Guide Aerial Application of Pesticide to Control Disease-Carrying Mosquitoes

What you need to know about aerial spraying for mosquito control.

Table of Contents

What is Eastern Equine Encephalitis (EEE)?

EEE is a rare disease caused by a virus spread by infected mosquitoes. The EEE virus is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain (encephalitis). It is transmitted through the bite of an infected mosquito. Transmission does not occur directly from person to person. EEE in humans is a severe disease, often fatal, and if not, many of those who survive have mild to severe brain damage.

Why is aerial pesticide spraying being conducted?

When the Massachusetts Department of Public Health (DPH) monitoring detects EEE virus in mosquito populations at sufficiently high levels in Massachusetts communities to be of public health concern for the wider spread of the virus into humans, aerial pesticide spraying with the product Anvil 10+10 is implemented with the intention of killing adult mosquitoes in order to reduce public health risks from EEE viral exposure. This action is taken after efforts to control mosquito abundance through killing larval mosquitoes in their nursery habitats with pesticides and through removal of suitable breeding habitat where possible. Concurrent with these efforts, the public is asked to limit outdoor activities around the times when mosquitoes are active (dawn and dusk), to wear protective clothing when outdoors at these times, and to employ mosquito repellents.

What is Sumithrin?

The product that is used for aerial spraying is Anvil 10+10, which contains the insecticide with the trade name Sumithrin (common name: phenothrin). This is a synthetic pyrethroid insecticide, similar to pyrethrum, which is derived from chrysanthemum flowers. The U.S. Environmental Protection Agency registered it for use in 1975 and Massachusetts registered it in 1980. It is used commercially (e.g., food handling establishments, for control of adult mosquitoes in residential and outdoor recreational areas), as well as by homeowners to control insects in homes and gardens and on pets (e.g., ticks and fleas). It is also used domestically to control head lice. It is classified as a "general use" product, meaning that its use is not limited to professionals, but may be purchased and used by the general public. Anvil 10+10 also contains piperonyl butoxide, which prolongs and enhances the toxicological effect of Sumithrin on organisms. These compounds are carried in a solution containing a petroleum distillate solvent.

How is Sumithrin applied to control mosquitoes?

Sumithrin is applied by aircraft in an ultra-low volume (ULV) mode. ULV sprayers dispense very fine aerosol droplets that stay aloft and kill flying mosquitoes on contact. ULV applications involve small quantities of the insecticide ingredient in relation to the size of the area treated, typically no more than 0.62 oz per acre.

How might I be exposed to Sumithrin?

Most people are not exposed to Sumithrin. Exposure is most likely for those people living or working near or in a place where Sumithrin is being sprayed for mosquitoes. Massachusetts aerially applied Sumithrin for EEE in 2006, 2010 and again in 2012, and monitored the environment to document the dispersal of the pesticide. It was not detected in any of 12 surface water bodies used as drinking water sources, or finished drinking water sampled multiple times after aerial spraying in 2006. In 2010, it was not detected in any of the water quality samples collected from six water treatment plants or the seven surface water sampling sites.  In 2012, Sumithrin again was not detected in any of the water quality samples collected from four drinking water sources and from 11 surface water sites after two spray events.  In all three years, no adverse impacts to biota were detected and no fish kills were reported. If a spray event occurs, a water sampling program in surface water bodies serving as sources of drinking water for communities being sprayed will be employed. Samples will be taken prior to spraying and additional samples will be collected shortly after spray operations take place and approximately 24 hours later. Results will be available within 72 hours.

How can Sumithrin affect my health?

Sumithrin has very low toxicity to humans. Short-term or accidental exposure to very high levels of Sumithrin can affect the nervous system, causing effects such as uncoordination, tremors, or tingling and numbness in the area of skin contact. Since Sumithrin is applied at very low concentrations, most people should not be expected to be exposed to amounts of the chemical that could produce any adverse health effects as a result of its use to control mosquitoes. Sumithrin applied aerially should not pose a threat to public health via ingestion of drinking water that might be taken from surface water bodies near spraying operations. This conclusion has been reached after projections of amounts of the pesticide that could land on the surfaces of waterbodies, coupled with mixing projections, were compared with known safe levels of this chemical in drinking water. Experience gained from the aerial application of Malathion in Massachusetts in 1990 and Sumithrin (Anvil 10+10) in 2006 to deal with EEE outbreaks at those times also helped confirm these projections. Experience elsewhere and published evaluations of human health risks associated with ULV Sumithrin applications suggest that risks from dermal and inhalation exposures after spraying are also well below levels of concern.

