Unltad 8ttt«i
Bl fiatMSion
of Pvilcfctai and To«te Soteune*
oi pM«d* Ptorwm n*-7«eci
. DC
o-EPA Pesticide
Fact Sheet
Name of Chemical:
Reason for Issuance:
Date Issued:
Fact Sheet Number:
TERBUTRYN
REGISTRATION STANDARD
SEPTEMBER 1986
104
Description of Chemical
Generic Name:
Common Name:
Trade Names:
EPA Shaughnessy Code:
2-(tert-butylamino)-4-(ethylamino)-
6-(methylthio)-s-triazine
Terbutryn
Iqran, Prebane (Great Britain only),
Terbutrex, Terbutryne, Clarosan,
GS 14260, and Short-stop (discontinued)
080813
Chemical Abstracts
Society (CAS) Number: 886-50-0
Year of Initial
Reqi strat ion:
Pesticide Type:
Chemical Family:
Producers:
1969
Herbicide
s. Triazine
Ciba-Geigy Corp. (U.S.);
Verolit Chemical Manufacturing Co.
Ltd.; and Makhteshim Agara (Israel)
Use Patterns and Formulations
Application Sites: Winter wheat, winter barley, grain
sorghum, fallow areas, and non-crop areas, including
railroad rights-of-way, to control broadleaf weeds and
grasses
Types and Methods of Application: Foliar apolicat-keji or
soil incorporation; broadcast application by qround
or aerial eguipment or band application •*"
-------
2
polication Rates: Ground application with water as carrier
at a minimum of 20 gal/A; 1.2 to 1.8 lb a.i./A for post
emergence in barley; 0.8 lb a.i./A for broadleaf control
to 2.9 lb a.i./A for broadleaf and grass control in
sorghum; and 4.0 lb a.i./A for short—term industrial weed
control. May be tank mixed.
Formulations: 95—96 % active inaredient (a.i.) manufacturing—
use product; 80% a.i. wettable powder and 80% a.i. dry
flowable end-use products
Usual Carrier: Water (minimum 187 L/ha or 20 gal/A)
3. Science Findings
Summary of Science Statement
Terbutryn has been found to be oncogenic in rats and has
been classified as a Group C oncogen (possible human
carcinogen). Acute toxicity studies indicate that Terbutryn
is relatively nontoxic (toxicity categories* III and IV).
Dietary risk is insignificant since residues are 0.01 ppm
or less and less than 1% of the U.S. wheat crop and less
than 2 of the U.S. sorghum crop are treated. Worker
exposure hazard from dermal exposure is the effect of
greatest concern, hut risks can be reduced substantially
through the use of protective clothing and equipment and
by packaqing in water soluble bags.
Terhutryn’s potential for contamination of groundwater
appears to be low; however, its major metabo].ite appears
to be more persistent and mobile. Additional data are
being required to evaluate the environmental fate of
metabolites.
The Aqency has determined that the registered uses of
this chemical will not generally cause unreasonable
adverse efects to humans or the environment if used in
accordance with the approved use directions and revised
precautionary statements prescribed by the Registration
Standard.
* Toxicity Categories are based on the acute toxicity of the
chemical (LD 50 or LC 50 values) and are used to determine
the appropriate siqnal word and precautionary language for
product labeling. Toxicity Category III requires the
signal word CAUTION and precautions against swa11o ft q,
inhaling, or contact with the skin and eyes, along ith
appropriate first aid instructions. Toxicity Category tV
also requires the signal word CAUTION, but no precautionary
statements are required. See 40 CFR 162.10.
-------
3
Chemical Characteristics
Physical State: crystalline solid or powder
Color: white
Odor: odorless to slightly ar natic
Melting point: 101—105° C
Dens ity: 1.12—1.302 q/cc
Soluhility (at 20—25° C)
58 ppm in water
25 g/l00 ml in isopropanol
10 g/l00 ml in xylene
30 g/100 ml in ethylglycolrnonOethYlether
30% in diethylalcohol
Vapor Pressure 9.6 x l0 mm Hg at 20° C
Dissociation constant pka 4.3 + or — 0.1 at 21° C
Stability Stable to dilute aqueous alkaline
and acidic solutions. Decomposed
by ultraviolet irradiation.
Hydrolyzed in strongly acidic or
basic medium. Half life (at 25° C),
>5 years in 0.1 N NaOH; 22+ or —3
days in 0.1 N HC1; and >6 years
in water (ph=7). Stable at room
temperature for at least 3 years
when dry.
Toxicological Characteristics
With the exception of one study, the acute toxicology data
baseis complete. Terbutryn acute studies place it in the
toxicity categories III and IV, or relatively non—toxic by
oral, dermal, and inhalation routes, and it is not irritating
to the eyes or skin.
