Hexazinone in freshwater and marine water
Toxicant default guideline values for protecting aquatic ecosystems
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
Hexazinone (CAS 51235-04-2) is a non-selective contact herbicide, which is absorbed by leaves and roots. It was introduced by DuPont de Nemours Co. Its IUPAC name is 3-cyclohexyl-6-dimethylamino-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione, formula is C12H20N4O2 and molecular weight 252.3. Hexazinone is readily soluble in water to 33 g/L at 25°C and it has a low log Kow (1.05).
Uses and environmental fate
Hexazinone is an effective post-emergence herbicide against a variety of annual and perennial weeds in tree plantations, sugarcane, pineapple and alfalfa (Tomlin 1994). In Australia it is commonly used in bark treatments of woody weed species, as well as on a variety of weeds in pine plantations, commercial/industrial areas and rights-of-way (NRA 1997a).
Hexazinone is stable in aqueous solution and breaks down only slowly in soils, with a DT50 of 1 to 6 months, depending on soil type and climate.
Freshwater algae: no data.
Freshwater fish: eight species, 48 to 96-hour LC50, 75 to 1620 mg/L (x 1000 µg/L).
No marine data available.
A freshwater low reliability trigger value of 75 µg/L was calculated for hexazinone 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.