Amitrole 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

Amitrole (CAS 61-82-5) is a triazine herbicide developed by Rhone-Poulenc Agrochemicals with a non-selective systemic mode of action, being absorbed by leaves and roots (Tomlin 1994). It inhibits formation of chlorophyll and regrowth from buds. Its IUPAC name is 1H-1,2,4-triazol-3-amine, molecular formula is C2H4N and molecular weight is 84.1. Amitrole is soluble in water at 280 mg/L at 23°C (Tomlin 1994), stable and forms salts with most acids or bases.

Uses and environmental fate

Amitrole is used extensively for control of grasses, broad-leaved weeds and bushes in orchards, vineyards and plantations, in cereal stubble and prior to sowing, and around railway tracks, fences and buildings. It also has some uses against aquatic weeds (Tomlin 1994, NRA 1997a). In Australia, amitrole has over 800 registered uses in over 25 location types for a wide variety of weed types, including grasses, burrs and blackberry (NRA 1997a). Amitrole is degraded microbially but persists in soils for 2 to 4 weeks.

Aquatic toxicology

Freshwater fish: four species 24 to 96-hour LC50 of 65 to 410 mg/L.

Freshwater crustaceans: two species 26 to 96-hour EC50 (immobilisation) of 22 to 58 mg/L.

Freshwater algae: one species, 24-hour EC50 (photosynthesis) of 3.75 mg/L could not be used.

No marine data were available.


A freshwater low reliability trigger value of 22 µg/L was calculated for amitrole using an assessment factor (AF) of 1000. In the absence of marine data, this was adopted as a marine low reliability trigger value. These figures should only be used as indicative interim working levels.


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.

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