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Bill Chameides

Bill Chameides

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Keeping the Skeeters Off

Posted: 05/ 4/11 11:44 AM ET

This post was modified on June 7, 2011.

More than 80,000 chemicals are produced, used, and present in the United States. This is one of their stories.

Is there a bug spray right for you?

2011-05-04-mosquitonetting.jpg
The fight against mosquito bites can take many forms, from the myriad sartorial options available (for the fashion-challenged) to the stuff you spray or smooth on to your skin. But which are the safest?

Oh, those pesky mosquitoes. Their bites not only itch, they're potentially dangerous: In 2010 almost 1,000 Americans tested positive for West Nile virus.

So what's a person to do? Staying indoors all summer long might work, but is a bit extreme. Also effective, I suspect, is decking yourself out head-to-toe with a mosquito net -- though such outfits don't quite fit my standard for stylish attire and I suspect many of you are not likely to sport such duds at your next picnic or your kid's baseball game.

Fortunately, there are alternatives. The good news: They provide varying levels of protection. The bad news: They can pose risks. Here's a quick rundown of options from the Centers for Disease Control.

mosquito
More than 2,500 species of mosquitoes roam the globe, according to the American Mosquito Control Association, with about 200 of them calling the U.S. home. Of these, 36 species have tested positive as carriers of West Nile virus. (Source: National Biological Information Infrastructure)

The Hi-Tech Solution: Pesticide-Laced Wear

If you're a catalog-receiver of any company hawking outdoor wear (and who isn't these days?), you've no doubt seen clothing impregnated with an insecticide (permethrin) that deters mosquitoes and other disease-carrying insects. Folks, these products have to be great -- just check out those smiles on the catalog models wearing the stuff!

Originally developed for the armed forces (who probably have little time to worry about bug spray), this insect-repellent clothing was approved for the public in 2003 (see here and here). According to the CDC, "permethrin-treated clothing repels and kills ticks, mosquitoes, and other arthropods and retains this effect after repeated laundering."

So what about this permethrin chemical? Perfectly safe? Not quite. Permethrin is a synthetic pyrethroid-class compound "likely to be carcinogenic to humans" when ingested orally and is highly toxic to freshwater and estuarine aquatic organisms. That's probably not as bad as it sounds: The Environmental Protection Agency ranks pesticides on a four-point scale ranging from very highly toxic (category I) to practically non-toxic (category IV).

The Chemical Marketplace
A series that looks at chemicals in everyday consumer products
     Aluminum and antiperspirants »
     BPAF »
     Dioxin and eggs »
     Fluoride and water »
     Formaldehyde and no-iron shirts »
     Insect repellents
     PBDE and fire retardants »
     PFOA and popcorn »
     TDCPP and the air»
     Triclosan and toothpaste »
     Trihalomethanes (THM) and
     showering »

Permethrin's toxicity ranking [pdf] is category III (slightly toxic) for eye-irritation potential, acute oral and acute dermal toxicity and category IV for dermal irritation potential.

What's important to bear in mind is that according to the CDC, permethrin "is intended for application to clothing and gear, but not directly to skin."

But if it's in our clothes, which are right next to our skin, what are the chances we won't absorb permethrin? Not good, says a 2010 German study in which volunteers wearing permethrin-impregnated clothing for 28 days during working hours showed much higher levels of permethrin metabolites in their urine on days 14 and 28. Four weeks after the wearing period, levels dropped off considerably but still remained higher than the control group's. Fortunately, subjects' permethrin levels remained below the World Health Organization's acceptable daily intake, but on the downside the rate of absorption was higher than that found in a 1994 assessment by the National Research Council on the chemical.

It's noteworthy that these clothes are marketed as a safe way to protect children from insect bites, although it's not clear how much research has actually assessed the effects of permethrin in children [pdf]. If you buy these togs for toddlers, you should probably monitor them to make sure they don't chew them as they are wont to do. Also be aware that some lines of children's pemethrin-impregnanted clothing may not be labeled with warnings.

