E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
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University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
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Pesticide
Information
Profile
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Tebuthiuron
Publication Date: 9/93
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TRADE OR OTHER NAMES
Some trade names include Spike, Brush Bullet, EL-103, Graslan, Perflan,
Herbec, Herbic and Reclaim.
REGULATORY STATUS
Tebuthiuron is registered by the U. S. Environmental Protection Agency
(EPA) as a general use herbicide. Products containing tebuthiuron must bear
the signal word "Caution" (10). Check with specific state regulations for
local restrictions which may apply.
INTRODUCTION
Tebuthiuron is a broad spectrum herbicide used to control weeds in
noncropland areas, rangelands, rights-of-way and industrial sites (10). It is
effective on woody and herbaceous plants in grasslands and sugar cane (2).
Weeds that are controlled by tebuthiuron include alfalfa, bluegrasses,
chickweed, clover, dock, goldenrod, mullein, etc. Woody plants take a period
of two to three years to be completely controlled (5).
Tebuthiuron is sprayed or spread dry on the soil surface, as granules or
pellets, preferably just before or during the time of active weed growth.
Rainfall enhances the initial control provided by this herbicide (8).
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
Skin, eye or clothing contact with the herbicide should be avoided (8).
It is classified as a moderately poisonous herbicide. Symptoms of tebuthiuron
poisoning in rodents include lack of energy, loss of appetite, muscular
incoordination and death. Vomiting occurred in cats and dogs (2, 11).
Tebuthiuron has high acute oral toxicity in experimental animals. The
amount of the herbicide that causes death to one-half (50%) of test animals to
which it is given is referred to as its lethal dose fifty, or LD50. The oral
LD50 for tebuthiuron is 644 mg/kg in rats, 57.9 mg/kg in mice, and 286 mg/kg
in rabbits. The dermal LD50 for tebuthiuron in rabbits is greater than 5,000
mg/kg. Neither skin irritation nor general overall intoxication were produced
in rabbits that had 200 mg/kg of the material applied to their skin (2, 3, 8).
67 mg of the herbicide in the eye of rabbits produced short-term
conjunctivitis, inflammation of the lining of the eye, but no irritation to
other eye parts, the cornea and iris (8). The inhalation by animals of 3.7
g/m3 technical tebuthiuron for 4 hours did not cause death or toxicity.
Tebuthiuron did not induce allergic reactions when tested on the skin of
guinea pigs.
CHRONIC TOXICITY
Decreases in body weight gain and red blood cell counts, along with
minor effects on the pancreas were seen in rats fed 125 mg/k/g/day for three
months (2). Exposure of rats to dietary doses of tebuthiuron as high as 80
mg/kg for 2 years was well tolerated with no indication of cumulative toxicity
or serious effects. Similarly, no toxic effects were observed in mice exposed
to doses as high as 200 mg/kg for most of their lifetime, or in dogs given
doses of 25 mg/kg for one year (8).
The EPA has established a Lifetime Health Advisory (LHA) level of 500
micrograms per liter (ug/l) for tebuthiuron in drinking water. This means
that EPA believes that water containing tebuthiuron at or below this level is
acceptable for drinking every day over the course of one's lifetime, and does
not pose any health concerns. However, consumption of tebuthiuron at high
levels well above the LHA level over a long period of time has been shown to
cause excessive weight loss and damage to the pancreas in animals studies
(14).
Reproductive Effects
The reproductive capacity of rats fed dietary concentrations of
tebuthiuron as high as 56 mg/kg was unimpaired through three successive
generations, and no abnormalities were detected in either parents or
offspring. Tebuthiuron administered to pregnant rabbits at doses as high as
25 mg/kg, and to rats at doses as high as 180 mg/kg produced no adverse
effects on either the mothers or offspring (8).
Teratogenic Effects
No teratogenic effects were observed when rats were fed tebuthiuron at
800 mg/kg body weight (3). A rat teratology study of tebuthiuron was negative
at 1,800 ppm (90 mg/kg), the highest dose tested. A rabbit teratology study
was negative at 25 mg/kg, the highest dose tested (1).
Mutagenic Effects
A mutation test on bacteria, the Ames test, was negative (1).