What are the health effects of Sumithrin to chemically sensitive individuals?

While no direct evidence exists about Sumithrin's potential effects on sensitive individuals, risk evaluations are cautious and consider variability in susceptibility across the human population. However, given that responsiveness in some sensitive individuals is hard to predict, some sensitive people may develop temporary eye, skin, nose and throat irritation, or breathing problems upon direct contact with Sumithrin. People with known sensitivities to chemicals or with existing respiratory conditions, such as asthma, are encouraged to stay indoors during spraying to reduce the chances of Sumithrin aggravating those conditions.

How likely is Sumithrin to cause cancer, birth defects, or reproductive effects?

Studies in animals have not reported effects on reproduction, birth defects, or cancer when animals were exposed to Sumithrin. The primary mode of action for Sumithrin is to target the nervous system. There are no data directly on whether Sumithrin causes cancer, birth defects or reproductive effects in people. The US EPA has determined that Sumithrin is unlikely to be carcinogenic to humans.

What are the ecological effects of Sumithrin?

Sumithrin is highly toxic to honeybees. It is also highly toxic to fish and other aquatic life forms; therefore, effects of aerial applications on aquatic biota, such as fish, cannot be ruled out. Sampling of surface waters will be conducted in conjunction with aerial application spraying. To reduce such risks, EPA has established specific precautions on the label including restrictions that prohibit the direct application of Sumithrin to open water or within 100 feet of lakes, streams, rivers, or bays. However, spraying will take place up to the shores of surface water bodies. This action is being taken to ensure the most comprehensive mosquito eradication, by treating all potential mosquito habitats. Associated with this operational decision is a risk of acute toxicity to aquatic organisms. A considered decision has been made by senior state environmental and public health authorities to incur this risk to aquatic biota in the interests of getting the most effective control of disease-carrying mosquitoes and thereby reducing the likelihood of these infected mosquitoes biting humans and transmitting the EEE virus to them. As previously noted, EEE infections are often fatal or cause severe, long-lasting neurological effects. To minimize exposure of susceptible organisms during pesticide application aerial applications will be made in the nighttime hours when fish are less likely to be at the surface feeding and honeybees are most likely to be in their hives.

What can I do to reduce any potential exposures if I am concerned?

You can reduce/eliminate your exposure risk to the insecticide by staying indoors during spraying. Otherwise, no special precautions are recommended. The active ingredients of the pesticide product as it is used for aerial application for mosquito control generally break down quickly and do not leave a toxic residue. Common-sense steps that can be followed in areas where aerial spraying is scheduled to take place include:

  • If the immediate area of your home is being sprayed, keep windows closed and fans off. Shut off air conditioners unless they have a setting for recirculating indoor air. In very hot weather, make sure you open the windows or turn fans and air conditioners back on soon after the aerial spraying is completed.
  • Rinse any homegrown fruits and vegetables with water.
  • Keep pets indoors during spraying to minimize their risk of exposure. Pets that remain outdoors could be exposed to small amounts of pyrethroids, but would not be expected to experience adverse health effects from the spraying. Again, there are many pesticide products (e.g., flea collars, pet shampoo, dips) containing Sumithrin that are used directly on pets to control ticks and insects.
  • If possible, shelter or cover outdoor holding areas for particularly sensitive animal groups, such as fish or other contained aquatic biota (i.e., small ornamental ponds containing fish, outdoor fish holding tanks). Pesticide applications will be at night and should not impact honeybee colonies since honeybees are inside the hives at night.
  • If skin or clothes or other items are exposed to the sprayed pesticide, wash with soap and water.
  • If the spray gets in your eyes, immediately rinse them with water or eye drops, and call your doctor.
  • Because Anvil breaks down quickly in sunlight and water, and considering dilution factors, no special precaution or waiting periods are recommended for outdoor swimming pools or beaches.

Where can I get more information?

More information on mosquito-borne diseases and public health issues can be found on the Massachusetts Department of Public Health (DPH) website or by calling the DPH Epidemiology Program at 617-983-6800. Also see DPH's fact sheet on aerial spraying, linked below.

General information on mosquito monitoring and control in your area can be obtained by contacting your local Mosquito Control District, or by calling the State Reclamation and Mosquito Control Board at 617-626-1776.

For questions regarding the water monitoring program, you can contact MassDEP's Southeast Regional Office in Lakeville at 508-946-2700.

Additional Resources for Where can I get more information?