PORTLAND, Ore. — Opponents of an upcoming measure in Portland, Ore. about adding fluoride to drinking water said that the fluoridation chemicals planned for the city’s water supply could contain a deadly amount of arsenic, according to the Portland Tribune.

Clean Water Portland, the main organization fighting the measure, used a lab analysis of Philomath’s fluoridated water to make this assumption.

Philomath uses fluorosilicic acid, which is the same chemical compound the Portland Water Bureau will use if voters approve of the measure, noted the article.

William Hirzy, a chemist at American University in Washington, D.C., said if the tested water matches Portland’s it could raise arsenic levels over 12 percent above the highest recorded levels in 2012, which he adds would be enough to cause five extra cases of lung or bladder cancer each year.

“Arsenic is a powerful toxin that has substantial health risks even at low levels,” Hirzy said. “It should not be added to Portland’s drinking water.”

David Shaff, administrator of the Portland Water Bureau, said he couldn’t comment fully until seeing the data.

“We’ll look at it and I’ll talk to the people who actually know something,” Shaff said, “and see if there is any level of concern we would have.”

Read the entire article here.