Factors to Consider in the PHA Process

This section describes factors health assessors must consider during the PHA process. It also describes the similarities and differences between the ATSDR PHA and EPA risk assessment processes.

Minimum Factors to Consider

By law, ATSDR is required to consider certain factors when evaluating possible public health hazards. At a minimum, during the PHA process health assessors need to consider the following factors:

  • Nature and extent of contamination. What is the spatial and temporal extent of site-related contamination? Have contaminants migrated off site? What media have been and/or continue to be affected (e.g., water, soil, air, biota)?
  • Demographics (population size and susceptibility). Who is being exposed, and do any special populations need to be considered (e.g., children, women of child-bearing age, pregnant women, lactating women, the elderly)?
  • Pathways of human exposure (past, current, and future). How might people be exposed to site-related contamination (e.g., drinking water, breathing air, direct skin contact)? What are the site-specific exposure conditions (e.g., duration and frequency of exposure)?
  • Health effects and disease-related data. How do estimated site-specific exposure doses and concentrations for the hazardous substances compare to those associated with observed health effects from toxicologic, epidemiologic, and medical studies? How do existing morbidity and mortality data on diseases compare with observed levels of exposure?

Every site is different. Not all of the elements of the PHA process will apply to all sites. The resources you need, and your level of evaluation will vary. Some sites require extensive data gathering (sampling) and evaluation of multiple contaminants and exposure pathways. Others require only a focused review of a single pathway with little contamination. It is also important for health assessors to evaluate and acknowledge what may be site-related and what is not.

Understanding EPA’s Risk Assessment Process

Congress authorized both ATSDR, using its PHA process, and EPA, using its risk assessment (RA) process, to evaluate spills or releases of hazardous substances in the environment to protect public health. The agencies collaborate during their efforts, with ATSDR serving in an advisory role and EPA serving in a regulatory role. Early in the RA process, ATSDR can sometimes influence EPA’s sampling efforts and priorities to obtain the most appropriate data to determine exposure and possible health outcomes. In turn, EPA uses information from ATSDR’s PHA process to help guide actions at sites. See a side-by-side comparison of ATSDR’s PHA and EPA’s RA processes in the table below.

ATSDR PHA and EPA RA Processes

ATSDR PHA and EPA RA Processes
Objective To characterize the nature and extent of human exposure to hazardous spills or releases and recommend screening, treatment or environmental changes to prevent or reduce future exposures, as well as ensure those interventions are implemented. To reduce or eliminate pollutants that could harm the environment and human health, as well as to guide regulators in determining safe regulatory limits and prioritizing Superfund sites for remedial action (“cleanup”).
Legislative Mandate CERCLA directs ATSDR to determine whether actions “should be taken to reduce human exposure to hazardous substances from a facility and whether additional information on human exposure and associated health risks is needed and should be acquired.” CERCLA requires EPA to assess “permanent solutions and alternative treatment technologies or resource recovery technologies that, in whole or in part, will result in a permanent and significant decrease in the toxicity, mobility, or volume of the hazardous substance, pollutant or contaminant.”
Key Activities Provides public health expertise on sampling methodologies and plans, cleanup options, public health measures, and the health implications of regulatory options to other federal agencies (including EPA), state agencies, private organizations, and individuals. Establishes and enforces environmental regulations to mitigate or eliminate releases. EPA requires responsible entities to clean up or pay for cleanup of spills or releases. EPA’s Brownfields program also funds cleanup of certain abandoned properties.
Timeframe Looks at past, current, and potential future exposures to hazardous contaminants. Looks at only current and future exposures to hazardous contaminants.
Exposure Pathway Evaluation Evaluates actual or likely pathways to assess if human exposure has occurred or is likely to occur. Evaluates all possible exposure pathways to assess risk to human health and the environment.
Use of Information Uses the same environmental data as EPA, but integrates site-specific exposure conditions, health effects data based on real observations, and specific community concerns. Uses standard (default) protective exposure assumptions to evaluate risk from potential site exposures to all contaminated media, regardless if exposures are occurring or could occur.
Purpose Conducts PHA activities to direct action to protect the health of the community. Conducts RA activities to determine necessary cleanup and remedial actions, designate releases at NPL sites, enforce regulatory action, and hold entities legally accountable for environmental violations. EPA uses ATSDR’s assessments to help inform actions at sites.
Type of Exposure Estimates Calculates numeric estimates of exposure doses, hazard quotients, and potential cancer risks based on site-specific parameters, and performs an in-depth analysis to determine if harmful health effects are possible. Provides a numeric estimate of theoretical risk or hazard, assuming no site cleanup, which generally overestimates the true potential impact of exposure (appropriate for exposure prevention and prioritizing site cleanup).
Featured Resource
EPA's Superfund Risk Assessment Website: Human Health Topics

This website provides the guidance that EPA follows when addressing hazardous waste sites and performing risk assessments.


Page last reviewed: August 4, 2022