Sethoxydim 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
Sethoxydim (CAS 74051-80-2; 71441-80-0) is a cyclohexanedione oxime herbicide first introduced by Nippon Soda Co. Ltd (Tomlin 1994). It is a selective, systemic herbicide, which is mostly absorbed by foliage. Its IUPAC name is (±)-(EZ)-2-(1-ethoxyiminobutyl)-5-[2-(ethylthio)propyl]-3-=hydrocyclohex-2-enone. Its formula is C17H29NO3S and molecular weight is 327.5. It is soluble in water of pH 7 to 4700 mg/L at 20°C and has a log Kow of 1.65 at pH 7 and 4.5 at pH 5.
Uses and environmental fate
Sethoxydim is used for grass control in cotton, clover, pasture, ornamentals and over 30 crops (NRA 1997a).
A half-life for sethoxydim (under illumination) was 5.5 d at pH 8.7 and 25°C (Tomlin 1994).
No data were found for sethoxydim although Tomlin (1994) reported 48-hour LC50 to trout of 38 mg/L and to D. magna of 1.5 mg/L (unscreened). An environmental concern level (ECL) (Section 126.96.36.199 of the ANZECC & ARMCANZ 2000 guidelines) of 2 µg/L would be suggested on this basis.
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.