Pollution assessment of heavy metal accumulation in the farmland soils of Beijing's suburbs

In this study, we used GIS to assess heavy metal concentrations and their spatial variations in Beijing's suburban farmlands. The Beijing soil heavy metal background values (background values), the primary standard of the Chinese Environmental Quality Standard of Soil (primary standard), and the Environmental Quality Standard of Green Food Production Site (green standard) were used as the standards for assessing soil heavy metals. Results showed that the average Hg value was higher than that of the primary standard. The Ni and Pb values were lower than the corresponding background values. From the percentage area, the concentration is 100% area with As, more than 93% area with Cr, Cu, Pb and Zn, and 67% area with Cd and Hg, meeting the primary standard; over 97% area met the green standard. The calculated Nemerow index showed that less than 3% of the samples were slightly polluted, indicating good environmental quality. But the accumulated pollution of Cd and Hg was relatively high in some areas which was mainly affected by the high density of the industry. The farmland soils in Beijing suburbs were found to be suitable for farming, but a small percentage of the soils exceeded the green standard; Cd and Hg levels require special attention.