Identification, Risk Assessment And Elemental Metrology Of Harmful Heavy Metals In Multi-media Environment In Typical River Valley City Of Xining

The city is the product of the development of human civilization. The development of cities facilitated economic and social development of mankind, at the same time, it brought a series of urban environment pollution and damage, and the structure and function of the balance of the entire biosphere are even affected. Industrial development, urban residents' daily activities and transportation take a lot of heavy metal pollutants into the urban environment. Characteristics of the metal pollutants is concealment, persistence, refractory, which results in the accumulation of heavy metals in urban environment and the threat to human health, directly or indirectly, through the soil, dust, water and other environmental media or food chain. Therefore, to study the content, pollution status, distribution law of heavy metals in a variety of urban environmental medium has an important meaning to carry out environmental risk assessment, pollution prevention and control and management of heavy metals in urban environmental media.This research studyed on heavy metal content and spatial distribution, potential ecological risk as well as population health risk and geochemical behavior characteristics and ecological effects of pollution with urban soil, street dust and water as research medium in Chinese western typical valley city-Xining,using multivariate statistics, spatial analysis, ecological risk assessment, population health risk assessment. In addition, the heavy metal content of different media were compared, and it analyzed the situation of heavy metal distribution in different media. The main conclusions are as follows:(1) The heavy metals Bi, Co, Cr, Ga, Pb, Sb, Sn, Th, U and Y in Xining's soil and street dust exceeded the background value. This indicates that most of the heavy metals have been affected by varying degrees human activities.(2) Potential risk assessment indicated the ecological risk of harmful heavy metals of Sb in soil was at strong level, and other heavy metals were at slight level. In the street dust, Sb was also at strong level, Cr and Pb were at middle level, and other heavy metals were at slight level. Cr, Pb and Sb are major environmental pollution factor.(3) The result of human health risk assessment showed that the total risk of the non-carcinogenic risk of Cr, As and Sb in soil and street dust was larger. The non-carcinogenic total risk to children of the three exposure routes in street dust exceeded the threshold value of 1.0, which indicated that the street dust in Xining pose a threat to child health. The total carcinogenic risk of different heavy metals under the mouth, respiratory and skin exposure pathways vary widely, as well, the total carcinogenic risk of the same heavy metal under different exposure pathways were also significant. The non-carcinogenic risk of hand-mouth intake was the highest and in this pathway the non-carcinogenic risk of Cr in street dust to children exceeded the threshold value which would cause harm to the health of children and more attentions should be paid.(4) This paper analysed the possible source of heavy mentals in soil and street dust with spatial analysis, correlation analysis and factor analysis. The results revealed the sources are complex, including transportation sources, natural sources, industrial sources, coal and oil-fired sources.(5) The heavy metals concentration in Xining water did not exceed the corresponding standards, but environmental risk assessment showed that the mean value of carcinogenic risk of Cr is 5.83×10-5/a, exceeding the ICRP threshold of acceptable risk level, which should cause the attention of risk decision-making departments. The mean value of carcinogenic risk of Cd is 2.41×10-7/a, which is within an acceptable risk level, however, there existed partial samples risk exceeding the threshold range which also need attention.(6) Correlation analysis of heavy metals in soil and street dust showed that Zn had a very significant positive correlation, which indicated that Zn had the same sources of pollution and there may be some kind of conversion mechanism. The content of heavy Metal Cr, Cu, Pb in urban street dust, soil and wate sorted by size is city street dust> urban soil> urban water and the enrichment factor of Cr is the highest in the three heavy metals.