Spatial Probability Human Health Risk Assessment Of Heavy Metals In Urban Topsoil Associated With Different Land Use

Urban soils play an important role in urban ecological environment, and it is not only the exchange of various contaminations, but also a potential source of secondary pollution in the urban ecological environment. With the characteristic of persistence, concealment, enrichment, and ecological and health risk, soil toxic metals contamination is particular concerned by the government and scholar at home and abroad. By conducting human health risk assessment of urban soil toxic metals, we can get knowledge of the urban soil environment quality and the potential risk to urban residents. And the human health risk assessment is of great importance to environmental management decision making.This dissertation firstly summarized the source, hazard and the pollution situation of urban soil toxic metals, and then gave an overview of the application of Geostatistics and Geographic Information System in the spatial distribution assessment of soil toxic metals. Next, the thesis discussed the situation of urban soil toxic metals health risk assessment. At last, based on the problems in the process of human health risk assessment of soil toxic metals, the dissertation provided a modified method of human health risk assessment, which integrates the spatial patterns of toxic metals simulated by sequential indicator simulation, different exposure models and local current land uses extracted by remote-sensing software into a dose-response model for human health risk assessment of toxic metals.In this dissertation, we took the soil Cr and Pb in Xiangjiang New District as a case study to prove the feasibility and efficiency of the modified spatial possibility human health risk assessment of toxic metals. The pollution levels of Cr and Pb in soil were first preliminarily studied by using geo-accumulation index, then the non-carcinogenic risk of soil Cr and Pb in Xiangjiang New District was evaluated by using the modified spatial possibility human health risk assessment of toxic metals. According to the evaluation results, the hazard index(HI) of Cr and Pb overall the Xiangjiang New District did not exceed the accepted level to adults. While to children, Cr and Pb exhibited hazard index(HI) higher than the accepted level around some areas. The assessment results indicated that Cr and Pb should be regarded as the priority pollutants of concern in Xiangjiang New District. According to the E-type risk map(average risk) of toxic metals, this dissertation firstly divided the Xiangjiang New District into A, B and C regions with HI(A)>HI(B) >HI(C). E-type HI values of Cr and Pb in region A exceeded safe level(1). E-type HI values of Cr and Pb in region B were between 0.5 and 1. And in region C, the E-type HI values of Cr and Pb did not exceed 0.5. With the limited budget consideration, a further layering based on the probability of risk in region A was suggested. The areas with high probability(>0.95) in region A were suggested to be the first priority areas for both Cr and Pb. While the areas with probability between 0.85 and 0.95 in region A were suggested to be the secondary priority areas. Finally, a preliminary hierarchical risk management policy was suggested in the dissertation. The modified method was proved useful due to its improvement on previous studies and calculating a more realistic human health risk. It can provide more comprehensive information to policy makers and help them make a more flexible, scientific, reasonable and effective risk management strategy.