【作者】 王振兴；

【导师】 柴立元； 杨志辉；

【作者基本信息】 中南大学 ， 冶金环境工程， 2011， 博士

【摘要】 铬盐及铬铁合金生产过程产生的大量含铬废渣历年堆存量达600万吨,其中的Cr(Ⅵ)通过迁移严重污染环境,危及人体健康。本文以某典型铬渣堆场为研究对象,调查Cr(Ⅵ)的污染现状,研究其迁移规律、暴露途径、暴露水平及健康风险特征,全面系统评价铬渣、土壤、蔬菜和地下水中Cr(Ⅵ)的健康风险,建立Cr(Ⅵ)在“铬渣-土壤-地下水”系统中的整体迁移模型,从时间和空间维度拓展人类健康风险评价基础理论,从规划和决策层面构建基于GIS的区域Cr(Ⅵ)污染动态健康风险评价预警综合管理平台。主要研究结果如下：(1)揭示了铬渣中Cr(Ⅵ)溶解释放的动力学机理,建立了模拟酸雨条件下铬渣中Cr(Ⅵ)的动态淋溶仿真模型,定量预测大气降水作用下Cr(Ⅵ)对土壤的污染强度,为防止铬渣对土壤和地下水造成污染提供科学依据。铬渣中Cr(Ⅵ)溶解释放规律服从Fick扩散定律,神经网络模型对酸雨淋溶铬渣释放Cr(Ⅵ)仿真结果效果较好,绝对平均误差率<1.40%。遗传算法优化后的指数衰减模型模拟结果较好,最大均方根误差优化率达76%。(2)研究了Cr(Ⅵ)在土壤中的迁移机理和污染规律,结合铬渣淋溶仿真模型建立了定量描述土壤中Cr(Ⅵ)迁移特性的数学模型,为土壤和地下水铬污染防治提供理论与技术支持。土壤对Cr(Ⅵ)的吸附是吸热反应、自发过程,符合拟二级动力学吸附模型和Freundlich等温吸附模型,吸附量随pH值降低而增大。利用土柱动态模拟试验测定了水动力参数和迁移参数(弥散系数、吸附分配系数、迟滞因子等),利用HYDRUS模型对土壤中Cr(Ⅵ)迁移模拟效果良好,相关系数达0.9986。(3)综合考虑酸雨淋溶、对流、弥散、吸附解吸及源汇项等条件,首次构建了定量描述Cr(Ⅵ)在“铬渣-土壤-地下水”系统中的整体迁移动力学数学模型,实现历史与未来污染的定量估计和有效预测,为我国铬渣、土壤和地下水的科学管理提供理论依据。结合实验所测地下水渗透系数、Cr(Ⅵ)吸附分配系数、迟滞因子等参数,针对研究区水文地质状况建立的地下水迁移模型的计算水头与实测水头差小于3米,地下水中Cr(Ⅵ)浓度的实测与模拟值均方误差为0.4303,所建模型基本可靠。结果显示铬渣的无害化处理对地下水环境质量具有明显改善作用。(4)提出了从时间和空间维度拓展健康风险评价理论的方法,应用迁移模型实现暴露剂量的动态预测,应用GIS技术扩大风险评价的地域尺度,实现基于暴露群体、土地利用类型、蔬菜种类和暴露途径的不同历史时期定量风险评价。结果表明：重风险主要分布于工业区,居住区风险最轻；铬渣堆场的致癌风险高达0.0204～0.0341,超出最高允许阀值数倍；蔬菜有将土壤中的高毒性Cr(Ⅵ)转化为低毒性Cr(Ⅲ)的能力,蔬菜中总铬平均含量超出阀值3倍多,白菜对铬的富集能力和健康风险在几种常见蔬菜中最高；直接土壤暴露的三个途径中,口腔摄入风险最大；地下水对成人和儿童的健康风险分别大于最高允许风险值70和150余倍。可见Cr(Ⅵ)具有很高毒性,对人类健康危害严重,特别是儿童这一脆弱群体。(5)构建了基于GIS的Cr(Ⅵ)污染动态健康风险评价预警综合管理平台,通过数据库管理和软件开发技术实现了铬渣淋溶、土壤和地下水迁移模型间的无缝耦合,以及健康风险的动态评价与预警,有效提高了环境管理的信息化程度。利用GIS的数据管理、空间分析与ArcEngine组件开发技术,以C/S(客户/服务器)为基本结构,ArcSDE为空间数据库引擎,通过对MATLAB与.NET的集成编程、遗传算法的实现、AutoCAD宏开发与Modflow的集成、模型间数据转换工具的开发等技术,将Cr(Ⅵ)在“铬渣-土壤-地下水”系统中的整体迁移模型与经时空拓展后的健康风险评价理论方法集成,构建了Cr(Ⅵ)污染动态健康风险评价预警综合管理平台,使人类活动与生态、人体健康等重大环境问题的研究纳入一个完整的大系统,有利于更好的揭示原因、本质和规律。为环境风险作出准确的评价和预测,使环境管理中重大问题的决策更具科学性。更多还原

