Human Health Risk Assessment
Introduction
A human health risk assessment is the process to estimate the nature and probability of adverse health effects in humans who may be exposed to chemicals in contaminated environmental media, now or in the future.
To explain this better, a human health risk assessment addresses questions such as:
- What types of health problems may be caused by environmental stressors such as chemicals and radiation?
- What is the chance that people will experience health problems when exposed to different levels of environmental stressors?
- Is there a level below which some chemicals don't pose a human health risk?
- What environmental stressors are people exposed to and at what levels and for how long?
- Are some people more likely to be susceptible to environmental stressors because of factors such as age, genetics, pre-existing health conditions, ethnic practices, gender, etc.?
- Are some people more likely to be exposed to environmental stressors because of factors such as where they work, where they play, what they like to eat, etc.?
The answers to these types of questions helps decision makers, whether they are parents or public officials, understand the possible human health risks from environmental media.
How does EPA conduct a Human Health Risk Assessment?
Human health risk assessment includes 4 basic steps, and is generally conducted following various EPA guidance documents.
- Planning - Planning and Scoping process
EPA begins the process of a human health risk assessment with planning and research.
- Step 1 - Hazard Identification
Examines whether a stressor has the potential to cause harm to humans and/or ecological systems, and if so, under what circumstances.
- Step 2 - Dose-Response Assessment
Examines the numerical relationship between exposure and effects.
- Step 3 - Exposure Assessment
Examines what is known about the frequency, timing, and levels of contact with a stressor.
- Step 4 - Risk Characterization
Examines how well the data support conclusions about the nature and extent of the risk from exposure to environmental stressors.
Why does EPA evaluate whether children may be at greater health risks than adults?
Almost 500 years ago Paracelsus (1493-1541) wrote: "Dosis facit venenum" or "the dose makes the poison." The relationship between dose and response (health effect) is still one of the most fundamental concepts of toxicology - or is it? For pollutants that act as developmental toxicants, the same dose that may pose little or no risk to an adult can cause drastic effects in a developing fetus or a child. Methyl mercury is but one example of a chemical that is much more toxic early in life. Scientists have become increasingly aware that children may be more vulnerable to environmental exposures than adults because:
- their bodily systems are developing;
- they eat more, drink more, and breathe more in proportion to their body size; and
- their behavior, such as crawling and hand-to-mouth activity, can expose them more to chemicals and microorganisms.
In light of what is now known about the greater susceptibility early in life to some stressors, Executive Order 13045 -- Protection of Children from Environmental Health Risks and Safety Risks -- was issued in 1997. This Executive Order directs that all federal agencies, including EPA, shall make it a high priority to identify and assess environmental health risks and safety risks that may disproportionately affect children; and shall ensure that their policies, programs, activities, and standards address disproportionate risks to children that result from environmental health risks or safety risks.
Note: To assist scientists in assessing risks specifically to children, EPA has developed A Framework for Assessing Health Risk of Environmental Exposures to Children along with specific guidance to risk assessors including Guidance on Selecting Age Groups for Monitoring and Assessing Child-Hood Exposures to Environmental Contaminants and Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens.