Department of Environmental Sciences & Engineering, Gillings School of Global Public Health, University of North Carolina-Chapel Hill, CB 7431, Chapel Hill, North Carolina 27599, USA.
Environ Sci Technol. 2013 Jun 4;47(11):5595-602. doi: 10.1021/es4003795. Epub 2013 May 23.
The migration of chlorinated volatile organic compounds from groundwater to indoor air-known as vapor intrusion-can be an important exposure pathway at hazardous waste sites. Because sampling indoor air at every potentially affected home is often logistically infeasible, screening tools are needed to help identify at-risk homes. Currently, the U.S. Environmental Protection Agency (EPA) uses a simple screening approach that employs a generic vapor "attenuation factor," the ratio of the indoor air pollutant concentration to the pollutant concentration in the soil gas directly above the groundwater table. At every potentially affected home above contaminated groundwater, the EPA assumes the vapor attenuation factor is less than 1/1000--that is, that the indoor air concentration will not exceed 1/1000 times the soil-gas concentration immediately above groundwater. This paper reports on a screening-level model that improves on the EPA approach by considering environmental, contaminant, and household characteristics. The model is based on an analysis of the EPA's vapor intrusion database, which contains almost 2,400 indoor air and corresponding subsurface concentration samples collected in 15 states. We use the site data to develop a multilevel regression model for predicting the vapor attenuation factor. We find that the attenuation factor varies significantly with soil type, depth to groundwater, season, household foundation type, and contaminant molecular weight. The resulting model decreases the rate of false negatives compared to EPA's screening approach.
从地下水迁移到室内空气中的氯化挥发性有机化合物——即所谓的“蒸气侵入”——可能是危险废物场所的一个重要暴露途径。由于在每个可能受到影响的家庭中采集室内空气在物流上通常是不可行的，因此需要筛选工具来帮助识别高风险家庭。目前，美国环境保护署（EPA）使用一种简单的筛选方法，采用通用的蒸气“衰减因子”，即地下水位以上土壤气体中污染物浓度与室内空气污染物浓度的比值。在美国，在受污染地下水之上的每个可能受到影响的家庭中，EPA 假设蒸气衰减因子小于 1/1000——即室内空气浓度不会超过地下水上方土壤气体浓度的 1/1000 倍。本文报告了一种筛选水平模型，该模型通过考虑环境、污染物和家庭特征改进了 EPA 的方法。该模型基于对 EPA 蒸气侵入数据库的分析，该数据库包含在 15 个州收集的近 2400 个室内空气和相应的地下浓度样本。我们使用现场数据开发了一个用于预测蒸气衰减因子的多级回归模型。我们发现，衰减因子随土壤类型、地下水深度、季节、家庭基础类型和污染物分子量而有很大差异。与 EPA 的筛选方法相比，所得到的模型降低了假阴性的发生率。