Acute oral toxicity 1.9 g/kg (males)
(rat) 2.1 g/kg (females)
Toxicity Category III
Acute inhalation Not available for technical, but
toxicity tests on 80% a.i. formulati irj
resulted in Toxicity Catego 1 III
Acute dermal toxicity >20.0 g/kg
(rabbits) Toxicity Category IV
-------
4
Primary derma]. No irritation at 72°
irritation (rabbits) Toxicity Category IV
Dermal sensitization Not a sensitizer
(guinea pigs)
Primary eye irritation Toxicity Category III
Chronic effects: The results of teratology and reproduction
tests in animals indicate that the use of terbutryn is not
expected to produce significant effects to humans in these
areas. No mutaqenic effects were observed in the available
studies; however additional mutagenic testing is required.
Terhutryn has been classified a group C oncogen, possible
human carcinogen, based on available oncogenicity studies.
Chronic feeding! Mouse: no evidence of oncoqenicity
oncogenicity Rat: two year feeding——at 3000 ppm,
positive for oncogenicity (Group C,
or possible human carcinogen).
Beagle dog: (6 month study)
NOEL: l0i g/kg/day
01*: l0 *
Teratoaenicity Not teratoqenic to rabbits or rats.
Reproduction Three generation reproduction study
(rats) showed decreased body weights and
food consumption.
Mutaqenicity Data limited but negative;
additional data required.
Major Routes of Exposure
The primary potential for exposure is through the skin
during mixing and loading or for flaggers who could be
subject to direct dermal exposure. Therefore, protective
clothing is required for mixers and loaders, and flaggers
must he in enclosed vehicles.
4. Physiological and Biochemical Behavioral Characteristics
Foliar and Root Absorption: Absorbed through both foliage
and roots with rapid foliar penetration.
* 01*: The mathematical factor for the potency of a hazard, such
as oncogenicitv——the 01* is a parameter of the linearized
multistage extrapolation model. It is used as a mu1f t lier
of the estimated exposure (in units of mg/kg/day) topbtain
the estimated 95% upper bound on risk. A change in the 01*
will result in a proportional change in risk.
-------
5
TranslocatiOn: Translocated through xylem from roots
and foliage, accumulating in the apical meristems.
Mechanism of Action: Terbutryn inhibits the photolysis
of water in the photosynthetic process.
Persistence: Terbutryn degrades by oxidation into hydroxy—
metabolites in plants and soils. Degradation *•s slow
in plants and ranges from 3 to 10 weeks in soil.
5. Environmental Characteriatics
The available data indicate that terbutryn will not leach
in agricultural soils. However, its major metabolite,
hydroxy—terbutryn, appears to be more mobile and persistent
and has the potential to leach to groundwater. The data
deficiencies have been identified and additional data
required to fill the data gaps.
Absorption and Leaching in Basic Soil Types: Terbutryn
is readily adsorbed in soils with a high and organic
matter or clay content. Adsorption is not irreversible
and depends on factors such as pH, temperature, and
moisture.
Microbial Breakdown: Microorganisms may play an important
role in the degradtion of terbutryn.
Loss fran PhotodeccxnpositiOn and Volitilization: Photo—
decomposition and volitilization are not significant
factors in dissipation of terbutryn the soil.
6. Ecological Characteristics
Available acute toxicity data indicate that terbutryn is
moderately toxic to warmwater fish and highly toxic to
coldwater fish. However, except for the direct applica-
tion to 6 inches of water, residues have been calculated
to be insignificant, even to the most sensitive aquatic
ani al species. Since the current uses of terbutryn do
not include direct applicatipn to water, its use is
unlikely to result in significant acute adverse effects
to aquatic animal species.
In terms of acute toxicity, data indicate that terbutryn
is practically non—toxic to waterfowl, upland gamebirds,
and honeybees.
The data base regarding toxicity data and non—target
organism effects is incomplete for both aquatic aii
terrestrial organisms.
The following toxicity figures apply to technical terbutryn.
-------
6
Hazards to Birds:
Avian acute oral toxicity: Greater than 4,640 mg/kq
in the mallard duck; greater than 2,000 mg/kg in
the mallard duck and pheasant.
Avian dietary toxicity: Greater than 4,640 ppm in the
mallard duck; greater than 20,000 ppm, and greater
than 2,000 ppm (two different studies) in U bwhite
quail.
Hazards to Aquatic Organisms:
Fish acute toxicity: 2.4 ppm in rainbow trout; 4.7 ppm
in crucian carp; and 4.8 and 2.7 ppm in bluegill
sunfish.
Aquatic invertebrate toxicity: 2.66 ppm for Daphrtia magna .
Hazard to Honeybees:
Relatively nontoxic to honeybees; 2.9% mortality at
236 micrograms per bee.
7. Endangered Species Hazard Assessment
There are sufficient toxicity and exposure data to indicate
that the currently registered uses of terbutryn are unlikely
to pose a hazard to endangered aquatic or avian species.
Since it is a relative non—selective herbicide, EPA has art
opinion from the Office of Endangered Species (OES) which
indicates that certain endangered plant species are likely
to be present in registered crop areas. Therefore, interim
protective labeling for endangered species in treated crop
areas is required. Potential impacts on endangered plant
species in non-crop areas have not yet been evaluated.
Protective labeling for non—crop areas may be required
after the Agency has reviewed additional required data and
consultations with OES are complete.
