Simazine in freshwater and marine water

​​Toxicant default guideline values for protecting aquatic ecosystems

October 2000

Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals’of the ANZECC & ARMCANZ (2000) guidelines.

The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.

Description of chemical

Simazine (CAS 122-34-9) is a triazine herbicide introduced by Ciba-Geigy AG. It has a selective systemic action and is absorbed through the roots. Its IUPAC name is 6-chloro-N2N4-diethyl-1,3,5-triazine-2,4-diamine, formula is C7H12ClN5 and molecular weight 201.7. It is slightly soluble in water to 6.2 mg/L and has a log Kow of 2.1 at 25°C (Tomlin 1994). The current analytical practical quantitation limit (PQL) for simazine in water is 0.2 µg/L (NSW EPA 2000).

Uses and environmental fate

Simazine is used for control of a wide variety of grasses and broad-leaved weeds in fruit, vines, nuts, pineapples, vegetables, flowers, sugarcane, coffee, tea, turf and in forestry (Tomlin 1994). In Australia, it has over 2700 registered uses (NRA 1997a). Simazine is stable in water, is decomposed by ultraviolet (UV) light and binds strongly to the soil surface. Loss from soil (DT50 of 11 to 70 days) is mainly by microbial degradation.

Aquatic toxicology

Freshwater fish: 15 species, although screening for figures exceeding the water solubility by a factor of 2 reduced this to seven species 24 to 96-hour LC50, 90 to 6600 µg/L.

Freshwater crustaceans: three species, 48-hour LC50 or EC50 of 1000 to 3700. Data from two species exceeded the water solubility by > 2 times.

Freshwater insects: two species, 48 to 96-hour LC50, 1900 to 3580 µg/L.

Freshwater algae: two species, 48 to 96-hour EC50, growth and population growth of 160 to 320 µg/L and for photosynthesis, only 2.24 µg/L (the latter figure was not applied).

Factors that modify toxicity

None were reported.


A freshwater moderate reliability trigger value of 3.2 µg/L was derived for simazine using the statistical distribution method with 95% protection and the default acute-to-chronic ratio (ACR). In the absence of marine data, 3.2 µg/L was adopted as a marine low reliability trigger value. This should only be used as an indicative interim working level.


ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

NRA 1997a. Database extraction of selected pesticides: Registered uses in Australia, National Registration Authority, July 1997, Canberra.

NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.

Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.