What’s in mosquito spray and how could it affect you? Or in the paraphrased words of Matt Damon in The Martian: Let’s science the shit out of this

This is a companion post to Hurricanes and the wisdom of reacting to a natural disaster with a man-made one, so if you haven’t read the beginning of that one, hop over there and then come back, fellow science geek. It’ll give some context for this post.

Done? Okay, so first let’s talk about the municipal pesticide d’jour, the aerial mosquito spray product naled. For reference, it’s the product used in the mosquito control districts near me that I mention in that other post, it’s what was used last year in Miami, and it’s what was used in the South Carolina incident I’ll get to in a second.

Naled is an adulticide. The CDC has written that “adulticiding, application of chemicals to kill adult mosquitoes by aerial or ground applications, is usually the least effective mosquito control technique.” And the New York Department of Health showed that 11 years of naled spraying was “successful in achieving short-term reductions in mosquito abundance,” but populations of the disease-carrying mosquito of concern “increased 15-fold over the 11 years of spraying.” In other words, it makes the mosquito problem worse over the long term.

Meanwhile, naled is a neurotoxin, an organophosphate that works by affecting the nervous system, similar to the way sarin gas works. Its use is banned in the EU. Why? Because they found it unsafe and ineffective.

EU on naled

At the very least, it is a proven, accepted and regulated-for fact that organophosphates bind to and reduce the availability of cholinesterase, a nervous system-regulating enzyme, in the human body. Cornell has a good summary of all the lovely things that happen to you as cholinesterase is inhibited. People who are regularly exposed to these chemicals are required to have their cholinesterase level checked periodically, and if it falls too low, they must not be exposed to organophosphates until their bodies recover. Obviously, citizens sprayed 2-3 times a year with ULV (ultra-low volume) concentrations aren’t exposed as often or to the extent as those who work with these chemicals daily, but the point is that they are not, in fact, safe. And, of course, there’s no information on what a lifetime of those 2-3 times-per-year exposures will result in, nor what that type of exposure combined with all the other chemical exposures humans face on a daily basis will do.

Now, let’s get into some of the questions and points raised in the spray/no spray debate that’s been going on here in Florida. One gem from an individual on a mosquito control board was that the EU removing naled from its market wasn’t “an actual warning of life or death,” implying, I suppose, that since naled won’t kill you outright, we shouldn’t worry about it.

Makes no sense

While that sinks in, let’s talk about what it will do.

The immediate effects of exposure are respiratory distress, headache, muscle twitching, nausea, diarrhea. Restlessness, seizures, depression and loss of consciousness are other potential effects. It crosses the placenta and is present in breast milk. When exposed to sunlight, it forms a breakdown product called dichlorvos, which interferes with prenatal brain development, reducing brain size 15 percent in animal studies. Dichlorvos is also carcinogenic. It has been shown in animal studies to increase aggressiveness and disrupt learning. And that’s not even saying anything about the solvents often used to apply naled, napthalene and 1,2,4 trimethylbenzene. The EPA has classified napthalene as a possible human carcinogen and 1,2,4 trimethylbenzene is a respiratory irritant that can depress the central nervous system, causing headache, fatigue, nausea and anxiety. Oh, also there’s not enough information to determine whether or not it’s a carcinogen, which doesn’t mean it isn’t, just that we don’t know.

But it won’t kill you dead on the spot. Fantastic.

Meanwhile, naled is highly toxic to beneficial insects like bees, birds, fish and other aquatic animals. Last year in S.C. millions of bees were killed after a single aerial spraying of naled. And what are the natural predators of mosquitoes? Beneficial insects like dragonflies, birds, fish that eat mosquito larvae, bats (I haven’t found anything yet that directly addresses how naled might affect bats specifically, but one can logically assume the effects could be similar to those it has on other mammals, not to mention the effects of reducing one of their food sources) and others…the very animals that suffer the toxic effects of naled and other pesticides. So you can be assured that repeated spraying of pesticides that reduce the populations of those animals will result in a surge in the mosquito population, as they reproduce much faster and in greater numbers than many of their predators. That’s what’s behind that aforementioned 15-fold mosquito population increase.

Fish kill

A massive 2016 fish kill likely caused by storm runoff that includes pesticides. Photo: Fox13

Now, another issue raised was that the spraying in these particular districts takes place after dusk when bees return to their hives and so, in theory, they shouldn’t be affected. Except that 1) bees aren’t the only pollinators out there any more than honeybees are the only type of bee that exists; 2) honeybees don’t, in practice, always hide themselves away at dusk. A variety of factors, such as extreme heat or varying light levels can cause them to be outside of the hive at irregular (to us humans) times; 3) there is some question as to whether or not the contractors hired to do the spraying actually stick to the rules about when it is to be done or if the best-practices are even followed—the spraying last year in South Carolina occurred between 6:30 and 8:30 a.m., well after sunrise. And at least one of the Mosquito Control Districts I’m talking about in Florida schedules its spraying for morning hours.

Morning spray scheduling


Another FAQ is some version of “So we can just ground fog everything then, right?” or “Please come ground fog my street.” Or even people gleefully recalling childhood escapades of chasing the fogging truck around, which is usually followed by “And I’m just fine.” First, let’s say you’re a smoker. Just because you don’t get lung cancer doesn’t mean smoking is risk-free. Here’s why ground fogging is not a better alternative to aerial spraying and why no one should be begging for it.

