It had already been known that triclosan could be converted to dioxin in the laboratory, and it was also known that sunlight causes triclosan to degrade in the environment. But it had not been known that the natural degradation resulted in dioxin, said researchers Kristopher McNeill, an assistant professor of chemistry, and William Arnold, assistant professor of civil engineering. They discovered that the reaction could occur in Mississippi River water exposed to ultraviolet light.
"This form of dioxin is at least 150,000 times less toxic than the most dangerous form," said McNeill. "But repeated exposure to chlorine, perhaps in water treatment facilities, could chlorinate triclosan. After chlorinated triclosan is discharged from the facility, sunlight could convert it into more toxic dioxins. Such a process could be a source of highly toxic dioxin in the environment."
"This study also shows that the disappearance of a pollutant such as triclosan doesn't necessarily mean an enviromental threat has been removed," said Arnold. "It may just have been converted into another threat."
The researchers began their study after reading numerous environmental studies that reported the presence of pharmaceutical compounds in surface waters around the nation. McNeill and Arnold decided that the logical next step was to examine the natural processes that led to the loss of such materials in the environment. Last year, the U.
Contact: Deane Morrison
University of Minnesota