The Skinny on Conventional Repellents

OK, if insect-repellent clothes are not your style, you could opt for a skin application. The CDC reports that two of these "provide repellent activity sufficient to help people avoid the bites of disease carrying mosquitoes": DEET, America's repellent of choice, and picaridin, Europe's chemical de guerre against mosquitoes. According to Picaridin.info, the chemical's efficacy is similar to DEET's but is "more pleasant to use and much less likely to cause skin irritation." Seems EPA agrees [pdf].

But remember pemerthrin concerns involve skin contact, the very action taken when using DEET or picaridin. So are they safe? Not entirely. EPA ranks picaridin as slightly to practically non-toxic, whereas DEET [pdf] gets a slightly toxic ranking.

DEET is still the workhorse pesticide for most Americans battling biting bugs. EPA estimates that a third of us use it every year [pdf] despite the fact that it's classified as a Group D carcinogen (i.e., not classifiable for human carcinogenicity) and has been linked to seizures in children. Nevertheless, EPA believes "normal use of DEET does not present a health concern to the general population" -- but with a significant caveat: so long as users follow "common sense" steps such as washing "treated skin with soap and water" after being outdoors.

How many of us follow that dictum or even knew about it? 

Going Naturel -- Biopesticides

mosquito
Why are mosquitoes attracted to one person over another? Though this is not completely understood, scientists think that the carbon dioxide we (et al vertebrates) exhale attracts mosquitoes. Various odors likely also play a role. And because they're attracted to heat, wearing dark clothes will get more of their attention than lighter ones. (Source: National Biological Information Infrastructure)

Don't need no stinkin' synthetic repellents? Then natural repellents may be the answer, and of the five registered by EPA, the CDC recommends three: oil of lemon eucalyptus, its synthesized version (p-Mentane-3,8-diol I), and IR3535.

First registered in 1948, oil of lemon eucalyptus is found naturally in leaves and twigs. PMD (the friendlier name for p-Mentane-3,8-diol) provides similar protection to repellents with low concentrations of DEET, and is listed as having no adverse effects save for irritating the eyes. While both versions are generally regarded as safe, it appears that most requirements for registration-testing were waived [pdf].

IR3535, the imposingly named biopesticide registered in the United States in 1999, is shorthand for an ethyl ester, a complicated organic compound. While synthetic, IR3535 falls under the natural umbrella because it's functionally identical to a naturally occurring compound.

Back in the day, my friends and I -- and hordes of others -- swore by Avon's Skin-So-Soft. Perhaps in response to this, and despite naysayers, Avon developed a Skin-So-Soft insect-repellent line with IR3535 as the active ingredient.

According to EPA, "no harmful effects to humans or the environment are expected" from IR3535, nor do "toxicity tests show ... IR3535 is ... harmful when ingested, inhaled, or used on skin." It may, however, be an eye irritant. Sounds pretty good to me. But there's a hitch -- how long it's effective. Tests indicate that IR3535's repellent ability fades faster than something like DEET [pdf].

Summary and the Stealth Option

So there are many ways to skin the mosquito-biting cat, varying from the geek-alert/sartorially challenged methods to those with toxicity risks. Many seem preferable to being feasted upon by blood-sucking bugs. So do make a choice.

But as you do, consider the stealth option. Did you know that some people are singularly attractive, even irresistible to mosquitoes, which seek their human prey (whose blood they need to reproduce) through a keen sense of smell? Mosquitoes home in on the bodies of these unfortunate mosquito-magnets -- and here's the key part -- forsaking all others.

The solution: Seek out such a person as your constant companion and your mosquito-bitten days will be over. How do I know this works? Well, let me answer that question by asking you a question. Have you met my lovely wife? She's really quite attractive. And just making sure she's about when I'm outside tends to take care of those pesky biting bugs... for me.

Modification: June 7, 2011. This post was modified in one place to clarify DEET's classification as a Group D carcinogen. The original phrase "a Group D (non-human) carcinogen" was replaced  with "a Group D carcinogen (i.e., not classifiable for human carcinogenicity)" along with a link to EPA's website for more on carcinogen classification.

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Crossposted with www.TheGreenGrok.com.

 

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