Malathion Profile

Malathion Profile

QUICK SUMMARY

• A pesticide used in agricultural and commercial settings
• Associated cancers: Non-Hodgkin lymphoma, prostate cancer (limited evidence)
• Most important route of exposure: Inhalation, skin contact
• Uses: Controls insects on field crops and blueberries, and in grain sheds, barns, and silos; emergency control for specific insects in fruit and berry crops
• Occupational exposures: Farm workers, pesticide applicators, and mosquito control applicators most likely to be exposed
• Environmental exposures: Via contaminated air near spray sites or touching objects with malathion residue
• Fast fact: Malathion is occasionally used to control the spread of West Nile Virus in Winnipeg.

General Information

Malathion is an organophosphate insecticide. It’s appearance can range from a colourless to amber liquid, with a strong skunk or garlic-like odour. Malathion may also be known as its chemical name, which is O,O-dimethyl dithiophosphate of diethyl mercaptosuccinate.[1] As of late 2016, 26 products registered with the Canadian Pest Management Regulatory Agency (PMRA) contain the active ingredient malathion and of these, seven are registered for domestic use.[2] Trade names include Fyfanon® and Gardal Rose®.[2] Malathion was re-evaluated by the PMRA in 2012 and certain uses were subjected to a phase-out period. These uses include larval mosquito control and applications to greenhouse food and non-food crops, residential lawns, or livestock.[3]

Malathion is used as a broad-spectrum insecticide in the agricultural and domestic sector. It is also used to control fruit fly and adult mosquito populations, for example in campaigns to eradicate the West Nile Virus.[4]

The International Agency for Research on Cancer (IARC) reclassified malathion as Group 2A, probably carcinogenic to humans , in its 2015 assessment of five organophosphate pesticides.[5] IARC came to this conclusion due to limited evidence of carcinogenicity in humans for non-Hodgkin lymphoma and prostate cancer.[6,7,8,9,10] There was also sufficient evidence in animal and in vitro studies for carcinogenicity, DNA and chromosomal damage, and hormonal disruption.[11,12]

Malathion irreversibly binds to cholinesterase, the enzyme responsible for breaking down acetylcholine throughout the nervous system in humans, animals, and insects.[13] Malathion can be metabolized into malaoxon, which is substantially more toxic.[13] Human studies show that malathion reduces cholinesterase activity, and can also cause respiratory, gastrointestinal, and neurological symptoms.[4,14] In animals, malathion is a known endocrine disruptor, teratogen (disrupts embryo or fetus development), and reproductive toxin,[14,15,16,17] although these effects have not been confirmed in human studies.

Regulations and Guidelines

Occupational exposure limits (OEL)[18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]

Canadian environmental guidelines and standards*

Canadian legal status[44]

Several provincial, territorial, and municipal governments have passed laws to reduce risk to human health and the environment from pesticide products, which may include a restriction on sales, production, or trade.[45,46] Although several provinces and one territory have implemented some form of cosmetic pesticide policy (QC, 2003; NB, 2009; ON, 2009; AB, 2010; PEI, 2010; NS, 2011; NL, 2012; YK 1994), only the Ontario and Nova Scotia legislation is considered strong enough to significantly reduce cosmetic pesticide exposure.[45] For example, Ontario’s Cosmetic Pesticide Ban Act, the most comprehensive restrictions on lawn and garden pesticides in North America, prohibits the cosmetic use of over 250 pesticide products and over 95 pesticide ingredients, including malathion.[47]

Main Uses

Malathion was first registered for use in Canada in 1953.[3] It was re-evaluated by the PMRA in 2012, and certain uses were subjected to a phase-out period; these uses include larval mosquito control, and applications to greenhouse food and non-food crops, residential lawns, or livestock.[3] Malathion is a broad-spectrum insecticide used in agricultural, commercial, and domestic sectors. It can be formulated into sprays, fogs, pellets, powders, shampoos, and lotions.[3,48]

Examples of malathion use in Canada include:

• Agriculture: to control pests in field crops such as alfalfa, clover pasture, cereal crops, cotton, safflower, soybean, sugar beets, corn, beans, and blueberries. It is registered for the emergency control of spotted wing drosophila in Canada for a variety of fruit and berry crops.[49,50] It is also used to control insects in storage areas such as grain sheds, barns, processing facilities, shipping crates, and silos.[51] Large-scale aerial applications of malathion are sometimes used.[14]

• Domestic: the technical registrant of malathion in Canada voluntarily discontinued a number of residential uses including structural (pet quarters, indoor uses), companion animals, turf, and residential outdoors.[3] In the past malathion was used to control the spread of West Nile Virus in Canada, although currently this only appears to be practiced in Winnipeg, Manitoba.[52,53] These mosquito control programs use an ultra-low volume of malathion applied via fogging in residential areas, and residents may register for buffer zones around their homes.[52] Malathion was used to treat head lice and scabies in Canada and the United States,[4] although such treatments are no longer used or available in Canada.[54,55]

• Commercial: to control indoor insects in food processing plants, schools, hospitals, golf courses, and dog kennels.[4]

Canadian Production and Trade

Since November 2006, the PMRA has tracked and reported sales information on Canadian pesticides . PMRA records show that the greatest amounts of malathion were sold in 2016, 2017 and in 2019, with greater than >100,000 kg a.i. sold.[56,57,58]  In these years, malathion was among the top 10 insecticides sold in Canada. TradeMap lists malathion export and import data; however, reporting for pesticides is not standardized and the data is incomplete.[59]

Environmental Exposures Overview

The public may be exposed to malathion via inhalation or by touching objects with the chemical residue. People living near spray sites or in areas where this insecticide is used for West Nile Virus and mosquito control measures may be exposed.[13] Exposure to malathion may also take place by ingesting contaminated food or drinking water. Pesticide residues, including malathion residues, are monitored by the Canadian Food Inspection Agency (CFIA) under the National Chemical Residue Monitoring Program (NCRMP).[60]

Malathion may contaminate the environment at its site of production or use through accidental or intentional releases.[13] If malathion is released to air it may exist as a particulate or vapour. The vapour phase of this chemical is broken down into hydroxyl radicals with a half-life of five hours.[13] The particle phase may fall to the soil or water with rainfall or independently. The half-life of malathion in soil is 1-17 days, where it may volatilize back into the atmosphere, bind to soil particles, get taken up by plants, or be metabolized by soil microbes.[61] In water, it also binds to sediments, with a half-life of 10 days, or two days in the marine environment.[13] Malathion does not biomagnify or bioaccumulate.[13]

Occupational Exposures Overview

The primary routes of occupational exposure to malathion are inhalation and dermal absorption. Occupational exposure can occur during mixing, loading, or applying pesticides.[62] The people most likely to be occupationally exposed to malathion are farm workers, pesticide applicators, and mosquito control applicators.[13,63]

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