Air Date: Week of November 3, 2006

Young bullfrog tadpole (Courtesy of Caren Helbing)

New research indicates that Triclosan, an antibacterial chemical used in scores of consumer products, is harmful to the hormonal system of developing frogs and, perhaps, humans. Steve Curwood interviews Professor Caren Helbing, a researcher in British Columbia, who says minute amounts of Triclosan could play a part in the worldwide amphibian die-off.

Transcript

CURWOOD: From the Jennifer and Ted Stanley Studios in Somerville, Massachusetts - this is Living on Earth. I’m Steve Curwood.

If you washed your hands, brushed your teeth or put on some deodorant today you may have exposed yourself to triclosan. Triclosan is probably best known as the bacteria-fighting ingredient in liquid soap, although it’s also used in everything from toothpaste to hot tubs to trash bags.

But now some scientists are telling us that minute amounts of triclosan - amounts found in the majority of America’s streams and rivers - can be enough to disrupt thyroid function in frogs, and perhaps humans.

On the line from the University of Victoria in British Columbia is Professor Caren Helbing. A paper based on her lab’s research appears in a recent issue of the journal Aquatic Toxicology. Professor Helbing, why expose bullfrogs to triclosan?

HELBING: Well, first of all frogs are very sensitive to thyroid hormone. Like other animals with a back bone, just like humans thyroid hormones are really important in growth and development. But in frogs it’s particularly evident because the young tadpole that you see swimming around in the pond actually needs to have thyroid hormone in order for it to change into a frog and what we’ve done is we’ve used that knowledge to enable us to test whether a thyroid hormone action, in other words affecting the tadpole, is affected by triclosan.

CURWOOD: What exactly did you find?

HELBING: Well, when we exposed young tad poles to triclosan itself triclosan didn’t really have much of an effect. But if we treated the young tadpoles with thyroid hormone to simulate metamorphosis in the tadpole then triclosan actually sped up the effects of thyroid hormone.

CURWOOD: And those effects were the legs growing quicker. What else happened?

HELBING: Yeah, the legs grew quicker. As well we also found that cells from the brain and from the tail actually responded differently to the presence of triclosan than when thyroid hormone was there.

CURWOOD: So if there’s no thyroid present in the tadpoles and you expose them to triclosan then there’s no effect. But then if you do add the thyroid hormone there is an effect. What does that tell you? What does that suggest is going on?

HELBING: What it’s telling us is that triclosan is acting on the ability of the hormone to do its job. And the implications of that are that during normal tadpole development that triclosan might actually be able to effect how the tadpole turns into a frog. But not only that also the implications are in people. People have to have the thyroid hormone in order to be healthy. And so possibly triclosan could effect how the thyroid hormone works.

CURWOOD: How close is the thyroid system in frogs and tadpoles as opposed to humans? I mean we don’t typically have tails and we don’t grow legs later on in life.

HELBING: No that’s true, we don’t have tails. But we do have brains. And the brain is a very very sensitive organ for thyroid hormone action; especially during early development around the birth period. And also through out life in adolescence and in adulthood the brain is very dependent on proper levels of thyroid hormone. So even though there are some obvious difference between frogs and people the fundamental biology is very very similar. And thyroid hormone is the exact same chemical in frogs compared to humans.

CURWOOD: Professor, why would you suspect triclosan in the first place?

HELBING: Well, triclosan, if you look at the chemical structure of triclosan it looks very much like thyroid hormone. So that was our first tip off that maybe it could behave either like thyroid hormone or it could effect how thyroid hormone works. The other thing that made us very interested in triclosan is that it’s found in so many different personal care products as well as it’s measured in many different water ways across North America.

CURWOOD: There was a recent study that shows that more than half of the rivers and streams in the US have readily detectible levels of triclosan. So your research has some pretty strong implications then.

HELBING: Yes. The really critical point in our research is that we looked at levels that were equivalent to ones that you can find in the environment. And to our amazement there were very profound effects on thyroid action.

CURWOOD: These levels were what like one drop of this triclosan in say, 300 Olympic swimming pools, something like that?

HELBING: Yeah it’s not very much.

CURWOOD: Now you’re doing basic scientific research. But there are going to be consumers listening to this who say, “Ok I use triclosan. I use the toothpaste that has it or I use the soap. It’s in my cutting board.” What should I do as a consumer with this stuff?

HELBING: Well, I would certainly think twice about whether you need and want triclosan in the products you’re using, certainly from the standpoint of its uses as an antibacterial agent and now with our work with potential implications on thyroid hormone, certainly on wildlife, maybe on humans too. Think twice about using it.

CURWOOD: Caren Helbing is an associate professor at the University of Victoria in British Columbia and you can find a link to her team’s research at our website loe.org. Thank you so much, professor.

HELBING: Oh, you’re welcome. It was a pleasure.

 

Links

"The Bactericidal Agent Triclosan Modulates Thyroid Hormone-associated Gene Expression and Disrupts Postembryonic Anuran Development" in Aquatic Toxicology

U.S. EPA on pesticides