E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/95
TRADE OR OTHER NAMES
Terbutryn is also called terbutryne. Trade names include Prebane, Igran,
Shortstop, Clarosan, GS 14260, Plantonit, Gesaprim Combi (with Atrazine 1:1),
Senate (with trietazine), and Igrater 50WP (with metobromuron 1:1)(3).
Terbutryn is a General Use Pesticide (GUP). The U.S. Environmental
Protection Agency has proposed the revocation of all tolerances for residues
of terbutryn in or on barley, sorghum, and wheat. They do not plan to
recommend action levels to replace the tolerances (Federal Register
59(138):37019). Many terbutryn product registrations have been cancelled. The
EPA has classified it as Toxicity Class III-slightly toxic. Products
containing terbutryn bear the Signal Word "Caution".
Terbutryn is a selective herbicide and a triazine compound. It is
absorbed by the roots and foliage and acts as an inhibitor of photosynthesis.
Terbutryn is a preemergent and postemergent control agent for most grasses and
many annual broadleaf weeds in winter wheat, winter barley, sorghum,
sugarcane, sunflowers, peas, and potatoes (6). It is also used as an aquatic
herbicide for control of submerged and free-floating weeds and algae in water
courses, reservoirs, and fish ponds (1). Terbutryn is available as a wettable
powder or a soluble concentrate (3, 6).
Terbutryn is slightly toxic. It affects the central nervous system in
animals leading to incoordination, convulsions, or labored breathing (5). At
extremely high dosages, the animals showed swelling and fluid in the lungs and
central nervous system (5).
The dose which kills half of the test animals, the LD50, is 2450-2500
mg/kg for rats and 3884 mg/kg for mice (2, 7). The LD50 for dermal exposure is
greater than 2,000 mg/kg for rabbits (3, 4).The concentration in air which
kills half of the test animals by inhalation, the LC50 (4 hours), is greater
than 8 mg of an 80% formulation per liter of air for rats (1). Terbutryn is
not a skin sensitizer (4).
A three generation reproduction study of rats showed that doses of 150
mg/kg/day of terbutryn caused decreased fertility indices in both male and
female rats. (4, 7).
Above doses of 500 mg/kg/day, pregnant rats produced offspring with
reduced weight and reduced bone formation in the front and rear paws. Pregnant
rabbits exposed to doses of 75 mg/kg/day also had offspring with reduced bone
In tests of terbutryn, no mutagenic effects were observed (4).
In a two-year feeding study of rats, doses of 150 mg/kg of terbutryn
caused cancerous tumor growth. However, there is no evidence of
carcinogenicity in mice. Terbutryn has been classified as a possible human
carcinogen by the U.S. EPA (4).
Long-term feeding at high doses of terbutryn can cause growth
retardation, kidney damage, liver damage and a decreased number of white blood
cells (5, 7).
Fate in Humans and Animals
When given orally to mammals, 73 to 85% of a terbutryn dose is eliminated
in metabolized form in the feces within 24 hours (1).
Effects on Birds
Terbutryn is only slightly toxic to birds. The LC50 (8-day dietary) is
greater than 20,000 mg/kg for bobwhite quail and pheasant and greater than
4640 mg/kg for mallard ducks (1, 4).
Effects on Aquatic Organisms
Terbutryn is moderately toxic to fish (3). However, except when applied
directly to 6 inches of water, residues have been calculated to be
insignificant even to the most sensitive aquatic animal species. The
concentration which is lethal to fish in water, the LC50 (96 hours), is 3
mg/kg for rainbow trout and 4 mg/kg for bluegill sunfish, carp, and perch (1).
Effects on Other Animals (Nontarget species)
Terbutryn is not toxic to bees (1). It is practically non-toxic to upland
game birds (3).
Breakdown of Chemical in Soil and Groundwater
Terbutryn is readily adsorbed in soils with high organic or clay content
(3). The half-life in soil is 14-28 days (1). Depending on the application
rate, the residual activity of terbutryn in soil is 3 to10 weeks. It is
slightly mobile to immobile in soils. Data indicate that it will not leach in
agricultural soils. However, its major breakdown product, hydroxy terbutryn,
is more mobile and persistent and has potential to leach to groundwater (3).
Breakdown of Chemical in Water
In water, terbutryn is not volatile. It will adsorb to sediment and
suspended particulate matter. Half-lives of 180-240 days have been reported
for degradation of terbutryn in pond and river sediment. It may be subject to
very slow hydrolysis and biodegradation in water (6).
Breakdown of Chemical in Vegetation
Terbutryn interferes with carbon dioxide assimilation and sugar formation
in plants. It is degraded to a breakdown product which is quite stable (1).
Further degradation in plants is slow (4).
PHYSICAL PROPERTIES AND GUIDELINES
Terbutryn is a white or colorless crystalline powder with no distinct
odor. It is stable to dilute aqueous alkaline and acidic solutions. It is
hydrolyzed in strong acid or basic solutions. It is decomposed by ultraviolet
irradiation. Terbutryn is stable for about three years at room temperature
when dry (4). It is not corrosive (6).
|Chemical Name: ||2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine
|Solubility in water: ||25 mg/l at 20 degrees C (6)
|Solubility in other solvents: ||Readily soluble in isopropanol, xylene, dioxane, chloroform, carbon tetrachloride, and acetone (6)
|Melting point: ||104-105 degrees C (6)
|Boiling point: ||154-160 degrees C (6)
|Partition Coefficient (octonol/water): ||3070 (1)
|Chemical class/Use: ||triazine/herbicide
|ADI (provisional): ||0.01 mg/kg (4)
|NOEL: ||0.1 mg/kg/day (female rats) (8)
|RfD: ||1 x 10 to the minus 3 mg/kg/day (8)
Ciba Geigy Agricultural Division
P.O. Box 18300
Greensboro, NC 27419-8300
Review by Basic Manufacturer:
Comments solicited: October, 1994
The Agrochemicals Handbook, Third Edition. 1994. Royal Society of
Chemistry Information Systems, Unwin Brothers Ltd., Surrey, England.
Bohmont, Bert. 1981. The New Pesticide Users Guide. B & K
Enterprises. Fort Collins, CO.
Meister, R.T. 1994. Farm Chemicals Handbook '94. Meister Publishing
Company. Willoughby, OH.
U.S. Environmental Protection Agency. 1986. Fact Sheet Number 104:
Terbutryn. U.S. EPA. Washington, DC.
Wagner, Sheldon. 1981. Clinical Toxicology of Agricultural Chemicals.
Oregon State University. Corvallis, OR.
U.S. Department of Health and Human Services. 1993. Hazardous
Substance Data Base. HHS. Washington, DC.
National Institute for Occupational Safety and Health (NIOSH). 1993.
Registry of Toxic Effects of Chemical Substances (RTECS). NIOSH. Cincinnati,
U.S. Department of Health and Human Services. 1994. U.S. EPA
Integrated Risk Information System (IRIS) database. HHS. Washington, DC.