TESTIMONY OF EMILY STRAKE, SENIOR PROJECT CHEMIST/RISK ASSESSORLANGAN ENGINEERING AND ENVIRONMENTAL SERVICES, INC.BEFORE THE US CONGRESSIONAL PFAS TASK FORCE
May 6, 2019
Thank you for the opportunity to be here today and to participate in this important roundtable discussion. My objective is to provide the PFAS Task Force with perspective as it relates to the many challenges and obstacles associated with the development of risk-based concentrations for per and poly-alkylated substances (PFAS). Risk-based concentrations, such as those promulgated by the United States Environmental Protection Agency (EPA) as Health Advisories, have two primary inputs: exposure and toxicity. For PFAS chemicals, there is a high degree of scientific uncertainty associated with each component.
Exposure assessment of PFAS is generally more complex than other environmental contaminants given their ubiquity in ambient air, food, and commercial products, and their mobility and distribution in soil, groundwater, surface water, and dust. Most exposures to PFAS in the environment involve concurrent exposure to a complex mixture of multiple PFAS contaminants. With variations in chain length and functional groups, there are thousands of possible permutations of PFAS; however, limitations in the current analytical methodology permit identification of only a few dozen.
The most prevalent exposure route for humans is through diet, including ingestion of potable water. Under the Safe Drinking Water Act, the EPA accounts for non-drinking water exposures to contaminants through development of a Relative Source Contribution (RSC). The RSC ensures that chronic, non-cancer health effects will not occur when all contributing exposure pathways are considered. Today, there is insufficient information to develop a RSC to capture exposure from all PFAS sources.
Just two PFAS are well-studied from a toxicological standpoint (perfluorooctanoic acid [PFOA] and perfluorooctane sulfonic acid [PFOS]). The database of available studies is significant and improving for several more, including perfluorobutanoic acid (PFBA), perfluorobutane sulfonic acid (PFBS), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA). The absence of toxicity information for most PFAS results in an inability to develop chemical-specific, risk-based concentrations for health screening and environmental risk management, and prevents assessment of the aggregate health hazards associated with simultaneous exposure. The current limitations in published toxicity values represents a significant uncertainty for the scientific and regulated communities.
Toxicity studies that provide data on chronic health effects are currently available for only four PFAS. More studies are necessary to understand potential neurobehavioral effects; multigenerational studies are necessary to assess reproductive and developmental health effects. Some epidemiological evidence indicates a probable link of PFOA with testicular and kidney cancer; however, occupational studies have not found associations with increases in cancer incidence. Additional long-term animal studies of PFAS-associated cancer potential are necessary to understand the cancer endpoint.
The recent pace of investigation suggests that toxicity values are likely to be subject to revision over time as new studies become available. As our understanding of all contributing PFAS exposure pathways becomes more complete, it will inform the development of enforceable standards. This reality suggests that stakeholders should anticipate iterative amendment of risk-based concentrations, as data gaps are resolved. In conclusion, development of scientifically defensible, risk-based PFAS concentrations will require the attention and focus of all stakeholders for many years to come. Reducing uncertainty related to our understanding of PFAS exposure and toxicity is essential to establish credible, health-protective criteria.