As promised in our November 2018 blog post, “ATSDR PFAS Update: No Final Report Yet, But Further Guidance on Minimal Risk Levels and Drinking Water Concentrations,” we are providing an update on the Agency for Toxic Substances and Disease Registry’s recent release of its final Toxicological Profile for Perfluoroalkyls (Tox. Profile). This represents the ATSDR’s final guidance on these substances.
The purpose of the toxicological profile is to “succinctly characterize[] the toxicologic and adverse health effects information for these toxic substances…,” which are developed under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA).
ATSDR’s minimal risk levels (MRLs) are what are called “screening values”—they are not designed or intended to be used as public water standards, but they can provide “valuable information about PFAS exposures and potential public health impacts.” ATSDR’s MRLs are published in terms of dosage amounts [usually in milligrams/kilogram/day (mg/kg/day)] and not in terms of concentration [e.g., parts per trillion (ppt)]. Doses and concentrations are different concepts. A dose is the amount of a substance to which a person is exposed over some time period. In other words, dose is a measurement of exposure. A concentration on the other hand is the amount of a substance present in a certain amount of soil, water, air, food, blood, hair, urine, breath, or any other media. The ATSDR explains “most MRLs contain a degree of uncertainty because of the lack of precise toxicological information on the people who might be most sensitive (e.g., infants, elderly, nutritionally or immunologically compromised) to the effects of hazardous substances.”
The ATSDR’s final guidance on perfluoroalkyls concludes that even though there are a “large number of epidemiological studies [that] have examined the potential of perfluoroalkyls to induce adverse health effects, most of the studies are cross-sectional in design and do not establish causality…” “…although the data may provide evidence for an association, it does not always imply that the observed effect is biologically relevant because the magnitude of the change may be within the normal limits or not indicative of an adverse health outcome.” In essence, “cause-and-effect relationships have not been established” for various evaluated conditions, including pregnancy-induced hypertension/preeclampsia, increases in serum lipids, decreased antibody response to vaccines, or small decreases in birth weight. (See Tox. Profile at p. 6.)
Intermediate-duration oral MRLs (as opposed to acute or chronic duration), were derived for PFOA, PFOS, PFHxS and PFNA based on laboratory animal data, but the databases “were not considered adequate for derivation of MRLs for the other perfluoroalkyls.” In addition, no MRLs were set for inhalation exposure. (See Tox Profile at p. 17, 20-21).
The ATSDR notes that “exposure above MRLs does not mean that health problems will occur. Instead, it may act as a signal to health assessors to look more closely at a particular site where exposures may be identified. MRLs do not define regulatory or action levels for ATSDR.”
As mentioned, the entire profile can be found here.