---

The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

---

E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Terbacil

Trade and Other Names: Trade names include Compound 732, DuPont Herbicide 732, Geonter, and Sinbar. This compound may also be found in mixed formulations with other herbicides.

Regulatory Status: Terbacil is registered by the U.S. Environmental Protection Agency (EPA) as a General Use Pesticide (GUP). The Signal Word CAUTION is required on containers of formulated terbacil. Terbacil is in EPA class IV - practically nontoxic.

Chemical Class: substituted uracil

Introduction: Terbacil is a selective herbicide used for control of both annual grasses, broad-leaved weeds, and some perennial weeds in sugarcane, apples, alfalfa, peaches, pecans, and mints. It is sprayed on soil surfaces preferably just before, or during, the period of active weed growth. Terbacil works in plants by inhibiting photosynthesis. It is a member of the substituted uracil chemical family. Terbacil is available in wettable powder formulations. Technical terbacil is 95% pure active material.

Formulation: Terbacil is available in wettable powder formulations. Technical terbacil is 95% pure active material.

Toxicological Effects:

• Acute toxicity: Terbacil has low acute toxicity [128]. Clinical signs of poisoning in rats include weight loss, pallor, prostration, and rapid breathing. In dogs, a single dose of 5 mg/kg caused repeated vomiting [128]. Terbacil may irritate the skin, eyes, and mucous membranes of the nose and throat. It is not a skin sensitizer [129]. The oral LD50 of terbacil is 5000 to 7500 mg/kg in rats [1,22]. The dermal LD50 is greater than 5000 mg/kg (the maximum feasible dose) in rabbits [1]. These rabbits did not show clinical signs of toxicity, nor any obvious gross changes caused by disease. No skin irritation and only mild eye irritation was seen in rabbits at this dose [23]. Similarly, there was no skin irritation or sensitization in terbacil-treated guinea pigs [23]. Dogs given 5000 mg/kg of terbacil exhibited vomiting and a lack of eye pupil responsiveness [128].
• Chronic toxicity: No evidence of toxicity was seen in 2-year studies of rats fed doses as high as 12.5 mg/kg/day, or in dogs fed doses as high as 6.25 mg/kg/day of terbacil. At 125 to 500 mg/kg/day, there was a lower rate of weight gain, liver enlargement, and other liver changes in rats. The highest dose produced a slight increase in liver weight in dogs [23].
• Reproductive effects: There were no adverse effects on lactation, fertility, birth rate, pup survival, or any other aspect of reproduction in rats fed 2.5 and 12.5 mg/kg/day of terbacil for three generations [23]. However, the average number of live rat fetuses per litter and the average final maternal body weight were significantly lowered in another study in the 103 and 391 mg/kg/day dosage groups [130]. Based on these data, adverse effects on reproduction in humans are not likely at expected exposure levels.
• Teratogenic effects: When doses of 30, 200, or 600 mg/kg/day were administered by gavage to pregnant rabbits on days 7 to 19 of gestation, adverse effects on the fetuses appeared only at the highest dose tested. This dose also produced maternal toxicity and increased maternal mortality. No adverse effects on the mothers or the pups were observed at lower doses. In another study, pregnant rats were fed doses of 23, 103, or 391 mg/kg/day on days 6 to 15 of gestation. Abnormalities occurred in the renal pelvis, and ureter dilation was found in pups from all the treatment groups [129]. Evidence of teratogenicity is inconclusive.
• Mutagenic effects: Terbacil was not mutagenic in several screening tests [129].
• Carcinogenic effects: No evidence of carcinogenicity was found in rats fed 2.5, 12.5, 125, or 500 mg/kg/day of terbacil for 2 years, nor in dogs fed as much as 12.5 mg/kg/day for 2 years [23]. When mice were fed dietary doses of 2.5, 62.5, or 250 mg/kg for 2 years, no increased incidence of cancer was found [130]. Terbacil does not appear to be carcinogenic.
• Organ toxicity: Liver changes have been seen in laboratory rats exposed to high doses of terbacil [23].

• Fate in humans and animals: In general, the uracil herbicides, the chemical class in which terbacil is included, are rapidly excreted in urine by mammals. This may account for their reportedly low toxicity [131]. When given in the feed of lactating cows at 5 and 30 ppm, terbacil was excreted in the milk at levels up to 0.03 and 0.08 ppm, respectively. No herbicide was detected in the cows' urine and feces [131].

