As with exposure to any chemical, a person’s health risk depends on a number of factors, including:
- How much TCE an individual was exposed to (the dose);
- How long the exposure lasted (the duration);
- How the person was exposed (breathing, drinking, eating or skin contact);
- Other factors associated with the individual (such as age, health, lifestyle choices, family traits, and other chemicals the person is exposed to).
Health risks can be categorized into acute effects and chronic/ sub-chronic effects. Acute effects are those that occur after short-term exposure (e.g. minutes, a few days) to very high concentrations of TCE (e.g. concentrations in the hundreds of thousands of micrograms per cubic meters (μg/m3) or greater). Symptoms of acute exposure can include drowsiness, decreased memory and perception, visual effects and anesthesia.
Chronic effects are those that occur after long-term exposure (e.g. years). Sub-chronic effects are those that occur after intermediate-term exposure (e.g. months). These effects include cancer (from chronic exposure) and non-cancer effects (from sub-chronic or chronic exposure). The main concern with TCE exposure is the risk of cancer. Overall, studies in humans and animals are highly suggestive of an increased risk for cancer in people who are exposed to elevated levels of TCE over long periods of time (e.g. workers exposed to levels 20,000 μg/m3).
Cancers that have been associated with TCE include kidney, liver and lymphoid tissue cancers. The risks of cancer associated with chronic exposures to low levels of TCE are as follows: An air level of TCE at 0.5 μg/m3 corresponds to a one in one million risk of cancer over a lifetime (70-year exposure). An air level of TCE at 5 μg/m3 corresponds to a one in one hundred thousand risk of cancer over a lifetime (70-year exposure). An air level of TCE at 50 μg/m3 corresponds to a one in ten thousand risk of cancer over a lifetime (70-year exposure).
Chronic and sub-chronic effects, other than cancer, are less understood and research is ongoing. Potential effects include those to the central nervous system, kidney, liver, respiratory, developmental and reproductive systems. However, it is generally recognized that cancer is the most sensitive health outcome.