Heavy Metals In Urban Topsoil:Hierarchical Health Risk Assessment And Quantitative Management System

Urban soils play a core role in regional environment media. Excessive inputs of heavy metals into urban soils have attracted extensive attention throughout the world due to their non-biodegradable nature and long biological half-lives for elimination from the body, and may lead to human health risk via different exposure pathways including inhalation, ingestion and dermal contact absorption, etc. During recent decades, public hazard events related to urban soil heavy metals occur frequently in many countries of the world and therefore establishing scientific urban soil environmental and safety management early-warning system becomes the key to protect the safety of residents. Though there is a recognized risk assessment and management frame system for the soil in the contaminated sites at home and abroad, a feasible set of economic and efficient urban soil environmental health risk assessment and quantitative management system template framework is missing and urgently needed. Therefore, in consideration of the latest progresses in soil science and the obvious differences between the soils characteristics in contaminated sites and the soils characteristics in cities and towns, to improve or develop the corresponding methods and technologies concerning health risk assessment, risk sources identification and quantitative risk management, which should be fit for different urban characteristics including different land uses, receptor spatial distributions, receptor life characteristics and degrees of economic investment for risk evaluation and management, is significant not only from scientific point of view but also from practical application point of view.This dissertation fistly summarized the heavy metal pollution characteristics in urban soils, and further the study evolution of urban soil heavy metal pollution evaluation, health risk assessment, risk management and uncertainty influence were reviewed and analysed. Based on these analyses, the main study contents and corresponding technical route were put forward to develop a set of scientific and efficient hierarchical health risk assessment and risk management system for urban soil heavy metals.The main works and novel achievements include the following elements:(1) The environmental geochemistry characteristics of soil heavy metals under different land uses from Xiandao district(XDD) were studied based on the field sampling, instrumental analysis, multivariate statistical analysis, and 3S technology(Remote Sensing, Geographical Information System and Global Positioning System). Based on these studies on mutual relationship among soil characteristics, land uses, heavy metal distributions and soil heavy meal fractionations, the pollution pattern of soil heavy metals and the corresponding influence factors were analysed and the entire data could be taken as the footstone not only for identification and prediction of pollution characteristics for soil heavy metals, but also for further pollution assessment and risk management.(2) A stochastic-fuzzy assessment model for soil heavy metals, based on the geoaccumulation index and the double weighting system which could characterize the biology-toxicity of different heavy metals and the bioavailability of different metal chemical fractionations, was developed. And the case study of XDD indicated the developed model could decrease the probability of misleading decision-making in following situations: overestimate/underestimate pollution levels when soil heavy metals were in high/low concentration but in low/high bioavailability. And compared with the common deterministic models, the stochastic-fuzzy model was more applicable to the poor or low precision data during the actual assessments and showed the heavy metal pollution levels with their corresponding confidence levels with better computational efficiency to supply more full-scale information to decision-maker. The potential risk pollutants could be selected according to the stochastic-fuzzy assessment results and therefore the developed model could be regarded as the preliminary risk identification tool for efficient health risk assessment.(3) A hierarchical health risk assessment method was originally established with the comprehensive consideration of heavy metal hierarchical bioavailability, their corresponding land use type and the possible receptor distribution density. Comparison of the hierarchical health risk assessment model and the classic health risk assessment model revelaed that the established model overcame the shortcomings including improper exposure assessment model selection which probably cause the over-treatment, possibly overestimating or underestimating the risk posed by heavy metals without considering of their specific chemical fractionations, neglecting the principle of “no exposure, no risk” which may lead to meaningless management for dissevering the exposure risk with the local receptor distribution and not developing the elastic regional risk management strategies to distinguish different control areas with relatively different priority which always make decision-makers hard to make the hierarchical risk management strategies for the efficient budget utilization. In short, the priority pollutants and the priority regions could be efficiently identified based on the hierarchical health risk assessment method and this study provided technical support for establishing the flexible regional risk management strategies which could facilitate reasonable allocation of cost for risk management. And it is of special value in developing countries for their insufficient management budget.(5) On the basis of the mentioned study above, the risk quantification management and decision-making system was established with consideration of cost-benefit consideration. The developed system, based on the urban soil environmental comprehensive information database which had integration of all the data concerning regional soils, possessed the capbilities of the efficient urban soil heavy metal hierarchical health risk assessment, the integrated source analysis, the induced hierarchical risk management and the early risk warning. With the help of this system, it is capable to identify risk sources and its responsibilities, to preliminarily develop the target and action content value of heavy metals under different land use, and to further put forward suggestions for the related laws and regulations system.According to characteristics of urban soil heavy metal pollution, the research difficulties and realistic demand in the study field of urban soil heavy metal assessment and management were systematacially analyzed. Several technological methods and models were established based on the field sampling and instrumental analysis, 3S technology, fuzzy mathematics, stochastic theory, multivariate statistical analysis and health risk assessment models. Based on these technological methods and models, the risk quantification management and decision-making system concerning urban soil heavy metals was developed and the well operability and efficiency of developed system was verified with the case study in XDD. This dessertation, on one hand, is helpful to enriched the domestic and foreign research content conerning the urban soil heavy metal pollution characteristics, to improve urban soil pollution assessment theory and method, and the developed risk management and decision-making system is of key theoretical signification. On the other hand, the case study of soil heavy metal from XDD was performed and the results could not only verify the established methods and models, but also make the surpport for the effective quantitative management of soil heavy metals and the ecological civilization development in XDD.