Ecological Effects:

• Effects on birds: Terbacil is slightly toxic to birds [131]. The 8-day dietary LC50 for terbacil is more than 56,000 ppm in Peking ducklings, and greater than 31,450 ppm in pheasant chicks [58]. The LD50 for terbacil in quail is greater than 2250 mg/kg [129].
• Effects on aquatic organisms: Terbacil is slightly to practically nontoxic to aquatic organisms. The 48-hour LC50 of terbacil is 86 mg/L in sunfish [1]. The LC50 for terbacil is 102.9 mg/L in bluegill sunfish and 46.2 mg/L in rainbow trout. Terbacil is slightly toxic to freshwater invertebrates, with an LC50 of 65 mg/L in Daphnia, a small freshwater crustacean. The LC50 for terbacil is greater than 4.9 mg/L in marine oysters and 49 mg/L in shrimp [129]. Terbacil does not bioaccumulate in bluegill sunfish [130]. Estuarine and marine organisms may be exposed to terbacil due to its use as a sugarcane herbicide [128]. A study on grass shrimp with an 84.7% formulated terbacil product was sufficient to characterize the herbicide as slightly toxic to marine invertebrates. The 48-hour LC50 of terbacil is 1000 mg/L in fiddler crabs [1].
• Effects on other organisms: Terbacil is nontoxic to bees [1].

Environmental Fate:

• Breakdown in soil and groundwater: Terbacil is highly persistent in soils [11]. Soil half-lives of 50 to 180 days have been reported [1,11]. Data from field dissipation studies showed that terbacil persistence in soil varied with application rate, rainfall, soil type, and mobility, as well as available oxygen [129]. In most soil types, terbacil has a relatively low tendency to be adsorbed. It also is highly soluble in water. Thus, terbacil is likely to be highly mobile in soil and potentially pollute groundwater [11,131]. Because of this, it should not be used on sandy or gravelly soils that have less than 1% organic matter, particularly if the water table is near the soil surface [128] and when deep tillage is used [132]. Leaching may be slower in soils that are finer textured and/or have higher organic matter content [128]. Terbacil was not detected in a national groundwater survey conducted by EPA [8]. In moist soils, terbacil is subject to microbial degradation. However, data suggest that recommended rates of terbacil use may result in its persistence for more than one growing season [8].
• Breakdown in water: Contamination of surface waters near terbacil-treated areas, and subsequent exposure of humans and non-target organisms, is possible due to terbacil's mobility in soil and its high water solubility [132]. Terbacil is stable in water and does not readily undergo hydrolysis or photodegradation [129].
• Breakdown in vegetation: At normal application rates, terbacil has residual phytotoxicity to affected species in treated soils for 1 to 2 years [128]. Terbacil residues were phytotoxic to oats planted 3 years after a previous application of the herbicide. For example, in alfalfa, 12% of terbacil plus its metabolites were still found 6 to 8 months after application [8]. Terbacil is most readily absorbed through the root system of plants to which it is applied. Less is absorbed through the leaves and stems of plants. Studies of sugarcane plants indicate that terbacil is moved, or "translocated," upward into the leaves after absorption by the roots [58].

Physical Properties:

• Appearance: Terbacil is a white, crystalline, odorless solid which is noncorrosive and nonflammable [1].
• Chemical Name: 3-tert-butyl-5-chloro-6-methyluracil [1]
• CAS Number: 5902-51-2
• Molecular Weight: 216.70
• Water Solubility: 710 mg/L @ 25 C [1]
• Solubility in Other Solvents: s.s. in mineral oils and aliphatic hydrocarbons; v.s. in methyl isobutyl ketone, butyl acetate, xylene, cyclohexanone, dimethylformamide, and strong aqueous alkalis [1]
• Melting Point: 175-177 C [1]
• Vapor Pressure: 0.0625 mPa @ 30 C [1]
• Partition Coefficient: 1.8921 [58]
• Adsorption Coefficient: 55 [11]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: 0.013 mg/kg/day [13]
• PEL: Not Available
• HA: 0.09 mg/L (lifetime) [130]
• TLV: Not Available

Basic Manufacturer:

DuPont Agricultural Products
Walker's Mill, Barley Mill Plaza
P.O. Box 8003
Wilmington, DE 19880-0038

• Phone: 800-441-7515
• Emergency: 800-441-3637
  

References:

References for the information in this PIP can be found in Reference List Number 10

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.