Bensulfuron 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

Bensulfuron (CAS 83055-99-6, as methyl ester) is a sulfonylurea herbicide, first introduced by DuPont. It is a selective systemic herbicide, adsorbed by foliage and roots and inhibits biosynthesis of amino acids essential for cell division and plant growth (Tomlin 1994). Its IUPAC name is a-(4,6-dimethoxypyrimidin-2-yl carbamoylsulfamoyl)-o-toluic acid, methyl ester, molecular formula is C₁₅H₁₆N₄O₇S and molecular weight is 396.4. It has increasing solubility in water with increasing pH; at pH 6 to 12 mg/L; at pH 7 to 120 mg/L and pH 8 to 1200 mg/L at 25°C (Tomlin 1994). It has a low log K_ow of 0.6 at pH 7.

Uses and environmental fate

Bensulfuron-methyl is used for weed control in irrigated rice (Tomlin 1994, NRA 1997a).

Bensulfuron-methyl has a half-life in rice field water of 4 to 6 days, but is most stable under slightly alkaline conditions (Tomlin 1994).

Aquatic toxicology

Freshwater algae: no data available.

Freshwater crustaceans: five species, 48 to 96-hour LC50, 802 to 12,200 mg/L (to 12.2 g/L). However, these were beyond the water solubility and could not be used to derive a guideline environmental concern level (ECL).

Freshwater fish: no data available.

Freshwater mesocosms: A single study, by Getsinger et al. (1994) studied the effect of bensulfuron on macrophytes over 12 months. Its design met the criteria except that it measured only one trophic level. Effects on plant biomass were noted at the lowest test concentrations of 25 µg/L but the species tested were mainly target species.

Guideline

There were insufficient data to derive even an ECL (see Section 8.3.4.5 of the ANZECC & ARMCANZ 2000 guidelines), although 800 µg/L is suggested from fish data. This may not be protective of non-target aquatic plants.

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.

Getsinger KD, Dick GO, Crouch RM & Nelson LS 1994. Mesocosm evaluation of bensulfuron methyl activity on Eurasian watermilfoil, Vallisneria, and American pondweed. Journal of Aquatic Plant Management 32, 1-6.

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.