Terbacil

Air & Water Reactions

Water soluble.

Reactivity Profile

A uracil derivative.

Trade name

COMPOUND? 732; DuPontTM? 732; EXPERIMENTAL HERBICIDE 732; GEONTER?; SINBAR?; TURBSVIL?; ZOBAR?[C]

Environmental Fate

Soil. In microbially active soils, tebuthiuron is degraded via demethylation. The average half-life in soil 12–15 months in areas receiving 60 inches of rainfall a year (Humburg et al., 1989).Groundwater. According to the U.S. EPA (1986) terbacil has a high potential to leach to groundwater.Plant. The major degradation products of [2-14C]terbacil identified in alfalfa using a mass spectrometer were (% of applied amount): 3-tert-butyl-5-chloro-6-hydroxymethyluracil (11.9) and 6-chloro-2,3-dihydro-7-(hydroxymethyl)-3,3-dimethyl-5H-oxaPhotolytic. Acher et al. (1981) studied the dye-sensitized photolysis of terbacil in aerated aqueous solutions over a wide pH range. After a 2-hour exposure to sunlight, terbacil in aqueous solution (pH range 3.0–9.2) in the presence of methylene blue (3 ppm) or riboflavin (10 ppm), decomposed to 3-tert-5-butyl-5-acetyl-5-hydroxyhydantoin. Deacylation was observed under alkaline conditions (pH 8.0 or 9.2) affording 3-tert-5- hydroxyhydantoin. In neutral or acidic conditions (pH 6.8 or 3.0) containing riboflavin, a mono-N-dealkylated terbacil dimer and an unidentified water-soluble product formed. Product formation, the relative amounts of products formed and the rate of photolysis were found to be all dependent upon pH, sensitizer, temperature and time (Acher et al., 1981).Chemical/Physical. Stable in water (Worthing and Hance, 1991).

Metabolic pathway

When rats are administered terbacil orally, the primary biotransformation products of terbacil in the urine are derived from hydroxylation of the 6-methyl group and are identified as the aglycone, glucuronide, and sulfate. The other conjugated metabolite is the mercapturic acid conjugate of the 6-methyl substituent. Minor metabolites are identified as sulfoxides and sulfone at the 6-methyl substituent of terbacil.

Agricultural Uses

Herbicide: Terbacil is a selective herbicide that treats a broad spectrum of broadleaf weeds and grasses. It is formulated as a wettable powder and is applied by aircraft or ground equipment on terrestrial food and feed crops (e.g., apples, mint/peppermint/spearmint, sugarcane, and ornamentals), forestry [e.g., cottonwood (forest/shelterbelt)], terrestrialfood (e.g., asparagus, blackberry, boysenberry, dewberry, loganberry, peach, raspberry, youngberry and strawberry), and terrestrial feed (e.g., alfalfa, sainfoin (hay and fodder), and forage). Not approved for use in EU countries. Registered for use in the U.S.