| 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. |
PDF Full Text Request