Sunlight can convert a common disinfectant used in anti-bacterial soaps into a low-grade form of dioxin, possibly resulting in some of the dioxin found in the environment, a University of Minnesota study has found.

The study dealt with triclosan, a compound used in anti-bacterial soaps, toothpastes, and other such products that has been found in the nation's waterways, including the Mississippi River, as part of a government analysis of consumer-related contaminants routinely flushed down household drains.

Working off that analysis, university researchers Wil-liam Arnold and Kristopher McNeill took Mississippi River water, added triclosan, and exposed it to ultraviolet light, or artificial sunlight.

Knowing triclosan can be converted into dioxin in the laboratory and that sunlight causes it to degrade, they learned something new: That natural degradation of triclosan produces a benign form of dioxin. Between 1 percent and 12 percent of the triclosan was converted into a form of dioxin that's 150,000 times less toxic than the most dangerous form.

They said even low levels of dioxin are worrisome, however, because it accumulates in organisms and becomes more concentrated in tissues as it moves up the food chain. In its most dangerous form, it's one of the most toxic chemicals known, causing cancer as well as reproductive and developmental problems. Incinerators burning chlorinated wastes are its major source.

Arnold and McNeill cautioned that the common practice of chlorinating wastewater containing triclosan and then exposing the triclosan to sunlight could produce a more toxic form of dioxin.

The study by Arnold and McNeill, an assistant chemistry professor, was published in the Journal of Photochemistry and Photobiology A: Chemistry. The U.S. Geological Survey, through the National Institutes of Water Resources, funded it.