Vertical distribution of heavy metals in soils and its influencing factors from a zinc smelting site
Six soil profiles were collected from an abandoned zinc smelting site in Hunan Province to study the vertical distribution characteristics of contents and chemical fractions of Cd,Cr,Pb,and Zn,and the influence factors of soil physical and chemical properties were analyzed.The results showed that high content of heavy metals was predominately accumulated in 0-3 m soil layer,and decreased with the increase in soil depth.The Cd content in profiles was high and migrated into the deep soil.The geomean contents of Cr,Pb,and Zn in soil profiles were decreased significantly followed the order of 0-3 m＞3-6 m＞6-8 m(P＜0.05).According to BCR(European Community Bureau of Reference)sequential extraction analysis,soil profile Cr content was predominated with residual fraction,accounting for 79.2%—93.0%of total content.The percentage of acid soluble fraction Cd and Zn,residual fraction Pb was increased with the soil depth increasing,indicating that high potential migration risks of Cd and Zn in soil profiles.The SEM-EDS(scanning electron microscope-energy dispersive spectroscopy)and XRD(X-ray diffraction)analysis results showed that there were much peaks of aluminosilicate minerals and SiO2 in soil.The mineral phase of ZnO were found in 1-1.5 m depth soil from point S6,and that of ZnCO3 appeared at 4-5 m and 6-8 m soil depth from point S3.This result indicated that critical smelting activities would cause the accumulation of Zn in soil.There was significant relationship between total content and chemical fractions of heavy metals in soil.Soil chemical properties of amorphous Fe2O3 promoted the migration of Cd,Pb and Zn in soil profile.The vertical distribution of heavy metals was controlled by pollution sources and soil physical and chemical properties.The results would provide scientific basis for effective prevention,control and remediation of heavy metal contaminated soil from smelting sites.
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