Sethoxydim in freshwater and marine water

​Toxicant default guideline values for protecting aquatic ecosystems

October 2000

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 K_ow 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).

Aquatic toxicology

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 8.3.4.5 of the ANZECC & ARMCANZ 2000 guidelines) of 2 µg/L would be suggested on this basis.

References

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.