8. Worker Exposure and Risk Analysis
A worker exposure evaluation and a dermal exposure risk
assessment have been conducted by EPA. The risk assessment
estimates were arrived at by using an estimate of the number
of man hours associated with various application techniques,
estimates of the hourly exposure for workers, and the calcu-
lated oncoqenic potency (01*) of terbutryn. Additional studies
have been required to further evaluate worker exposure.
In order to reduce risks to workers EPA is requisiflp protective
clothing and equipment, soluble bag packaging, and restricted
use classification.
-------
7
10. Tolerance Reassessment
Tolerances for terbutryn have been established for the raw
agricultural commodities listed below:
Crop Tolerance Food Factor mg/day (1.5 kg )
barley 0.1 ppm 0.03 0.000045
sorghum 0.1 ppm 0.03 0.000045
wheat 0.1 ppm 10.36 0.015540
Dietary Assessment
The Provisional Acceptable Daily Intake (PADI) was set
using a six month dog feeding study with a no observed
effect level (NOEL) of 10 mg/kg/day, based on mucosal
thickening of various segments of the small intestine and
submucosal ].ymphoid hyperplasia in the pyloric region of
the stomach seen at 25 and 50 mg/kg/day.
Applying a safety factor of 1,000, since a NOEL was not
determined in the chronic rat study, a Provisional Acceptable
Daily Intake (PADI) of 0.0100 mg/kg/day can be calculated.
This is equivalent to a Maximum Permissible Intake (MPI)
of 0.6 mg/day for a 60 kg individual. The Theoretical
Maximum Residue Contribution (TMRC) for terbutryn in the
daily diet, based on the total tolerances and daily food
intake of 1.5 kg, is 0.000260 mg/kg/day. Under these
conditions 2.6% of the PADI has been utilized. Daily
dietary exposure to terbutryn is thus substantially less
than the calculated acceptable daily intake for humans.
Currently tolerances for residues are expressed as terbutryn
per Se, and the nature (identity) of metaholites is not
adequately understood. Therefore, additional metabolism
studies have been required of the registrant.
11. Summary of EPA Positions and Rationales
The Agency has determined that initiation of a Special
Review is not warranted because the oncogenic risk can
be reduced substantially by the incorporation of various
protective measures (described below) on all product
labels. Although terbutryn is a Group C oncogen (possible
human carcinogen), dietary risk is insignificant, and
risks to workers can be sufficiently reduced through
protective measures.
In order to protect workers, terbutryn will be c1as ek fied
as a restricted use pesticide, and workers will be ‘reQuired
to wear protective clothir ; flagç ers will be requifed to
be in enclosed vehicles; and products will be packaged in
water soluble bags.
-------
8
Because additional data are needed to support existing
tolerances as well as to establish tolerances for meat,
milk, poultry, and eqqs, feeding arid grazing restrictions
will be placed on all raw agricultural commodities.
Metabolism in plants and animals is not adequately
understood but metabolites of terbutryn which contain
an intact triazine ring are of toxicological concern.
Therefore, data are required on plant and animal meta-
bolism, and recistrants are required to provide the
appropriate validated mehtodology as well as storage
stability and residue data for all metaho].ites with an
intact triazine ring.
The major environmental metabolite of terbutryn,
hydroxy-terbutryn, appears to have a high potential
to reach groundwater. Additional field studies have
been required.
EPA will issue registrations for substantially similar
terbutryrt products. However, new uses will be issued
only on a case—by—case basis after considering the
effects on the theoretical maximum residue contribution
(TPIRC), the maximum permissable intake (MPI), and the
oncogenic risks.
12. Summary of Data Gaps
PRODUCT CHE ?ISTRY
Manufacturing Process 8 months
Discussion of impurities B months
ENVIRONMENTAL FATE
Photodegradation (water, soil) 9 months
Anaerobic Soil Metabolism 27 months
Field Dassipation Study (soil 27 months
Rotational Crop Study (confi d) 39 months
Fish Accumulation Study 6 months
FISH AND WILDLIFE
Avian Dietary (upland gamebird) 6 months
Freshwater Fish LC 50 6 months
Acute Estuarine and Marine 9 months
Organism LCç 0 Studies
Fish Early Life—Stage and Aquatic 12 months
Invertebrate Life Cycle Studies
Non-target Phytotoxicity 9 month ’
-------
9
TOXI COLOGY
Acute inhalation (Rat)
21-Day Derma]
Chronic Toxicity (Rodent)
Mutagenicity Battery
General Metabolism
RESIDUE CHEMISTRY
8 months
8 months
6 months
12 months
12 months
Metabolism Studies (ruminants, poultry)
Uptake, Distribution, and Metabolism
Storage Stability Data
Processed Commodity Data
Residues of Concern on
Grain and Milled Products
13. Contact Person at EPA
18 months
18 months
15 months
24 months
24 months
Robert J. Taylor
U.S. Environmental protection Agency
Registration Division (TS—767 C)
401 M Street, S.W.
Washington, D.C. 20460
(703) 557—1A30
DISCLAIMER : The information presented in this pesticide Fact
sheet is for informational purposes only and may not be used
------- |