A lot of household products nowadays claim to be antibacterial—containing compounds that kill viruses, bacteria, and other germs on contact. But what happens to these compounds when they get washed down the drain? You'll hear one worrisome possibility in this Science Update.
The bad side of a bug killer. I'm Bob Hirshon and this is Science Update.
If you use an antibacterial hand sanitizer, cutting board, or toothbrush, chances are it's impregnated with Triclosan. This antibacterial compound can kill germs and keep people from getting sick, but Triclosan may also have a bad side: it could harm the environment.
That's according to a new study by University of Minnesota chemist Kristopher McNeill, and his colleagues.
Well, what we found is that Triclosan, which is an antibacterial, when you put it in natural water and shine sunlight on it, it converts into a dioxin. And this is not necessarily something you'd like to see because dioxins have this reputation for being incredibly toxic.
McNeill says Triclosan is washed into streams and rivers through treated human waste water. He and his colleagues found that up to twelve percent of this Triclosan gets converted into a particular form of dioxin. While this form isn't that dangerous to humans, it could have disastrous effects on plants and other animals.
Now his team is looking at what happens to other common chemicals that get dumped down the drain.
I think this is a good example of a compound doing something maybe a little bit unexpected, and I think this is going to be a very general phenomenon. We're going to see this happening with lots of compounds.
For the American Association for the Advancement of Science, I'm Bob Hirshon.
Making Sense of the Research
The word "antibacterial" can be found on hundreds of products these days. It wasn't that long ago that soap was just soap and a sponge was a sponge. But times have changed, and "antibacterial" sells. If it's antibacterial, it must be good, right?
This is one of several studies that suggest otherwise. As the report mentions, dioxins are a serious environmental concern. There are 75 different varieties, spanning a wide range of toxicity. And while the dioxins discussed here aren't dangerous enough to harm people directly, they can wreak havoc on wildlife. Here's a short list of their possible effects on fish and other animals: reduced fertility and hatching rates, birth defects, stunted or slowed growth, cancer, anemia, brain and nerve malfunctions, and immune system problems.
Why are dioxins so problematic? One reason is that they appear to mimic the effects of certain natural hormones in animals. When exposed to the dioxin at a crucial stage of development, it's like getting an extra dose of hormone. The result can be a mixup in the animal's body formation.
This study shows that just because something is harmless in one form doesn't mean it stays harmless forever. Many other "harmless" compounds break down into nastier components over time. And this isn't the only concern that the explosion of antibacterial products has caused. Other scientists are worried that they're acting like antibiotics, and contributing to the growth and evolution of antibiotic-resistant bacteria.
But at least they kill bacteria, right? Well, maybe not. For example, some studies suggest that plain old soap disinfects just as well as antibacterial soap. That's partly because antibacterial ingredients like Triclosan can take up to two minutes to work—when was the last time you left soap on your hands for that long? And besides, a lot of diseases are caused by viruses, not bacteria, and antibacterial soaps don't do a thing against viruses.
Now try and answer these questions:
- What are dioxins?
- What is their relationship to the antibacterial ingredient Triclosan?
- If the chemical is harmful to fish and wildlife, how could it harm people indirectly?
- Do you use antibacterial products regularly? Why or why not? What attracts people to these products? What are some ways to find out if they are really necessary?
Dioxin Research at the National Institute of Environmental Health Sciences, which is part of the National Institutes of Health, provides some sound information about dioxin.
Antibacterial Household Products: Cause for Concern, by Tufts University's Stuart Levy, is a paper presented at the Centers for Disease Control's 2000 Emerging Infectious Diseases Conference in Atlanta. The paper is fairly technical, but a good overview for advanced students.