While many city officials tout the benefits of adding fluoride to the public water supply, some Austin activists question the safety of the practice on the grounds that the additive is a hazardous waste.

Members of Fluoride Free Austin distributed fliers warning against fluoridation — a practice that has been used in Austin for nearly 30 years — as part of an Earth Day celebration Wednesday at the Austin Farmers’ Market at Triangle Park. Rob Love, a psychology graduate student at UT and member of Fluoride Free Austin, said fluoride is only beneficial to oral health if applied topically.

“Look at your tube of toothpaste,” Love said. “Do you want to swallow those ingredients? No, but we are forced to consume them in our drinking water.”

Many big cities add fluoride to the water supply as a means of improving dental health. But a number of smaller environmental groups and opponents say it poses substantial health risks.

Fluoride naturally occurs at about 0.2 milligrams of fluoride per liter of water. The Centers for Disease Control and Prevention calls fluoridation one of the 10 greatest public health achievements of the 20th century and defines optimally fluoridated water as containing between 0.7 and 1.2 milligrams of fluoride per liter of water, depending on the maximum temperature in the region. For warmer regions like Texas, cities use less hydrofluorosilicic acid, assuming that people drink more water.

According to a November report by the city of Austin, the Austin Water Utility uses on average about 0.75 milligrams of fluoride per liter of water, well below the Environmental Protection Agency’s 4-milligrams-per-liter maximum contaminant level.

Rae Nadler-Olenick, founder of Fluoride Free Austin, said the group is also concerned with the source of the hydrofluorosilicic acid — the fluoride additive.

The Mosaic Company, a global producer of phosphate fertilizer, produces the hydrofluorosilicic acid for Austin and other cities. Mosaic mines phosphate in rock form and adds sulfuric acid to the rock to produce a gas, which liberates fluorine and silicone from the rock.

Mosaic logistics coordinator Andy Martin said trace amounts of heavy metals, including arsenic, are in the hydrofluorosilicic acid at about 0.1 milligrams per liter but are not dangerous at minute levels.

Jane Burazer, assistant director of treatment at the utility, said the fluoride additive from Mosaic meets all the purity requirements set by the National Sanitation Foundation and is safe. Burazer said opponents of the practice view Mosaic’s mining process negatively because they see it as a byproduct of the phosphate fertilizer industry.

“They have the ability to produce and sell two different products,” Burazer said. “A lot of books refer to [hydrofluorosilicic acid] as a waste product, but it’s how you look at it — either as a waste stream or a dual stream.”

Nadler-Olenick agrees with the former. She founded the group in 2008 after she learned her husband, a construction worker who had been diagnosed with osteopenia, a precursor to osteoporosis, was in a high-risk group for fluoride poisoning because of the large quantities of water he consumed. Since then, the group, which has had many supporters and a solid core of 10 people, has been addressing the City Council and plans to speak at Thursday’s council meeting.

In the city’s 2009 report, Philip Huang, medical director of the Travis County Health and Human Resources Department, said adverse effects associated with the ingestion of excessive amounts of fluoride only occur after long-term exposure to high levels of the element. Skeletal fluorosis, or bone disease, occurs when people ingest more than five times the amount of fluoride typically found in fluoridated water, and dental fluorosis, seen as brown stains on teeth, requires more than 30 times the optimal amount.

“It has been rigorously evaluated,” Huang said in an interview with The Daily Texan, “so I agree with what most other major health groups say, that it has very positive public health benefits and it is safe.”