In Millions of Homes, High Fluoride in Tap Water May Be a Concern

Top: Water tower in Comfort, Texas. Visual: Marcus Wennrich/ iStock/Getty Images Plus

In communities across the U.S., water contains levels of fluoride some experts say could be harm developing brains.

The town of Seagraves sits on the high plains of West Texas, not far from the New Mexico border. Nearby, water pumped from the Ogallala Aquifer irrigates fields of peanuts and cotton.

Dissolved in that West Texas water are copious amounts of fluoride. The tap water in Seagraves contains levels of the mineral that many experts believe could have neurotoxic effects, lowering children’s IQs. The science on that effect is unsettled, and most experts say better research is needed. But nearly everyone agrees that at some point, high fluoride levels ought to be a matter of greater concern — even if they don’t always agree on what that point is.

Many cities add low levels of fluoride to drinking water in a bid to prevent tooth decay, but the policy has long been controversial. Lost in that debate are the roughly 3 million Americans whose water naturally contains higher concentrations of fluoride — often at levels that even some fluoridation advocates now acknowledge could have neurodevelopmental effects.

People in Seagraves and similarly affected communities are unlikely to be notified of those potential risks. Federal and state regulations require water utilities to tell customers receiving high-fluoride water that it could leave brown patches on children’s teeth, or even, at high levels, cause a rare skeletal condition.

But, at least so far, the emerging science on neurological effects is not reflected in regulations. Consumer notices rarely, if ever, mention the possibility that fluoride could affect brain development. Nor do they contain advisories for pregnant women, even as many scientists, including some federal government researchers, now say there’s substantial evidence that such elevated fluoride levels can be harmful to developing fetuses.

Perhaps nowhere is the issue more pervasive than Texas, where, according to data supplied to Undark by the Texas Commission on Environmental Quality, hundreds of communities have elevated fluoride levels, and several dozen are in clear violation of EPA regulations.

Lost in that debate are the roughly 3 million Americans whose water naturally contains higher concentrations of fluoride — often at levels that could have neurodevelopmental effects.

As a result, children across Texas, and in hundreds more communities around the United States, may routinely be exposed to potentially neurotoxic levels of a common mineral, while their caregivers receive little notification about those potential risks.

In a recent interview, Anne Nigra, an environmental health scientist and drinking water expert at Columbia University, described the evidence of harm as “robust” and “very compelling,” even at levels far below those found in Seagraves.

In most of the United States, water sources contain little or no naturally occurring fluoride. But in some places, fluoride leaches from rocks into the groundwater. In West Texas, for example, the groundwater of the Ogallala Aquifer soaks through layers of fluoride-rich volcanic ash, hundreds of feet below the arid plains. By the time it comes out of the ground, water there may have concentrations of fluoride upwards of 5 milligrams per liter — more than seven times higher than the levels recommended for communities that add fluoride to their water.

Without specialized testing, consumers could never know it was there. “Fluoride is odorless and tasteless and totally transparent,” said Joel Podgorski, a geoscientist at the Swiss Federal Institute of Aquatic Science and Technology. In a 2022 paper, he and a colleague mapped the global distribution of natural fluoride hotspots. Around 180 million people worldwide, they estimated, get water with natural fluoride levels above what the World Health Organization recommends. Hotspots include eastern Brazil, large areas of northwestern India, and pockets of North America, mostly west of the Mississippi River.

High Fluoride Levels in Texas Drinking Water

In hundreds of Texas communities — small cities, rural water districts, mobile home parks, suburban developments — the tap water contains concentrations of fluoride above 2 mg/L, reaching levels that some experts say may harm fetus’ and children’s neurological development. [Shown below] are locations where concentrations exceeded 2, 3, 4, or 5 mg/L at any time between January 2020 and May 2023.

There’s widespread scientific agreement that ingesting too much fluoride can cause teeth to have a mottled appearance or become pitted, a condition called dental fluorosis. At very high exposures, fluoride can also weaken and deform bones.

The science is less clear-cut regarding effects on brain development. Starting in the 1990s, some studies from China suggested that children exposed to high levels of fluoride tended to have lower IQ scores. More recent research, conducted in Canada and Mexico, has suggested that even lower exposures — of the kind a person gets by drinking artificially fluoridated water at 0.7 mg/L — could be harmful to young children and developing fetuses. That evidence has prompted pitched debates among scientists and policymakers about the consequences of artificial water fluoridation. (The evidence of cognitive harm to adults is sparse.)

But many scientists, including some who say the evidence is inconclusive at lower levels of fluoride exposure, say there’s stronger evidence of harm as the concentration climbs.

“If I was speaking to someone from one of these communities, and it’s someone who was pregnant, or thinking about becoming pregnant, or who had a young child, I would certainly want them to have that information.”

Since 2016, for example, a team of scientists at the U.S. National Toxicology Program has conducted a systematic review of fluoride research. In a recent draft report, they conclude “with moderate confidence, that higher fluoride exposure” — meaning levels at or above 1.5 mg/L — “is consistently associated with lower IQ in children.”

“I think that there is pretty convincing evidence that at relatively high doses, fluoride exposure can have some impact on children’s IQ,” said David Eaton, a toxicologist and professor emeritus at the University of Washington who spent years as an adviser to the National Toxicology Program.

The public “should be aware of the science,” said Howard Hu, a physician and epidemiologist at the University of Southern California who has studied fluoride exposure. The evidence of some kind of effect, he said, “is pretty darn strong.”

It’s not clear how much of that scientific conversation reaches residents of towns like Seagraves, where fluoride levels consistently top the legal limit of 4 mg/L.

The U.S. Environmental Protection Agency sets those limits, and officials there are aware of recent research on fluoride and brain development. During a recent court case, an EPA scientist said that higher levels of fluoride likely had neurotoxic […]

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