PFAS is an issue filled with complexity, difficulty, and uncertainty. The good news is that the USEPA does a good job with technical assessments, and the risk assessment framework is similar to that of the international risk standard, ISO 31000.
The concerning news is that risk terminology is a "cottage industry" rich with many differences, the standard methods for USEPA risk assessment are filled with the application of large uncertainty factors, and the statutes for determining risk characterization (i.e., regulatory doses) are different in soil, groundwater, surface water, and air.
USEPA is open that their approach is weight-of-evidence. This means that the science may be quantitative, but conservative judgment (and subjectivity) is applied in the risk assessment process. The public, state rulemaking bodies, and state agencies are left to sort out non-environmental factors based on various risk characterizations that are a hybrid of objective and subjective approaches.
PFAS
PFAS, or perfluoroalkyl or polyfluoroalkyl substances, are fluorinated carbon-chain compounds. PFAS has been used in fire response, industrial applications, and consumer products for decades. For these reasons, PFAS is also found in landfills and wastewater treatment facilities. PFAS chemicals are manufactured and produced worldwide.
There are over 7000 PFAS compounds that have properties that allow them to repel water and oil. For this reason, PFAS chemicals do not break down easily over time and have been dubbed "forever chemicals."
The health effects of PFAS compounds are largely unknown.
PFAS Uses
PFAS has been used in fire response, industrial applications, and consumer products for decades. For these reasons, PFAS is also founded in landfills and wastewater treatment facilities. PFAS chemicals are manufactured and produced worldwide.
PFAS Groupings
Three types of PFAS are in the process of being more heavily regulated. USEPA is in the final steps of developing compliance standards for PFOS and PFOA. GenX is a third form of PFAS specific to North Carolina but not to every state.
PFAS Regulation
Regulating this expansive group of chemicals can be difficult and complex. We understand that PFAS does not break down easily, but we do not fully understand how it is transported from one media to another. Our traditional sampling methods and laboratory standards have had to be improved to the "parts per trillion" level. And we simply do not have enough data from the field or human health studies.
USEPA recognizes the importance of the threshold concept in a regulatory context. Desired exposures are based on the lowest thresholds within a population. Getting from the science to the lowest thresholds within a given population is where technical judgment comes into play.
It is noteworthy that most of the human health analysis is not derived from studies on human beings. The studies on humans further complicate this since few focus on the targeted classes for protection, such as infants and the elderly. Therefore, several levels of uncertainty factors are applied in the risk analysis by USEPA.
USEPA Human Health Risk Assessments
USEPA Human Health Risk Assessments have a risk assessment component and a risk management component. The risk assessment component is performed by USEPA and results in a risk criterion. Risk mitigation, including regulatory doses or concentrations, is normally performed at the state level to incorporate local situations, affordability, state laws, and available treatment technologies.
Ideally, the federal risk assessment aspect and the state risk management evaluations would inform one another simultaneously. In practice, some state-specific issues are being addressed concurrently, but much work is done after the federal criterion is approved.
USEPA and ISO 31000 Are Similar
The risk assessment performed by USEPA consists of determining a reference dose, including uncertainty factors applied to it based on data confidence and probable exposure. The terminology in human health risk assessments and the international risk standard differs, potentially leading to confusion or misunderstanding when introduced to hybrid regulatory decision-making bodies and the public. However, the basic processes of the risk assessment followed by risk treatment decisions are the same.
USEPA Risk Assessments
EPA created the Integrated Risk Information System (IRIS) Program in 1985 to provide an internal database of human health assessments for chemicals found in the environment. The goal of the IRIS Program was to foster consistency in evaluating chemical toxicity across the Agency. Since then, the IRIS Program has also become an important public resource. The IRIS Program has evolved with the state of the science to produce high-quality, evidence-based assessments and provide increasing opportunities for public input into the IRIS process.
EPA created two Agency-wide workgroups at that time, the Carcinogen Risk Assessment Verification Endeavor Workgroup (CRAVE) and RfC/RfD Workgroup. These workgroups were formed to reach Agency consensus scientific positions on human health effects that may result from chronic oral or inhalation exposure to chemicals found in the environment.
USEPA Risk Analysis and Uncertainty Factors
Uncertainty factors are part of the risk analysis and a meaningful component of the RfD (Reference Dose). Uncertainty factors consist of multiples of 10, each representing a specific uncertainty inherent in the available data.
According to USEPA, while the original selection of safety factors appears to have been rather arbitrary (Lehman and Fitzhugh, 1954), subsequent analysis of data (Dourson and Stara, 1983) lends theoretical (and in some instances experimental) support for their selection. Further, some scientists, but not all, within the EPA interpret the absence of widespread effects in the exposed human populations as evidence of the adequacy of traditionally employed factors.
One and five uncertainty factors are applied to research data to develop the reference dose. Four are a binary choice of 1 to 10, and the fifth is a judgment between 1 and 10.
Use a 10-fold factor when extrapolating from valid experimental results in studies using prolonged exposure to average healthy humans.
Use an additional 10-fold factor when extrapolating from valid results of long-term studies on experimental animals when studies of human exposure are unavailable or inadequate.
Use an additional 10-fold factor when extrapolating from less than chronic results on experimental animals when there are no useful long-term human data.
Use an additional 10-fold factor when deriving an RfD from a LOAEL instead of a NOAEL.
Use professional judgment to determine the MF, which is an additional uncertainty factor greater than zero and less than or equal to 10.
The math of five factors yields the net effect that the reference dose will be 10 to 100,000 times the level determined by its underlying experiments. USEPA documents that references doses are frequently one order of magnitude higher than the underlying measurements due to uncertainty factors.
