What is Malathion?

Malathion is an organophosphate compound with the formula C₁₀H₁₉O₆PS₂. In its pure form, it is a colourless liquid, but in technical-grade solutions, it appears brownish-yellow with a garlic-like smell. It is man-made and does not occur naturally. Known as maldison in Australia and New Zealand, malathion is an insecticide with low toxicity to humans.

What is Malathion used for?

Malathion is used:

• As a pesticide for agricultural crops, stored products, golf courses, home gardens, and outdoor trees and shrubs.
• To kill mosquitoes and Mediterranean fruit flies in large outdoor areas, especially in California and Florida.
• For flea control on pets and head lice treatment on humans.
  It is commonly sprayed on crops or applied aerially over wide areas.

In the Environment

• Malathion enters the environment through spraying and settles on soil, plants, water, or surfaces.
• While most stay in the applied area, rain, fog, or wind can move it elsewhere.
• It is typically broken down within weeks by sunlight, water, and bacteria.
• In soil, malathion degrades quickly and is unlikely to reach groundwater in significant amounts.
• In water, it breaks down rapidly due to bacteria and water action.
• In air, it reacts with sunlight to form a more toxic compound, malaoxon.
• On dry soil or surfaces like pavements and playgrounds, it breaks down more slowly.

Sources & Routes of Exposure 

Source of Exposure

• General population: Exposure occurs mostly through consuming contaminated food or water. People near sprayed areas may be exposed through skin contact, inhalation of mist, or residue ingestion.
• Occupational exposure: Workers handling or applying malathion face the highest exposure risk, as do farm workers entering treated fields prematurely.

Routes of Exposure

• Inhalation: Minor route for the general population.
• Oral: Primary route for the general population through food or water.
• Dermal: Main route for workers, minor for the general population.

Health Effects

• Nervous System: Malathion disrupts normal nervous system function, potentially affecting other organs. High exposure can cause symptoms like difficulty breathing, chest tightness, vomiting, cramps, diarrhoea, blurred vision, salivation, sweating, dizziness, or loss of consciousness. In severe cases, it can lead to death. Prompt medical treatment can prevent long-term effects.
• Low Exposure: Generally, no health issues occur with low exposure levels.
• Reproductive Health: No evidence suggests malathion impacts reproduction.
• Cancer: There is no conclusive evidence linking malathion to cancer in humans. The IARC classifies malathion as "unclassifiable" for carcinogenicity.

Safety

First Aid Measures

• Inhalation: Move to fresh air. Keep warm and rested. Supply oxygen if needed and seek medical help immediately.
• Skin contact: Remove contaminated items. Wash thoroughly with soap and water. Seek medical help if needed.
• Eye contact: Rinse eyes with cold water or saline for 20 minutes. Get medical attention immediately.
• Ingestion: Rinse mouth with water. Do not induce vomiting. Seek medical attention immediately.
• Advice to physician: Administer atropine promptly in adequate doses—it may save lives.

Exposure Controls & Personal Protection

Engineering Controls

• Ensure good ventilation and properly designed control systems. Follow all relevant safety, environmental, and fire regulations.

Personal Protective Equipment (PPE)

• Respirator: Use a full-face respirator approved for pesticide dust or mist. Follow agency and manufacturer guidelines.
• Clothing: Wear impervious protective clothing to prevent skin contact.
• Gloves: Use chemical-resistant gloves.
• Eye Protection: Use splash-proof safety goggles and a face shield.
• Emergency Eye Wash: Ensure an eye wash station is nearby for emergencies.

Regulation

United States

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.

Australia

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.