lambda-Cyhalothrin: Uses, Health Effects, Safety and Regulation

Lambda-cyhalothrin is a pyrethroid insecticide. It disrupts the gating of sodium channels that conduct nerve impulses in insects. It is used mainly to control lepidopteran larvae on crops such as cotton and cereals. Animal tests show it is highly to moderately toxic to people when ingested. Still, EPA classifies it as not likely to be carcinogenic to humans. It is highly toxic to bees in laboratory tests, and also to fish and aquatic life. It persists for 158.7 days in soil under aerobic conditions, measured as a DT50 value. The EPA registered it in 1988, and the acceptable daily intake in food is 0.0025 mg/kg bw per day.

What Is Lambda-Cyhalothrin?

Lambda-cyhalothrin is a pyrethroid insecticide, as a 2009 study by Jeffrey M Giddings describes it. Lambda-cyhalothrin is composed of isomers found in cyhalothrin, so it is not the same as cyhalothrin itself. The technical material is a colorless to beige solid with a mild odor. Its water solubility is 5 x 10 -3 mg/L, a measured property that defines its behavior in water. Pyrethroids are synthetic versions of pyrethrins, which are extracted from chrysanthemum flowers.

How Does Lambda-Cyhalothrin Work in Insects?

Lambda-cyhalothrin works in insects by disrupting the gating mechanism of the sodium channels that generate and conduct nerve impulses. Lambda-cyhalothrin delays the closing of the sodium channel gate, which keeps nerve fibers excited for a prolonged period. Paralysis and death follow rapidly when an insect ingests the compound or meets it externally. Temperature influences insect paralysis and the toxicity of lambda-cyhalothrin. A 2015 review by Hiroo Ichikawa lists the voltage-gated sodium channel as the target for pyrethroids.

What Is Lambda-Cyhalothrin Used For?

Lambda-cyhalothrin is used mainly to control lepidopteran larvae on crops such as cotton and cereals. Lambda-cyhalothrin products are registered for several settings, per the 2020 EPA proposed interim registration decision for lambda- and gamma-cyhalothrin. Key uses include:

• Agricultural crops: Growers apply it to crops such as cotton and cereals against lepidopteran larvae, which was its first and still its main use.
• Cattle ear tags: Producers use registered ear tags on cattle, which places the product directly on livestock.
• Food handling establishments: Operators treat these sites with registered products, which are formulated as ready-to-use sprays, liquids and granules.
• Ornamental gardens, lawns and turf: Homeowners and turf managers treat gardens, lawns, turf and golf courses, and both lambda- and gamma-cyhalothrin have products labeled for residential uses.
• Termite treatments: Pest controllers use it against termites, a structural use outside farms and gardens.

How Toxic Is Lambda-Cyhalothrin to People?

Lambda-cyhalothrin is highly to moderately toxic to people when ingested, judged by animal tests. Lambda-cyhalothrin is highly toxic to mice and moderately toxic when applied to the skin. The U.S. EPA categorizes lambda-cyhalothrin as moderately toxic for eye effects. The acute dermal LD50 is 632 to 696 mg/kg in rats. Exposure from label use is low compared with the doses fed to laboratory animals, which covers people and pets. Pesticides must undergo laboratory testing for short-term (acute) and long-term (chronic) health effects before EPA registration. A 2023 study by Alagarasan Naveen reports that a 54-year-old male farmer died 10 days after poisoning. The cause was severe neurotoxicity from lambda-cyhalothrin.

What Are the Acute Oral LD50 Values for Lambda-Cyhalothrin?

The acute oral LD50 values for lambda-cyhalothrin are 79 mg/kg for male rats and 56 mg/kg for female rats. In mice, the acute oral LD50 of lambda-cyhalothrin is 19.9 mg/kg. Sex changes the value in rats, since females die at a lower dose than males. LD50 is the dose in milligrams of chemical per kilogram of body weight that kills half of the treated animals. LD50 does not reflect effects from long-term exposure, such as cancer, birth defects or reproductive toxicity. Alagarasan Naveen of the departments of forensic medicine and toxicology reported a fatal human case.

Does Lambda-Cyhalothrin Affect Development or Reproduction?

Lambda-cyhalothrin does not affect development at or below 30 mg/kg/day in a rat study. The sources give no separate reproduction result for lambda-cyhalothrin. The maternal toxicity NOAEL in that rat study was 10 mg/kg/day. The U.S. Environmental Protection Agency, the national U.S. agency that registers and reviews pesticides, received a developmental neurotoxicity study for lambda-cyhalothrin. The 2007 Federal Register notice on lambda-cyhalothrin pesticide tolerance classed that submission as unacceptable. Some developmental parameters in it were inadequately tested. Developmental and neurodevelopmental studies in rats and rabbits show no evidence of increased susceptibility in infants and children. EPA does not believe that fixing the study’s deficiencies would meaningfully change its risk evaluation.

