Malathion is an organophosphate parasympathomimetic that binds irreversibly to cholinesterase and has the molecular formula C10H19O6PS2.  It is a colourless liquid in pure form and a brownish-yellow liquid with a garlic smell when part of a technical grade solution. It is manufactured and does not occur naturally in the environment.  Malathion is an insecticide of relatively low human toxicity. In Australia and New Zealand it is known as maldison. 
Malathion is a pesticide that is used to kill insects on agricultural crops, on stored products, on golf courses, in home gardens, and in outdoor sites where trees and shrubs are grown at home; it is also used to kill mosquitoes and Mediterranean fruit flies (medflies) in large outdoor areas. Additionally, malathion is used to kill fleas on pets and to treat head lice on humans. It is usually sprayed on crops or sprayed from an airplane over wide land areas, especially in the states of California and Florida.
In the Environment 
Once malathion is introduced into the environment, usually from spraying on crops or in wide urban/residential areas, droplets of malathion in the air fall on soil, plants, water, or man-made surfaces. While most of the malathion will stay in the areas where it is applied, some can move to areas away from where it was applied by rain, fog, and wind. Malathion stays in the environment from a few days to several months, but is usually broken down within a few weeks. It is broken down to other chemical compounds by water, sunlight, and bacteria found in soil and water. Malathion does not tend to stick to the soil and is rapidly broken down by bacteria; thus, it is unlikely that malathion will reach groundwater in significant amounts. In water, malathion breaks down quickly by the action of the water and the bacteria in the water. In air, malathion is broken down by reacting with other chemicals formed naturally in the air by sunlight, to form a more toxic product called malaoxon. If malathion is present on dry soil or on man-made surfaces such as sidewalks, pavements, or playground equipment, it usually does not break down as fast as it would in moist soil.
Sources & Routes of Exposure 
Sources of Exposure
- The general population is not likely to be exposed to high levels of malathion.
- Exposure to malathion predominantly occurs through ingestion of contaminated food or water.
- People living near areas where malathion is sprayed have a greater risk of being exposed through dermal contact with contaminated plants and soils, inhalation of mist formed during application, and ingestion of residues in food or water.
- Workers involved in the production, formulation, handling, and application of malathion are likely to have the highest levels of exposure.
- Farm workers who enter treated fields prior to the passage of the appropriate restricted entry intervals may also be exposed to high levels of malathion.
Routes of Exposure
The following are the routes of exposure for malathion:
- Inhalation – Minor route of exposure for the general population.
- Oral – Predominant route of exposure for the general population through ingestion of contaminated food or water.
- Dermal – Minor route of exposure for the general population. Predominant route of occupational exposure.
Health Effects 
Malathion interferes with the normal function of the nervous system. Because the nervous system controls many other organs, malathion indirectly can affect many additional organs and functions. Exposure to high amounts of malathion in the air, water, or food may cause difficulty breathing, chest tightness, vomiting, cramps, diarrhoea, watery eyes, blurred vision, salivation, sweating, headaches, dizziness, loss of consciousness, and death. If persons who are exposed accidentally or intentionally to high amounts of malathion are rapidly given appropriate treatment, there may be no long-term harmful effects. If people are exposed to levels of malathion below those that affect the function of the nervous system, few or no health problems seem to occur. This has been shown in studies with volunteers who inhaled or swallowed small known amounts of malathion. There is no evidence that malathion affects the ability of humans to reproduce. There is also no conclusive proof that malathion causes cancer in humans, although some studies have found increased incidence of some cancers in people who are regularly exposed to pesticides, such as farmers and pesticide applicators. The International Agency for Research on Cancer (IARC) has determined that malathion is unclassifiable as to carcinogenicity to humans.
First Aid Measures
- Inhalation: Remove source of contamination or move victim to fresh air. Keep affected person warm and at rest. Supply oxygen if necessary. Treat symptomatically and supportively. Seek medical advice immediately.
- Skin contact: Remove contaminated clothing, shoes and leather goods. Gently wipe of excess chemical. Wash skin gently and thoroughly with water and non-abrasive soap. Seek medical advice if necessary. Persons who become sensitised may require specialised medical management with antiinflammatory agents.
- Eye contact: Immediately flush eyes with gently flowing cold water or saline solution for 20 minutes, holding the eyelid(s) open. Seek medical attention immediately.
- Ingestion: Have victim rinse mouth thoroughly with water. Do not induce vomiting, due to the aromatic solvent. Seek medical advice immediately.
- Advice to physician: Atropine must be administrated as early as possible and could save lives, if given in time and in an adequate dosage.
Exposure Controls & Personal Protection
- It is essential to provide adequate ventilation.
- Ensure that control systems are properly designed and maintained.
- Comply with occupational safety, environmental, fire and other
Personal Protective Equipment
If engineering controls and work practices are not effective in controlling exposure to this material, then wear suitable personal equipment including approved respiratory protection.
- Respirator: An approved full-face respirator suitable for protection from dusts or mists of pesticides is required. Limitations of respirator use specified by the approving agency and the manufacturer must be observed.
- Clothing: Employee must wear appropriate protective (impervious) clothing and equipment to prevent skin contact with the substance.
- Gloves: Employee must wear appropriate chemical resistant protective gloves to prevent contact with this substance.
- Eye protection: Employee must wear splash-proof safety goggles and face shield to prevent contact with this substance.
- Emergency eye wash: Where there is any possibility that an employee’s eyes may be exposed to this substance, the employer should provide an eye wash fountain or appropriate alternative within the immediate work area for emergency use.
OSHA: The Occupational Safety & Health Administration has set the following Permissible Exposure Limit (PEL) for malathion:
- General Industry: 29 CFR 1910.1000 Z-1 Table — 15 mg/m3 TWA; Skin
- Construction Industry: 29 CFR 1926.55 Appendix A — 15 mg/m3 TWA; Skin
- Maritime: 29 CFR 1915.1000 Table Z-Shipyards — 15 mg/m3 TWA; Skin
ACGIH: The American Conference of Governmental Industrial Hygienists has set a Threshold Limit Value (TLV) for malathion of 1 mg/m3 TWA – Inhalable fraction, Vapour and aerosol; Skin; Appendix A4 – Not Classifiable as a Human Carcinogen; BEI – Appendix A: Carcinogens
NIOSH: The National Institute for Occupational Safety and Health has set a Recommended Exposure Limit (REL) for malathion of 10 mg/m3 TWA; Skin
EPA: The Environmental Protection Agency states that the following levels of malathion in drinking water are not expected to cause effects that are harmful to health:
- 0.2 milligrams per litre (mg/L) for 1 day, 10 days, or longer-term exposure for children, and
- 0.1 mg/L for lifetime exposure of adults.
EPA also has set maximum levels of malathion residues in meat and dairy products, vegetables, fruits, tree nuts, cereal grains, and grass forage, fodder, and hay. EPA requires notification to the Agency of spills or accidental releases of 100 pounds or more of malathion to the environment.
Safe Work Australia: Safe Work Australia has established a Time Weighted Average Concentration (TWA) for malathion of 10 mg/m3 for a 40-hour workweek.