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Trichlorfon Trichlorfon,
an organophosphate pesticide, is used to control a variety of indoor and
outdoor insect pests in agricultural, residential and commercial sites
ranging from chicken coupes to golf courses to residential homes. The U.S.
Department of Agriculture was the first to register this pesticide in
1955. In 1995, U.S. Environmental Protection Agency’s (EPA)
Reregistration Eligibility Document identified several data gaps on the
effects of trichlorfon on human health and the environment. Mode of Action
Trichlorfon
acts on the target insect as both a contact poison and as a stomach
poison. Trichlorfon, like all organophosphates, are cholinesterase
inhibitors, meaning that the chemical binds irreversibly to the active
site of an essential enzyme for normal nerve impulse transmission,
acetylcholine esterase (AchE), inactivating the enzyme. The insect,
therefore, loses control over its own nervous system and is paralyzed. Toxicity
EPA
has categorized trichlorfon as a toxicity category II pesticide (on a
scale of I to IV, I being the highest toxicity rating), and is required to
have the signal word DANGER printed on the label (U.S. EPA 1997). While
trichlorfon is considered to be moderately toxic by ingestion and skin
absorption, it is readily absorbed through the skin and can result in skin
sensitization (allergies). Inhalation results in respiratory problems
(shortness of breath, coughing,) and bloody or runny nose. Eye contact
will cause bleeding, blurred vision, pain and pupil constriction. Within a
few minutes to twelve hours after exposure, systemic effects such as
vomiting, abdominal cramps and diarrhea will be experienced. The
primary effects of trichlorfon are seen in the central nervous system,
symptoms include: loss of reflexes, slurred speech, involuntary muscle
contractions, severe depression, irritability, confusion, impaired memory,
insomnia, psychosis and paralysis (ETN 2001). A 60-day study in rats fed
100mg/kg/day decreased cholinesterase activity to under half the normal
level. Studies
show that trichlorfon can cause abortions in rats and fetal abnormalities
in mice, hamsters and rats. The insecticide is a mutagen in mice when
given in small repeated doses. Long-term exposure to trichlorfon can also
result in edema (excessive fluid) of the brain, liver damage, inflammation
of the lungs and heart muscle changes (ETN 2001). Carcinogenicity
Trichlorfon
is classified as a “Likely” carcinogen for high doses of exposure and
“Not Likely” for low doses of exposure in EPA’s Weight-of-Evidence
categories. Carcinogenic effects were seen in rats and other available
data suggests that this chemical does contribute to the production of
tumors of the kidneys, lungs and mammary in animal studies (U.S. EPA
2000). Ecological Effects
Trichlorfon
is toxic to wildlife. It is highly toxic to birds, cold and warm water
fish, beneficial insects, non-target insects and aquatic invertebrates.
The acute bird oral toxicity is 40-47 mg/kg. Symptoms of poisoning (i.e.
regurgitation, trembling, wing-beat convulsions) have been seen as little
as ten minutes after exposure. The acute toxicity to freshwater fish is
between 1.67 and 180 ppm (parts per million) (ETN 2001). Environmental Fate
Organophosphates
have a tendency to persist and bioconcentrate in ecosystems. Trichlorfon
is very mobile in soils of different textures and organic contents, very
soluble in water and does not absorb to soil particles. Therefore, it is
likely to contaminate groundwater. Its half-life in aerobic soils varies
from 1 to 27 days, depending on the fertility of the soil. Approximately
99% of trichlorfon applied to alkaline water conditions (pH 8.5) was
broken down within two hours. Pond water that had acidic conditions (pH
5.0) stayed stable for two hours. However, one of the breakdown products
of trichlofon is dichlorvos (DDVP), an insecticide, which stayed present
in the water for approximately 526 days at 20 degrees Celsius (ETN 2001) Data Gaps
EPA
concluded that the data available was insufficient in order to completely
evaluate the effects of the pesticide on human health and the environment.
Studies have been requested for estuarine or marine mollusk acute
toxicity, the aquatic invertebrate life cycle, terrestrial field
dissipation, worker exposure and field drift. More data is also needed to
show the action of trichlorfon in water. References: Extension
Toxicology Network (ETN). 2001. Pesticide Information Profiles:
Trichlorfon. <http://pmep.cce.cornell.edu/profiles/extoxnet/pyrethrins-ziram/trichlorfon-ext.html>. U.S.
EPA. 2000. List of Chemicals Evaluated for Carcinogenic Potential. Office
of Pesticide Programs. Washington, DC. U.S. EPA. 1997. “Reregistration Eligibility Document.” Office of Pesticide Programs. Washington, DC. <http://www.epa.gov/oppsrrd1/REDs/index_h2z.html#T>.
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