Deltamethrin: Uses, Health Effects, Safety and Regulation

Deltamethrin is a pyrethroid, a synthetic chemical modeled after the pyrethrin components of pyrethrum. It kills insects by acting on their nerve membranes. It is used on golf courses, ornamental gardens, lawns and outdoor perimeter treatments. Deltamethrin is low in toxicity when touched or breathed in, and low to moderately toxic if eaten. Its health effects include nerve, skin, eye and immune effects. In soil it persists for 11 to 72 days in aerobic laboratory tests. It is regulated through US EPA registration, which began in 1994, and through food tolerances. To use it more safely, start with the product label, because a product used as directed limits exposure.

What Is Deltamethrin?

Deltamethrin is in the chemical class of pyrethroids, synthetic chemicals modeled after the pyrethrin components of pyrethrum. Deltamethrin consists of one pure compound, unlike most other pyrethroids. Technical grade deltamethrin is odorless, non-corrosive crystals that are colorless or white to light beige. Researchers first described deltamethrin in 1974, and it entered the marketplace in 1978.

Pyrethrins are natural insecticides extracted from chrysanthemum flowers, and pyrethroids are their synthetic versions. Deltamethrin is formulated as aerosols, sprays, dusts, granules and wettable powders. The year of initial registration with the US Environmental Protection Agency (EPA) was 1994. Chinese Chalk is an illegal, unregistered product that can contain deltamethrin as the active ingredient.

A 2020 study by Iga Hołyńska-Iwan examines how pyrethroids affect human and animal health.

How Does Deltamethrin Kill Insects?

Deltamethrin kills insects by acting on their nerve membranes. Deltamethrin delays the closing of the activation gate for the sodium ion channel. Deltamethrin is a Type II pyrethroid. Type II pyrethroids have an α-cyano group that induces long-lasting inhibition of the sodium channel activation gate. Deltamethrin is effective against insects via ingestion and direct contact. Pests that come in contact with or feed on deltamethrin become paralyzed and die.

In a 2005 study, Bradberry of City Hospital found pyrethroids some 2250 times more toxic to insects than mammals. Mammals have a higher body temperature, a larger body size and a decreased sensitivity of the ion channel sites. These traits explain why deltamethrin harms insects more than mammals.

Researchers observed that deltamethrin may affect ion channels other than sodium channels, possibly due to phosphorylation. The sodium channel action is described above, while the role of other channels remains uncertain.

What Is Deltamethrin Used For?

Deltamethrin is used on golf courses, ornamental gardens, lawns and outdoor perimeter treatments. Deltamethrin is registered on cotton, corn, cereals, soybeans and vegetables for mites, ants, weevils and beetles. Indoors, deltamethrin is registered for spot and crack and crevice treatments and for pet collars.

Chinese Chalk is not a registered use, yet this illegal product can contain deltamethrin as the active ingredient.

A 2022 study by Natalia Bravo found organophosphate and pyrethroid pesticides extensively used in agriculture. Malaria control is another documented use. Pyrethroid long-lasting insecticidal nets were the principal form of malaria vector control in all study areas.

Is Deltamethrin Used Against Malaria Mosquitoes?

Yes. Deltamethrin is used against malaria mosquitoes in pyrethroid long-lasting insecticidal nets. Long-lasting insecticidal nets are mosquito nets treated with a pyrethroid insecticide that keeps working for years. Pyrethroids act on nerve membranes in mosquitoes by delaying the closing of the activation gate for the sodium ion channel.

The 2018 PubMed Central article records PermaNet 2.0 nets distributed in Benin in 2014 with 55 mg/m2 of deltamethrin. Net distributions gave coverage of one net per two people across all five study sites. These nets were the principal form of malaria vector control in all study areas.

Anopheles is the mosquito genus that carries malaria in Africa and India. Resistance to insecticides is widespread in anopheles mosquitoes in sub-Saharan Africa and India, especially to pyrethroids. Evidence suggests that using a long-lasting insecticidal net provides protection against malaria, even in areas with pyrethroid resistance.

In 2012, the World Health Organization (WHO) released the Global Plan for Insecticide Resistance Management in Malaria Vectors. The WHO is the UN health agency that sets the global malaria and insecticide resistance plans.

How Toxic Is Deltamethrin?

Deltamethrin is low in toxicity when touched or breathed in, and low to moderately toxic if eaten. Deltamethrin has a 4-hour inhalation LC50 of 2.2 mg/L in rats. Technical grade deltamethrin did not irritate intact or abraded rabbit skin.

