1145559 - Best Science and Practices in ATSDR Evaluations of Vapor Intrusion Exposure Pathways

The Agency for Toxic Substances and Disease Registry (ATSDR) is an environmental public health agency that assesses potential health impacts from exposure to hazardous substances and recommends appropriate actions to prevent or reduce exposures. To understand exposures at vapor intrusion sites and make public health recommendations to reduce potential exposures, two key issues need to be examined: (1) estimating whether measured indoor air concentrations are likely to adequately represent actual exposures, and (2) distinguishing indoor and outdoor “background” sources from subsurface sources in indoor air.

First, understanding the data quality of measured indoor air samples is needed to determine if measured indoor air concentrations are likely to adequately represent actual exposures for assessing the potential for health impacts. Following EPA’s guidance, ATSDR requires multiple samples collected in multiple (hot and cold) seasons to assess indoor air data and perform health evaluations. In addition, ATSDR frequently looks at historical meteorological records, contaminant concentrations, and contaminant proximity to the buildings to further inform recommendations. ATSDR strongly recommends the use of indicators, tracers, and surrogates, as described in EPA Science in Action fact sheets, for all sampling events to help show whether indoor air sampling likely captured dormant or active vapor intrusion conditions.

Second, determining the source of indoor vapors allows ATSDR to better target recommendations to address vapor intrusion or to provide health education for reducing background source exposures. ATSDR compares concurrent subslab/crawlspace, indoor, and outdoor vapor concentrations to see where contaminants may be moving from areas of high concentration to areas of low concentration. Other methods include comparing attenuation factors for chemicals with similar properties (recalcitrant or degradable), comparing contaminant ratios in different media (referred to as enrichment factors), and comparing measured indoor air concentrations to the range of probabilistically modeled indoor air concentrations.

This talk will share case studies of how these practices are applied to public health assessments and share ATSDR resources for working with communities during vapor intrusion investigations.

Disclaimer: The findings and conclusions in this presentation have not been formally disseminated by the Centers for Disease Control and Prevention/the Agency for Toxic Substances and Disease Registry and should not be construed to represent any agency determination or policy.

Author affiliations: