Accumulation Characteristics Of Typical Heavy Metals In Soils In Mining Downstream Area

In last three decades, the extent and range of pollution of heavy metals in agricultural soils was becoming more and more serious, and had become one of the main environmental problems in food security of the world. It had aroused the concern of more and more of scientists from environmental and soil sciences. The mining types in China was complex with widely distribution in all the country, mineral resources development activities was aware of the main causes bringing about pollution of heavy metals in atmospheric, soil and groundwater environments in the mining downstream areas. In order to understand the pollution characteristics and spatial distribution patterns of heavy metals in soils of cultivated lands in the downstream areas of representative minings in the Shaoxing city, three agricultural production sites located at mining downstream areas (including Lizhu iron mine, Pingshui copper mine and Dongguan Yinshan lead-zinc mine) were selected to characterize the concentrations and spatial distribution of heavy metals (Cu,Zn,Pb,Cd,As,Hg,Cr) in the soils, agricultural products and surface waters, and to evaluate pollution risk of the soils with heavy metals. The purpose of the study was to provide the foundation for reasonable utilization and remediation of soils near the mines. The following results were obtained from the study.1. Farmland soils in all three mining downstreamareas were generally contaminated with heavy metals, the extent of heavy metal pollution decreased with distance from the mines. The change in concentrations of heavy metals in the surface soil was the most obvious. The changing extent of different heavy metals in the soils with the distance varied and decreased in the order of Cu, Zn, Pb, As> Cd> Hg, Cr. Vertical migration of Cd and Cu in the soil profile is relatively obvious, while the that of Pb is relatively weak.2. Pollution evaluation of heavy metals in the soils using Nemerow comprehensive pollution index method showed that mean comprehensive index of heavy metals in farmland soils of the downstream area of Lizhu iron ore mining was1.07, and most of soils in the area had reached slight to moderate pollution degree. Mean comprehensive index of heavy metals in farmland soils of the downstream area of Pingshui copper mine mining was2.92, and most of soils in the area had reached moderate or above pollution degree. Mean comprehensive index of heavy metals in farmland soils of the downstream area of Dongguan Yinshan lead-zinc nine was20.23, and it had severe pollution degree.3. There were obvious differences in pollution types of heavy metals in farmland soils among three mining downstream areas. Soils in downstream area of Lizhu iron ore mining was mainly comanimated with Cd and Zn, those of Pingshui copper mine mining was mainly comanimated with Cu, Cd and Zn, and those of Dongguan Yinshan lead-zinc nine was mainly Pb and As. The differences in spacies of main heavy metals of the polluted soils were related to their deposits. The concentrations of Cr and Hg in the farmland soils of downstream areas of all three mines were relatively low, and their pollution was not obvious.4. Analysis results of heavy metals in agricultural products and surface water from part of the farmland production sites showed that contents of heavy metals in agricultural products exceed their safety standards, and were not suitable for growing food crops. Surface water also has the problem with heavy metal pollution. 5. Based on above results, it was suggested that increased efforts of environmental protection measures should be adopted to control the release of heavy metals from the mines. And combined action of both adjustment of land use and treatment of polluted soils should be carried out to ensure the safety of agricultural products in the downstream areas of minings. For formland with serious pollution of heavy metals, land use should be changed from grain crops to non-grain crops. And for farmland contaminated with low concentrations of heavy metals, both agricultural and chemical measures could be used to improve soil quality.