2. RELEVANCE TO PUBLIC HEALTH 2.1 BACKGROUND AND ENVIRONMENTAL EXPOSURES TO TETRACHLORO- ETHYLENE IN THE UNITED STATES The use of tetrachloroethylene as a dry cleaning agent, chemical intermediate, and metal degreasing agent

The use of tetrachloroethylene as a dry cleaning agent, chemical intermediate, and metal degreasing agent has led to its release to the environment. It has also been shown to be produced naturally by several temperate and subtropical marine macroalgae, but the majority of exposure to tetrachloroethylene is still through anthropogenic sources. It is primarily released to the air where it is slow to degrade, with estimated atmospheric half-lives of approximately 100 days. Data compiled from the EPA Air Quality System indicate that the ambient atmospheric level of tetrachloroethylene is typically <1 μg/m . Due to its long atmospheric half-life, it is subject to long-range transport and has been identified in atmospheric samples in remote locations such as Antarctica where no local sources of this substance exist. Levels for tetrachloroethylene in the indoor air tend to be higher. The median value for indoor air in the United States, from 2,195 entries in the EPA’s database of volatile organic contaminants (VOC-AMBI), was approximately 4.9 μg/m, with an average value of 20.7 μg/m .