As most of our readers know, our firm has written extensively on PFAS, and we recently gave a 30 minute, free webinar on the important findings of the ATSDR’s toxicological profile on per- and polyfluoroalkyl substances (PFAS). The webinar discussed the Agency for Toxic Substances and Disease Registry’s role in setting minimal risk levels (MRLs) for toxic substances, including comprehensive analyses of selected contaminants that are deemed most harmful to human health. Because the PFAS profile is perhaps the most thorough evaluation of the medical science and literature on PFAS, we are constantly monitoring any developments. Today, we are reporting on ATSDR’s adoption of water contamination MRLs.
As many know, people can expose themselves to per- and polyfluoroalkyl substances (PFAS) by drinking contaminated municipal water or private well water or, for example, by eating fish caught in PFAS contaminated water, among other ways. Drinking water is the primary exposure source of concern. ATSDR’s MRLs are what are called “screening values” – they are not designed or intended to be used as public water standards, but they do 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.
Just last week, the ATSDR released drinking water concentrations for perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid (PFHxS) and perfluorononanoic acid (PFNA) – the four PFAS family of chemicals that have been garnering the most scrutiny. The MRL screening values released in the initial public draft report, in a nutshell, can be converted into drinking water concentrations for adults and children based on mathematical equations and information about a person’s body weight, and how much water they drink each day. When ATSDR uses an average adult’s or child’s weight and water intake to convert these MRLs into drinking water concentrations, the individual concentrations (also referred to as environmental media evaluation guides) are: PFOA: 78 ppt (adult) and 21 ppt (child); PFOS: 52 ppt (adult) and 14 ppt (child); PFHxS: 517 ppt (adult) and 140 ppt (child); PFNA: 78 ppt (adult) and 21 ppt (child).
These concentration numbers are of a different utility than the Health Advisories (“HAs”) or Maximum Contaminant Levels that are meant to indicate the potential occurrence of health impacts (remember the outcry about the much lower concentrations inferred from the ATSDR report as compared to those HAs adopted by the EPA!) In sum, these individual concentrations are used to compare to concentrations in drinking water to determine if further evaluation is needed at a particular site. As we discussed in our webinar, issues surrounding co-exposure (exposure to multiple PFAS substances) still exist, but these concentration numbers do provide further guidance to public utilities and other important actors in studying the nature and extent of contamination in water at a site.
We still await the final report from the ATSDR, and we will provide any further updates on the toxicological profile as they become available.