What Are the Symptoms of Lambda-Cyhalothrin Poisoning?

The symptoms of lambda-cyhalothrin poisoning range from temporary skin sensations to seizures and coma. Lambda-cyhalothrin poisoning produces five groups of symptoms. Key symptoms include:

• Skin tingling, burning and prickling, mostly on the face: These abnormal skin sensations are unique temporary symptoms of pyrethroid exposure, and facial tingling in lab workers began within 30 minutes of exposure and lasted 6 hours to 2 days.
• Irritation of the skin and of the respiratory and digestive tracts: Lambda-cyhalothrin may cause this irritation, which is milder than the systemic effects below.
• Nausea, vomiting, tremor and hypersalivation: These signs reflect nervous system involvement, and they were frequent among patients with type 2 pyrethroid poisoning.
• Dizziness, headache, anorexia and fatigue: These systemic symptoms follow absorption, and they are less specific than skin tingling.
• Seizures and coma in severe poisoning: These signs mark the most severe poisonings.

Nausea and vomiting occurred in 81.3% of 43 type 2 pyrethroid patients, a 2022 study by Manna Sera Jacob shows. Tremor occurred in 32.6% and hypersalivation in 20.9% of those patients. Paraesthesia occurred in 6.2% of type 1 and 32.6% of type 2 pyrethroid patients.

How Should Lambda-Cyhalothrin Exposure Be Treated?

To treat exposure, start with decontamination, which a 2002 study by William M Simpson calls the most important intervention. In a lambda-cyhalothrin poisoning case, decontamination meant changing the patient’s clothes and washing the body surface. Lambda-cyhalothrin exposure should be treated without a specific antidote, because most pesticide poisonings have none. Supportive care follows, with intravenous fluid resuscitation and continuous monitoring of vital signs, as in the same case. Gastric lavage is indicated if ingestion occurred within 60 minutes of patient presentation. Syrup of ipecac is no longer recommended for routine use.

Does Lambda-Cyhalothrin Cause Cancer?

No. Lambda-cyhalothrin does not cause cancer, as EPA classifies it as not likely to be carcinogenic to humans. Rats fed lambda-cyhalothrin for 2 years showed no evidence of carcinogenicity, and the NOAEL was 2.5 mg/kg/day. Mice fed 15 and 75 mg/kg/day showed more mammary tumors. The results were equivocal and could not be attributed to carcinogenicity. Sufficient evidence shows that lambda-cyhalothrin has no significant potential to cause mutagenicity. The 2001 NPIC Oregon State University lambda-cyhalothrin general fact sheet still lists a group D carcinogen classification, an older label.

Is Lambda-Cyhalothrin Harmful to Bees?

It depends. Lambda-cyhalothrin is highly toxic and harmful to bees in laboratory tests. A field study with a lambda-cyhalothrin product found no increased risk to bees. The LD50 is 0.97 micrograms per bee by ingestion and 0.051 micrograms per bee by external exposure. A 2024 study by Ji-Yeong Choi found an acute LD50 of 0.058 µg a.i. per larva in honey bee larvae. The chronic LD50 in larvae is 0.040 µg a.i. per larva. Adult deformation rates exceeded 30% in all lambda-cyhalothrin treatment groups.

Is Lambda-Cyhalothrin Harmful to Fish and Aquatic Life?

It depends. Lambda-cyhalothrin is highly toxic and harmful to fish and aquatic life in tests, yet field exposure is lower. The 96-hour LC50 for fish ranges from 0.078 to 2.3 µg/L in laboratory tests. New Zealand EPA proposed classifying lambda-cyhalothrin as hazardous to the aquatic environment, acute Category 1 and chronic Category 1. Jeffrey M Giddings reported in Ecotoxicology (London, England) median HC5 values of 40.9 ng/L for fish. The median HC5 for invertebrates is 1.05 ng/L. Adsorption to soil and sediment reduces exposure and may lessen the risk to aquatic organisms. Field studies with lambda-cyhalothrin products found no significant adverse effects to fish.

How Long Does Lambda-Cyhalothrin Persist in Soil and Water?

Lambda-cyhalothrin persists for 158.7 days in soil under aerobic conditions, measured as a DT50 value. Lambda-cyhalothrin is persistent in aerobic water and sediment, with a retained total system DT50 of 146.2 days. The 2022 New Zealand EPA classification and endpoints science memo gives both DT50 values. A 2008 study by Li-Ming He found a photolysis half-life above 3 weeks under natural irradiation. Under UV, the photolysis half-life is below 10 minutes. Lambda-cyhalothrin is quite stable in water at pH below 8 and hydrolyzes under alkaline conditions. Its fate in aquatic ecosystems depends on suspended solids and aquatic organisms. Low water solubility and no volatility limit its movement in water.

