EPA’s decision to propose limits on four PFAS in drinking water through a novel Hazard Index (HI) approach aimed at addressing the dose-additivity of chemical mixtures is winning mixed reviews, with one utility source warning it could result in overly strict treatment mandates while one environmentalist says it is a good way to address risks of mixtures.
The water utility source warns that EPA’s use of the HI approach could require treatment even where the levels of the chemicals by themselves do not exceed tough health advisory levels (HALs) the agency has set for some PFAS.
But some environmentalists, like Melanie Benesh, vice president of government affairs at the Environmental Working Group (EWG), notes in her twitter feed March 14 that EPA’s proposed HI approach “is a way of acknowledging that there are risks from combined exposures, even if each individual exposure is considered safe.”
However, another environmental group is questioning EPA’s use of the approach, fearing it could result in misinterpretations.
Kyla Bennett, science policy director for Public Employees for Environmental Responsibility, tells Inside PFAS Policy she would have preferred EPA to have adopted a standard approach setting a maximum contaminant level (MCL) using parts per trillion units, for ease of use, rather than the HI approach.
But Bennett also contends that the regulation should be broader than just these handful of PFAS, arguing without such an approach, companies will likely develop regrettable substitutions, tweaking their formulas to develop different, replacement PFAS for the chemicals subject to EPA regulation.
“EPA’s proposed regulations are baby steps forward, but are too little and too late,” she said in a press statement following the proposed rule’s announcement, noting that at least 14,000 PFAS have been identified.
At issue is EPA’s adoption of the HI method when setting standards for four of the six per- and polyfluoroalkyl substances (PFAS) subject to its landmark proposed Safe Drinking Water Act (SDWA) regulation.
The proposed rule seeks to set traditional MCLs, enforceable cleanup standards, for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) -- the two most studied PFAS -- at 4 parts per trillion (ppt), the level at which most laboratories can reliably detect those two contaminants.
The proposal would also regulate the four additional PFAS -- hexafluoropropylene oxide (HFPO) dimer acid, which is more commonly referred to as a GenX chemical; perfluorononanoate (PFNA), perfluorohexanesulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS) -- in mixtures under the general HI approach.
EPA is proposing a maximum contaminant level goal (MCLG) -- the level at which no anticipated adverse health effects occur and that allow for an adequate margin of safety -- and an MCL for these four substances, but not through a traditional unit of measure. Instead, the proposed MCLG and MCL for the four is an HI of 1.0 (unitless).
MCLs are set as close as feasible to an MCLG, but take into account technical feasibility and cost.
Health-Based Water Concentration
To determine the HI for mixtures of any these four PFAS, water systems would monitor and compare the amount of each PFAS in drinking water to its associated Health-Based Water Concentration (HBWC), which is the level at which no health effects are expected for that PFAS individually, EPA says in a fact sheet on the proposal. To come up with a comparison value for a chemical, water systems would divide the amount of the chemical in a drinking water sample by the HBWC.
Water systems would then add the comparison values for each PFAS contained within the mixture. If the value is greater than 1.0, it would be an exceedance of the proposed Hazard Index MCL for these four PFAS, the agency adds.
The agency in the proposed rule sets out the HBWCs for all four. They are 9.0 ppt for PFHxS, 10 ppt for GenX chemicals, 10 ppt for PFNA, and 2,000 for PFBS.
EPA says in another fact sheet that such an approach is needed because “many PFAS are found together and in different levels and combinations. Estimating risk by considering one chemical at a time may underestimate the health risks associated with exposure to many PFAS at the same time.”
EPA says in the rule that as it examined health effects data, it found that exposure through drinking water to a mix of PFAS “can be assumed to act in a dose-additive manner. . . . This dose additivity means that low levels of multiple PFAS, that individually would not likely result in adverse health effects, when combined in a mixture are expected to result in adverse health effects.” EPA as a result decided to use an HI approach.
