Source Apportionment Of Heavy Metals In Soil And Their Effects On Bacterial Community In Lujiang Mining Area,Anhui Province

Lujiang County is a rich area of non-metallic mineral resources in Anhui Province,especially the alum mine in Fanshan Town,Lunan area.Alunite is rich in mineral resources and has a long mining history.The’ three wastes’ heavy metal pollutants produced in the process of mining,mineral processing and smel ting pose a great threat to the surrounding environment of the mining area and the safety of people’s lives and property.Therefore,it is of great significance to carry out the analysis of heavy metal pollution sources and the study of bacterial community and diversity in mining soil to control heavy metal pollution and establish ecological restoration system.In this study,50 typical characteristic points were determined by the diffusion of Dafan Mountain as the center.By measuring the physical and ch emical proper ties of soil and the content of heavy metals,the pollution status and pollution sources of soil heavy metals in the mining area were scientifically evaluated.Illumina MiSeq high-throughput sequencing technology and PICRUSt function prediction analysis were used to explore the diversity and ecological function of soil bacterial communities with different levels of heavy metal pollution.The main conclusions are as follows:(1)The average pH values in the study area were 4.12 in the 0～10 cm soil layer and 4.09 in the 10-20 cm soil layer.Most of the total potassium(TK)and total phosphorus(T P)were at rich levels;most of the total carbon(TC),total nitrogen(TN)and organic matter(OM)were at medium and low levels.The average contents of As,Cd,Cu,Mn and Ni were 47.38,2.03,30.89,77.76,4.08 mg/kg in the 0～10 cm soil layer,and 50.62,2.24,30.82,71.39,3.62 mg/kg in the 0～10 cm soil layer.Except for Mn and Ni,the average contents of As,Cd and Cu were higher than the soil background values in Anhui Province.The median values of As and Cd in 10～20 cm soil layer were 1.28 and 7.17 times of the soil pollution risk screening values.The average contents of As and Cd increased by 3.24 and 0.21 mg/kg with the increase of soil depth,respectively,indicating that As and Cd pollution in soil was serious and different degrees of enrichment occurred.(2)The spatial distribution characteristics of five heavy metals in different layers were analyzed by ArcGIS ordinary Kriging interpolation method.It was found that the contents of As and Cd in 0～10 cm soil layer were significantly lower than those in 10～20 cm soil layer,and the high contents were concentrated in the northeastern and southern regions of the study area.The content of Cu in 0～10 cm soil layer was significantly higher than that in 10～20 cm soil layer,which may be due to the weak infiltration capacity of Cu or the upward migration.The spatial distribution of Mn and Ni contents in 0～10 cm and 10～20 cm soil layers was extremely similar,and the high value areas were concentrated in the northern and western regions of the study area.(3)Based on the absolute factor-multiple linear regression model(APCS-MLR),UNMIX and positive matrix factor molecular method(PMF)model,the source analysis was carried out from the aspects of source type,source contribution and applicability.Four major pollution sources of heavy metals in the soil of the study area were found.Mn and Ni represent coal-fired sources,with a contribution rate of 38.15%.Cd represented traffic sources,with a contribution rate of 20.62%.As represented natural sources,with a contribution rate of 24.28%.Cu represents the source of atmospheric deposition,with a contribution rate of 16.95%.In a word,human activities are the main pollution sources of soil environmental pollution in the study area.(4)According to the evaluation results of single factor pollution index,geoaccumulation index and potential ecological risk index,the pollution degree of five heavy metals from high to low was Cd>As>Cu>Ni>Mn.The Cd pollution in the soil of the study area was the most serious,and Mn and Ni were at a pollution-free level.The average value of Nemerow comprehensive pollution index in the whole study area is 16.29,which is at the level of severe pollution.The high ecological risk areas are mainly concentrated in the southern and eastern regions of the study area.(5)The results of health risk assessment showed that hand-mouth intake was the main way of soil heavy metal exposure in the mining area.The non-carcinogenic risk of children was greater than that of adults.The carcinogenic risk values of adults and children exceeded the threshold(1×10-4),and the non-carcinogenic risk and carcinogenic risk of heavy metal As were the highest.The health risk assessment results based on the PMF model found that the probability of non-carcinogenic and carcinogenic risks of different pollution sources to adults and children is roughly similar.Effective control of natural sources is extremely important for preventing health risks for adults and children.(6)There were significant differences in soil bacterial communities under different levels of heavy metal pollution,and the contents of TK,TN and OM were the highest in the medium pollution level(L1).The dominant soil bacterial communities at the phylum level were Proteobacteria,Acidobacteria and Firmicutes,respectively.At the genus level,they are Escherichia-Shigella,Terracidiphilus and Streptococcus,respectively.In addition,RDA and correlation network analysis showed that As,Cd,TP,TK and pH were important environmental factors affecting soil bacterial community structure.PICRUSt function prediction analysis showed that the soil bacteria in the bauxite mining area mainly involved 47 sub-functions such as carbohydrate metabolism,transcription,energy metabolism,cell growth and death of secondary product metabolism,showing functional richness.