【Abstract】 Large quantities of chromium-containing slag that were generated in chromium production over the years amounted to 6 million tons. Cr(Ⅵ) in the slag transported into and polluted the environment, which greatly endanged human health. In this research, a typical factory in Hunan Province was taken as study object. Systemic studies were carried out to found out the characters of Cr(Ⅵ) in the slags, including transportation, exposure route, exposure level, and associated health risks. Site specific health risks of Cr(Ⅵ) in slag, soil, groundwater and different specieses of vegetables were researched in detail. A transport model for Cr(Ⅵ) in the "slag-soil-groundwater" system was built. The health risk assessment theory was extended in both spatial and temporal dimension. An environmental risk management flat was established based on GIS, transport model, and extended health risk assessment theory. The main results were as follows:(1) Release rules of Cr(Ⅵ) leaching from slags under simulated acid rain were researched and dynamically simulated. Results indicated that the balance of Cr(Ⅵ) in the leachate obeyed the Fick’s law. The artificial neutral network model was efficient to similate the releasing behavior (mean error<1.40%). In addition, the genetic algorithm was also efficient to optimize the linear regression model (maxmium RMSE=76%).(2) The transport mechanism and pollution laws of Cr(Ⅵ) in soil were researched. The adsorption process was found to be endothermic and spontaneous in nature.Results were discussed and indicated the best fit was obtained with the Freundlich isotherm model. The results also showed that the kinetics of adsorption were best described by a second-order expression rather than a first-order model. The soil conductivity, fluid dynamic dispersivity, adsorption distribution coefficient and retardation factor of Cr(Ⅵ) in soil were also estimated. The correlation coefficient between the measured and simulated results was 0.9986.(3) Considering the conditions of acid rain, convection, dispersion, adsorption, desorption, sources and sinks, a transport model for Cr(Ⅵ) in the "slag-soil-groundwater" system was researched. The permeability coefficient, distribution coefficient, retardation factor and other hydraulic parameters were estimated in laboratory. The differences of measured and simulated groundwater head values were all less than 3 m. The mean square error of measured and simulated Cr(Ⅵ) concentrations was 0.4303. Therefore, the model was basically reliable.(4) The health risk theory was extended by the transport model and GIS technology. Potential health risks were assessed based on different kinds of site-specific exposure parameters, vegetables, exposure pathways, individuals and the cultivation habits of homegrown vegetables. Most high hazard quotients were located in the industrial areas and attributed to soil ingestion and Chinese cabbage. Results also showed that the population in the study area was at risk, especially in the industrial site.(5) A GIS-based, regional and dynamic environmental risk assessment/early-warning management platform was established. With the use of GIS technologies, including spatial data management, spatial analysis and component development, the basic structure of C/S (Client/Server), the spatial database engine of ArcSDE, the integrated programming of MATLAB, genetic algorithms and.NET, the integration of AutoCAD macro development and Modflow software, and the data conversion tools for models were all used or developed for the platform. The migration model of Cr(Ⅵ) in the "slag-soil-groundwater" system and the spatial-temporal extended health risk assessment method were both integrated in the platform. The platform put human activities, ecological and environmental issues, and human health into a large system, which made it more efficient and scientific to solve problems in environmental risk assessment, prediction, management, and decision-making.更多还原