Contamination Characteristics And Health Risk Assessment Of Heavy Metals In A Typical Coal Mine City

Industrial activities such as coal mining and burning have caused a certain degree of heavy metal pollution in cities.Heavy metals are accumulated in soils,atmosphere,vegetables and grain crops,and threaten human health through multiple exposure pathways.Therefore,heavy metal pollution assessment and source apportionment can provide theoretical basis for comprehensive prevention and control of heavy metal pollution.In addition,the health risk assessment of heavy metals to population is helpful for protecting the soil environment safety and residents' health.Firstly,surface soils were collected from 6078 sites to analyze the pollution degree of 12 heavy metals.The average concentrations of heavy metals were higher than the local background values with the exception of Mn.Zn,Cu,Cd,Hg,Pb and As concentrations exceeded their corresponding Grade ? value by 1.46%,0.14%,37.96%,1.02%,0.6%and 6.73%of all samples,respectively.The single factor analysis of variance suggested that Zn,Cu and Cd contents were significantly higher in soils of farmland and land for construction than in woodland soils.And the contents of Hg,Pb,Mo and V were higher in the land for construction soils than in farmland and woodland soils.But the land uses exerted no influence on the As,Sb,Cr,Fe and Mn concentrations.ArcGIS,Spearman correlation analysis and PMF model were used for source apportionment.The results showed that Zn,Cu and Cd mainly came from agricultural and industrial activities.Pb,Sb,Hg and As mainly originated from vehicle emissions and coal combustion by atmospheric deposition.Industrial practices such as coal mining,chemical industries and metal smelting were the main sources of Hg,Cd,Mo and V.The parent materials played a vital role in Mn,Cr and Fe enrichment in soils.Secondly,17 atmospheric depodition samples were collected and the contents of Hg and Cd were analyzed.The results sheowed that atmospheric Hg and Cd deposition fluxes in the city exhibited an obvious spatial variability.And the content in the industrial area was significantly higher than that in agricultural and forest area.Curvilinear regression analysis suggested that the atmospheric Hg deposition fluxes were positively related with Hg contents in soils(R2 = 0.86359,P<0.001).In addition,atmospheric Cd deposition fluxes were also positively correlated with Cd contents in soils when the farmland soil sample sites were not included in the fitting(R2 = 0.82458,P<0.001).When they were included,there was no significant relationship between them(R2 = 0.2039,P = 0.05).The accumulation of Hg and Cd concentration in topsoil due to the influence of atmospheric deposition will increase rapidly in the next 30 years.After 30 years,the Hg and Cd concentration will increase slowly.Hg and Cd will almost completely deposit into the surrounding soils within the next 30 years.Finally,a total of 197 vegetable,grain crop and soil samples were collected in this study to analyze the enrichment ability of five heavy metals.The results showed that the enrichment ability of leafy vegetables to 5 heavy metals was higher than that of grain crops,and the order of enrichment coefficient was Cd>Hg>Pb?As>Cr.Non-carcinogenic risk assessment of heavy metals in dietary pathway to exposure population showed that the non-carcinogenic exposure risk of vegetables,eapecially leafy vegetables,was higher than that of grain crops.Non-carcinogenic risk was mainly derived from As and Cd.Non-carcinogenic risk assessment of heavy metals intake in farmland soil showed that whether one of heavy metals or five heavy metals were taken into account,the non-carcinogenic risk of heavy metals was low for both adults and children.The non-carcinogenic risk of heavy metals for children was significantly higher than that for adults,especially Pb and As.Carcinogenic risk assessment of heavy metals intake in farmland soil showed that the order of potential carcinogenic risk for adults was Cr>As>Cd,which was less likely to cause cancer risk.However,when three heavy metals were considered at the same time,they may cause potential carcinogenic hazards to exposed children,and the main contributing sources are As and Cr.