Diazinon (IUPAC name: O,O-Diethyl O-[4-methyl-6-(propan-2-yl)pyrimidin-2-yl] phosphorothioate), a colourless to dark brown liquid, is a thiophosphoric acid ester developed in 1952 by Ciba-Geigy, a Swiss chemical company. It is a non-systemic organophosphate insecticide formerly used to control cockroaches, silverfish, ants, and fleas in residential, non-food buildings. Diazinon was heavily used during the 1970s and early 1980s for general-purpose gardening use and indoor pest control. A bait form was used to control scavenger wasps in the western U.S. In 2004, residential use of diazinon was banned but it is still approved for agricultural uses. Diazinon kills insects by inhibiting acetylcholinesterase, an enzyme necessary for proper nervous system function. It has a low persistence in soil, with a half-life of between 2 to 6 weeks.
Diazinon is used throughout the world to control a wide range of sucking and chewing insects and mites on a range of crops, including deciduous fruit trees, citrus fruit, bananas, vegetables, potatoes, beet, sugar cane, coffee, cocoa, tea, tobacco, cotton, and rice. It is also used to control agricultural soil-dwelling insects, and is applied as a sheep dip to control ectoparasites such as sheep scab and blow fly strike. Diazinon use in homes controls cockroaches, ants, and carpet beetles, and is in insecticidal pet collars.
In the Environment 
- Diazinon can be released into the environment during its production and use as a pesticide.
- Diazinon is moderately persistent and mobile in the environment.
- In air, diazinon is relatively quickly transformed into diazoxon; the estimated half-life for this reaction is 4 hours.
- Diazinon released to surface water or soil is subject to volatilisation, photolysis, hydrolysis, and biodegradation.
- The half-life of diazinon ranges from approximately 70 hours to 12 weeks in surface water and 10 to 200 days in soil.
- Diazinon does not bioaccumulate in aquatic organisms.
Sources of Exposure 
- The general population may be exposed via diazinon-contaminated air, water, or food, but there is little potential for high level exposure because home and garden uses for diazinon have been banned.
- Significant inhalation exposure is likely only near areas where diazinon is produced or used as a restricted pesticide.
- Oral exposure may occur by drinking contaminated water or eating foods containing diazinon residue.
- Significant dermal exposure is likely only near areas where diazinon may be used as a restricted pesticide.
- Occupational exposure may occur at facilities that produce diazinon or in working environments where diazinon is used as a pesticide. Inhalation and dermal exposure are the predominant routes of exposure for workers during production, handling, and application.
Health Effects 
The World Health Organisation (WHO) classifies diazinon as a class II ‘moderately hazardous’ pesticide. The acute oral LD50 (the dose required to kill half a population of laboratory animals) for rats is 1,250 mg/kg, and for mice it is 80-135 mg/kg(12). Diazinon, poisons humans and insects through its effects on nerve enzymes. It combines chemically with the acetylcholinesterase enzyme and inactivates it. This enzyme is essential for the control of nerve impulse transmission. Loss of acetylcholinesterase allows the accumulation of acetylcholine, the substance secreted by nerves that activates muscles, glands, and other nerves. Accumulation of sufficient levels of acetylcholine at junctions between nerves muscles will cause muscle contractions or twitching. Accumulation of acetylcholine at junctions between nerves and glands results in gland secretion; and accumulation between nerves in the brain causes sensory and behavioural disturbances. The main symptoms of acute diazinon poisoning are headache, nausea, dizziness, pin-point pupils, blurred vision, tightness in the chest, difficulty in breathing, muscle weakness or twitching, difficulty in walking, vomiting, abdominal cramps, and diarrhoea. Effects on the central nervous system may include confusion, anxiety, drowsiness, depression, difficulty in concentrating, slurred speech, poor recall, insomnia, nightmares, and a form of toxic psychosis resulting in bizarre behaviour.
Based on inhibition of the enzyme acetylcholinesterase, the daily administered no-observed-adverse-effect-level (NOAEL) for humans is 0.025 mg/kg body weight per day, according to WHO. Other reports suggest no-effect doses have ranged from 0.02 mg/kg/day in humans to 0.1 mg/kg/day in rats(20). In sub-chronic and chronic toxicity studies conducted in mice, rats and dogs, systemic toxicity occurred with decreases in body weight and body weight gains. There are also potential concerns about breakdown products. In animals diazinon is converted to diazoxon (where the sulphur molecule is substituted for oxygen), a compound that is a strong enzyme inhibitor.
Diazinon is not considered carcinogenic by agencies such as the International Agency for the Research on Cancer, or the US EPA. However, use of diazinon by farmers in Iowa and Minnesota has been linked to increased risk of non-Hodgkins lymphoma, a rare form of cancer. Similar links were found in the 1980s in Nebraska.
First Aid Measures
- Call a poison control centre or doctor immediately for treatment advice.
- If swallowed: Have a person sip a glass of water if able to swallow. Do not induce vomiting unless told to do so by a poison control centre or doctor. Do not give anything by mouth to an unconscious person.
- If on skin or clothing: Take off contaminated clothing. Rinse skin immediately with plenty of water for 15 to 20 minutes.
- If inhaled: Move person to fresh air. If person is not breathing, call 000 or an ambulance, then give artificial respiration, preferably mouth-to-mouth if possible.
- If in eyes: Hold eye open and rinse slowly and gently with water for 15-20 minutes. Remove contact lenses, if present, after the first 5 minutes, then continue rinsing eye.
Exposure Controls/Personal Protection
- Engineering Controls: When handlers use closed systems, enclosed cabs, or aircraft in a manner that meets with requirements listed in the Worker Protection Standard (WPS) for agricultural pesticides [40CFR 170.240 (d)(4-6)], the handler PPE requirements may be reduced or modified as specified in the WPS.
- Respiratory Protection: Not normally required, if vapours exceed acceptable levels, wear a MSHA/NIOSH approved pesticide respirator with cartridges for pesticide vapours.
- Eye Protection: Chemical goggles or shielded safety glasses.
- Skin Protection: Wear protective clothing: long-sleeved shirts and pants, hat, rubber boots with socks. Wear rubber or chemical resistant gloves.