Study On Source Of Harmful Elements Such As Lead In Soils From The Typical Area, Hunan Province

With the rapid development of economy, the accumulation of harmful elements such as lead, caused by human activity, has increased in the environment. The harmful elements of anthropogenic source are more hazardous. They also can enrich in the surface layer in the process of weathering. And this natural source always has less hazard, so it’s very important to identify the source of harmful elements in the soils. We study on two types of the soils in Hunan province in this paper, whose parent rocks are slate and granite. Two type soils are both collected in the areas of the background and the polluted areas, the content of harmful elements in the surface layer is similar to it in the deep layer in the areas of background and is higher than it in the deep layer in the polluted areas. We compare the physical and chemical indicators, mineral composition and the features of harmful elements of the profile soils in the two areas, which are the same parent rock, and explore how the physical and chemical indicators affect the distribution of harmful elements. We also identify the source of harmful elements such as lead by the method of enrichment factor, heavy metal species, magnetic susceptibility and lead isotope.Study shows that soil texture in the study area is controlled by parent rock type, pH and CIA are controlled by climate, and surface soil has high organic carbon and CEC. The clay mineral composition of the soil whose parent rock is granite includes kaolinite, illite, chlorite, and montmorillonite, while the clay composition of the slate soils includes kaolinite, illite and montmorillonite. In the slate soils, harmful elements in the surface layer are significantly higher than that in the deep layer soils in the polluted areas, while harmful elements in the surface layer are slightly higher than that in the deep layer soils in the background areas. In the granite soils, harmful elements in the surface layer are significantly higher than that in the deep layer soils in the polluted areas, while harmful elements in the surface layer are close to that in the deep layer soils in the background areas. We infer that the vertical distribution of harmful elements is mainly controlled by their own element geochemical behavior and also under the influence of soil properties.. Titanium was used as a natural reference element, we calculate the anthropogenic content of lead and cadmium in the profile soils by enrichment factor. Results show soils, which have different parent rock, both contain a large amount anthropogenic source in the surface soils. Activity ratio of harmful elements in surface soils in pollution area is significantly higher than that in background area. Magnetic susceptibility of the soils in polluted area is significantly higher than that in the background area, and there is a positive correlation to the content of harmful elements. Lead isotope research shows that lead isotope composition of surface soils in the polluted area is similar to that of the atmospheric deposition(dry and wet). By the study in this paper, we can infer that surface soils in the polluted areas are contaminated by human activities, and they have a high risk.