Carcinogenic Effects
No tumor-producing effects were observed in a two-year rat feeding
study, up to and including 1,600 ppm (80 mg/kg), the highest dose tested. A
two-year oncogenic study on mice was negative at 1,600 ppm (240 mg/kg), the
highest dose tested (1). Data from laboratory studies are inadequate for EPA
to determine if tebuthiuron can increase the risk of cancer in humans (14).
Organ Toxicity
Long-term consumption of tebuthiuron at high levels well above the
Lifetime Health Advisory level of 500 ug/l for drinking water has been shown
to cause excessive weight loss and damage to the pancreas in animals studies
(14).
Fate in Humans and Animals
In rats, rabbits, dogs, mallards and fish, tebuthiuron is readily
absorbed into the bloodstream from the gastrointestinal tract, rapidly
metabolized, and then excreted in the urine (8). Tests indicate that the
herbicide is broken down and excreted within 72 hours, primarily as a variety
of urinary metabolites (2).
ECOLOGICAL EFFECTS
Effects on Birds
Tebuthiuron is not hazardous to birds. The oral LD50 for mallard ducks
is greater than 2,000 mg/kg (8). A 30-day feeding of 1,000 mg/kg tebuthiuron
to hens had no effect (3).
Effects on Aquatic Organisms
Tebuthiuron is not hazardous to aquatic organisms (8). The lethal
concentration fifty, or LC50, is that concentration of a chemical in air or
water that kills half of the fish exposed to it for a set time period. The
LC50 for rainbow trout is 144 mg/l, and 112 mg/l for bluegill (3, 10). The
96-hour LC50 is greater than 160 mg/l for goldfish and fathead minnow (9).
The 48-hour LC50 for Daphnia, a small, freshwater crustacean, is 297 mg/l (8).
The LC50 for fiddler crab is greater than 320 ppm, the LD50 for pink shrimp is
more than 48 ppm (8).
Effects on Other Animals (Nontarget species)
If tebuthiuron is used correctly, it should not pose a threat to bees
(3).
ENVIRONMENTAL FATE
Breakdown of Chemical in Soil and Groundwater
Tebuthiuron has all the characteristics of a material with a high
potential for groundwater contamination. It is highly soluble in water (2,500
ug/ml), adsorbs only weakly to soil particles (Koc = 80 mg/l), and is highly
persistent in soils (soil half-life = 360 days) (11). Tebuthiuron is easily
moved with moisture in the soil. The EPA considers tebuthiuron to be one of a
group of pesticide compounds that have the greatest potential for leaching
into, and contaminating, groundwater. It was not found in groundwater in a
U.S. groundwater survey conducted by the EPA (6).
In field studies, tebuthiuron has seldom been detected below the top 24
inches of soil. Little or no lateral movement has been observed after
tebuthiuron has adsorbed to clay or organic matter in the soil (8).
In areas receiving 40 to 60 inches of annual rainfall, the time that it
takes for half of the tebuthiuron to break down in soil is 12 to 15 months.
This time period is known as its soil half-life. It takes longer for the
herbicide to break down in areas that have less rainfall. The half-life for
tebuthiuron is also greater in muck and other high organic soils, regardless
of rainfall (8).
Some tebuthiuron is broken down in the soil by 'microbes,' through the
process of microbial degradation. However, tests indicate that this may not
be the primary way by which tebuthiuron is degraded. Photodecomposition, or
breakdown by sunlight, is negligible, as is volatilization, by which it
changes from a solid to a gaseous form (8).
Breakdown of Chemical in Water
No degradation was observed in a 33-day study of photolysis of
tebuthiuron in water (13).
Breakdown of Chemical in Vegetation
Tebuthiuron is readily absorbed through roots. It is less likely to be
absorbed by the leaves. Since the herbicide can be harmful to nontarget
plants and trees, it should not be applied, nor any of its application
equipment drained or flushed, on or near desirable trees or plants, nor on
areas to which their roots extend. Tebuthiuron is readily translocated by the
roots to other plant parts. It is effective by inhibiting photosynthesis, the
process by which plants receive light from the sun and convert it into energy
(8).
PHYSICAL PROPERTIES AND GUIDELINES
Tebuthiuron is an off-white to buff colored crystalline solid with a
pungent odor (13). Tebuthiuron is compatible with other herbicides. It is
stable under normal storage conditions, but may pose a fire hazard if exposed
to heat or flame. It poses a fire and explosion hazard in the presence of
strong oxidizers. Thermal decomposition of tebuthiuron may release toxic
oxides of carbon, nitrogen and sulfur (12). It is stable in aqueous media at
pH's between 5 and 9. At high temperatures, it is hydrolyzed by strong
alkalis and strong acids. It is noncorrosive to metals and polyethylene (8).
