TRANSPORT AND BIODEGRADATION OF VOLATILE ORGANIC COMPOUNDS IN THE VADOSE ZONE

暴露评估，环境风险的重要组成部分 分析，需要定量的方法来估计 污染物在环境介质中的分布和持久性。 挥发性化合物（VOC），如TCE、DCE、甲苯、对硝基苯酚和 萘在EPA优先污染物清单上， 在超级基金垃圾场发现的美坦钠是一种用于大面积 农业中的数量。从最初放置在包气带， 这些挥发性污染物进入地下水和空气， 是人类最重要的两种接触途径。在土壤中， 它们可以通过微生物代谢转化为化合物， 比原来的污染物危害性大或小。 将进行研究，以调查基本过程 包括扩散和对流传输、吸附/解吸，以及 生物降解，影响的命运和运输的液体和 土壤和地质沉积物中挥发性有机化合物的气相。研究将 注重耦合和相互依存的物理，化学， 生物过程决定运输和分布 化学混合物。将进行实验室规模的柱研究 使用土壤和地质沉积物来确定多重 环境过程对挥发性有机化合物向大气迁移的可能性的影响 地下水和大气。持久性代谢物产生于 生物降解将在 免疫化学项目和分析核心。蒸汽的估计 浓度的可能为各种废物场地的情况将提供 热修复项目的研究人员。灰尘样本将 提供给肺暴露项目，以评估 吸附在灰尘上的化学物质对健康的潜在危害。化学品和 土壤沥滤液中的代谢物将使用 青鳉和基于细胞的生物测定。 挥发性有机化合物传输过程与野外地质条件的关系 包气带的属性，如沉积相，粒度， 将确定有机碳、分选和矿物学。定量 这些关系的描述将被纳入 确定性和随机模型的运输在包气带， 包括二维和三维流动数值模拟实验 以及单一液相（溶解在水中的VOC）和 气相包气带的热水输送模式， 可以在昼夜强烈的地表加热条件下使用， 通过实验室和现场实验进行开发和测试。该模型 将与化学挥发模型相结合， 流入大气层大气成分的验证 将基于激光雷达测量的边界层超过100米 按比例绘制的图可以达到几公里的区域尺度。这些模型将 用于评估现场范围内潜在的人类接触水平。

Exposure assessment, an essential component of environmental risk analysis, requires quantitative approaches for estimating the distribution and persistence of pollutants in environmental media. Volatile compounds (VOCs), such as TCE, DCE, toluene, p-nitrophenol, and naphthalene are on the EPA Priority Pollutants List and are commonly found at Superfund waste sites. Metam sodium is a fumigant used in large quantities in agriculture. From initial placement in the vadose zone, these volatile contaminants move into the groundwater and the air which are the two most important exposure routes for humans. While in the soil, they may be transformed by microbial metabolism into compounds which are either more or less hazardous than the original contaminants. Studies will be conducted to investigate the fundamental processes including diffusive and convective transport, sorption/desorption, and biodegradation that affect the fate and transport of both the liquid and vapor phases of VOCs in soil and geological sediments. Research will focus on the coupled and interdependent physical, chemical, and biological processes determining the transport and distribution of chemical mixtures. Laboratory-scale, column studies will be conducted using soil and geological sediments to determine the effect of multiple environmental processes on the potential for movement of VOCs to the groundwater and atmosphere. Persistent metabolites resulting from biodegradation will be identified with the assistance of the Immunochemical project and the Analytical Core. Estimates of vapor concentrations. likely for various waste site scenarios will be provided to investigators in the thermal remediation project. Samples of dust will be provided to the pulmonary exposure project in order to assess the potential health hazard of chemicals sorbed to dust. Chemicals and metabolites in leachate from soil will be tested for toxicity using the medaka and cell based bioassays. Relationships between VOC transport processes and field-scale geological attributes of the vadose zone such as depositional facies, grain size, organic carbon, sorting and mineralogy will be determined. Quantitative descriptions of these relationships will be incorporated into deterministic and stochastic models of transport in the vadose zone which include two and three-dimensional numerical modeling experiments of flow and transport of a single liquid phase (VOC dissolved in water) and a gaseous phase. A heat-water transport model for the vadose zone, which can be used under conditions of strong diurnal land surface heating, will be developed and tested with laboratory and field experiments. This model will be coupled with the models of chemical volatilization to obtain the flux into the atmosphere. The validation of the atmospheric component will be based on lidar measurements of the boundary layer over 100 m scale plots up to regional scales of a few kilometers. These models will be used to evaluate potential human exposure levels at the field scale.