and Gemmatimonade were found these 6 main phyla account for more than 85%of the total bacterial population.Most bacterial species were reduced under single and repeated exposures to CNMs,and in particular the relative abundance of Acidobacteria,Gemmatimonade and Bacteroidota in MWCNT and C₆₀ soils was much lower under single exposure than under repeated exposures.However,the relative abundance of proteobacteria increased under CNMs exposure,indicating high resistance and high carbon mineralization rates in the soil.（3）MWCNT-COOH,MWCNT-OH,MWCNT-NH₂ and STZ were placed in saturated soil columns to study:（1）The effects of three multi-walled carbon nanotubes on the migration and transformation of STZ in soil;（2）The concentration of STZ in soil was analyzed by high performance liquid chromatography.The results showed that more than half of the STZ in the soil environment could be removed by fixation or degradation within30 days under natural conditions.In the control group,the concentration of sulfathiazole decreased with the increase of soil depth.In the treatment group of multi-walled carbon nanotubes modified with different ligands,most of the STZ were located in the first layer,indicating that the functionalized multi-walled carbon nanotubes had a certain adsorption capacity for STZ,thus reducing the downward transport of STZ.Moreover,the adsorption capacity of MWCNT-OH for STZ was greater than that of MWCNT-COOH.（4）The effects of MWCNT-COOH,MWCNT-NH₂,MWCNT-OH and STZ combined exposure on the metabolic function and structure of soil microbial communities were investigated by Biolog-Eco plate and high-throughput sequencing.For AWCD values,MWCNT-COOH,MWCNT-NH₂,MWCNT-OH and STZ combined exposure had no significantly difference from the soil exposed to STZ alone,but had significantly difference from the soil exposed to MWCNT alone,indicating that the toxicity of the combined exposure of MWCNT and STZ mainly depended on the toxicity of STZ.MWCNT adsorption of STZ had little effect on soil microbial carbon metabolism.MWCNT and STZ exposure increased the relative abundance of Proteobacteria in soil and decreased the relative abundance of Acidobacteria in soil.We found that MWCNT-COOH,MWCNT-OH and MWCNT-NH₂ combined with STZ inhibited the carbon metabolism of soil microorganisms and decreased the diversity of soil microorganisms at the same time.