Is mosquito spraying dangerous?

BOSTON — With an outbreak of a potentially fatal disease spread by mosquitoes in Massachusetts this year, the Department of Public Health has begun spraying insecticides in parts of the state.

At least four cases of Eastern Equine Encephalitis, commonly known as EEE, have been identified this summer, leading to aerial spraying to reduce the mosquito population along with the risk for EEE.

So what is being sprayed from overhead? State department of public health experts say its two chemicals: Sumithrin (d-Phenothrin) and piperonyl butoxide.

What are they? 

Sumithrin is a synthetic chemical made to replicate a natural substance found in chrysanthemums. That naturally-ocurring pesticide is produced by the flowering plants to keep mosquitoes away. The synthetic version is produced in larger quantities to mimic those effects.

Piperonyl butoxide is a chemical called a synergist. That means it's an ingredient added to insecticides to make them more effective, despite having no insecticidal function. The synergist will stop or slow down an insect's natural processes that block insecticides.

Are they harmful? 

The dangerousness of a chemical is broken down into a number representing that chemical's toxicity. The acute toxicity is measured by determining how many milligrams of a chemical are needed per kilogram of a person's weight in order to kill at least 50 percent of a population. This number is called the Lethal Dose 50 percent, or LD50.

According to the National Institutes of Health Library of Medicine's TOXNET, Sumithrin has an LD50 of >10,000. According to TOXNET, the LD50 of piperonyl butoxide is between 4,500 and >10,000.

To compare, rat poison (strychinine) has an LD­50 of 2, nicotine has an LD50 of 188, caffeine has an LD50 of 192, Aspirin has an LD50 of 850 and Tylenol has an LD50 of 2,400.

The American Council on Science and Health and the National Institutes of Health both consider these chemicals to have extremely low toxicity.

Does more spraying make it worse? 

No. Simply put, chemicals do not build up in your system thanks to your liver. According to the American Council on Science and Health, the liver processes chemicals and turns them into water-soluble compounds that are excreted in the urine. Studies have indicated 95 percent of a small amount of Sumithrin was processed by the liver within 48 hours.

Does it absorb through the skin? 

No. You would have to directly inhale the spray for any of the chemicals to significantly make it into your bloodstream. Despite having low toxicity, residents are advised to remain indoors when the spraying is underway. According to the American Council on Science and Health, "when it is inhaled in large quantities by humans, Sumithrin can cause 'nausea, vomiting, throat irritation, headache, dizziness, and skin and eye irritation.'" So its best to avoid coming into direct contact with the spray even if it isn't going to be harmful.

As the weather cools, experts say the mosquito population will drop but until the first hard frost, they won’t be gone.

The NIH says the concern for viruses like West Nile, Zika and EEE are far greater than the low toxicity from the chemicals in the spray.

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