Enrichment characteristic and health risk assessment of heavy metals in soils derived from black shale in Chengkou area,Chongqing
Soils derived from black shale weathering in Chengkou area,Chongqing were sampled and analyzed for concentration and geochemical speciation of heavy metals to investigate enrichment characteristic and human health risk assessment.The results indicate that elevated concentrations of most heavy metals in the soils underlain by black shale exceed the national soil background values,even the risk screening values,especially for Mo,Cd,As and Tl.The results of carcinogenic risk assessment model show that most of the TCR values of As for children and adults exceed the risk safety limit;most of the TCR values of Cr for children and adults fall into the range of the risk screening value and the risk safety limit,with a few TCR values exceeding the risk safety limit;all the TCR values of Pb for children and adults are less than the risk screening value.Sequential extraction of carcinogenic elements shows that As(92.53%—99.51%),Cr(89.22%—97.87%)and Pb(62.59%—89.74%)in soils mainly exist in residual faction that is difficult to be directly available by organisms,indicating that the carcinogenic risks from As,Cr and Pb in soils are negligible.However,Cd mainly exists in exchangeable fraction(13.04%—36.82%),carbonate fraction(18.69%—30.11%)and Fe-Mn oxide fraction(17.79%—31.07%)in soils,showing high bio-availability.Because the total carcinogenic risk TCR values of Cd exceed the risk screening value,and some of the TCR values are close to or even exceed the risk safety limit.Therefore,Cd in our studied soils may pose potential carcinogenic risks to local humans.
black shale soilheavy metalenrichment characteristicgeochemical speciationcarcinogenic risk
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