| Chemical Abstract Number (CAS #) |
5902512
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| Synonyms | Terbacil |
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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 |
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| Molecular Formula | C9H13ClN2O2 |
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| 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.
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| Apparent Color | WHITE CRYSTALLINE POWDER ; COLORLESS CRYSTALS
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| Odor | ODORLESS
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| Melting Point | 175-177 DEG C
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| Molecular Weight | 216.65
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| Density | 1.34 @ 25 DEG C/25 DEG C
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| Sensitivity Data | MAY IRRITATE EYES, NOSE, THROAT, & SKIN.
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| 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.
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| 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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