When you use anti-bacterial soap, there’s a good chance there’s an ingredient called triclosan in it. It’s also added to things like body washes, some toothpastes, and dishwashing soap. You can find it listed as an ingredient on the label for many of those products.

But the Food and Drug Administration says there’s no evidence that using soap with triclosan in your home or office is any better at keeping you from getting sick than regular soap and water. (Health experts say a good rule of thumb is to wash your hands with soap and water for 20 seconds: the length of time it takes to sing the “happy birthday” song twice.)

The FDA says triclosan is not known to be hazardous to humans. But the agency is re-evaluating the safety of triclosan in light of animal studies showing the chemical alters hormone regulation… and also because of studies suggesting that triclosan contributes to making bacteria resistant to antibiotics.

A new study in the journal Environmental Science and Technology finds triclosan is showing up in freshwater lakes, including Lake Superior.

Bill Arnold is a professor of civil engineering at the University of Minnesota and an author of the study, and he joins me now. Professor Arnold, you and your team took core samples from the sediment of eight lakes of different sizes in Minnesota. What’d you find?

Arnold: “We found that in all the lakes there’s triclosan in the sediment, and in general, the concentration increased from when triclosan was invented in 1964 to present day. And we also found there are seven other compounds that are derivatives or degradation products of triclosan that are also in the sediment and also increasing in concentration with time.”

RW: How are these compounds getting into the lakes?

Arnold: “So triclosan goes through the wastewater treatment system, and the wastewater treatment plant actually does a pretty darn good job of removing it. 90 to 95 percent of it is taken out, but we use so much triclosan that the rest of it gets through, and three of the compounds we found are chlorinated triclosan derivatives, and they’re formed in the last step of wastewater treatment, when the wastewater is disinfected before it’s discharged and the disinfectant is chlorine. So that creates these three new compounds. And then triclosan and these three new compounds, when they’re exposed to sunlight, each of them undergoes a reaction that forms a dioxin, so that’s where the other four compounds come from.

RW: Are these at levels that could be of concern?

Arnold: “The triclosan appears to be approaching levels that could be of concern, because it’s known to be toxic to algae. So – we didn’t look at the levels in the water, but in the sediment, but in some cases they’re rather high in the sediment. For the other compounds we’re not sure, because the toxicity of them really hasn’t been studied.

RW: The trade group for the cleaning products industry continues to maintain the safety of triclosan. But at the same time… both the FDA and the Environmental Protection Agency are re-evaluating the effects of triclosan on human health and the environment… at this point, from your perspective, what’s the bottom line here for consumers?

Arnold: “I think this is a case where consumers can certainly put pressure on the market. So if consumers look at their products and don’t buy things with triclosan, they’re making their voice heard. Or they can also talk to the retailers and the manufacturers and tell them they don’t want this product if that’s the choice they make, if they don’t like the fact that it’s going beyond their sink and into the environment.”

RW: Do you think that we know enough yet to evaluate whether it’s hazardous – either to human health or to other organisms?

Arnold: “I don’t think we know quite enough yet. The toxicologists need to get involved and look at the full suite of compounds that are formed and then the human health people need to do their thing as well. I’m not qualified to do either of those. That said, Canada has decided they’ve got enough information and last year, deemed it toxic to the environment.”

Bill Arnold is a professor of civil engineering at the University of Minnesota.

That’s the Environment Report. I’m Rebecca Williams.