Reported oral LD50 values for rats start at 30 mg/kg in an oily vehicle. They exceed 5000 mg/kg in an aqueous vehicle. The substance used to administer deltamethrin influences the oral LD50 by affecting absorption. Laboratory animals are purposely given doses high enough to cause toxic effects. Scientists then judge the effects on people.

The α-cyano group of Type II pyrethroids induces long-lasting inhibition of the sodium channel activation gate. These pyrethroids act on the nerves for longer.

A 2022 study by Federica Parlato from Hospital Santa Maria described an intentional oral ingestion. The suicide attempt caused seizures and coma from non-convulsive status epilepticus.

How Toxic Is Deltamethrin to People and Other Mammals?

Deltamethrin is toxic to people and other mammals only at high doses. Dogs given 100 mg/kg of deltamethrin orally vomited, became hyperexcitable and had stiff hind legs. Three human volunteers who ingested a single 3 mg dose showed no signs or symptoms.

The dermal LD50 for rats ranges from 700 mg/kg to more than 2940 mg/kg. Dogs and cats that eat enough deltamethrin can vomit, drool, lose coordination and have muscle tremors. The 2250-fold gap between insects and mammals, noted earlier, explains why these doses are so high.

In a 1989 study in Archives of toxicology, F He reviewed 573 acute pyrethroid poisonings, reported from 1983 to 1988. Of these, 325 were acute deltamethrin poisonings in Chinese literature.

In people, intentional oral deltamethrin ingestion in a suicide attempt caused seizures and coma from non-convulsive status epilepticus.

How Toxic Is Deltamethrin to Honeybees?

Deltamethrin is toxic to honeybees, with an oral and a contact LD50 of 51 ng per bee in laboratory tests. Deltamethrin did not harm bees in field studies at rates up to 12.5 g of active ingredient per hectare.

Formulated deltamethrin products had a repellent effect on bees lasting 2 to 3 hours.

A 2018 study by Piccolomini of Montana State University tested the adult alfalfa leafcutting bee, Megachile rotundata, a nontarget insect. Adult females were exposed to deltamethrin at 0.0013 to 0.0075 μg per bee.

How Toxic Is Deltamethrin to Fish and Birds?

Deltamethrin is toxic to fish, with a 96-hour LC50 of 0.91 to 3.50 μg/L for technical grade, depending on species. Deltamethrin is practically non-toxic to birds when ingested, with an acute oral LD50 above 4640 mg/kg in mallard ducks. Deltamethrin is not expected to affect fish when used properly, because it binds tightly to soil and breaks down quickly.

Midge larvae had a 28-day LC50 of 16 pg/L in water with artificial sediment. Natural sediment had no effect on survival. Differences in toxicity were attributed to the bioavailability of deltamethrin in sediment.

A 2008 study by Colette Thomas from the University of Technology Sydney tested three Australian native species. These were a cladoceran, a freshwater shrimp and rainbow fish larvae. River water reduced deltamethrin toxicity to two native species by 1.8 to 6.3 fold. All LC50 values stayed below 0.26 μg/L.

What Are the Health Effects of Deltamethrin?

The health effects of deltamethrin include nerve, skin, eye and immune effects. Key effects include:

• Nerve effects (neurotoxicity): Neurotoxicity was observed across species, sexes, exposure durations and routes in the EPA database. Severe poisoning can bring seizures and coma.
• Skin tingling, itching, burning or numbness: Skin contact can cause these sensations. They are transient and reversible.
• Transient eye irritation: Technical grade deltamethrin caused eye irritation in rabbits that resolved within 72 hours.
• Immune suppression in rats with repeated dosing: Female rats fed deltamethrin for 84 days at 6 mg/kg or for 14 days at 15 mg/kg showed immunosuppression. Young rats aged 11 and 21 days were about 16 and 7 times more sensitive than adult rats to oral deltamethrin.
• No human chronic data: No human data were found on the chronic health effects of deltamethrin.

In 2022, Federica Parlato documented intentional oral deltamethrin ingestion that caused seizures and coma.

Iga Hołyńska-Iwan from the Department of Pathobiochemistry and Clinical Chemistry notes that pyrethroids are relatively safe for humans and animals.

What Are the Symptoms of Deltamethrin Exposure?

