On Tuesday, Michael Connett, lead attorney representing the Fluoride Action Network and plaintiffs, made his final attempt to convince U.S. district judge Edward Chen that the 80-year-old practice of water fluoridation is lowering IQ in children and should be banned.

Throughout the proceedings of the final day of the lawsuit, Connett argued that despite uncertainty surrounding the exact concentration at which fluoride causes harm, the evidence that plaintiffs presented over the last two weeks makes it clear that fluoride is a neurotoxin. He encouraged the judge not to let the "perfect be the enemy of the good".

"We do not need for every piece of the puzzle to fit before we take steps to prevent harm," Connett nearly shouted during the hearing. "We need to take action when we have evidence of risk, and we have that here."

The hearing was the final day of the second phase of the long-delayed fluoride lawsuit. The lawsuit was filed by FAN, Moms Against Fluoridation, and individual plaintiffs who are seeking to prove that fluoride is a neurotoxin and should be banned. The plaintiffs filed suit after the EPA's 2016 decision to deny their petition.

Brandon Adkins, a Department of Justice attorney representing the EPA, repeatedly told Judge Chen that his court would be an "outlier" if he ruled in favor of the plaintiffs. Adkins claimed the EPA's expert witnesses, Dr. Stanley Barone, and Dr. David Savitz, proved that the evidence of fluoride's neurotoxicity is not clear enough to rule against the agency.

Adkins stated that for the plaintiffs to prevail, they must prove that fluoride is a neurotoxin at 0.7 milligrams per liter, and the EPA does not believe they have done so.

Adkins noted that if the court rules in favor of the plaintiffs, the judge would have to select a "point of departure", i.e., the point at which harm from water fluoridation begins. He insisted that to rule in such a way would be an error on the court's part.

"The court would be in uncharted territory if it were to rely on a systematic review to do that here," Adkins stated. Ruling against the EPA, he said, "would not reflect the best available science".