Lead author: Allison Camp
Malathion is an organophosphate (OP) insecticide that is a neurotoxin. It was first registered in 1956, and remains in use. Although malathion has a lower level of toxicity to humans than many other OP pesticides, it is highly toxic to aquatic organisms and bees. The EPA estimated in 2006 that approximately 15 million lbs of malathion was applied in the United States, with the majority being used for the USDA Boll Weevil Eradication Program (#EPA 2006). The maximum level of malathion residue that the Food and Drug Administration (FDA) and Environmental Protection Agency (EPA), allow on food crops is 8 parts per million (ppm) (#ATSDR 2003).
Malathion (diethyl (dimethoxyphosphinothioylthio)succinate), in an organophosphate insecticide (#PPDB 2011). Pure malathion is a clear liquid, however the technical-grade solution, which contains impurities is an amber liquid (#ATSDR 2003).
Malathion is used to control a broad spectrum of insects including: ants, aphids, fleas, fruit flies, hornets, mites, mosquitoes, moths, spiders, thrips, ticks, wasps, and weevil. Malathion is used for pest control on a wide range of agricultural food and feed crops, the most common of which are blueberries, raspberries, strawberries, limes, cotton, cherries, garlic, greens, dates and celery. For agricultural sites, application amount ranges from 0.175-6.25 lbs active ingredient (a.i.) per acre. It is also approved for residential use, but at rate of 0.000085-0.0003 lb a.i. per square foot (#EPA 2006). Beyond application to plants, malathion is a component of personal hygiene products used for lice control (See Flea Dip) (#ASTDR 2003).
Malathion can be applied by aircraft, duster, fogger, ground boom, irrigation, sprayer or spreader. Malathion is available in many different formulations, including ready-to-use liquid, dust, pressurized liquid and emulsifiable concentrate (#EPA 2006).
Malathion has been a registered pesticide since 1956 and is still in use (#EPA 2006). Malathion is the primary pesticide used in the USDA Boll Weevil Eradication Program, which began in the late 1970's to protect cotton crops in the southern United States continued until 2008 (#USDA 2006, #USDA 2008).
In 1998 in Florida, an outbreak of Mediterranean fruit flies (Medflies) threatened to significantly decrease agricultural yields. In an effort to minimize damage, the Medfly Eradication Program was implemented by federal and state authorities. Malathion and another organophosphate, diazinon, were applied to areas of concern. Within 5 months of application, 123 people reported symptoms consistent with pesticide exposure, such as respiratory distress, gastrointestinal distress, neurological problems, skin reaction, and eye distress (#CDC 1999).
During 2005, malathion was one of many insecticides used to control mosquitoes potentially carrying West Nile Virus in the United States (#ATSDR 2005).
Exposure to malathion can occur in several different ways: oral, dermal, inhalation, or eye contact. Oral exposures typically involve consumption of contaminated food or water, while dermal exposure occurs during handling of treated crops or during residential use. Inhalation exposure commonly occurs near agricultural fields where malathion is applied and often is the result of spray drift. Inhalation of malathion is also a risk when insecticides are used in homes where ventilation is poor (#EPA 2006, #ATSDR 2003).
Malathion is quickly metabolized by the body, and does not accumulate. Metabolites are excreted in the urine within several days. One of the metabolites, malaoxon, is more toxic that malathion (#EPA 2006, #ATSDR 2003).
In acute oral doses symptoms are similar to other cholinesterase (ChE) inhibitors and include: numbness, decreased coordination, dizziness, tremor, nausea, blurred vision, difficulty breathing, slow heartbeat, headache and tingling sensations (#EXTOX 1996,#CDC 1999). Accidental death in humans from malathion has been documented (#EXTOX 1996). Toxicity may vary based on gender, as male and female rats displayed different LD50 values for an oral dose (5400 and 5700 mg/kg, respectively) (#EPA 2006).
In a chronic toxicity study, human volunteers ingested a low dose for 1.5 months without detrimental effects to blood ChE activity (#EXTOX 1996).
According to the EPA, malathion has, "suggestive evidence of carcinogenicity" (#EPA 2006).
Malathion has low soil and water persistence. The half-life of malathion in soil is 1-25 days (#EXTOX 1996), however it is mobile. Malathion can leach out of soil into groundwater, and has been detected in groundwater in CA, MS, and VA (#EPA 2006). Malathion has low persistence in water as well, with a half-life of <1 week in river water (#EXTOX 1996).
Rat acute oral LD50: 1178mg/kg
Rat inhalation LC50: >5mg/l
Birds acute oral LD50: 359 mg/kg
Fish 96hr LC50: 0.018mg/l
Aquatic invertebrates 48hr EC50: 0.0007mg/l
Honeybees 48hr LD50: 0.16 μg/ bee
Malathion is slightly toxic to mammals, moderately toxic to birds, and highly toxic to aquatic organisms, both freshwater and estuarine, as well as bees (#EPA 2006, #PPDB 2011).
Agency for Toxic Substances & Disease Registry. 2005. "Toxicologic Information About Insecticides Used for Eradicating Mosquitoes (West Nile Virus Control)" [Accessed 05-17-11]
Agency for Toxic Substances & Disease Registry. 2003. "Toxicological Profile for Malathion" [Accessed 05-17-11]
Center for Disease Control. 1999. "Surveillance for Acute Pesticide-Related Illness During the Medfly Eradication Program -Florida, 1998." [Accessed 05-17-11]
Extenstion Toxicology Network. 1996. "Pesticide Information Profile- Malathion." [Accessed 05-17-11]
Pesticide Properties DataBase. 2011. "Malathion" [Accessed 05-17-11]
United States Department of Agriculture Animal and Plant Health Inspection Service. 2008. "Cotton Pests." [Accessed 05-17-11]
United States Department of Agriculture Animal and Plant Health Inspection Service. 2006. "Questions and Answers: The EPA's Risk Assessment on Malathion."
United States Environmental Protection Agency. 2006. "Reregistration Eligibility Decision for Malathion." [Accessed 05-17-11].
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