Status Of Heavy Metals In Soil Environmental Quality And The Potential Ecological Risks Assessment In Cultivated Soils In The Suburbs Of Beijing

This study was divided into two testing part. The cultivated soils in Changping, Tongzhou, Shunyi, Haidian, Chaoyang, Fengtaiand Daxing districts in the suburbs of Beijing were selected with758 sampling points to assess the accumulation status and potential ecological risk of six heavy metals of As, Cd, Cr, Cu, Hg and Pb. The individual pollution index, synthetical pollution index and potential ecological risk index were calculated with National Soil Heavy Metals standards (GB 15618-1995 Grade Ⅱ) and the background level of heavy metals in Beijing as the assessment criteria to explore the accumulation degree and the pollution status of soil heavy metals.The first testing experiment results showed that:The cultivated soils in Changping, Tongzhou, Shunyi, Haidian and Daxing districts in the suburbs of Beijing were selected with74 sampling points to assess the accumulation status and potential ecological risk of six heavy metals of As, Cd, Cr, Cu, Hg and Pb. The individual pollution index, synthetical pollution index and potential ecological risk index were calculated with National Soil Heavy Metals standards (GB15618-1995 Grade Ⅱ) and the background level of heavy metals in Beijing as the assessment criteria to explore the accumulation degree and the pollution status of soil heavy metals. Results showed that heavy metals concentration in the cultivated soils did not exceed the national standards Grade Ⅱ and could satisfy the safety qualification. Lead, Cu and Cd might have homology, but Cr had not similar source as the others. The six heavy metals in soils showed certain accumulation effects. Cadmium and Hg were in a higher potential risk grade, and especially Hg in Haidian district reached a very high potential risk level. About 17% of the soil samples had potential ecological threat to a certain degree. The high accumulation degree and potential ecological risk grade occurred in relatively developed districts like Haidian, Tongzhou and Changping. Analyses showed that human activities had influenced soil environmental quality in recent years. Therefore, we should take immediate regional monitoring management and related measures in accordance with the principles of territorial administration.To understand the effect of intense human activities in suburbs on environmental quality, we obtained 758 measurements of the heavy metals in the agricultural top soils of the Beijing suburbs. Multivariate statistical analysis and geostatistical analysis were used to perform a basic analysis of the heavy metal concentrations, the distribution characteristics and the pollution sources of the agricultural soils in these suburbs. The results indicated the presence of eight heavy metals in the agricultural soils of the Beijing suburbs at levels at least sometimes exceeding the background values:Cr, Cu, Pb, Cd, As, Hg, Zn and Ni. In particular,100% of the measured Cr concentrations exceeded the background value, and Cr, Cu, Cd, As, Hg and Zn, Pb and Ni were present at 1.96,1.27,1.54,1.12,1.95,1.27,0.87and 0.80 times their background values, respectively. The results of correlation, factor and spatial structure analyses showed that Cu, Cd, Pb and Zn were strongly homologous, whereas Hg and Cr showed a certain degree of heterogeneity. The analysis further indicated that the Cu, Cd, Pb and Zn pollutants were mainly associated with the road distribution and land use status; in addition to natural factors, different agricultural production measures in the various areas were important factors that affected the spatial distribution of the soil Cr concentration; the major sources of Hg pollution were the landfills for industrial waste and urban domestic garbage, and the spatial distribution of As was more likely to be affected by composite pollution. The distribution regions of the heavy metals indicated that except for Hg and Cr, the high heavy metal levels occurred in districts and counties that had higher organic matter concentrations, such as the northwestern and southeastern suburbs of Beijing. There was no significant Ni pollution in the agricultural soils of the Beijing suburbs.