Question

What is the level or goal for setting exposures for non-cancer risks involved with POLLUTION? How is it characterized for non-cancer AND cancer risks?

Answer 1

Toxic air pollutants are the poisonous substances in the air that come from natural sources (for example, radon gas coming up from the ground) or from manmade sources (for example, chemical compounds given off by factory smokestacks) and can harm the environment or the health. Inhaling toxic air pollutants can increase the chance of health problems. Breathing these toxic substances can increase the risk of non-cancer effects such as emphysema or reproductive disorders.

Risk assessment is used to estimate the increased risk of health problems in people who are exposed to different amounts of toxic substances. A risk assessment for a toxic air pollutant combines results of studies on the health effects of various animal and human exposures to the pollutant with results of studies that estimate the level of people's exposures at different distances from the source of the pollutant. The steps involved in risk assessment can be:

1) Hazard identification : What health problems are caused by pollutant?

2) Exposure assessment : How much of the pollutant do people inhale during a specific time period?

3) Dose response assessment: What are the health problems at different exposures?

4)Risk characterization: What is the extra risk of health problems in the exposed population?

The dose response relationship for a particular pollutant can describe the association between exposure and the observed response (health effect).

1) In Dose-response relationship for cancer, there is an assumption that that there are no exposures that have "zero risk", that is, even a very low exposure to a cancer-causing pollutant can increase the risk of cancer. United States Environmental Protection Agency(EPA) also assumes that the relationship between dose and response is a straight line -- for each unit of increase in exposure (dose), there is an increase in cancer response. The graph can be seen as below.

2) Dose-response relationship for noncancer effects. It is assumed that a dose may exist below the minimum health effect level for which no adverse effects occur. EPA typically assumes that at low doses the body's natural protective mechanisms repair any damage caused by the pollutant, so there is no ill effect at low doses. However, for some substances noncancer effects may occur at low doses. The graph can be seen as below.

• Dose-Response Relationships

Noncancer Risks:

Health reference levels refer to the exposure levels that will not cause significant risks of non-cancer health effects. Long-term exposure to levels below these levels are assumed to produce no ill effects. Health reference levels are an example of one index that government agencies use in characterizing non-cancer health risks. These levels are usually developed from exposure levels that do not produce ill effects in experimental animals. These exposure levels are adjusted to account for animal-human differences (such as breathing rate) and for underlying uncertainties (such as the difference in sensitivity between healthy adults and more sensitive people like children and the elderly).

Risk analysts then compare the health reference levels with the exposure estimates to determine how many people are exposed to concentrations higher than the health reference level.