The symptoms of deltamethrin exposure range from skin paresthesia to convulsions. Key symptoms include:

• Skin paresthesia: Paresthesia was the most common symptom from dermal exposure in occupational pyrethroid studies and is not linked to systemic poisoning. It is transient and reversible over hours, sometimes lasting up to 48 hours.
• Nausea and vomiting: People who ingested large amounts of deltamethrin had nausea and vomiting.
• Abdominal pain and muscle twitches: The same people who ingested large amounts of deltamethrin had abdominal pain and muscle twitches.
• Convulsions and loss of consciousness: A 25-year-old woman with severe occupational poisoning after spraying deltamethrin in cotton fields had convulsions and lost consciousness.
• Dog and cat signs: Dogs and cats that eat enough deltamethrin can vomit, drool, lose coordination and have muscle tremors.

A 2022 study by Manna Sera Jacob described a clinical series in India. The incidence of nausea and vomiting was 81.2% vs. 81.3% across the two pyrethroid groups.

In 2005, Bradberry described a protracted sodium influx in Toxicological reviews. This sodium tail current may be the mechanism causing paraesthesiae.

What First Aid Is Needed After Deltamethrin Exposure?

To get first aid after deltamethrin exposure, start with the product label and follow its First Aid instructions carefully. Note that exposure to deltamethrin occurs when it is touched, eaten or breathed in. Contact the Poison Control Center, the US poison information service that gives treatment advice by phone. Call the Oregon State University service NPIC at 1-800-858-7378 to report a pesticide incident.

Skin sensations from deltamethrin usually go away within 48 hours. Testing for deltamethrin and its metabolites has not been well studied in humans. The clinical significance of these tests is unknown.

F He covered the clinical manifestations and diagnosis of acute pyrethroid poisoning in 1989.

Does Deltamethrin Cause Cancer?

No. Deltamethrin does not cause cancer in people. The EPA concluded that deltamethrin is not likely to be carcinogenic to humans. The International Agency for Research on Cancer is the WHO agency that classifies cancer hazards. It classified deltamethrin as Group 3, not classifiable as to its carcinogenicity to humans.

In a 1990 study in Cancer letters, Cabral gave mice 1, 4 and 8 mg/kg body weight for 2 years. Mice given 1 and 4 mg/kg had more lymphomas, but 8 mg/kg did not. Rats had more thyroid tumours, with no clear dose-response relationship. Deltamethrin does not appear to be carcinogenic in mice or rats. The 1990 study in Cancer letters notes that further studies are needed.

No human data were found on carcinogenic effects of deltamethrin. The EPA does not consider deltamethrin to be a mutagen based on negative bacterial and chromosome assays.

Does Deltamethrin Affect Reproduction or Development?

It depends. Deltamethrin can affect reproduction in male rats and development in pups at high doses. No human data were found on the reproductive, developmental or teratogenic effects of deltamethrin. Prenatal studies found no fetal harm.

Male rats given 1 and 2 mg/kg per day for 65 days had lower testis weights. Their mating success was 50% lower. Plasma testosterone in male rats fell by day 14 and stayed low 21 days after treatment.

Rats aged 11 and 21 days were about 16 and 7 times more sensitive than adults to oral deltamethrin. A developmental neurotoxicity study found more vocalization in handled pups and lower body weight at high doses.

The offspring of rabbits fed up to 100 mg/kg during days 6 to 19 of gestation showed no teratogenic effects. Prenatal studies in rats and rabbits found no adverse effects on fetuses or offspring from deltamethrin.

A 2007 study by Linda Frazier in the Journal of agromedicine covers reproductive disorders linked to pesticide exposure. Counseling patients about reproductive and developmental effects of pesticides involves assessing exposure levels and reducing the absorbed dose.

How Long Does Deltamethrin Persist in the Environment?

Deltamethrin persists in soil for 11 to 72 days in aerobic laboratory tests on sandy or silt loam. The half-life is the time required for half of the compound to break down in the environment. In four terrestrial field studies, the soil half-life ranged from 5.7 days up to as long as 209.0 days.

The aquatic half-life ranged from 8 to 48 hours in one study, and from one to four hours elsewhere. Deltamethrin was still detectable in pond sediment 306 days after two ponds were treated. The half-life of deltamethrin on vegetative surfaces ranges from 5.9 to 17.0 days.

In 2008, Colette Thomas of the University of Technology Sydney tested deltamethrin in river water and salinity.

Deltamethrin is more persistent in soils with a high clay or organic matter content. Researchers detected maximum levels in air 14 hours after a pond was sprayed with deltamethrin. Deltamethrin has little potential to leach into groundwater due to its strong tendency to bind to soil organic matter.