How Is Lambda-Cyhalothrin Regulated by the EPA?

Lambda-cyhalothrin is regulated by the EPA as an insecticide that the agency registered in 1988. The 2014 California DPR active ingredient page for lambda-cyhalothrin says it is registered in California and in the United States. Lambda-cyhalothrin is not a California restricted material. The Department of Pesticide Regulation is California’s state agency that regulates pesticides. California’s reevaluation status for lambda-cyhalothrin is concluded, following a final decision on pyrethroid products issued in July 2014. That decision covers pyrethroid products, not only the active ingredient.

What Did the EPA Propose for Lambda-Cyhalothrin Under Registration Review?

Under registration review, EPA proposed a decision for lambda-cyhalothrin. The decision is interim and groups lambda-cyhalothrin and gamma-cyhalothrin. The proposed interim decision lets EPA move forward with the completed parts of the review. It puts interim risk measures in place before the review ends. Risks of concern arise for aquatic invertebrates, and freshwater and estuarine/marine fish, from indoor down-the-drain, residential, commercial and turf uses. Jeffrey M Giddings put the median HC5 at 1.05 ng/L for invertebrates and 40.9 ng/L for fish in 2009. EPA will complete endocrine screening before the registration review of lambda-cyhalothrin ends.

How Is Lambda-Cyhalothrin Regulated in the European Union?

Lambda-cyhalothrin is regulated in the European Union as an approved active substance. Lambda-cyhalothrin was included in Annex I to Directive 91/414/EEC on 1 January 2002. It is deemed to be approved under Regulation (EC) No 1107/2009. Gamma-cyhalothrin was approved as a new active substance on 1 April 2015 by Commission Implementing Regulation (EU) No 1334/2014. The European Food Safety Authority is the EU agency that assesses pesticide residues and risks for the European Commission. EFSA published its reasoned opinion on lambda-cyhalothrin residue levels on 2 December 2015. The 2017 EFSA Journal focussed assessment of lambda-cyhalothrin maximum residue levels covers that opinion. EFSA reviewed the existing maximum residue levels because they might lead to consumer intake concerns. The residue assessment does not replace the full MRL review for all authorised uses of gamma-cyhalothrin.

What Reference Doses Apply to Lambda-Cyhalothrin Residues in Food?

The acceptable daily intake for lambda-cyhalothrin residues in food is 0.0025 mg/kg bw per day. EFSA sets these reference doses, which apply to lambda-cyhalothrin, with an acute reference dose of 0.005 mg/kg bw. The 0.0025 mg/kg bw per day value comes from a rat multigeneration study with an uncertainty factor of 200. The 0.005 mg/kg bw value comes from a 1-year dog study with an uncertainty factor of 100. The 2001 NPIC Oregon State archived technical fact sheet on lambda-cyhalothrin gives a no-effect dose of 2.5 mg/kg/day. That dose comes from the two-year rat feeding study. Acute exposure from food and water uses 46% of the acute population-adjusted dose in the general U.S. population. Infants under 1 year use 61% of that dose. Chronic exposure from food and water uses 17% of the chronic population-adjusted dose for the general U.S. population. Children aged 1 to 2 years use 50% of that dose. The population-adjusted doses are the level of concern divided by all applicable uncertainty factors.

How Can People Use Lambda-Cyhalothrin More Safely?

To use lambda-cyhalothrin more safely, people should follow the 4 steps below. The product label sets the first rule for lambda-cyhalothrin.

1. Read the product label for personal protective equipment and safety requirements, because the label gives that specific information.
2. Wear chemical-resistant gloves, even when the label gives no PPE information, because many consumer products omit it.
3. Keep the product out of water that bees can reach, including puddles, because contaminated water exposes bees.
4. Avoid applying to blooming plants, including weeds, unless the label and regulations allow a late-evening application, because bees visit flowers.

Ji-Yeong Choi, writing in Insects, found adult deformation rates above 30% in bees exposed to lambda-cyhalothrin.

Which Protective Equipment Is Recommended When Using Lambda-Cyhalothrin?

To start using lambda-cyhalothrin, begin with the recommended protective equipment, chemical-resistant gloves. Chemical-resistant gloves are recommended even when the label gives no PPE information. Many consumer pesticide products do not include information about personal protective equipment on the label. Check the label first for other garments. Lab workers reported skin irritation or burning that developed 45 to 60 minutes after exposure. A fatal case that Alagarasan Naveen described in 2023 shows how severe lambda-cyhalothrin poisoning can become.