Once EPA finalizes the rule, expected by year’s end, it will require water systems to conduct initial monitoring for the six chemicals within three years. EPA says it will allow systems to use previously collected monitoring data, such as that for the Unregulated Contaminant Monitoring Rule 5, to satisfy initial monitoring requirements.
Betsy Southerland, a former EPA waste and water official is applauding the agency’s HI approach for addressing mixtures of four PFAS, noting EPA offers a “great defense” of the approach -- dubbed the “general Hazard Index” approach -- which allows for the most sensitive health effects, even if they differ, caused by each chemical in the mixture to be considered.
Southerland notes that the agency chose a “general HI” rather than a “target organ HI.” This allows for the four chemicals to differ as to the health endpoint -- the most sensitive health effect -- that triggers their risk values. In contrast, a target organ HI “requires all chemicals in a mixture to have reference values based on the same organ (e.g., liver) or organ system (e.g., fetal development),” she adds.
“Because PFAS chemicals have not been systematically studied for every possible health effect, it is unlikely they would all be assessed for effects on the same organ or organ system,” she says. “The general HI approach allows those chemicals to be included in dose additivity.”
She notes too that EPA adds that all four of the chemicals “have detrimental effects on some of the same organs or organ systems even though the most sensitive health endpoint used to calculate the reference value differs” among the four PFAS.
EPA in the draft rule indicates the general HI approach is “a more health protective indicator of risk.” It says, “The target-organ specific HI approach produces a less health protective estimate of risk than the general HI when a contaminant impacts multiple organs because the range of potential effects has been scoped to a specific target organ, which may be one of the less potent effects or for which there may be significant currently unquantified effects.”
Health Advisory Levels
But the utility source says one “preliminary issue” with the rulemaking is that a water system could exceed the MCL for two of the four chemicals subject to the HI approach -- GenX or PFBS -- even where they are present at levels below EPA’s HALs.
That seems to conflict with how EPA framed its HALs in the past, the source says. EPA has said HALs “indicate the level of drinking water contamination below which adverse health effects are not expected to occur,” according to an EPA June 2022 press release referencing the new levels at the time.
The source believes it will be challenging for water systems to communicate to the public the HI that results. The source also notes that while dose additivity has been validated and well-established scientifically, the source wonders if its application in this situation is scientifically appropriate. In particular, the source notes that the four compounds have toxicity values based on three different health endpoints -- thyroid, liver and developmental effects, while the source contends that dose-additivity is linked to the chemicals’ sharing common health effects.
In the proposed rule, EPA also says it is now issuing a preliminary regulatory determination to regulate the four additional PFAS, alongside its issuance of the NPDWR. While EPA in 2021 made a final regulatory determination to regulate PFOA and PFOS, it did not do so for the other four, but agency officials last year signaled EPA was weighing regulating additional PFAS that could possibly be co-removed when water is treated to take out PFOA and PFOS.
“New information demonstrates that these [additional four] PFAS meet the SDWA criteria for regulation including that they may have adverse health effects, that they are likely to be found in public water systems with a frequency and at levels of concern, and that there is a meaningful opportunity for health risk reduction through a national drinking water regulation,” EPA says in the draft rule, noting it will take public comment on the preliminary determination prior to finalizing that determination and finalizing the NPDWR.
EPA establishes an MCLG based on a toxicity value, which is typically a reference dose it develops, but similar toxicity values, such as those developed by the Agency for Toxic Substances and Disease Registry (ATSDR), can also be used if representing the best available science, the agency says in its MCLG Summary Document for a Mixture of Four PFAS, also released March 14 for public comment. EPA previously developed final toxicity values for GenX chemicals and PFBS -- which triggered it to move ahead with non-regulatory drinking water HALs last June at 10 ppt and 2,000 ppt, respectively. Meanwhile, ATSDR in 2021 established toxicity values in the form of minimal risk values for PFNA and PFHxS. -- Suzanne Yohannan (syohannan@iwpnews.com)
