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I have a confession to make. I have always spent a lot of time outdoors, doing field work and bird watching. But, I don’t like to be a meal for insects.
So I love DEET. What’s more, I believe that a lot of Americans spend a lot more time outdoors because of DEET, and that is ultimately good for the environment (see my 20 July posting here). Undoubtedly DEET has prevented cases of Lyme disease and West Nile Virus in this country, and countless cases of malaria and dengue fever in more tropical regions. Without DEET, I doubt I would have survived the field work for my Ph.D. thesis in Okefenokee Swamp.
It does worry me a bit that a strong bottle of DEET can dissolve a plastic table cloth, take the printing off a ball-point pen, and turn a plastic wine glass cloudy. But in its 60-year existence, DEET has not been found to be carcinogenic. Someday that may change, but for now, I am willing to accept the track record. My friends who alternatively slather on healthy, organic repellants and eat copious quantities of garlic are usually covered with mosquito bites.
DEET is absorbed through the human skin. Some is metabolized in the liver, and DEET residues are excreted in urine. It also washes off in the shower. Thus, DEET is a component of waste water. It is not removed by water-treatment plants and ends up as a low-level contaminant in freshwaters, where it has been shown to have toxic effects on some fishes at very high levels—1000X what is found in the environment. If a good replacement can be found without these effects, I would certainly switch.
DEET is more accurately known as N,N-Diethyl-meta-toluamide. It was once thought to block a mosquitoes ability to smell human odors, but more recently has been shown simply to smell really bad to insects. Whatever the mechanism, it doesn’t seem to cast much of a protective halo around me, even with heavy use. If I miss a spot on the back of my neck, a mosquito will surely bite me there.
Knowing the mechanism of its function will certainly help researchers identify a new and better DEET, and some chemists are actively screening compounds for potential efficacy as a replacement for DEET. Others are working on the removal of DEET from wastewater using photoxidation with visible light.
But for now, it’s summer time. DEET can help you enjoy the woods!
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Syed, Z. and W.S. Leal. 2008. Mosquitoes smell and avoid the insect repellent DEET. Proc. Natl. Acad. Sci. USA 105: 13598–13603.
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