Is Listerine Mouthwash Poisoning Our Water Supply?

Jami asks…When I was in 6th grade my teacher insisted that people should only bathe once every 3 days. She also claimed that Listerine (remember this was the 1980s when it was still amber colored and tasted like medicine) was poisoning our water table. To this day I wondered how much truth was in what she claimed. She said that when we spat the Listerine into the sink it would work it’s way into the water table and we’d end up drinking polluted water.

The Right Brain responds:

This claim does have the ring of an urban legend about it so we checked Snopes.com to debunk it but had no luck. So, we’ll have to do this the hard way. Let’s see if we can find any evidence that Listerine is poisoning the water supply.

There are four key active ingredients that make Listerine so, uh…”Listeriney.” (The rest is pretty much water, alcohol, flavor, color, etc.)

• Eucalyptol (0.092%)
• Menthol (0.042%)
• Methyl Salicylate (0.060%)
• Thymol (0.064%)

We did a little research on each of these to determine a) how toxic they are and b) how likely they are to build up in the water supply.

Eucalyptol oil can be poisonous if you chug down enough. Based on the medical record, it looks like you’d have to swallow about half an ounce before you’d have serious symptoms. Even then, people who ingested that much almost all recovered within a day or two. Plus, consider that you’d have to swallow about 2 dozen bottles of Listerine to get half an ounce of pure Eucalyptol. Furthermore, having Eucalyptol diluted in water makes it even more difficult to ingest enough to be a problem. Is swallowing small amounts over a long period of time dangerous?  We couldn’t find any direct data, but it’s not soluble in water so it is easily separated out during purification processes.

Reference: http://www.inchem.org/documents/pims/pharm/

This ingredient has been well researched and found to degrade rapidly in water (DT50 16 days.) Therefore, the risk of environmental pollution is low.

Reference: D. Hu and J. Coats, Evaluation of the environmental fate of thymol and phenethyl propionate in the laboratory, Pest Manag Sci 64:775–779 (2008)DOI: 10.1002/ps.1555

Menthol is taken orally in a number of forms including candy (as part of peppermint oil) or cough drops.  The typical human oral dose is 60-120 mg menthol so this won’t be poisonous even at high levels in the water supply.

Reference: http://www.inchem.org/documents/jecfa/jecmono/v042je04.htm

If we’ve said it once, we’ve said it 5 or 6 times, the dose makes the poison. Methyl saliclyate is used in small amounts as a flavoring agent at no more than 0.04% but at high concentrations in it’s In pure form it is toxic. The lowest published lethal dose is 101 mg/kg body weight in adult humans.  You many have also heard the story of seventeen-year-old the cross-country runner who died in April 2007 from topical absorption of methyl salicylate from muscle-pain relief products. Luckily, the potential for bioaccumulation is low because although methyl salicylate is soluble in water it is readily biodegradable so it will not be persistent.

Reference:

While we don’t pretend to be toxicologists, based on the information we’ve found there doesn’t appear to be much credence to the notion that Listerine is poisoning our water supply. Of course we’re sure all the Listerine Deniers will beg to differ.

Fun Bonus Fact: Listerine is named after Joseph Lister, one of the father’s of antiseptic surgery. If he had lent his first name to this product instead of his last, it would be called “Josephine” and that would be just plain weird.