SPECTRUM

Chemical Fact Sheet

Chemical Abstract Number (CAS #) 5902512
CASRN 5902-51-2
SynonymsTerbacil
2,4(1H,3H)-Pyrimidinedione, 5-chloro-3-(1,1-dimethylethyl)-6-methyl-
3-tert-Butyl-5-chloro-6-methyluracil
Geonter
Sinbar
Analytical Method EPA Method 633
Molecular FormulaC9H13ClN2O2

Link to the National Library of Medicine's Hazardous Substances
Database for more details on this compound.

Use USED FOR SELECTIVE CONTROL OF MANY ANNUAL & SOME PERENNIAL WEEDS IN APPLES, BLUEBERRIES, PEACHES, CITRUS, ALFALFA, MINT, & SUGARCANE. SELECTIVE PRE-EMERGENCE HERBICIDE FOR PARTIAL CONTROL OF SOME GRASSES. Control of most annual grasses and broad-leaved weeds, and some perennial weeds in established asparagus lucerne pecans, strawberries.
Apparent Color WHITE CRYSTALLINE POWDER ; COLORLESS CRYSTALS
Odor ODORLESS
Melting Point 175-177 DEG C
Molecular Weight 216.65
Density 1.34 @ 25 DEG C/25 DEG C
Sensitivity Data MAY IRRITATE EYES, NOSE, THROAT, & SKIN.
Environmental Impact Terbacil will be released to the environment during its use as a herbicide. In the ambient atmosphere, terbacil is expected to exist in both th vapor and particulate phases. In the vapor phase, terbacil will readily degrade by reaction with photochemically produced hydroxyl radicals (estimated half-life of 10.6 hrs). Particulate phase terbacil may be removed from air via dry deposition. In soil, biodegradation will be slow, but important. Half-lives of terbacil in aerobically incubated soils were 2-5 months. Photodegradation may occur on soil surfaces exposed to sunlight. Based on measured Koc values of 41 and 51, terbacil is expected to leach in soil and have little adsorption potential. If released to water, biodegradation may be important based on studies in soil. Photodegradation in near surface waters exposed to sunlight may be an important removal process; terbacil had a photolytic half-life of about 1 month in an aqueous solution at pH 8.1. Adsorption from the water column to sediments and suspended material and volatilization from water should not be important environmental pathways. Workers may be exposed via dermal contact and inhalation of dust.
Environmental Fate Terrestrial fate: In top soil, 50% still remains 5-7 months after applying 4.5 kg/hectare. TERRESTRIAL FATE: According to data in the U.S. Department of Agriculture's Pesticide Properties Database, a degradation half-life of 120 days was estimated for terbacil in soil . Half-lives of terbacil in aerobically incubated soils were 2-5 months . Terbacil may photodegrade on terrestrial surfaces; terbacil had a photolytic half-life of about 1 month in an aqueous solution at pH 8.1 . Experimental Koc values of about 41 and 51 suggest weak adsorption to soil. Terbacil has been characterized as having the potential to contaminate groundwater below sandy soils ; however, it has not been detected in groundwater monitoring studies. TERRESTRIAL FATE: Field studies indicate that terbacil persistence in soil varies with application rate, soil type, and mobility. A half-life of 1-2 months was observed for 14C terbacil (unspecified placement of the label) applied at 2 lb ai/A to a silt loam soil contained within a 4 by 15-inch cylinder driven into the soil. Residues persisted for greater than or equal to a year in a silt loam soil treated with 14C terbacil (unspecified placement of the label) at 4 lb/A; the radioactive residues were mobile to 8-12 inches (max depth sampled) with 14 percent of the applied radioactivity persisting in the upper 12 inches of the treated soil 1 year after treatment. Terbacil residues remained in the upper 12 inches of a clay soil at concns of 0.01-0.4 ppm 13 months after application. Only 20 percent terbacil applied at 2.24 and 4.48 kg/ha/yr for three consecutive years to a sandy soil persisted for 1 year following each of the last 2 applications. Average terbacil levels ranged from 0.41 to 0.73 lb/A in the upper 18 inches of fine sand soils which had received multiple applications of terbacil at 4-20 lb/A over a 2-5 yr period . AQUATIC FATE: Based on estimated BCF values of 2 and 15 and an estimated Henry's Law constant of 1.2X10-10 atm-cu m/mole at 25 deg C, bioconcentration in fish and volatilization from water should not be important fate processes of terbacil in water systems. Experimental Koc values of about 41 and 51 suggest weak adsorption to sediments. Rapid hydrolysis should not occur in aquatic systems; less than 2 percent of a 5 ppm terbacil aqueous solution degraded in the dark after 6 weeks at 15 deg C and pH 5, 7, and 9 . Several studies indicate that terbacil will photodegrade in near-surface waters exposed to sunlight; terbacil had a photolytic half-life of about 1 month in an aqueous solution at pH 8.1 . No data were located on the biodegradation of terbacil in water; however, aerobic biodegradation half-lives of 2-5 months in soil indicate that microbial degradation may occur in water under aerobic conditions. ATMOSPHERIC FATE: Based on measured vapor pressures of 4.7X10-7 and 5.4X10-6 mm Hg at 29.5 and 54 deg C, respectively , the vapor pressure at 25 deg C can be estimated to be about 2.9X10-7 mm Hg for terbacil from an Antoine relationship. According to a suggested classification scheme , this vapor pressure value indicates that terbacil should exist in the vapor and particulate phases in the ambient atmosphere. Vapor phase terbacil is readily degraded in the ambient atmosphere by reaction with photochemically formed hydroxyl radicals; the half-life for this reaction in air can be estimated to be about 10.6 hrs(1,SRC). Particulate phase terbacil may be removed from air via dry deposition. EFFL: LEVELS & TOTAL DISCHARGE OF TERBACIL AFTER APPLICATION @ RATE OF 4.5 KG/HA TO FIELD @ FORT PIERCE, FLA, WERE MEASURED IN DRAINAGE WATER FOR 13 DAYS. OVERFLOW WATER VOL HIGHEST IN SURFACE TILLAGE (ST) PLOTS. ONLY 1-2% OF AMT APPLIED WAS DETECTED IN DRAINAGE WATERS.

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