Research On Soil Risk Assessment And Classification Method Based On Land Use Types

With the acceleration of urbanization,the demand for land is increasing in China.The closure and relocation of industrial enterprises in urban areas has left a large number of potentially contaminated sites in Chinese cities.Many contaminated sites require land use changes,and the residual pollutants in the soil and groundwater are harmful to human health and environmental quality at the sites.In recent years,the supervision and management of contaminated sites has been prioritized by the Chinese government.A standard and a system for managing contaminated sites have been initially established in China.Activities including the investigation of soil pollution,soil risk assessment,risk control,remediation and later-period management are clearly stipulated.However,China is still in the development stage in terms of the technical methods for risk control at contaminated sites.Issues related to the assessment of health risks at contaminated sites,risk classification,risk control,and mitigation strategies still present problems in China.The contents and the main results of this study are as follows:(1)Taking urban traffic land use as an example,this dissertation compared the results of risk assessment based on an established pollution model that considers specific types of planned land uses with the results of risk assessment using technical guidelines.The exposure routes and exposure parameters of urban road land,subway land,and traffic station land were established.Taking the abandoned pesticide production site as an example,a carcinogenic risk assessment based on the semi-volatile organic compounds hexachlorobenzene and benzo[a]pyrene was conducted.The results indicated that the carcinogenic risk value using guidelines recommended parameter considered the common six general exposure pathways(oral ingestion;dermal contact with soil;inhalation of soil-derived dust;inhalation of soil vapors outdoors from surface and sub-soil;and inhalation of soil vapors indoors)is much higher than that considered exposure pathways and exposure parameters based on specific land use planning.The commonly considered hexachlorobenzene and benzo[a]pyrene carcinogenic risk values exceeded the maximum acceptable level(10-6)and were 23.9-and 109-fold higher than the carcinogenic risk values,respectively.(2)Conceptual models of pollution suitable for different types of land use were established for volatile organic compounds(VOCs)and semivolatile organic compounds(SVOCs).Soil screening values were determined for different geographical zones and different types of urban construction land planning to provide guidance for health risk assessment at contaminated sites.In China,urban development can involve at least eight land uses:urban residential(R),public administration/service(A),commercial/service(B),industrial(M),logistics storage(W),transportation(S),public utility(U),and park green space(G).To the above,we applied conceptual models and exposure pathways of VOCs and SVOCs.Exposure parameters were investigated for six regions and the above eight land uses for different soils,climates,and population behavior characteristics:north,east,south,northwest,northeast,and southwest(covering China entirely).Risk controlling values(RCVs)corresponding to a lifetime cancer risk of 10-6 were calculated using the C-GAC Model introduced by ’Chinese Technical Guidelines for Risk Assessment of Contaminated Sites’ with the above exposure parameters to identify potentially significant levels of contamination that warrant further investigation.The results revealed two main patterns:(1)the soil RCVs for the six regions(north,east,south,northwest,northeast,and southwest)revealed some between-region variability(up to 230%);and(2)the organic pollutants tested across the eight types of land use showed maximum values up to 302.5 times the minimum value.(3)Based on existing research,a comprehensive risk index of contaminated sites was constructed with three layers(risk sources,exposure pathways,and receptors).The index included four levels,seven broad categories,and 23 sub-indexes.Analytic hierarchy process(AHP)was used to determine the index weight of each layer.Fuzzy comprehensive evaluation and binary semantic combination were applied to improve the accuracy of the evaluation results.Meanwhile,priority levels for different contaminated sites could be set in the same risk level.The classification results of contaminated sites in abandoned agricultural pharmaceutical plants based on the established index system and evaluation model showed that the comprehensive risk level of contaminated sites is level 2,and the Two-tuple semantic model is(2,-0.2965).(4)For large contaminated sites that are not unexploited currently,this dissertation proposed a method to delineate the risk control area referring to the industrial health protection distance of the original enterprises in the site.A technical method to evaluate the health risks of three environmental elements in sites contaminated with polycyclic aromatic hydrocarbons was established.Based on this method,the air early warning system and method were proposed.The results showed that it is reasonable to delimit the control area based on the existing environmentally sensitive target and the health protection distance of the originally polluted workshop or factory.Warning concentrations of Benzo(a)pyrene and Naphthalene were calculated using carcinogenic risk level of 10-7,the results were more close to the existing standard.Therefore,it is reasonable to use the results to determine the warning concentrations of PAHs.