The following quote was taken last year from the website of my own mosquito control division. I wish I had taken a screen capture, as I now can’t find this quote on that site: “Control of adult mosquitoes is generally accomplished by the application of ultra-low volume (ULV) sprays containing malathion, Dibrom, or pyrethroids.” (emphasis mine)

Malathion is another neurotoxin. For mosquitoes and humans. From http://npic.orst.edu/factsheets/malagen.html: “Malathion kills insects by preventing their nervous system from working properly.” I’m skipping the part about how it works for brevity, but go read it at that link. We should all know what we’re being exposed to and how it works. “People, pets and other animals can be affected the same way as insects if they are exposed to enough malathion. About the same amount of malathion will be taken into the body whether you breathe it in or you swallow it. Malathion is also readily taken into the body through skin, though the amount absorbed will depend on where the exposure occurs on the body. Malathion can become more toxic if it has been sitting for a long time, especially in a hot place.” I included that last part because it’s very important to think about how these chemicals are stored, handled and mixed. Are they stored in a municipal storage facility/warehouse that’s not climate controlled? Are the containers transparent or opaque? Are these containers stored in a facility with windows where they could be exposed to direct sunlight? Are they mixed and left to sit a long time on an hot airstrip while the pilot prepares? All of these scenarios and more can change the toxicity of these chemicals in myriad ways.

Malathion drums

Photo: FAO

And here’s another thing nobody talks about. What are the effects of these chemicals on the endocrine system? (For more on what the endocrine system is, what it does, and how it’s affected by chemicals: http://theorganicadventurer.com/2013/12/22/triclosan-ban/ and http://theorganicadventurer.com/2014/01/09/bpa-the-real-kitchen-nightmare/ and http://theorganicadventurer.com/2014/02/07/thbpbpthpt-phthalates/.) The thing is we really have no idea what the effects are on the human endocrine system of breathing these pesticides in, ingesting them and absorbing them through our skin. The Food Quality Protection Act of 1996 amended the Federal Food Drug and Cosmetic Act and the Federal Insecticide, Fungicide, and Rodenticide Act, basically requiring (among many other things) that effects on the endocrine system be considered. But in its 2006 review of naled, although the EPA acknowledged that they were required to consider those effects, they said, basically, that the science for measuring the effects wasn’t there yet (page 50-51). All we can hope, I suppose, is that future reviews (naled is under review right now) will take those effects into account. Meanwhile, animal studies indicate negative impacts on the endocrine system.

Endocrine system

The endocrine system is extremely complex, not fully understood and affects almost every system and process of the body. Graphic: LadyofHats

Moving on to Dibrom, one of the formulations that include naled: We’ve already talked about naled, but one more interesting thing about that breakdown product, dichlorvos, is that a 1993 study indicated a higher number of childhood brain cancers reported by families that used the chemical. Many, many other instances of human and animal cancers are discussed in a Cornell review. There are studies about pesticides and prostate cancer, parental pesticide exposure and subsequent childhood cancer, pesticide (including dichlorvos) exposure and leukemia in adult males, malathion and childhood leukemia…I mean, we could do this all day.

Another ingredient in Dibrom is trichlorfon. It was found to cause a “severe reduction” in brain weight in animal studies. The point that the timing of fetal exposure seemed to be key in determining neurological damage is a point that people were trying to make during last year’s debate over the role in microcephalic outcomes of the pesticides used to eliminate Zika vectors. I’m really not sure how well that point was made or understood, but the thing is we don’t know. Human studies without informed consent are unethical and illegal. Except then why is it not illegal to dump chemicals on entire cities full of kids, pregnant women, chemically sensitive people, whether they consent to it or not, as long as you call it a “public health crisis”?

Dibrom commercial warning

The last one, pyrethroids, is a large class of pesticides, and municipalities tend not to specify exactly which one(s) they use. The original idea for them came from observing that certain compounds in chrysanthemums (flowers) had insecticidal properties. However, those compounds break down quickly. So chemical companies figured out how to synthesize them from petroleum byproducts (fact sheets will say “derivatives,” but make no mistake, this was designed partly as a strategy to use up petrochemical waste).

Pyrethroids are generally touted as the “least toxic” of the insecticides. But this is a misconception, due to the research origins of the compounds, that has been passed along through the years. Why? Because animal studies show liver damage, people have reported asthma and skin rashes, etc. A 2014 study out of UC Davis showed a higher incidence of autism and developmental delays in children whose mothers, while pregnant, lived close to where pyrethroids and other organophosphates were being used.

Pregnant woman in field

Another problem with pyrethroids is the other chemicals that are commonly added to them for spraying. One is piperonyl butoxide, another nerve agent (see above). Its side effects are skin sensitivity, eye irritation, and, in animal studies, liver toxicity (tumors) and lower body weights. The EPA classifies it as a Class C carcinogen, meaning it is a possible human carcinogen based on animal-study evidence. Also, the various solvents added to pyrethroids (to keep them dissolved in solution for spraying) present health risks, including, but not limited to, the fact that they are corrosive to the eyes. Pyrethroids are also extremely toxic to fish, tadpoles, bees and other animals, as are the other insecticides listed above. Besides the fact that mosquitoes have developed resistance to permethrin (a pyrethroid), so it’s not even very effective anymore.

There’s more, partly because there are many more chemicals and combinations of chemicals used to kill mosquitoes, but hopefully I’ve made the point that none of this stuff is good for us.

I would love to know what you think or if you have any questions. Do you think the existing data gaps represent a tolerable risk or not? Do we even know enough about our own physiology yet to be able to accurately assess risk? And if you want the rest of the context for all this, especially the question of whether or not any potential risk is tolerable if there are other risk-free solutions, hop back over to the companion post.

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