developed for woody plant and broadleaf weed control along rights-of-way
and on industrial sites, triclopyr is also used in forest site
preparation, replacing the banned 2,4,5-T. Dow registered triclopyr in
1973, and several formulations are now available. The triethylamine salt (Garlon
3A™) is used to control woody plants when applied to cut surfaces by
means of tree injection, girdle, or stumpspray. The butoxyethyl ester (Garlon
4™) is used as a basal spray or in aerial applications. M4450™
contains a mixture of triclopyr and picloram, a restricted use herbicide
with a history of groundwater contamination.
triclopyr resembles 2,4,5-T and, like this phenoxy herbicide, mimics plant
growth hormones called auxins, interfering with the normal plant growth
response. It is readily absorbed through both roots and leaves, and
translocates throughout the plant.
is of low to moderate acute toxicity in mammals. The rat oral LD50
for technical triclopyr is reported to be 630-720 mg/kg, and is higher,
2000-3000 mg/kg, for formulated products. Triclopyr and its products are
reported to be slightly to moderately irritating to the skin. Of greatest
concern, Garlon 3A™ can cause permanent impairment of vision. Effects on
the eye can include severe conjunctival irritation, moderate internal
redness, and moderate to severe corneal injury. Washing is not effective
in preventing these effects. Garlon 4™ is not an eye irritant.
and chronic feeding studies in dogs and rodents found kidney and liver
testing in bacterial systems has yielded negative results, although
bacterial mutagenicity screens are thought to be invalid for predicting
the carcinogenicity of chlorinated hydrocarbons. A dominant lethal test in
rats indicated a weakly positive mutagenic effect, but no similar effect
was seen in mice.
defect studies on rats and rabbits showed no birth defects in pups, but
the rat study reported fetotoxicity including delayed skull bone
ossification. This effect may be secondary to maternal toxicity. The
fetotoxic NOEL (No Observable Effect Level) in this study was 50 mg/kg,
and the maternal NOEL is <50 mg/kg.
two existing rodent cancer studies submitted to EPA are considered
inadequate and new studies are required. However, the mouse study results
show a statistically significant increase in benign pulmonary tumors,
while malignant tumor increases were not statistically significant. An
independent pathologist, Ruth Shearer, Ph.D., reviewed this data and noted
that the dose levels used were 8-fold less than usually deemed appropriate
for testing oncogenicity.
4™ is extremely toxic to rainbow trout and bluegills, with LC50s over
500 ppm. Studies on mallard ducks indicate triclopyr is of low acute oral
toxicity, and subchronic studies on quail and ducks also report low
toxicity. There are no bird field studies.
degradation of triclopyr is due primarily to photodegradation and
microbial decomposition. Somewhat persistent, soil half-life is strongly
dependent on specific soil type and climatic conditions. Garlon labels
suggest that conifer seedlings not be planted in soil sprayed within six
months, suggesting that the soil will remain toxic to conifers in that
period. A Swedish study found residues persisting for 1 to 2 years, and in
some cases beyond 2 years. Under favorable degradation conditions, 95°F
and high moisture, Dow reports a half-life of 46 days.
breakdown products, trichloropyridinol and trichloromethoxypyridine, are
generally more persistent than the parent compound, with half-lives
ranging from 8-279 days and 50-300 days respectively. The toxicity of
these metabolites has not been studied.
is considered mobile based on its ability to desorb from soil particles
and organic matter, as well as its solubility in water. While degradation
is rapid in water exposed to sunlight with a reported half-life of 10
hours in 25°C water, triclopyr is stable for up to nine months, the length
of the study, in the absence of light (i.e. ground or well water). Contamination
of surface waters is also a concern. Runoff-monitoring studies in Oregon
found residues of 6 ppb in runoff water 5 months after treatment at 3
1983. Control of Vegetation on Utility and Railroad-Rights-of-Way.
Prepared for the Commonwealth of Massachusetts Generic Environmental
Impact Report. Cambridge, MA.
R.W. 1983. Affidavit in Alaska Survival, et al. v. Weeks, et al. Civil
Action No. A82-253 in the U.S. District Court for the District of Alaska.
W.T. 1984. Pesticide Background Statements. Volume I. Herbicides.
Agriculture Handbook No. 633. Forest Service. Washington, DC.
EPA. 1990. Personal communication with Tom Luminello. Special Review and
Reregistration Division. Office of Pesticide Programs. Washington, DC.
EPA. 1984 Toxicology One-liner for Triclopyr. Office of Pesticide
Programs. Washington, DC.