Risk Exposure
Depending on the dose employed, exposure to a given chemical may result in various toxic effects. The exposure assessment includes consideration of the size and nature of the populations exposed and the magnitude, frequency, duration, and routes of exposure, as well as evaluation of the nature of the exposed populations.
The USEPA's Public Health and Integrated Toxicology Division (PHITD) performs integrated epidemiological, clinical, animal, and cellular biological research and statistical modeling to provide the scientific foundation in support of hazard identification, risk assessment, and standard setting to protect public health and the environment.
PHITD scientists identify at-risk populations and evaluate the environmental risk to multiple aspects of human health, including reproduction, pregnancy, pre- and postnatal development, and the cardiac, immune, nervous, and endocrine systems. It uses an "Assay to Outreach" approach where fundamental research is performed to understand toxicological responses and mechanisms; these assays are confirmed in clinical and population-based studies that link environmental conditions to health.
Risk Characterization (Criterion)
Risk characterization is the final step in the risk assessment and the first input to the risk management (regulatory action) process. The purpose of risk characterization is to present the risk manager with a synopsis and synthesis of all the data that should contribute to a conclusion with regard to the nature and extent of the risk, including:
The qualitative ("weight-of-evidence") conclusions as to the likelihood that the chemical may pose a hazard to human health.
A discussion of the dose-response information considered in deriving the RfD (Reference Dose), including the uncertainty factors.
Data on the shapes and slopes of the dose-response curves for the various toxic endpoints, toxicodynamics (absorption and metabolism), structure-activity correlations, and the nature and severity of the observed effects.
Estimates of the nature and extent of the exposure and the number and types of people exposed.
Discussion of the overall uncertainty in the analysis, including the major assumptions made, scientific judgments employed, and an estimate of the degree of conservatism involved.
The kind of toxicity data used by EPA's Risk-Screening Environmental Indicators (RSEI) model and how the toxicity weights are calculated and selected for use in RSEI results, including RSEI Hazard and RSEI Scores, are provided on the USEPA website.
RSEI uses toxicity data from EPA's Integrated Risk Information System (IRIS) where possible. For chemicals with incomplete information in IRIS, RSEI uses the following sources (in order of preference):
EPA's Office of Pesticide Programs (OPP) Acute Chronic and Reference Doses Table lists.
The Agency for Toxic Substances and Disease Registry (ATSDR) Minimum Risk Levels (MRLs).
California Environmental Protection Agency (CalEPA) Approved Risk Assessment Health Values.
EPA's Provisional Peer Reviewed Toxicity Values (PPRTVs).
EPA's Health Effects Assessment Tables (HEAST).
Derived Values. For a prioritized group of chemicals for which sufficient data was not found in the above sources, a group of EPA expert health scientists reviewed other available data to derive appropriate toxicity weights.
For each chemical, RSEI determines the following values, where possible:
Oral slope factor (OSF) in risk per mg/kg-day.
Inhalation unit risk (IUR) in risk per mg/m3.
Reference dose (RfD) in mg/kg-day.
Reference concentration (RfC) in mg/m3.
Risk Mitigation
Once the risk characterization is completed, the focus turns to risk management. Per USEPA, the risk manager utilizes the results of risk assessment, other technological factors, and legal, economic, and social considerations in reaching a regulatory decision. These additional factors include efficiency, timeliness, equity, administrative simplicity, consistency, public acceptability, technological feasibility, and the nature of the legislative (federal or state) mandate.
Risk management decisions must be made on a case-by-case basis because these risk management factors may impact different cases. And those decisions are desirably consistent, yet not necessarily identical.
One primary example is the federal statutes.
The Clean Water Act calls for decisions with "an ample margin of safety."
The Safe Drinking Water Act (SDWA) calls for standards that protect the public "to the extent feasible."
The Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) calls for "an ample margin of safety," taking benefits into account.
A chemical with a specific RfD may be regulated under different statutes and situations through the use of different regulatory doses (RgDs). Per USEPA, the risk manager selects the appropriate statutory alternative after carefully considering the various environmental risk and non-risk (non-environmental) factors, regulatory options, and statutory mandates in a given case.
Public review and public comment are a required part of the process at both federal and state levels.
Summary
PFAS is an issue filled with complexity, difficulty, and uncertainty. Regulating this expansive group of chemicals can be difficult and complex. Many PFAS do not have enough data to determine a Reference Dose and Drinking Water Equivalency Level. Little information about health effects is known for many PFAS compounds. Field sampling and laboratory processes are evolving to "parts per trillion." And transport mechanisms between water, air, and solids are not understood well.
The good news is that the USEPA does a good job with technical assessments, and the risk assessment framework is similar to that of ISO 31000.
The concerning news is that risk terminology is a "cottage industry" rich with many differences, the standard methods for USEPA risk assessment are filled with the application of large uncertainty factors, and the statutes for determining risk characterization (i.e., regulatory doses) are different in soil, groundwater, surface water, and air.
USEPA is open that their approach is weight-of-evidence. This means that the science may be quantitative, but conservative judgment (and subjectivity) is applied in the risk assessment process. The public, state rulemaking bodies, and state agencies are left to sort out non-environmental factors based on various risk characterizations that are a hybrid of objective and subjective approaches.
Note: This article uses several USEPA reference documents.
JD Solomon Inc provides solutions for facilitation, asset management, and program development at the nexus of facilities, infrastructure, and the environment. JD is a current member and former chairman of the North Carolina Environmental Commission, the state's environmental rulemaking body. Sign-up for monthly updates.
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