Characteristics Of Soil Heavy Metal Pollution And Human Health Risk Assessment Near Coal Mines Of Shanxi Province And The Effect On Soil Nematode Community Structure

Objective:Heavy metal is one of the most important pollutants in farmland soil in China,which has negative effects on soil animals,plants,microorganisms,and even on animals and humans through food chain transfer.The study aims at:1.clarifying the content,pollution level and ecological risk characteristics of heavy metals,and exploring the main pollution sources and contribution proportion of soil heavy metals in farmland near coal mines of Shanxi Province;2.clarifying the heavy metal content and migration accumulation characteristics of maize in farmland near coal mines,establishing the prediction model of maize heavy metal content based on soil heavy metal content and studying the human health risks exposed by soil heavy metals and maize heavy metals;3.clarifying the soil nematode abundance and community characteristics in spring and autumn near coal mines of Shanxi Province,and exploring the effect on soil nematode community structure from soil heavy metal pollution.Methods:1.This study had selected the farmland near the coal mining area of 7 cities(Shuozhou,Xinzhou,Gujiao,Linfen,Yangquan,Changzhi and Jinzhong)in Shanxi Province according to the production capacity of coal mines,and collected 9 soil samples at each sampling site using the snake sampling method.There were 1080 surface soil samples and 120 composite samples,with a total of 120 sampling points.The concentrations of 11 soil heavy metals(Cr,Ni,As,Mn,Cd,Pb,Hg,Zn,Cu,Sb and Se)were determined by inductively coupled plasma mass spectrometry(ICP-MS)and the soil heavy metals contamination status was evaluated by the contamination factor,Nemerow index,pollution load index and potential ecological risk index.Correlation analysis was used to study the correlation between soil heavy metals and principal component analysis was used to qualitatively explore the sources of soil heavy metal pollution;absolute principal component score-multiple linear regression(APCS-MLR)model was used to quantitatively explore the contribution rate of pollution sources to soil heavy metals.2.The contents of 11 heavy metal elements in maize samples were determined by ICP-MS,among which 3 elements were not detected.The concentrations of 8 maize heavy metals(Cr,As,Mn,Cd,Pb,Hg,Zn,Cu)were analyzed and the migration and accumulation characteristics of heavy metals in maize were explored by the biological accumulation coefficient.The prediction model of maize heavy metal content was established by multiple linear regression to analyze the influencing factors.Human health risk model was used to calculate non-carcinogenic and carcinogenic risks exposed by soil heavy metals and maize heavy metals,and determine the impact of variation and uncertainty on the results of health risk assessment.3.Soil samples near coal mines were collected in 7 cities of Shanxi Province during spring and autumn to identify soil nematode genera by morphological observation,and the quantity and distribution of nematode genera and four trophic groups were counted.The soil nematode community structure was analyzed by the abundance,ShannonWiener diversity index,Pielou index,maturity index,nematode channel index,enrichment index and structure index.Multiple linear regression model was used to analyze the relationship between nematode community index and soil heavy metal content,along with the effect on soil nematode community structure from soil heavy metal pollution.Results:1.The results showed that the concentrations of heavy metals Pb,Hg,Mn and Zn in96.25%,80.42%,74.17% and 71.25% of the samples exceeded the background values of heavy metals in Shanxi Province,respectively.Except for As,Sb and Cr,the contamination factors of other heavy metals were all greater than 1,soil Hg pollution was severe,and Se,Pb,Cd,Zn,Ni,Mn and Cu pollution was moderate;pollution load index values showed that the soil was pollution-free;Nemerow index value indicated heavy pollution of compound soil heavy metal;among all ecological hazards of soil heavy metals,the ecological risk of Hg was high,the ecological risk of Cd showed moderate,and the ecological risk of other heavy metals showed mild;the potential ecological risk index showed that the potential ecological risk of soil heavy metals in the study area was at a medium level.The results of source analysis showed that coal mining was the main source of soil heavy metals,except in GJ and XZ area,where natural activities were the main sources.2.The average concentration of maize Zn and Cr exceeded the standard.Maize had the highest bioenrichment ability for Cr,followed by Zn.There was a strong correlation between heavy metal content in maize and soil.The heavy metal Cd in maize was the most affected by soil heavy metal,followed by Cu.Soil heavy metals,mainly Cd,Mn,As and Cu,had synergistic and antagonistic effects on 8 heavy metals in maize.The results of soil health risk assessment showed that there was little non-carcinogenic threat to human health exposed by soil heavy metal,and the carcinogenic risk was within the acceptable range.Children were more susceptible to non-carcinogenic risks and carcinogenic risks than adults exposed by heavy metal pollution.Hand-oral ingestion was the main exposure route for non-carcinogenic risk and carcinogenic risk.Sensitivity analysis result showed that soil As and Ni concentrations contributed more to noncarcinogenic health risks and carcinogenic health risks in the population,respectively.Heavy metals in maize posed non-carcinogenic and carcinogenic threats to the health of the local population.Maize As and Cr concentrations contributed the most to the noncarcinogenic risk and carcinogenic risk through maize ingestion,respectively.3.A total of 31 nematode genera were identified in this study,including 13 bacterivores,6 fungivores,9 plant-parasites and 3 omnivorous and carnivorous.The total abundance,relative abundance of plant-parasites and fungivores,maturity index of plantparasites and structure index were higher in autumn,while the relative abundance of bacterivores,channel index,enrichment index,Pielou index and Shannon-Wiener diversity index were higher in spring.The 11 soil heavy metals had synergistic and antagonistic effects on the indices of nematodes community,mainly including the total abundance of nematodes and the relative abundance of bacterivores.The contents of five heavy metals(Zn,Cr,Mn,Pb and As)in soil played an important role in predicting the total nematode abundance.Conclusion:The concentrations of heavy metals Pb,Hg,Mn and Zn in soil had significantly exceeded the background values,which could not be ignored.Coal mining was the main source of soil heavy metals,except in GJ and XZ area,where natural activities were the main sources.Soil As and Ni and maize As and Cr contributed the most to the health risks of local residents.Soil heavy metal has a significant influence on nematode community structure.Nematode channel ratio,diversity index and total abundance of nematodes could predict soil heavy metal content and ecological risk,with high prediction accuracy.