焦化场地包气带区土壤苯的精细化风险评估

苯系物是以煤炭为原料的焦化企业主要挥发类有机污染物（VOCs）.我国现行技术导则在评估VOCs呼吸暴露健康风险时推荐Johnson-Ettinger（J&E）蒸气入侵模型，该模型简单易用，但在某些实际场地应用中存在过于保守的问题，采用双元平衡模型（Dual Equilibrium Desorption，DED）对J&E模型进行校正后可以在一定程度上克服该问题.基于河北省某焦化厂前期土壤调查结果，选取约30 000 m2污染较重的区域开展苯土壤气通量专项调查并进行精细化风险评估，采用J&E-DED模型计算苯的室内呼吸暴露途径健康风险，并与基于J&E模型和实测土壤气挥发通量计算的风险结果进行比较.结果表明:①基于J&E模型、J&E-DED模型、实测土壤气挥发通量计算研究区域土壤苯的致癌健康风险均超过1.00×10-6，对人体存在不可接受的致癌风险.②基于J&E-DED模型计算的风险值比基于J&E模型计算的风险值更接近于基于实测土壤气挥发通量计算的风险值.③当场地土壤性质偏砂性时，可为土壤气中VOCs的扩散迁移提供相对贯通的自由通道，致使整个污染区域土壤气的浓度和风险分布比较均匀.④对J&E-DED模型评估苯室内人体呼吸暴露健康风险时的敏感性参数进行分析发现，地基裂隙中空气体积比对结果的影响最明显（达190.6%），影响最小的是土壤孔隙水体积比和土壤容重，其他参数对结果均有比较明显的影响.研究显示，该场地地质条件下，J&E-DED模型对于反映土壤中苯的人体健康风险具有较好的适用性，可以在一定程度上克服J&E模型计算结果过于保守的问题. 

Refined Risk Assessment of Soil Benzene in Unsaturated Zone of Coking Site

Benzene series (BTEX) are the main volatile organic pollutants (VOCs) emitted by coking industries. The current technical guidelines in China recommend the use of the Johnson-Ettinger (J&E) vapor intrusion model for the health risk assessment of VOCs respiratory exposure pathways. Although this model is simple and easy to use, it can provide conservative estimate in practical applications. On the other hand, research shows that this problem can be overcome to a certain extent by the J&E-Dual Equilibrium Desorption (J&E-DED) model. Based on the survey results of a coking plant in Hebei, this study selected about 30, 000 m2 of heavily polluted areas to carry out a special survey of benzene soil gas flux to conduct a refined risk assessment. The J&E-DED model and J&E model were compared with the measured soil gas volatilization flux. The results showed that based on the J&E model, J&E-DED model, and measured soil gas volatilization flux, the carcinogenic health risk of soil benzene in the research area exceeded 1.00×10-6, which is unacceptable carcinogenic risk to the human body. The calculated risk value of J&E-DED model was closer to the risk-based measured soil gas volatilization flux. It is worth noting that sandy site soil provided a relatively continuous free channel for the diffusion and migration of soil VOCs, resulting in a more even distribution of soil gas concentration and a risk in the entire polluted area of concern. When the J&E-DED model was used to assess the indoor respiratory exposure health risk of benzene, the sensitivity revealed that soil air volume ratio in the filled foundation cracks had the most significant impact on the results (190.6%). Whereas, soil water content-soil porosity and soil bulk density had the least impact. Other parameters also had obvious effects on the results. The research results show that under geological site conditions, the J&E-DED model has good applicability in predicting human health risks of benzene in the soil. In addition, it can overcome to some extent the problem of excessive conservatism found in the J&E model.