Federal environmental regulators won’t need to reevaluate acceptable fluoride levels in American drinking water, after a federal appeals panel ruled a San Francisco federal judge essentially took over a case when he ruled in favor of plaintiffs claiming fluoride in drinking water could be contributing to IQ loss in American children.
On May 21, a three-judge panel of the U.S. Ninth Circuit Court of Appeals threw out the order from U.S. District Judge Edward M. Chen, who had sided with a D.C.-based activist group in ruling the U.S. Environmental Protection Agency (EPA) must consider the alleged neurological effects of fluoride, as well the dental and skeletal benefits, when setting acceptable drinking water limits.
In the ruling, issued as an unpublished order, the appeals judges said it was clear to them that Chen had violated a bedrock principle of the American legal system when he “commandeered” the case.
Specifically, the appeals panel said Chen had violated the so-called party presentation principle, which generally limits judges to deciding cases only on the evidence and arguments presented by the parties involved. In this instance, however, the appeals judges agreed with the EPA that Chen had overstepped by putting the case on hold to await the results of additional studies that were not part of the case record.
“The district court’s (Chen’s) ‘takeover’ of the evidentiary presentation, in combination with its repeated refusal to respect the decisions made by the parties in the case, violated the party presentation principle and constitute an abuse of discretion,” the appeals panel wrote.
“The district court’s (Chen’s) ‘radical transformation’ of the case by holding the case in abeyance for a year and a half and declining to rule on the first trial record as requested by both parties went ‘well beyond the pale.'”
The panel included Ninth Circuit judges Sidney R. Thomas and Ronald M. Gould and Montana U.S. District Judge Brian M. Morris, who sat on the panel by designation. The Ninth Circuit handles appeals from federal courts in the states of California, Washington, Oregon, Idaho, Montana, Nevada, Arizona, Hawaii and Alaska.
The appellate decision overturned Chen’s 2024 ruling, requiring the EPA to investigate whether flouridation in water “poses an unreasonable risk of reduced IQ in children.”
The decision had come about eight years after the activist group known as Food & Water Watch took advantage of a revised federal law known as the Toxic Substances Control Act to petition the EPA to review its rules for fluoride in water to specifically weigh the alleged harmful effects of fluoride on children’s brain development.
Fluoride has been added to many U.S. drinking water supplies for decades since scientists first took note of its ability to improve human health by preventing cavities in teeth and improving oral health.
However, over those decades, the use of the substance has come under increased scrutiny, as critics of the longstanding fluoridation programs have pointed to studies they say show the sustained ingestion of fluoride can produce harmful effects, particularly in children.
In his decision, Judge Chen asserted there was a “growing and robust body of evidence” that pointed to a link between the ingestion of fluoride by mothers and their children and “cognitive impairment in children.”
In his decision, Chen pointed to research from the federal U.S. National Toxicology Program generally points to a loss of one IQ point in children for every 0.28 milligrams per liter (mg/L) of fluoride detected in a pregnant mother’s urine.
The judge called that estimation “highly concerning,” as “maternal urinary fluoride levels for pregnant mothers in the U.S. range from 0.8 mg/L at the median and 1.89 mg/L depending upon the degree of exposure.”
Currently, the EPA allows fluoride levels of up to 4 mg/L in drinking water, and has set an “optimal” level of 0.7 mg/L to further public dental health goals.
Citing that study, the judge ordered the U.S. EPA to begin formulating new possible rules limiting fluoride levels in drinking water.
“The trial evidence in this case establishes that even if there is some uncertainty as to the precise level at which fluoride becomes hazardous, under even the most conservative estimates of this level, there is not enough of a margin between the accepted hazard level and the actual human exposure levels to find that fluoride is safe,” Judge Chen wrote.
Nearly a year and a half after the EPA appealed, the Ninth Circuit sided with the federal regulatory agency, agreeing Judge Chen had acted outside his authority in reaching his decision.
They sent the case back to the lower court for further proceedings in the case.
The ruling was praised by the American Dental Association, which had filed a brief in support of the EPA before the Ninth Circuit in 2025.
They said they believed the ruling will provide an opportunity to “correct a fundamental misunderstanding and misapplication of the prevailing scientific literature on the safety of fluoride and community water fluoridation,” the ADA said.
“We hope that the lower court takes the opportunity now to correct the record and provide reassurance to the American public, policymakers, and any doubters about the safety and value of community water fluoridation in the face of ongoing misinformation sparked by this previous court decision,” said ADA President Rich Rosato.
Chen was appointed by former President Barack Obama.
Thomas and Gould were appointed by former President Bill Clinton.
Morris was appointed by Obama.
