What is Simazine?

Simazine is an herbicide of the triazine class, with the molecular formula C7H12ClN. Under normal conditions, Simazine is a white crystalline powder. When mixed with air, its dusts can be explosive. When heated, Simazine breaks down to give toxic fumes. It melts at 225 degrees Celsius. Simazine is not very soluble in water but dissolves well in organic (carbon-containing) solvents. Like atrazine, a related triazine herbicide, it acts by inhibiting photosynthesis. It remains active in the soil for 2–7 months after application.

What is Simazine used for?

Simazine is a herbicide used to prevent weeds from growing before they emerge. It's applied to:

• Deep-rooted crops: Such as artichokes, asparagus, berries, broad beans, and citrus fruits.
• Non-crop areas: Like farm ponds and fish hatcheries to control unwanted plants.
• Corn fields: This is where it's most commonly used, often mixed with another herbicide called AAtrex.
• Fruit trees: Mixed with paraquat to control weeds around apples and peaches.
• Non-crop areas: Combined with herbicides like Roundup or Oust for places where no crops are grown.
• Christmas trees: Mixed with Surflan to protect Christmas tree farms from weeds.

Corn and ornamental plants: Combined with Dual to manage weeds in cornfields and ornamental plant areas.

Simazine Hazards

Environmental Effects

At high levels, Simazine is classified as toxic to wildlife, particularly aquatic organisms. Simazine applied to soils or hard surfaces may run off into water bodies. Some can also seep into groundwater, although this is limited by its relatively low solubility in water. Simazine in the atmosphere is usually deposited onto soils or water bodies, and that which remains is broken down within a matter of hours. Simazine can persist in soils and waters for a considerable time, and it has been found far from its point of release. For this reason, Simazine pollution is of concern at a global as well as local level.

Sources & Routes of Exposure

Source of Exposure

Individuals most likely to be exposed to simazine include:

• Farmers and Agricultural Workers: Those who handle or apply simazine or herbicide mixtures containing simazine on fields or orchards.
• Family Members on Farms: People living on farms or orchards where simazine has been used.
• Pesticide Applicators: Workers applying simazine to control weeds on vacant lots, right-of-ways, turf, golf courses, or ornamental shrubs.
• Handlers of Contaminated Clothing: Individuals who handle or launder clothing contaminated with simazine.
• Factory Workers: Employees working in facilities that manufacture simazine.
• Consumers of Contaminated Water: People who drink water tainted with simazine.
• Consumers of Contaminated Food: Individuals eating food products with simazine residues or its breakdown products.

Routes of Exposure

Simazine can enter the body through inhalation of contaminated air, ingestion of tainted water, or dermal contact with simazine, making awareness of all potential exposure routes essential for safety.

Health Effects

Acute Effect

Toxicity: Simazine is slightly to practically non-toxic.

• Oral LD50: >5000 mg/kg (rats and mice).
• Dermal LD50: 3100 mg/kg (rats), >10,000 mg/kg (rabbits).
• Inhalation LC50: >2 mg/L (rats, 4 hours).
• Formulated products are generally less toxic via all exposure routes.

Skin and Eye Irritation:

• Non-irritating to rabbit skin and eyes except at high doses.
• Patch tests in humans show simazine is not a skin irritant, fatiguing agent, or sensitizer.
• Occupational exposure may cause rashes or dermatitis.

Symptoms: Triazine herbicides (like simazine) disturb energy metabolism (thiamin and riboflavin functions), with symptoms including:

• Difficulty walking, tremors, convulsions, paralysis.
• Cyanosis, slowed respiration, pinpoint pupils, gut pain, diarrhoea.
• Impaired adrenal function.

Animal Effects:

• Rats given 5000 mg/kg showed drowsiness and irregular breathing.
• Single oral doses of 4200 mg/kg caused anorexia, weight loss, and death in rats.
• Sheep and cattle are particularly susceptible, with doses of 500 mg/kg proving fatal.
• Poisoned sheep showed lower food intake, higher water intake, incoordination, tremors, and hindquarter weakness.

Chronic Effects

90-Day Feeding Studies:

• Reduced body weight at doses of 67-100 mg/kg/day.
• Kidney toxicity at 150 mg/kg/day.

