LOS ANGELES, Feb. 21 — Plans to add fluoride to Southern Californians’ tap water this summer are raising concerns that parents may not know of the potential risks of using fluoridated water to mix infant formula.

The Metropolitan Water District (MWD), which supplies 18 million people in six counties throughout the region, in July will begin adding fluoride to the water it delivers to 26 local water districts, some of which already fluoridate. But since MWD made the decision to fluoridate, the American Dental Association (ADA) — the nation’s leading authority on dental health — has for the first time acknowledged the dangers of fluoridation to children and issued a warning to the public.

In a Feb. 20 letter to MWD General Manager Jeffrey Kightlinger, the Environmental Working Group (EWG), which has led a national campaign to re-examine the risks and benefits of fluoridation, urged the district to take aggressive action to make sure all its customers are fully informed of the ADA’s warning.

“It is deeply troubling that children, including bottle-fed infants, will begin drinking fluoridated water without the benefit of the ADA warning and in spite of the many [other] serious concerns [about fluoridation] raised by the National Academy of Sciences last spring,” EWG wrote. “Public water supplies should be safe for all consumers, young and old alike.” (The letter is available at www.ewg.org.)

Last November, the ADA — long a strong advocate of fluoridation, said: “Infants less than one year old may be getting more than the optimal amount of fluoride” if they consume formula or food prepared with fluoridated water. ADA added: “If using a product that needs to be reconstituted, parents and caregivers should consider using water that has no or low levels of fluoride.”

(www.ada.org/prof/resources/positions/statements/fluoride_infants.asp)

EWG calculated that about 240,000 babies under one year old live in the MWD service area. “Many of these babies will be bottle-fed for at least some portion of their first year, and their parents need to know about the ADA warning and the risks that fluoride may pose to their children’s health.,” said the letter to Kightlinger. Copies were sent to the MWD board, representatives from local water agencies, and local and state elected officials.

The group urged MWD to provide the ADA warning to every customer it serves, and to make sure information about the warning is provided to the news media, medical and dental offices, schools, day care centers and other facilities.

ADA’s warning said babies exposed to fluoridated water may ingest more fluoride than recommended by the National Academy of Sciences’ Institute of Medicine, placing them at elevated risk of developing fluorosis, a defect of the permanent teeth resulting in dark staining and, in severe cases, substantial corrosion of the enamel. The Centers for Disease Control estimate that about 30 percent of children drinking fluoridated water have some degree of fluorisis.

Fluorosis, however, is not the only health risk of childhood fluoride exposure. A March 2006 report from the National Academy of Sciences identified fluoride as a potent hormone disrupter that may affect normal thyroid function. A 2006 peer-reviewed study by four Harvard scientists and doctors strongly supports ongoing concerns that fluoridated water is linked to osteosarcoma (an often fatal form of bone cancer) in boys.