Exposure Guidelines:
No occupational exposure limits have been established for tebuthiuron by
OSHA, NIOSH, or ACGIH (12).
| NOEL: | 50 mg/kg in 90-day rat feeding study; 40 mg/kg in 2-year rat feeding study (systemic NOEL) (1) |
| TMRC (theoretical maximum residue contribution): | 0.2232 mg/day based on a 1.5 kg daily diet (1) |
| MPI (Maximum Permissible Intake): | 12 mg/day for 60-kg human (1) |
| ADI: | 0.20 mg/kg/day based on a two-year rat feeding study (NOEL) of 20 mg/kg/day) and using 100-fold safety factor (1) |
Physical Properties:
| CAS: | 34014-18-1 |
| H20 solubility: | 2,300 ppm (7); 860 ppm (7); 0.25 g/100 ml at 25 degrees C (8) |
| Solubility in other solvents (in g/100 ml): | 25.0 in chloroform; 17.0 in methanol; 7.0 in acetone; 0.61 in hexane; 0.37 in benzene; acetonitrile 6.0 (8) |
| Melting point: | 161.5 x 164 degrees C (with decomposition) (8) |
| Vapor pressure: | 2 x 106 mmHg at 25 degrees C (8) |
| Hydrolysis half-life: | greater than 9 weeks (7) |
| Soil/Field dissipation half-life: | 360 days (11); highly persistent (7) |
| Koc: | 80 g/ml (11) |
| Kd: | 0.2-10.0; Class 5; very mobile (7) |
| Chemical Class/Use: | Urea carbamate herbicide |
BASIC MANUFACTURER
DowElanco
9002 Purdue Rd.
Indianapolis, IN 46268-1189
Review by Basic Manufacturer:
Comments solicited: November, 1992
Comments received: December, 1992
REFERENCES
Federal Register. 48 FR 24396. June 1, 1983. U.S. Government
Printing Office. Washington, DC.
Gosselin, R. E., et al. 1984. Clinical toxicology of commercial
products. Fifth edition. Baltimore, MD: Williams and Wilkins.
Hartley, D. and H. Kidd (eds.). 1983. The Agrochemicals Handbook.
Nottingham, England: Royal Society of Chemistry.
McEwen, F. L. and G. R. Stephenson. 1979. The use and significance
of pesticides in the environment. NY: John Wiley and Sons, Inc.
Thomson, W .T. 1983. 1983. Herbicides. Agricultural Chemicals,
Book II. Fresno, CA: Thomson Publications.
U.S. Environmental Protection Agency. 1987 (Feb.). Environmental
News. Office of Public Affairs (A-107). Washington, DC.
_____. 1984. Memorandum from Stuart Z. Cohen. List of potential
groundwater contaminants. Office of Pesticides and Toxic Substances.
Washington, DC. Photocopy.
WSSA Herbicide Handbook Committee. Herbicide Handbook of the Weed
Science Society of America, 6th Ed. WSSA, Champaign, IL. 1989.
Worthing, C. R. (ed.). 1983. The pesticide manual: A world
compendium. Croydon, England: The British Crop Protection Council.
Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister
Publishing Company, Willoughby, OH.
U.S. Department of Agriculture, Soil Conservation Service. 1990
(Nov.). SCS/ARS/CES Pesticide Properties Database: Version 2.0 (Summary).
USDA - Soil Conservation Service, Syracuse, NY.
Occupational Health Services, Inc. 1991 (Feb. 21). MSDS for
Tebuthiuron. OHS Inc., Secaucus, NJ.
DowElanco. Letter of Nov. 13, 1991 from Merlyn Jones, Product
Registration Manager, DowElanco, Indianapolis, IN.
U.S. Environmental Protection Agency. 1989 (Jan.). Health Advisory
Summary: Tebuthiuron. US EPA, Washington, DC.
Disclaimer: Please read
the pesticide label prior to use. The information contained at this web
site is not a substitute for a pesticide label. Trade names used herein
are for convenience only; no endorsement of products is intended, nor is
criticism of unnamed products implied. Most of this information is historical
in nature and may no longer be applicable.
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