Practical and Biological Considerations of Implementing Acute Action Levels for TCE in Indoor Air

摘要

Background. The current inhalation reference concentration (RfC) for trichloroethene (TCE) is based on two noncancer endpoints-immune system effects and developmental effects. The U.S. EPA is currently evaluating short-term exposure limits for TCE in indoor air with the goal of protecting a specific sensitive subpopulation (the developing embryo/fetus) from a specific noncancer outcome (congenital cardiac defects). EPA Region 10 recommends not to be exceeded, average 21-day (formation of the cardiovascular system) levels of 2.0 μg/m3 and 8.4 μg/m3 for exposure to TCE in indoor air in residential and commercial settings, respectively. It is also anticipated that other state and/or regional EPA offices will establish one or more short-term (e.g., 8 or 24 hour) exposure levels, which will trigger “prompt” or “immediate” action including possible occupant removal and or relocation. Current options for evaluating short-term exposure consist of extrapolation of a single measurement of TCE in indoor air over the entire exposure period assuming that the concentration is constant over time; collection of initial and confirmation samples on an expedited basis and subsequent assumption that detected concentrations will remain essentially the same; or, collection of longer term samples using passive sampling devices or a consecutive series of measurements using traditional sampling equipment. The latter approach may not be adequately protective since the time required for sampling and subsequent analysis could include a substantial portion of the early gestation window and thus would not be protective of possible current receptors.