The U.S. EPA has made a remarkable decision recently to protect the health of people exposed to trichloroethylene (TCE) in indoor air, primarily as a result of vapor intrusion of TCE vapors from groundwater. The Region 9 EPA has proposed a Remedial Action Level (RAL) for acute (short term) exposure to TCE of 15 micrograms per cubic meter (ug/m3) or 2.8 parts per billion by volume (ppbv). RALs are developed to protect residents exposed to chemicals in indoor air. The regional EPA staff is awaiting approval from EPA headquarters. This exposure limit was proposed to prevent against possible cardiac birth defects when pregnant women are exposed to TCE vapors. TCE is one of the most common chemical contaminants found in the environment. It is used primarily as vapor degreasing solvent to clean metal parts.
This new RAL was proposed as part of the cleanup efforts for the Middlefield-Ellis-Whisman (MEW) Superfund site in Mountain View, CA. The proposed exposure limit is based on EPA’s recently completed health assessment of TCE that set a reference concentration (RfC) for chronic exposure to TCE of 2.0 ug/m3. This reference dose is a level that EPA estimates a person can inhale over the course of their lifetime without causing any adverse health effects.
What’s unique about this proposed exposure limit is that EPA chose to use the reference concentration, which is considered a continuous lifetime exposure, as a daily average exposure. The proposed RAL assumes that a single daily exposure during the first trimester of pregnancy could result in an adverse developmental effect. I believe this is the first time that EPA has proposed a short term exposure limit for any chemical. This is a remarkable event.
The chemical industry of course has cried foul, arguing that using the RfC to create a short term exposure limit is inappropriate and that there is too much uncertainty about short term exposures to TCE. A report prepared by consultants for the chemical industry went on to say that by creating the short term RAL, the agency is considering “an overly strict standard that will cause unnecessary precautions and alarm.” No surprises there.
What it actually does is provide genuine protection for people exposed to TCE (and likely other chemicals) in homes where vapor intrusion occurs from contaminated groundwater. This is a good thing that EPA should be applauded for and encouraged to do more of. Local residents in CA support the EPA’s proposal. The Center for Public Environmental Oversight who has been active at the MEW Superfund site and on vapor intrusion issues has written to EPA asking that headquarters adopt the Region 9 proposal nationwide. EPA has not yet made a decision.
In the meantime, several states including California and New Jersey are following the EPA Region 9‘s lead and have begun using or are considering developing short term exposure limits for TCE. If you are involved in a situation with vapor intrusion of volatile chemicals like TCE, use the short term exposure limit for TCE as a guide to evaluating the risks you face. It’s a lot better than what the chemical industry would have you use.