Putting The National Toxicology Program's Fluoride Review In Context: Natural Groundwater Levels Are The Real Issue

By Kevin Westerling,
@KevinOnWater

Despite renewed public concern over fluoride and cognition, the National Toxicology Program’s findings focus on high‑fluoride groundwater conditions — not the controlled levels used in U.S. drinking water systems. Understanding that distinction is critical for utilities navigating policy questions and community expectations.

Every few years, the drinking water sector revisits a familiar battleground: the safety and purpose of adding fluoride. The latest spark comes courtesy of the National Toxicology Program (NTP), whose 2024 monograph on fluoride exposure and neurodevelopment has revived concerns among critics while confusing even many seasoned observers.

But according to author and longtime drinking water expert Joseph A. Cotruvo, the renewed controversy may rest on a fundamental misunderstanding. Cotruvo emphasizes that the NTP claimed findings arise from naturally elevated groundwater in certain locales — not from managed, controlled levels in community systems. That distinction — between natural, sometimes excessive fluoride in groundwater and carefully controlled levels in public supplies — is, in Cotruvo’s view, central to understanding the real issue. His full analysis in the Journal AWWA explores this nuance with technical clarity and historical grounding.

A Report That Changed Midstream

The NTP’s monograph has had a long, winding path through peer reviews, revisions, and debate. Early drafts labeled fluoride a “presumed neurodevelopmental hazard,” a phrase that quickly spread across advocacy networks. Peer reviewers at the National Academies pushed back, and the August 2024 revision softened the conclusion to “moderate confidence” in an association between high fluoride exposure and reduced IQ in children.

What went largely unnoticed is what the report did not do:

• It did not examine fluoridated drinking water systems in the U.S. or Canada.
• It did not offer a risk–benefit analysis.
• And it did not conclude that controlled levels at recommended setpoints pose a public health risk.

Where the Data Comes From — And Why It Matters

According to Cotruvo, several methodological issues warrant attention. Of the 72 studies initially reviewed by NTP, only 19 met their “high‑quality” threshold — and none were conducted in the United States. Most came from regions where naturally occurring fluoride can exceed 4 mg/L (the U.S. maximum contaminant level [MCL] for about the last 40 years), far above the ~0.7 mg/L target used in U.S. practice. These high‑fluoride groundwater conditions — not controlled levels — form the basis of the associations described. In Cotruvo’s view, that nuance is essential for the industry to understand.

What’s Actually At Stake?

Misinterpretation of the monograph has policy and operational consequences. Several states have moved to limit or ban fluoride additions, often citing the report while overlooking decades of evidence showing oral‑health benefits for low‑income families.

Cotruvo also notes that the NTP did not identify acceptable U.S. studies to substantiate its neurodevelopmental conclusions. For that reason, he argues that EPA should conduct carefully designed, definitive U.S. studies before considering any changes to national fluoride standards.

He further points out that de‑fluoride treatment can be prohibitively expensive for small systems, making sweeping regulatory changes especially challenging. Because dental fluorosis risk primarily affects children up to about age eight, Cotruvo suggests that communities with naturally high‑fluoride groundwater could instead use variances or exemptions paired with required provision of bottled water for affected children — and, where appropriate, pregnant women. According to Cotruvo, this targeted approach would protect those at risk without undermining the well‑established benefits of controlled fluoride levels for the broader population.

The Bigger Picture

Cotruvo’s full analysis explores:

• why the scientific foundation of the NTP report deserves scrutiny,
• how U.S. fluoride regulations are being reevaluated,
• the public‑health consequences of losing controlled levels, and
• the communities facing genuine risk from naturally elevated groundwater.

In short: the debate is being focused in the wrong place, Cotruvo argues.

For anyone in drinking water, public health, or regulation — especially those facing local pressure — the Journal AWWA article offers critical, timely context that is too often overlooked.

Read the full expert analysis here: https://awwa.onlinelibrary.wiley.com/doi/10.1002/awwa.70026