2-Year Chronic Feeding Study:

• Rats given 5 mg/kg/day showed no signs of toxicity.
• At 15 mg/kg/day, some liver cell degeneration occurred but did not progress as the liver adapted.

Other Chronic Effects:

• Tremors, damage to the testes, kidneys, liver, and thyroid.
• Disturbances in sperm production and gene mutations in test animals.

Reproductive/Developmental Effects

• Rats: No adverse effects on reproductive capacity or development in a three-generation study at 5 mg/kg/day.
• Rabbits: High rates of fetotoxicity and decreased birth weight at 75 mg/kg/day.
• Humans: Reproductive effects are unlikely under normal exposure circumstances.

Teratogenic Effect

• Rabbits: No dose-related teratogenic effects when administered 5, 75, or 200 mg/kg during pregnancy.
• Rats: Chronic inhalation of 0.3 mg/L over 8 days showed no developmental abnormalities.
• Simazine does not appear to be teratogenic.

Mutagenic Effects

• Simazine has produced negative results in most mutagenicity tests on bacterial cultures.
• Mixed results (positive and negative) in tests on human lung cell cultures.
• Simazine increased sex-linked lethal mutations in male fruitflies when injected but not when fed to larvae. Other mutagenicity tests in fruitflies were negative.
• Likely non-mutagenic or weakly mutagenic.

Carcinogenic Effects

• Mice: Simazine was not tumorigenic at a maximum dose of 215 mg/kg/day over 18 months.
• Rats: Doses as low as 5 mg/kg/day produced excess tumours (thyroid and mammary) in female rats.
• Carcinogenic status is inconclusive due to inconsistent data.

Organ Toxicity

• Damage to the testes, kidneys, liver, and thyroid has been observed in test animals exposed to simazine.

Simazine Safety Handling

First Aid Measures

• Inhalation: Remove affected person to fresh air until recovered.
• Ingestion: If swallowed, do NOT induce vomiting; seek medical advice immediately and show this container or label or contact the Poisons Information Centre on 13 11 26 (Aust). Make every effort to prevent vomit from entering the lungs by careful placement of the patient.
• Skin: Remove contaminated clothing and launder before re-use. Wash affected areas thoroughly with soap and water.
• Eye: If in eyes, hold eyelids open and wash with copious amounts of water for at least 15 minutes.
• First Aid Facilities: If poisoning occurs, contact a doctor or the Poisons Information Centre (Australia) on 13 11 26.

Fire & Explosion Information

• Suitable Extinguishing Media: Water, foam, carbon dioxide, or dry chemical.
• Hazards from Combustion Products: Non-flammable. If involved in a fire, it will emit oxides of nitrogen, oxides of carbon, and possibly hydrogen chloride.
• Special Protective Equipment for firefighters: Breathable air apparatus may have to be worn if material is involved in fires, especially in confined spaces.
• Other Information: STOP FIRE WATER FROM ENTERING DRAINS OR WATER BODIES.

Exposure Controls & Personal Protection

Engineering Controls

• Handle in well ventilated areas; generally, natural ventilation is adequate.

Personal Protective Equipment

• Respiratory Protection: If dusts are present, wear a class P1 dust mask.
• Personal Protective Equipment: It is good practice to wear suitable personal protective equipment (PPE).
• When opening the container, preparing spray, and using the prepared spray, wear cotton overalls buttoned to the neck and wrist and a washable hat, elbow-length PVC gloves, and goggles.
• Re-entry period: Do not enter treated area until spray has dried.

Hygiene Measures 

• After use and before eating, drinking or smoking, wash hands, arms, and face thoroughly with soap and water.
• After each day's use, wash contaminated clothing and safety equipment.

Regulations

United States

Drinking Water Standards:

EPA: The Environmental Protection Agency has established the following drinking water guidelines for simazine: 

• MCLG (maximum contaminant level goals): 0.004 mg/L
• MCL (maximum contaminant level): 0.004 mg/L
• HAL (health advisory level) (child): 1- to 10-day: 0.07 mg/L; Longer-term: 0.07 mg/L

Occupational Exposure Limits:

• No occupational exposure limits for simazine have been set by OSHA, NIOSH, or ACGIH 

Australia

• Safe Work Australia has not set an exposure standard for simazine

Australian Drinking Water Guidelines December 2013: Based on human health concerns, simazine in drinking water should not exceed 0.02 mg/L.