Pesticide Information

Pesticides Used for Vector Control Spraying

What is permethrin?

Permethrin is an insecticide in the pyrethroid chemical family. Pyrethroids (also known as synthetic pyrethroids) are insecticides chemically similar to pyrethrins found in natural pyrethrum. Natural pyrethrins are extracted from the flowers of the chrysanthemum, which have been recognized for centuries for their insecticidal activity. Pyrethroids do not have the extent of adverse effects on non-targets unlike other insecticide groups.

Pyrethroids are widely used in public health applications because of their relative safety for humans, high insecticidal potency at low dosages and rapid knock-down effects. First developed in 1973, pyrethroids are more stable to light than natural pyrethrum. Permethrin was originally registered for use by the United States Environmental Protection Agency (U.S. EPA) in 1979, and was re-registered in 2006.

What is permethrin used for?

Permethrin is registered for use on/in numerous food/feed crops, livestock and livestock housing, modes of transportation, structures, buildings (including food handling establishments), Public Health Mosquito abatement programs, and numerous residential use sites including use in outdoor and indoor spaces, pets, and clothing (impregnated and ready to use formulations).

According to Agency data, the EPA cites that approximately 2 million pounds of permethrin are applied annually to agricultural, residential and public health uses sites. The majority of permethrin, over 70%, is used in non-agricultural settings; 55% is applied by professionals, 41% is applied by homeowners on residential areas, and 4% is applied on mosquito abatement areas.

Permethrin is a restricted use pesticide for crop and wide area applications (i.e., nurseries, sod farms) due to high toxicity to aquatic organisms, except for wide area mosquito adulticide use. It is a general use pesticide for residential and industrial applications. Permethrin also has non-FIFRA pharmaceutical uses as a pediculicide for the treatment of head lice and scabies. The Food and Drug Administration (FDA) approves use of the pesticide-containing pharmaceutical under the Federal Food, Drug, and Cosmetic Act (FFDCA).

How much product does DCCHS apply when spraying occurs?

When Dallas County Health and Human Services sprays for adult mosquitoes the applications rate of active ingredient is no greater than .007 pounds per acre (AI)/acre). Most agriculture applications are performed at a rate of 0.2 to 0.4 pounds per acre.

What are the effects on other insects from spraying?

Extensive studies have shown little effect on insects from Ultra Low Volume (ULV) fogging for adult mosquitoes. ULV applications use Ultra Low Volumes, i.e. less than 1.0 ounce per acre, in microscopic sized droplets of a low toxicity product. We can minimize the negative non-target effects through the combination of ULV technology, limiting applications to periods of high annoyance or disease threat, and selecting the period of the evening when many other non-target insects are not active. Please note that although permethrin does present toxicity to bees, many bees are not flying/pollinating at the time mosquito spraying is performed.

What are the effects of permethrin exposure in humans?

Pyrethroids do not accumulate in the body and their excretion is rather rapid, even after repeated administrations: typically, 90% of the administered dose is excreted in urine and feces within a week after treatment. In addition, Permethrin has been used for many years, with no human poisoning cases reported. No indication exists that permethrin has a significant adverse effect on humans when used as recommended. It has induced skin sensations and paraesthesia in exposed workers, but these effects disappear within 24 to 48 hours. Transient numbness, itching, tingling, and burning sensations have been reported in a small percentage of humans after dermal exposure to permethrin when it was used to treat head lice (World Health Organization, 1990).

With respect to mosquito applications, many people do not risk any exposure to permethrin if their windows are closed and they are within their homes during a mosquito spraying application. The ULV spray does not stay in the air for much longer than 2-3 hours. The product will adhere to vegetation and therefore, people are not breathing in permethrin from a mosquito control application the morning after an application.

What is the half-life of permethrin?

In soil the average half-life of permethrin in aerobic soils is 39.5 days, with a range from 11.6 to 113 days. Permethrin binds tightly to soil and is broken down primarily by microorganisms, but also by photolysis.

When exposed to water some of the product is degraded. Some degradation also occurs due to sunlight while in the water column but the majority binds tightly to the sediment. The average half-life range for permethrin in the water column is about 19 to 27 hours, however permethrin adsorbed to sediments can persist more than a year. Permethrin is not likely to contaminate groundwater due to its low water solubility and strong adsorption to soil.

How much permethrin can people be exposed to?

The U.S. EPA has determined a Reference Dose (RfD) of 0.25 mg/kg/day for both acute and chronic dietary exposures to permethrin. The RfD is an estimate of the quantity of chemical that a person could be exposed to every day for the rest of their life with no appreciable risk of adverse health effects. The reference dose is typically measured in milligrams (mg) of chemical per kilogram (kg) of body weight per day. No human data were found on chronic effects of permethrin.

The U.S. EPA has not determined a Maximum Contaminant Level (MCL) for permethrin in drinking water. However, a limit of 0.3 mg/L was set by the World Health Organization (WHO) as a guideline for permethrin in drinking water when it is applied to water for mosquito control.

The Agency for Toxic Substances and Disease Registry (ATSDR) determined Minimum Risk Levels (MRLs) for oral exposures to technical grade permethrin of 0.3 mg/kg/day for acute oral exposures (up to 14 days) and 0.2 mg/kg/day for intermediate durations (15-364 days).

Is permethrin linked to the honey bee die off?

Funding has allowed for collaborative comparative studies to be initiated, including many professionals and experts from across the country to further investigate the phenomenon of Colony Collapse Disorder (CCD). CCD was largely documented in 2006 and was initially linked to varroa mites. Research on the declining bee population is only just beginning; with pathogens, environmental chemicals, and nutritional stressor being some of the most recent causes being considered. One class of pesticides under close scrutiny by beekeepers and the press are neonicotinoids, which are known to be quite toxic to honey bees. We strongly encourage you to review the current literature available to stay informed.