Assessment of soil heavy metals pollution in the chemical industrial areas of Nanjing peri-urban zone

To investigate influences of intensive human activities on soil environment dynamics in the peri-urban zone, it was conducted in an area of 20km2 in the vicinity of the Nanjing Chemical Industrial Park. Totally 54 samples of topsoil were collected in an aerophoto-based gridding design and the concentrations of heavy metals Cu, Zn, Pb, Cr, Cd, Hg and As in the soils sampled were analyzed. First of all, the results of statistical analysis indicated that concentrations of the heavy metals detected in the studied soils did not exceed the safety values of national soil quality criteria with the exception of Hg. Although the concentrations of a few metals in the some sampled sites slightly exceeded their average background values, the spatial variations of the concentrations of those metals, however, paralleled the pedo-geochemistry of the study area. Hg concentration in the soils from 37% of the sampled sites was higher than environmental safety criteria according to the national soil quality standard, suggesting that Hg might be considered as a dominant element causing soil heavy metal pollution in the area. Furthermore, the spatial variability of soil pollution in terms of heavy metals was investigated by combining pollution evaluating with geostatistical methods, and potential sources and possible entrance paths of heavy metal pollutants in those plots with measurable pollution were discussed. It was preliminarily concluded that intensive application of metal-containing agrochemicals during long-term vegetable planting was the major cause leading soil heavy metal pollution. The possibility, however, that irrigation by contaminated surface water and land application of organic composts derived from a variety of wastes and sludge also significantly contributed to soil heavy metal pollution in some cases, could not be excluded.