Ecological Risk Assessment And Bacterial Community Characteristics Of Heavy Metals In Soils Of A Chromium Residue Plant In A Karst Area

Guizhou Karst region is located in the south of China and belongs to the world Natural Heritage center.It is rich in microbial species,but its ecological environment is very fragile and vulnerable to damage.Once damaged,it is difficult to recover.Due to the rapid and accelerated development of modern science and technology in China and regions,most of the factories have to be transformed or closed down.However,the huge industrial heavy metal waste pollution left by the factories for a long time has led to the increasingly severe problem of heavy metal pollution in this region.At present,there is a large demand gap for heavy metals in the country.However,high concentration of free hexavalent chromium and other heavy metals will be produced in the production process,which will pose a threat to people’s health and also pollute the ecological environment.Is karst land within the scope of the ecological environment in the world today and degradation,severely damaged areas in the region of heavy metal pollution of the waste chromium slag factory will bring in karst areas of large negative economic effects,in order to completely rebuild this land structure and land ecological system,not only must the comprehensive recovery of forest vegetation,more thorough reconstruction of the surface soil,It is also necessary to put forward more reasonable and economic countermeasures for soil pollution and microbial ecosystem restoration as soon as possible.It is not common to use soil microbial and enzyme activities to reveal soil properties in karst areas.In this study,soil samples from five typical regions were collected and the relationship between surface soil microbial diversity and major environmental factors was revealed by high-throughput sequencing technology.In this paper,the distribution characteristics of heavy metal pollution in soil and the harm of heavy metal pollution in soil were studied by taking waste chromium slag plant and its surrounding surface soil as the research object.The soil enzyme activity and fungal community characteristics in different polluted soil areas of chromium residue plant were studied.The changes of soil quality in different areas of chromium residue plant were explored,and the main environmental factors affecting soil enzyme activity and fungal community were revealed during the production process of waste chromium residue plant,which provided scientific reference for pollution control of chromium residue plant.The results show that:（1）The contents of Cu,Pb,Zn,Mn,Ni and other metals in the main heavy metal indexes are determined to be within the limits of 128.08-18.17,97.69-42.54,2121.67-131.75,859.58-401.42,216.58-27.83 respectively.Compared with the local soil background values（Cu:79.0mg/kg,Pb:67mg/kg,Zn:139 mg/kg,Cd:0.71mg/kg,Ni:33 mg/kg,Mn:846 mg/kg）of the abandoned chromium slag plant,the six heavy metals all exceeded the background values.According to the analysis of nemerow comprehensive pollution index,five different land use types were heavily polluted soil（P_N>3）,and the order was CA（8.09）>FW（7.28）>UR（6.99）>IF（6.55）>FO（5.92）.From the correlation study and principal component analysis,it can be concluded that Cr and Ni,Zn and Cu,Pb,Zn have the same main pollution sources.The main source is the deposition and migration of heavy metals accumulated in chromium slag plant for a long time.（2）The contents of soil organic matter（SOM）,total phosphorus（TP）,available phosphorus（AP）,available nitrogen（AN）and ammonium peptide nitrogen（NH₄⁺-N）were the highest in the downstream and the lowest in the workshop.Catalase（CAT）,acid phosphatase（ACP）,urease（UE）and sucrase（SC）activities were the lowest in workshop area.The peroxidase（POD）activity was 40.441μmol·d^-1·g^-1,6.350μmol·d^-1·g^-1,20.169μg·d^-1·g^-1 and 4.002 mg·d^-1·g^-1,respectively.In general,soil urease and sucrase activities and soil catalase and other active enzymes were most complex and sensitive to the change and trend of soil heavy metal pollution.When some heavy metal pollutants with some elements in common soil fertility of soil enzyme activity,its content is more obvious tend to mainly by the characteristics of physical and chemical and mechanical properties of the soil itself significantly influence,the content of soil,available p in the soil,p H is a significant impact on soil enzyme activity of several important physical and chemical factors,The significant changes of soil enzyme activity and soil physical and chemical properties were in the same direction and driving.In conclusion,the input of nitrogen and phosphorus should also be given priority in the management of soil remediation in abandoned industrial factories in karst areas,providing an important scientific proof basis for soil remediation projects and ecological environment protection planning in mining areas that have been damaged by heavy metal pollution.（3）At phylum level,Actinobacteria,Proteobacteria,Acidobacteria and Chloroflexi were the dominant species;At class level,Alphaproteobacteria,Actinobacteria,Vicinamibacteria,Gemmaproteobacteria and Chloroflexi are the dominant species.In general,under the interaction of heavy metals and soil environmental factors,microbial abundance was more likely to be affected by soil environmental factors,and soil total phosphorus（TP）,nitrate nitrogen（NO₃⁺-N）and most heavy metal elements were the main influencing factors of microbial change.Actinobacteria is similar to most heavy metals and has the strongest tolerance to heavy metals.Metal element Pb has certain selectivity to the growth and reproduction of bacteria,that is,different metal elements have different effects on soil bacteria groups.In conclusion,the input of nutrient elements and the selection of dominant strains should be considered in the restoration and treatment of abandoned plant areas.In this paper,through in-depth analysis,the change of microbial community and internal driving factors in heavy metal polluted environment were understood,which provided a theoretical basis for the treatment of contaminated soil in waste chromium slag plant.On karst area polluted by heavy metals on soil physical and chemical properties and microbial diversity research,can to a certain extent,reflect the soil polluted by heavy metals after the condition of soil properties and restore the balance of ecological system,easy to design more targeted for contaminated soil in the future the repair plan of ecological system of governance to improve the contaminated area.