Distribution of Heavy Metal Contents of Soils in an Industrial Area of Zibo, China

A systematic soil sampling including 32 topsoil samples and 80 subsurface soil samples were collected to investigate the distribution of heavy metal (HM) contents of soils in an industrial area of Zibo, China. Both the total contents and water soluble contents of 6 HM (Cu, Pb, Cd, Cr, As, Hg) were analyzed to assess the enrichment and mobilization ability of the elements. The relative cumulative frequency (RCF) curve and robust statistical methods were used to distinguish anthropogenic influenced samples from background for these elements. Results showed that the baseline and background calculated in this study was close to the background of Shandong province. The upper limits of baseline and background were preferred for evaluation criterions to quality standards in China. Comparing of the baseline with background shows an accumulation of HM in the surface soils. The subsurface soils were less contaminated than top layers. The enrichment of Pb and Hg is significant in this area. The main accumulation area located at the surface soils around small chemical plants and sewage ditches in the area. The water available fractions of HM in surface soils were unusually higher than subsurface soils, indicating a potential risk for natural leaching. Decontamination of HM was needed in the polluted area.