The Associated Press

MINNEAPOLIS - Sunlight can convert a common disinfectant into a mild form of dioxin and might produce some of the dioxins known to contaminate the environment, two University of Minnesota scientists reported Monday.

Scientists already knew that triclosan - an anti-bacterial chemical used in some soaps, toothpastes, dishwashing detergents and other products - could be converted into dioxin in the laboratory. They also knew sunlight can break triclosan down.

But they didn't know until now that this natural breakdown could result in dioxin, said chemistry professor Kristopher McNeill and civil engineering professor William Arnold. They determined that it happens in water exposed to ultraviolet light, and theorized that this could account for some of the dioxin found in the environment.

The particular form of dioxin they looked at is far less toxic than the most dangerous form, McNeill said. But he said triclosan can be altered by repeated exposure to chlorine, perhaps in water treatment facilities, and that sunlight might convert this chlorinated triclosan into more toxic dioxins in the environment.

For the study, published in the Journal of Photochemistry and Photobiology, McNeill and Arnold added triclosan to Mississippi River water and shined ultraviolet light on it. They found that between 1 percent and 12 percent of the triclosan was converted to the mild form of dioxin.

Arnold said this might not be harmful by itself, but it suggests that more serious problems may be caused when triclosan enters the environment. They plan to conduct further studies to find out.

Dioxins have been linked to cancer, reproductive and developmental problems and immune system damage. Even small quantities are worrisome because they accumulate in the food chain.

The widespread use of triclosan has been criticized for potentially making bacteria more resistant to it. Dr. Stuart Levy, an expert on drug resistance at the Tufts University School of Medicine in Boston, is among those who say routine triclosan use doesn't reduce disease any more than plain soap and water, and that its use should be limited to critical situations such as hospitals to protect the most vulnerable patients.

The finding that triclosan can be converted into dioxin by sunlight is just one more reason why it shouldn't be used in so many products, Levy said.

Steve Karnowski may be reached at skarnowski@ap.org.

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