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EPA-Expo-Box (A Toolbox for Exposure Assessors)

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Highly Exposed or Other Susceptible Population Groups

Overview

Highly Exposed

EPA’s Guidelines for Exposure Assessment suggest that it is often helpful for risk assessors to characterize and quantify the magnitude of risk for specific highly exposed, highly sensitive, or highly susceptible subgroups within the larger population. Considering vulnerabilityand susceptibility in an assessment is critical to protect those populations at greatest risk when making risk management decisions. Incorporating measures of population vulnerability (differential exposures), including racial, social, and cultural aspects, in developing and implementing environmental laws, regulations, and policies is an important goal of EPA’s Environmental Justice program.

An individual’s lifestage might affect his or her susceptibility to chemicals or pollutants (see Lifestages module). Different population groups might also experience varying susceptibilities, and there are intrinsic and extrinsic (or acquired) factors that affect an individual’s or population’s susceptibility to pollutants.

Factors Affecting Susceptibility
Intrinsic Factors (Biological) Extrinsic Factors (Exposure-Related)
  • Age and lifestage
  • Gender
  • Race/ethnicity
  • Genetic polymorphisms
  • Disease status
  • Socioeconomic status
  • Nutrition status
  • Geographic proximity
  • Lifestyle

Intrinsic, or biological, susceptibility factors include age, lifestage, gender, race/ethnicity, and genetic polymorphisms. These biological factors cannot be changed. Toxicokinetic differences among individuals that affect how easily a chemical is absorbed, metabolized, and excreted are also important factors. Extrinsic, or exposure-related, factors include socioeconomic status, disease status, nutrition status, geographic proximity to sources of exposure, and various lifestyle choices. In many cases, these factors can be changed. See below for additional discussion of some of these extrinsic factors.

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Extrinsic Population Factors Affecting Exposure
Population Factor Discussion

Disease status

Individuals with pre-existing diseases could be more susceptible to pollutants. For example, an individual with asthma might be more susceptible to air pollutants.

Pre-existing medical conditions can directly influence the underlying processes involved in the response of an individual to a contaminant condition by making an individual less resistant to infection.

Socioeconomic status (SES)

Some communities (e.g., low income, minority, indigenous groups) bear greater exposure and disease burdens associated with where they live, work, or play that can increase their risk of adverse health effects from environmental hazards. Some studies have found that location of pollution sources (e.g., high-traffic roadways, industrial site, hazardous waste site) correlates positively with a location’s composition of minority, low-income, or indigenous populations (U.S. EPA, 2013).

Factors such as socioeconomic status (income, level of education, occupation) or lifestyle may have indirect effects on environmental exposures and health outcomes. For example, people with low incomes may not have the same access to health care as those in higher socioeconomic groups (U.S. EPA, 2000).

Diet/nutrition status

Susceptibility can vary based on diet (e.g., consumption of nutritious food) that can be modified to build the immune system and reduce susceptibility.

People who consume higher than average amounts of fish and shellfish (e.g., some ethnic and tribal groups) could have higher exposure to contaminants that biomagnify in the aquatic food chain than other population groups.

Geographic proximity

Certain population groups can be highly exposed to contaminants because of geographic proximity to the sources of these contaminants. Population groups at risk of high exposure due to geographic proximity could include workers at a facility that is a source of a stressor or residents near such sources. Specific examples might be people living downwind from a coal-burning power plant, those near and using a polluted water body (e.g., for fishing or recreation), or those living or working near roadways with high levels of vehicular traffic (U.S. EPA, 2003).

Individuals living in housing near major roadways or in buildings in disrepair (e.g., with peeling paint) might have higher exposure to certain types of contaminants (e.g., lead, particulate matter, vehicle exhaust) than individuals in other settings.

Lifestyle

Susceptibility can vary based on lifestyle factors (e.g., exercise, smoking, alcohol consumption) that can be modified to build the immune system and reduce susceptibility.

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There are some population groups that are culturally or economically disposed to higher rates of fish ingestion than the general population (e.g., various ethnic, tribal subsistence populations). These population groups are most vulnerable to exposure by intake of contaminated fish from specific locations. Their catch of fish may not be "diluted" by fish from other water bodies. In addition, subsistence fishers might have increased vulnerability given that the fish they catch could be a primary source of food for themselves or for their families.

Examples of other pathways of exposure to consider for ethnic/tribal groups are:

  • Ingestion of game;
  • Soil ingestion;
  • Time spent in sweat lodge;
  • Sediment exposure via basketmaking;
  • Mercury-containing ethnic medicines;
  • Proximity to nuclear waste; and/or
  • Proximity to mines and associated waste/tailings.

EPA works with partners in tribal governments to strengthen and implement public health and environmental protection programs and reduce exposures to these tribal communities. EPA also promotes the exchange of ideas to work effectively with tribal governments. See EPA’s American Indian Environmental Office Tribal Portal for additional information.

There are a number of tools that can be used to assess differences in exposures for highly exposed or susceptible population groups (see below). These include tools for tribal populations as wells as other populations that may experience greater exposure with environmental contaminants due to racial or cultural factors, geographic area, unique activity patterns, preferences, behaviors, and various sociodemographic characteristics. Additional tools related to exposure media and routes of exposure that are relevant to specific population groups are described in the Media and Routes Tool Sets of EPA-Expo-Box.

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