U.S. EPA Proposes Nationwide Drinking Water Standards for So-Called “Forever Chemicals”
On Tuesday, March 14, 2023, the United States Environmental Protection Agency (EPA) proposed National Primary Drinking Water Regulation (NPDWR) for six per- and polyfluoroalkyl substances, known as “PFAS,” and commonly referred to as “forever chemicals.” The proposed rules would set very low limits for six target PFAS contaminants: PFOA, PFOS, PFHXS, PFNA, PFBS and HFPO-DA (commonly known as “GenX”). The new rules would apply only to public drinking water and would set a limit of 4 exceeded 4 parts per trillion (ppt) for PFOS or PFOA. For PFNA, PFHxS, PFBS and GenX, the proposal would limit any mixture containing one or more of these substances based on a “hazard index calculation” to determine if the combined levels for these PFAS substances poses a potential risk.
A hazard index is a long-established tool used by the EPA, for example in Superfund cases, to understand the health risks from chemical mixtures. A hazard index uses the sum of fractions to calculate a value. If the value calculated is greater than 1.0, it is considered a violation of the proposed hazard index maximum contamination limit, or MCL. Under the proposed rule, each of the four target PFAS substances is divided by a different health-based value (HBV) and then added up. For PFNA, the HBV is 10 ppt, for PFHxS the HBV is 9 ppt, for PFBS the HBV is 2,000 ppt and for GenX it is 10 ppt. The concentrations for each of these substances is divided by its HBV and then totaled up and compared to the MCL of 1.0.
The proposed rule also sets non-enforceable Maximum Contamination Level Goals (MCLGs) for each of these constituent PFAS substances. For PFNA, PFHxS, PFBS and GenX, the MCLG is the same as the MCL of 1.0 based on the hazard index calculation explained above, but for PFOS and PFOA, it is zero ppt. While non-enforceable, this means that the EPA is suggesting that any level of either PFOA or PFOS in public drinking water should be an issue and the goal of the utility should be its complete and total removal.
PFAS are commonly referred to as “forever chemicals” because they break down very slowly over time. According to the EPA, current scientific research suggests that exposure to high levels of certain PFAS may lead to adverse health effects. However, research is still ongoing to determine how different PFAS can lead to a variety of health effects. Research is also trying to better understand the health effects associated with low levels of exposure to PFAS over longer periods of time.
Prior to the new proposal, the EPA had not set national drinking water standards for PFAS substances but had published what are referred to as Health Advisory Limits (HALs) for PFOA and PFOS. Like MCLGs, HALs are non-enforceable and are intended only as guidance to state and local authorities. The EPA initially published a HAL of 70 ppt for both PFOA and PFOS. However, in June of last year, the EPA lowered the interim HALs for PFOA and PFOS to 0.004 and 0.02 ppt, respectively.
While the proposed MCLs of 4 ppt for PFOA and PFOS are several orders of magnitude higher than the prior HALs of 0.004 and 0.02 ppt, it is important to note that the minimum reporting level (MRL) based on today’s technology is generally considered to be around 4 ppt for both PFOA and PFOS. This means that any detection of these substances in public drinking water will be an exceedance under the new proposal.
Under the new rules, utilities that operate public drinking water systems would be required to monitor for these target PFAS substances, notify the public of the applicable MCLs, and in the event of an exceedance, reduce the levels to below the MCLs. It should be noted, however, that these rules are only proposals at this point, and no action is required unless and until the rules are finalized. The EPA anticipates finalizing these regulations by the end of 2023. The EPA is currently requesting public comments on the proposed rules.
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