Human Health Risk Assessment
A human health risk assessmentThe likelihood that a given exposure or series of exposures may have damaged or will damage the health of individuals. 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.
A human health risk assessment includes four steps, which begin with planning:
- Planning - Planning and Scoping process
EPA begins a human health risk assessment by planning the overall approach with dialogue between the risk manager(s), risk assessor(s), and other interested parties or stakeholders. Members of the team:
- identify risk management goals and options;
- identify the natural resources of concern;
- reach agreement on scope and complexity of the assessment; and
- decide on team member roles.
- Step 1 - Hazard Identification
The risk assessor(s) examine 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
The risk assessor(s) gather information to determine the numerical relationship between exposure and effects.
- Step 3 - Exposure Assessment
Once steps 1 & 2 are identified, the risk assessor(s) examine what is known about the frequency, timing, and levels of contact with the stressor.
- Step 4 - Risk Characterization
Risk characterization includes two major components—risk estimation and risk description.
"Risk estimation" compares:
- the estimated or measured exposure level for each stressor and plant or animal population, community, or ecosystem of concern; and
- the data on expected effects for that group for the exposure level.
"Risk description" provides information important for interpreting the risk results. This includes:
- whether harmful effects are expected on the plants and animals of concern;
- relevant qualitative comparisons; and
- how uncertainties (data gaps and natural variation) might affect the assessment.
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.
Risk Assessment & Children
To discuss children's health, we first would like to mention the concept of "life stages," since a person's age can influence how susceptible they are to the health risks posed by pollutants in the environment. Children and the elderly are often most at increased risk.
Children are often more heavily exposed to toxins in the environment than adults because pound for pound, children breathe more air, drink more water, and eat more food than adults. Children's behavior patterns, such as playing close to the ground, increase their exposure to potential toxics.
In addition, children may be more vulnerable to environmental hazards because their systems are still developing, which often makes them less able to metabolize, detoxify, and excrete toxins. Environmental risks to children include asthma-exacerbating air pollution, lead-based paint in older homes, treatment-resistant microbes in drinking water, and persistent chemicals that may cause cancer or induce reproductive or developmental harm.
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.
Learn more about protecting children's environmental health
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.
- EPA.A Framework for Assessing Health Risk of Environmental Exposures to Children. Washington, DC.
- EPA. Guidance on Selecting Age Groups for Monitoring and Assessing Child-Hood Exposures to Environmental Contaminants. Washington, DC.
- EPA. Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens. Washington,DC.
Other key resources include:
- EPA. Highlights of the Child-Specific Exposure Factors Handbook (Final Report). Washington, DC.
- EPA. Child-Specific Exposure Factors Handbook (Final Report) 2008. Washington, DC.
- EPA. Aging and Toxic Response: Issues Relevant to Risk Assessment (Final). Washington, D.C.
- EPA. Strategy for Research on Environmental Risks to Children. Washington, DC.
- EPA. Guidelines for Developmental Toxicity Risk Assessment. Washington, DC.
- Interagency Coordinating Comm. The National Children's Study of Environmental Effects on Child Health and Development. Environmental Health Perspectives 111(4): 640-646, (2003).