Dioxins are a group of highly toxic compounds that are persistent environmental pollutants. People are exposed to dioxins through the environment and the food chain — the highest levels of these compounds are found in soils, sediments and food such as dairy products, meat, fish and shellfish. And, according to the World Health Organization (WHO), this exposure can cause reproductive and developmental problems, damage the immune system, interfere with hormones and also cause cancer.

So you would never flush dioxins into your water supply, right? If you use antibacterial soaps and other antibacterial products, you could be doing the equivalent of just that.

In 2003 and 2009, University of Minnesota civil engineering professor William Arnold and his colleague Kristopher McNeill published their discovery that the antibacterial agent triclosan, when exposed to sunlight, generates a specific group of four dioxins. Now, in a new study, a team of scientists from the University of Minnesota’s Institute of Technology, Pace Analytical (Minneapolis), the Science Museum of Minnesota and Virginia Tech, have documented how triclosan is transformed into dioxins that are accumulating in the environment. This research, just published in the journal Environmental Science and Technology, concludes dioxins originating from triclosan (found in many hand soaps, deodorants and dishwashing liquids) account for a huge increase in total dioxins now polluting Mississippi River sediments.

Efforts to cut down on dioxin contamination resulting from industrial pollution have been underway for several decades. However, the issue of triclosan in antibacterial consumer products has been virtually ignored. And the research team has found that over the last 30 years, while levels of all the other dioxins have dropped by 73 to 90 percent, the levels of dioxins derived from the antibacterial soap ingredient triclosan have risen by 200 to 300 percent.

For the new study, which was headed by Jeff Buth, a recent University of Minnesota Ph.D. graduate in chemistry, the researchers examined sediment samples from Lake Pepin, an enlargement of the Mississippi River located 120 miles downstream from the Minneapolis-St. Paul metropolitan area. They analyzed sediment cores (which contain a record of accumulated pollutants in the lake over the past 50 years) and checked for amounts of triclosan, the four dioxins derived from triclosan, and the entire family of dioxin chemicals.

The results? In the most current sediments, triclosan-derived dioxins account for about 30 percent of the total dioxin mass. “These four dioxins only come from triclosan. They didn’t exist in Lake Pepin before triclosan was introduced,” Dr. Arnold said in a statement to the media.