How Is Deltamethrin Regulated?

Deltamethrin is regulated through US EPA registration, which began in 1994, and through food tolerances. For deltamethrin, EPA sets a food tolerance only when it finds a reasonable certainty of no harm from aggregate exposure. The registrant requested the 2023 tolerances under the Federal Food, Drug, and Cosmetic Act. This US law sets the rules for pesticide residues in food.

The 2023 Federal Register notice reduces the 10X safety factor for infants and children to 1X, except for inhalation exposure. EPA groups pyrethroids together because they share the ability to interact with voltage-gated sodium channels. The Codex limit for pulses is 1 ppm, while the EPA tolerance for dried legumes is 0.07 ppm.

What Residue Limits Apply to Deltamethrin on Food?

Residue limits apply to deltamethrin on food as tolerances and maximum residue limits. The EPA tolerance for deltamethrin on dried shelled legume subgroups 6-22E and 6-22F is 0.07 ppm. Codex sets a maximum residue limit of 1 ppm for deltamethrin on pulses.

The National Pesticide Information Center gives the reference dose in its 2010 fact sheet. The reference dose for deltamethrin is 0.01 mg/kg per day, the daily lifetime exposure with no appreciable risk.

Food and water uses take 26% of the acute population adjusted dose for children aged 3 to 5.

In 2006 the USDA Pesticide Data Program analyzed 9030 fruit and vegetable samples. The program is a USDA national survey of pesticide residues on produce. One sample had detectable deltamethrin residues, eight times below the tolerance.

Is Deltamethrin Approved in the European Union?

Yes. Deltamethrin is approved in the European Union, and Commission Implementing Regulation (EU) 2024/1734 covers its renewal evaluation. The regulation of 21 June 2024 assigns the renewal review to a Member State.

Sweden is the evaluating competent authority for the renewal of the approval of deltamethrin. The rapporteur allocation changed following the notification submitted by the United Kingdom of its intention to withdraw from the Union.

On 28 August 2023, the Authority requested additional information for deltamethrin on approval criteria. The approval criteria under assessment sit in points 3.6.5 and 3.8.2 of Annex II. Annex II belongs to Regulation (EC) No 1107/2009, the EU law that governs plant protection products.

Iga Hołyńska-Iwan from Nicolaus Copernicus University in Torun noted that WHO recommends pyrethroids for personal protection against malaria and Zika.

How Can Deltamethrin Be Used More Safely?

To use deltamethrin more safely, start with the product label, because a product that is used as directed limits exposure. Limit exposure to deltamethrin by reading and following label directions, and take steps to minimize exposure. Check the signal word, because signal words for deltamethrin products range from Caution to Danger. Signal words reflect the combined toxicity of all ingredients. Avoid unregistered products such as Chinese Chalk at all times.

Natalia Bravo wrote in Environmental research that organophosphate and pyrethroid pesticides are extensively used in agriculture. This heavy use results in higher exposures among farmworkers.

What Protective Equipment Is Needed When Using Deltamethrin?

The protective equipment needed when using deltamethrin is basic PPE: chemical resistant gloves, long sleeves and goggles. Key items include:

• Chemical resistant gloves: Gloves are part of basic PPE. Formulated deltamethrin products can cause slight to moderate skin irritation, and other ingredients affect the degree.
• Long sleeves: Long sleeves cover the skin. Rats absorbed 3.6% of the deltamethrin applied to their skin, which was excreted within 24 hours.
• Goggles: Goggles complete the basic set. Basic protective equipment is advised even when consumer labels omit PPE details.
• The product label’s PPE instructions: Read the product label for specific information on personal protective equipment and safety requirements.

Natalia Bravo wrote in 2022 that farmworkers have higher exposures to pyrethroid and organophosphate pesticides than residents. Urine tests for deltamethrin and its metabolites are not well studied in humans. Their clinical significance in humans is unknown.

How Long After Deltamethrin Application Is It Safe to Re-enter?

Workers cannot re-enter areas treated with deltamethrin for as long as the restricted entry interval of 12 hours lasts. A 2021 Bayer CropScience label for Delta Gold 100 sets this interval after application. Safe re-entry waits until the interval ends.

Deltamethrin and its metabolites were detected in worker urine within 12 hours of occupational exposure. They stayed detectable for up to 48 hours post-application. The label applies the Worker Protection Standard, 40 CFR part 170, to agricultural use. The label applies to worker entry into treated areas during the interval. The requirements apply only to uses of this product that are covered by the Worker Protection Standard.