Spatial Variation And Risk Assessment Of Soil Heavy Metals In E-waste Dismantling Area

Soil heavy metal pollution is a hot issue in the studies of environmental pollution in the worldwide,whereas E-waste is a major source of heavy metals and has become the fastest growing waste. Wenling is the national famous e-waste dismantling area, and also a typical agricultural region. This research studied the spatial variation regulation and vertical distribution of soil heavy metals in the e-waste dismantling area in Wenling.based on geostatistics and Moran’s I,Methods. The main research conclusions are as follows:(1) Compared to the soil background values of Zhejiang province, the soil heavy metals, including Cd, Cu, Pb, Zn and Ni had shown a certain contamination accumulation characteristics in the study areas. Compared to the second level of Environmental Quality for Soil in China, the ratios of cleaning,slight cleaning( red line), light pollution, moderate pollution and severe pollution were 42%, 38%, 14%,4% and 2%, respectively. The concentrations of Cd, Cu and Ni, especially Cd, were relatively high in the study areas and had high heavy metals activation rates which was a threat to the agricultural production security. The e-waste dismantling industries of computers,televisions and electrical appliances are the main components of industries in Wenling city, which is the main source of e-waste leading to the soil heavy metals.(2)Cd, Cu, Pb and Zn all showed a moderate spatial autocorrelation, and strong spatial correlation with Ni. The Nugget of Cd,Cu,Ni,Zn and Pb were 0.391,0.364,0.079,0.515 and 0.214, respectively.High-high spatial-cluster areas were mainly distributed in Daxi Town and Zeguo Town, whereas Low-low spatial- cluster areas were mainly distributed in the northeast of the study area. The low-high outliers were mainly located closely to the high- high spatial-cluster areas.The spatial distribution of soil Cd and Pb showed a decreasing trend from northwest to Southeast, a decreasing trend from north to south of Cu, and a decreasing trend from northeast to southwest of Ni.The effective state of Cd, Cu,Pb and Zn in soils had similar spatial distribution patterns.(3)The concentrations of heavy metals Cu,Zn and Pb in soils of the heavy contaminated area, the moderate contaminated and the contrast area had a decreasing trend.The regularity of soil heavy metal contents including Cu、Pb and Zn in soil layers showed as:surface layer > bottom layer > middle layer,showed that soil adsorption and leaching effected the migration of heavy metal. Ni was mainlydistributed in the lower level, which mainly affected by parent material. Heavy metal Cu, Pb and Zn in the upper soil decreased at a faster rate than the lower soil layer, and the soil layer of 60 cm tended to be flatten, showed that the ability of soil adsorbing heavy metals was surface layer>lower layer. There were differences between abilities of heavy metal migration in the same section, with a result of Zn>Cu>Pb. The change trends of heavy metal contents in different sections were similar, and heavy metals contents was not decreased with the depth of the soil, but showed fluctuations with a certain range, which showed that the migration of heavy metals were affected by soil physical and chemical properties.