Department of Health
331-673 • Revised November 1, 2021
Summary
In October 2017, the State Board of Health (board) accepted a petition from ten organizations to establish drinking water standards for per- and polyfluoroalkyl substances (PFAS). Board authority to adopt such standards comes under RCW 43.20.050(2), RCW 70.119.080(1), and RCW 70.142.010.
To support the board, the Washington Department of Health (department) released draft state action levels (SALs) for five PFAS in November 2019. These PFAS occur in Washington drinking water and had sufficient scientific information to recommend a value. We presented the draft rule language at stakeholder workshops and at numerous meetings with stakeholders. After evaluating the feedback from these events and from two public comment periods, we updated our technical document and lowered our recommendation for the PFBS SAL from 1,300 to 345 ng/L to better protect infants. We also revised the PFNA SAL from 14 to 9 ng/L based on new evidence of serum half-life in humans. The PFHxS SAL was revised slightly to correct our calculation of average maternal body weight used in the infant exposure model. The revised SAL values are part of the proposed rule being considered for adoption by the State Board of Health in 2021.
The recommended SALs for PFOA, PFOS, PFNA, PFHxS, and PFBS are shown in Table 1. The department developed these recommended values after evaluating primary scientific literature on PFAS and reviewing health protective values in recent toxicological assessments by U.S. federal and state agencies. The health protective values we selected are based on immune, developmental and thyroid hormone effects observed in toxicity testing in laboratory animals. While epidemiological data were not used quantitatively to derive these values, they were considered as part of the evidence base.
The SALs were calculated like a maximum contaminant level goal (MCLG) under the Safe Drinking Water Act. They assume that 20-50 percent of the daily acceptable exposure can come from a drinking water source. Because four of these PFAS are highly bioaccumulative, we used a model to estimate accumulated exposure over many years of drinking water consumption. Specifically, we used a model developed by the Minnesota Department of Health, to estimate age-specific exposure to PFOS, PFOA, PFNA, and PFHxS when they occur in community drinking water. This model accounts for maternal transfer of PFAS to the growing child at the time of birth and during breastfeeding.
The SALs represent the maximum level in tap water that we consider to be without health concern for long-term consumption in daily drinking water. The SALs were developed to specifically protect early life stages of development (fetal, infancy) because these periods of rapid development are potentially more susceptible to adverse effects of these PFAS, and infants have relatively high exposure to contaminants in drinking water. Acting at these levels is consistent with the mission of providing safe and reliable drinking water and consistent with the SDWA.