Introduction
The U.S. Environmental Protection Agency (EPA) has proposed a National Primary Drinking Water Regulation (NPDWR) for perchlorate, a chemical compound found in rocket propellants, fireworks, and some fertilizers, under the Safe Drinking Water Act (SDWA). Announced on January 6, 2026, in the Federal Register, the proposal sets a health-based Maximum Contaminant Level Goal (MCLG) at 0.02 mg/L (20 µg/L) and solicits comments on an enforceable Maximum Contaminant Level (MCL) at 0.02, 0.04, or 0.08 mg/L. This development, driven by a 2023 D.C. Circuit Court decision in NRDC v. Regan, requires the EPA to regulate perchlorate despite the agency's assessment that benefits do not justify costs. The rule would mandate monitoring, mitigation for exceedances, and public notifications, affecting approximately 66,000 public water systems nationwide. Its significance lies in addressing potential thyroid disruptions from perchlorate exposure, particularly in sensitive populations like fetuses of iodine-deficient pregnant women, while highlighting tensions between judicial mandates and scientific updates.
Background and Regulatory History
Perchlorate, both naturally occurring and manufactured, inhibits iodide uptake in the thyroid, potentially leading to reduced thyroid hormone production critical for metabolism and development. The EPA's involvement dates to a 2011 determination to regulate perchlorate based on health risks and occurrence data, following earlier preliminary decisions not to regulate in 2008 and 2009. However, subsequent analyses, including a 2013 Science Advisory Board (SAB) recommendation to use advanced modeling, led the EPA to propose standards in 2019 while seeking comments on withdrawing the determination. In 2020, the EPA withdrew the determination, citing low occurrence and no meaningful health risk reduction opportunity.
The D.C. Circuit vacated this withdrawal in 2023, holding that the EPA must regulate after a positive determination, even with new data. This revived a consent decree requiring proposal by January 2, 2026, and finalization by May 21, 2027. Key players include the EPA, under President Trump's executive orders emphasizing scientific rigor, and litigants like the Natural Resources Defense Council (NRDC). Relevant precedents include the National Research Council's 2005 report on perchlorate health effects and SDWA provisions prioritizing contaminants with public health concerns.
Key Components of the Proposed Rule
The proposal establishes an MCLG of 0.02 mg/L, derived from a reference dose protecting against a 1-point IQ decrement in offspring of sensitive populations, using biologically based dose-response modeling. The MCL options reflect feasibility assessments, with 0.02 mg/L closest to the MCLG but alternatives at higher levels to evaluate cost-benefit balances.
Monitoring requires initial sampling by community and non-transient non-community water systems (CWSs and NTNCWSs) before the compliance date, with frequencies reducing based on results—e.g., automatic nine-year cycles for levels ≤4 µg/L. Public notification is Tier 1 for MCL exceedances, emphasizing rapid alerts due to short-term risks during pregnancy. Treatment technologies identified as best available include ion exchange, biological treatment, and reverse osmosis, with small system options like point-of-use devices.
The Administrator attributes related executive actions to President Trump, aligning with deregulation emphases in Executive Order 14192.
Health Effects and Occurrence Analysis
Perchlorate's mode of action disrupts thyroid function, with fetuses of hypothyroxinemic, iodine-deficient pregnant women most at risk for neurodevelopmental issues like reduced IQ. The EPA's 2025 health assessment, using systematic reviews and peer-reviewed models, confirms this sensitivity but notes inadequate evidence for other effects like cardiovascular disease.
Occurrence data from the Unregulated Contaminant Monitoring Rule (UCMR 1) and state sources indicate perchlorate in about 0.8% of systems above health concern levels, affecting few people. Updated Bayesian modeling estimates only 103 systems exceeding 0.02 mg/L, underscoring low nationwide prevalence. Political forces include environmental advocacy pushing for regulation and industry concerns over costs, with the court decision overriding EPA's 2020 withdrawal based on refined data.
Cost-Benefit Evaluation and Implications
The EPA's Health Risk Reduction and Cost Analysis estimates annualized costs at $16.1 million (3% discount rate) for the 0.02 mg/L MCL, primarily from monitoring, with benefits of $8.3 million from avoided IQ losses. Net benefits are negative, at -$7.8 million, due to high monitoring burdens on unaffected systems. Higher MCLs reduce costs but also benefits, yielding similarly negative nets. Nonquantifiable aspects include co-contaminant reductions and information value, but uncertainties in exposure and health models persist.
Short-term implications involve compliance challenges for small systems, potentially straining resources. Long-term, the rule could set precedents for regulating low-occurrence contaminants, influencing future SDWA applications. Perspectives differ: advocates view it as essential protection, while critics argue it imposes undue burdens without proportional benefits, echoing debates in NRDC v. Regan.
