The formaldehyde dispute - Part B: scientific critique of EPA's formaldehyde occupational exposure values (OEVs) and proposed alternative occupational exposure limits (OELs).
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In 2024, the U.S. Environmental Protection Agency (EPA) finalized its Integrated Risk Information System (IRIS) Toxicological Review and Toxic Substances Control Act (TSCA) Risk Evaluation for formaldehyde. After analyzing all the data that they deemed relevant, TSCA relied on IRIS's proposed inhalation reference values to establish an 8-hour occupational exposure value (OEV) of 0.11 ppm derived from epidemiological evidence of nasopharyngeal cancer. They also developed a 15-minute OEV of 0.17 ppm based on the goal of preventing sensory irritation. In an earlier draft of EPA's TSCA Risk Evaluation, they initially proposed an 8-hour OEV of 0.011 ppm derived from residential exposure studies of children, but this was withdrawn. This review examined EPA's methodology, the nearly 40 years of scientific literature underlying the EPA's conclusions, and the more than 300 public comments, which were submitted to the draft IRIS Toxicological Review (Docket ID: [EPA-HQ-ORD-2010-0396]) and draft TSCA Risk Evaluation (Docket ID: [EPA-HQ-OPPT-2023-0613]). A minimum of five significant flaws were identified and discussed: (1) heavy reliance on epidemiological studies which had serious confounding factors and design limitations; (2) application of default uncertainty factors which were too high given the robust human data; (3) use of exclusion criteria which dismissed high-quality studies from being considered; (4) the use of a linear no-threshold (LNT) model despite decades of substantial evidence for a threshold-driven mode of action (MOA); and (5) neglect for a validated biologically based dose-response (BBDR) model which may have been the most robust ever developed. Based on our weight-of-evidence evaluation of toxicological, mechanistic, and epidemiological data, we propose occupational exposure limits (OELs) of 0.3 ppm (8-hour TWA) and 1 ppm (15-min STEL). These values are grounded in controlled human exposure studies of asthmatics and non-asthmatics and supported by an internationally accepted BBDR model estimating an approximately 1 in 940,000 increased cancer risk for workers. As such, these OELs protect against sensory irritation, asthma, and other adverse effects, as well as carcinogenicity. They are also aligned with limits adopted by other domestic and international regulatory bodies. Immediately before this paper was accepted, EPA released their Updated Draft Risk Calculation Memorandum: Formaldehyde for public comment, which proposed to drop their promulgated OEVs (0.11 ppm and 0.17 ppm) and adopt an 8-hour OEV of 0.3 ppm to protect against sensory irritation and cancer, similarly to what was recommended in this paper.