MPH 530 Module 7 Chemical Risk Assessment Example

Forever Chemicals and the Four Steps: Applying Risk Assessment to PFAS in Drinking Water

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Master of Public Health Program, Aspen University

MPH 530: Environmental Issues in Public Health

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Forever Chemicals and the Four Steps: Applying Risk Assessment to PFAS in Drinking Water

Thousands of chemicals are used in commerce, and public health agencies must decide which pose risks worth acting on. Chemical risk assessment offers a structured way to judge those risks from evidence. This paper explains the four-step risk assessment framework and applies it to per- and polyfluoroalkyl substances, known as PFAS or forever chemicals, found in the drinking water of a composite town beside a firefighting training site.

The Framework

A landmark federal report set out risk assessment as four steps: hazard identification, dose-response assessment, exposure assessment and risk characterization. It also recommended keeping risk assessment, a scientific process, separate from risk management, which weighs policy, cost and social values in deciding what to do (National Research Council, 1983). That separation remains central to how agencies regulate chemicals.

What PFAS Are

PFAS are a large family of synthetic chemicals with carbon-fluorine bonds that resist heat, water and grease. They have been used in nonstick cookware, stain-resistant fabrics, food packaging and firefighting foam. The same bonds that make them useful make them extremely persistent in the environment and in the body, where some remain for years.

The Composite Town

A town of 18,000 people draws water from wells near a regional firefighting training site where foam containing PFAS was sprayed for decades. Testing found combined PFOA and PFOS concentrations of 70 parts per trillion in two wells. Residents asked whether their water was safe and what the exposure meant for their children.

Step 1: Hazard Identification

Hazard identification asks whether a chemical can cause harm. A review of PFAS exposure and health found significant associations with adverse immune outcomes in children and with dyslipidemia as the strongest metabolic outcome, while evidence for cancer came mainly from highly exposed manufacturing communities (Sunderland et al., 2019). The weight of evidence identifies PFAS as hazards to immune and metabolic health.

Step 2: Dose-Response Assessment

Dose-response assessment asks how the likelihood or severity of harm changes with dose. In a birth cohort in the Faroe Islands, a doubling of major PFAS concentrations in children's blood at age 5 was associated with a 49% lower overall antibody concentration after routine vaccinations, and with higher odds of antibody levels falling below protective thresholds at age 7 (Grandjean et al., 2012). Such findings, at exposures found in the general population, pushed regulators toward very low limits.

Step 3: Exposure Assessment

Exposure assessment estimates how much people take in and by what routes. Drinking water contaminated by firefighting foam is a major source near airports and military bases, and food, food packaging, dust and consumer products also contribute (Sunderland et al., 2019). In the composite town, water was the dominant pathway, and bottle-fed babies had the highest intake for their weight.

Step 4: Risk Characterization

Risk characterization integrates the first three steps into a statement of risk and its uncertainty. The table summarizes the application to the town.

Uncertainty

Every step carries uncertainty: which PFAS matter most, how mixtures act, how animal and cohort findings translate to other populations and how long exposures lasted. Risk assessors address uncertainty with safety factors and ranges rather than single numbers. The key question for managers is whether uncertainty justifies delay or caution.

The Precautionary Principle

The precautionary principle holds that when an activity threatens serious or irreversible harm, lack of full scientific certainty should not postpone protective action. For PFAS, reviewers have argued that lessons from older compounds show limited data should not delay action on newer replacement PFAS (Sunderland et al., 2019). Precaution is especially relevant for persistent chemicals that remain in bodies and ecosystems.

Risk Management

Risk management options for the town include immediately providing bottled water or filters to households with infants and pregnant women, installing granular activated carbon or ion exchange treatment at the wells, blending with cleaner sources, offering blood testing with clear interpretation, pursuing cost recovery from the responsible party and supporting a regional plan to stop foam use. National drinking water limits of 4 parts per trillion each for PFOA and PFOS, set in 2024, provide a regulatory target. Each option was compared on speed, cost, reliability and how completely it would cut exposure for the most sensitive residents.

Communicating Risk

Residents want to know what the numbers mean for their families. The health department held meetings explaining what PFAS are, what the town's levels mean compared with standards, what steps are being taken and what residents can do now. Blood test results were explained in context, since there is no clinical treatment to remove PFAS from the body.

Biomonitoring

National biomonitoring surveys have measured PFAS in the blood of nearly all Americans tested. Levels of the older compounds have declined since manufacturers phased them out, while replacement PFAS are harder to track. Biomonitoring in exposed communities helps characterize exposure but cannot identify individual health effects.

Cumulative and Mixture Effects

People are exposed to many PFAS at once. Regulators increasingly consider groups of PFAS together using hazard indexes, because assessing each compound separately may underestimate combined risk. Mixture assessment is a frontier of risk assessment for many chemical classes.

Community Involvement

Residents in PFAS-affected communities have often driven testing and action, organizing to demand data and cleanup. Including residents in advisory groups, sharing all test results and explaining uncertainty honestly builds trust and helps agencies set priorities that reflect community concerns.

Conclusion

The four-step risk assessment framework gives public health a disciplined way to evaluate chemical hazards like PFAS: identifying harm, describing dose-response, estimating exposure and characterizing risk with its uncertainties. Applied to the composite town, it shows exposure well above levels of concern and supports prompt protective action. Keeping science and management distinct, while applying precaution for persistent chemicals, helps protect communities.

References

Grandjean, P., Andersen, E. W., Budtz-Jørgensen, E., Nielsen, F., Mølbak, K., Weihe, P., & Heilmann, C. (2012). Serum vaccine antibody concentrations in children exposed to perfluorinated compounds. JAMA, 307(4), 391-397. https://doi.org/10.1001/jama.2011.2034

National Research Council. (1983). Risk assessment in the federal government: Managing the process. National Academies Press. https://doi.org/10.17226/366

Sunderland, E. M., Hu, X. C., Dassuncao, C., Tokranov, A. K., Wagner, C. C., & Allen, J. G. (2019). A review of the pathways of human exposure to poly- and perfluoroalkyl substances (PFASs) and present understanding of health effects. Journal of Exposure Science & Environmental Epidemiology, 29(2), 131-147. https://doi.org/10.1038/s41370-018-0094-1