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: 9/93
TRADE OR OTHER NAMES
A formerly used common name was DMTP (26). Trade names include Bay
29493, Baycid, Baytex, Dalf, DMTP, Entex, Lebaycid, Mercaptophos,
Prentox Fenthion 4E, Queletox, S 1752, Spotton, Talodex, Tiguvon.
Fenthion is classified by the U.S. Environmental Protection Agency
(EPA) as a Restricted Use Pesticide (RUP) due to the special handling
warranted by its toxicity. All bird control products, as well as non-domestic,
non-granular formulations of 70% and greater are RUPs (22).
RUPs may be purchased and used only by trained certified applicators (4, 21).
Fenthion may not be used on food crops (2). Products containing
fenthion must bear the signal word "Warning" (26). Check with specific
state regulations for local restrictions that may apply.
Fenthion is a contact and stomach insecticide used against many
sucking, biting pests, especially fruit flies, stem borers, mosquitoes,
and Eurygaster cereal bugs (26). In mosquitoes, it is toxic to both the
adult and immature forms (larvae) (18). Once used extensively in the
U.S. for controlling intestinal worms, fenthion no longer has FDA
approval due to an excess number of poisoning deaths (19). Fenthion is
available in dust, emulsifiable concentrate, granular, liquid
concentrate, spray concentrate, ULV and wettable powder formulations
While it is effective as an insecticide, it is also moderately
toxic to mammals, and highly toxic to birds. Based on its high toxicity
to birds, fenthion is used in various parts of the world for weaver bird
control. Pest control operators have used it to control pigeons around
public buildings, as well. For bird control, use is made of fenthion's
contact action and its ready absorption through the skin. It is applied
as a paste to roosting areas when utilized for such purposes (10).
Fenthion has been tested in dogs and cows for possible control of
Fenthion is one of a class of insecticides referred to as
organophosphates. These chemicals act by interfering with the
activities of cholinesterase, an enzyme that is essential for the proper
working of the nervous systems of both humans and insects. Please refer
to the Toxicology Information Brief on cholinesterase-inhibition for a
more detailed description of this topic.
Fenthion is moderately toxic if ingested, inhaled, or absorbed
through the skin. It affects the central nervous, cardiovascular, and
respiratory systems, and may irritate eyes and mucous membranes (14).
As with all organophosphates, fenthion is readily absorbed through the
skin. Skin which has come in contact with this material should be
washed immediately with soap and water and all contaminated clothing
should be removed. While symptoms of poisoning may be delayed in
animals, in cases of human poisonings, symptoms have generally been
immediate. Deaths are primarily due to respiratory failure (5).
Several cases of intentional or accidental human poisonings via
ingestion and/or dermal exposure are known (8, 19). Individuals with
respiratory ailments, recent exposure to cholinesterase inhibitors or
impaired cholinesterase production, or with liver malfunction may be at
increased risk from exposure to coumaphos (27).
The organophosphate insecticides are cholinesterase inhibitors.
They are highly toxic by all routes of exposure. When inhaled, the
first effects are usually respiratory and may include bloody or runny
nose, coughing, chest discomfort, difficult or short breath, and
wheezing due to constriction or excess fluid in the bronchial tubes.
Skin contact with organophosphates may cause localized sweating and
involuntary muscle contractions. Eye contact will cause pain, bleeding,
tears, pupil constriction, and blurred vision. Following exposure by
any route, systemic effects may begin within a few minutes or be delayed
for up to 12 hours. These may include pallor, nausea, vomiting,
diarrhea, abdominal cramps, headache, dizziness, eye pain, blurred
vision, constriction or dilation of the eye pupils, tears, salivation,
sweating, and confusion. Severe poisoning will affect the central
nervous system, producing incoordination, slurred speech, loss of
reflexes, weakness, fatigue, involuntary muscle contractions, twitching,
tremors of the tongue or eyelids, and eventually paralysis of the body
extremities and the respiratory muscles. In severe cases there may also
be involuntary defecation or urination, psychosis, irregular heart
beats, unconsciousness, convulsions and coma. Death may be caused by
respiratory failure or cardiac arrest (27).
Some organophosphates may cause delayed symptoms beginning 1 to 4
weeks after an acute exposure which may or may not have produced
immediate symptoms. In such cases, numbness, tingling, weakness and
cramping may appear in the lower limbs and progress to incoordination
and paralysis. Improvement may occur over months or years, but some
residual impairment will remain (27).
The amount of a chemical that is lethal to one-half (50%) of
experimental animals fed the material is referred to as its acute oral
lethal dose fifty, or LD50. The oral LD50 for fenthion in rats is 180
to 298 mg/kg, 150 mg/kg in rabbits, 260 mg/kg in guinea pigs, and 88 to
145 mg/kg in mice (1, 2, 11, 13, 27). The dermal LD50 in rats is 330 to
1,000 mg/kg, and 500 mg/kg in mice (1, 26, 27).
The lethal concentration fifty, or LC50, is that concentration of a
chemical in air or water that kills half of the experimental animals
exposed to it for a set time period. The inhalation 1-hour LC50 for
fenthion is rats is 2.4 to 3.0 mg/l (27).
Repeated or prolonged exposure to organophosphates may result in
the same effects as acute exposure including the delayed symptoms.
Other effects reported in workers repeatedly exposed include impaired
memory and concentration, disorientation, severe depressions,
irritability, confusion, headache, speech difficulties, delayed reaction
times, nightmares, sleepwalking and drowsiness or insomnia (27).
Prolonged exposure to fenthion may result in flu-like symptoms, such as
loss of appetite (anorexia), weakness, and malaise (14).
There was no evidence of weight loss or decreased food consumption
in dogs that were given 50 mg/kg of fenthion in their diets for one year
Single injections of 40 or 80 mg/kg of fenthion into the abdominal
cavities of pregnant female mice caused poisoning in the developing
fetuses, particularly when administered on days 10 through 12 of
gestation. There were significantly more abnormalities in the offspring
of female mice that had received 40 mg/kg on days 8 or 10 of pregnancy.
Fetuses were injured primarily by dosages that caused toxicity in the
maternal mouse (8). No influence was seen on reproduction in other 3-
generation studies of mice (1). After administration of 0.5 mg/kg/day
for 30 days, the eggs laid by surviving mallards had markedly reduced
fertility (20). Once in the bloodstream, fenthion may cross the
Some reduction in fetal weight occurred, but no defects were found
in mice that were given intraperitoneal doses of up to 80 mg/kg of
fenthion in single day or 3-day periods during the period of gestation
in which organs are formed (17). Other tests on mice and rats did not
show teratogenic effects from fenthion (1). No teratogenic effects were
seen in five generations of mice that drank water containing 60 parts
per million (ppm) fenthion (8).
Tests on mice did not show mutagenic effects from fenthion (1).
The National Cancer Institute performed carcinogenicity tests on
fenthion that indicated that this insecticide may be a carcinogen in
male mice (12). However, no carcinogenic effects were observed in other
two-year feeding studies of rats and mice (1).
Fenthion primarily affects the nervous system through inhibition of
cholinesterase, an enzyme required for proper nerve functioning. No
delayed neurological effects were found in chickens with single and
repeated applications of fenthion (1). Within four weeks of exposure to
a dietary concentration of 250 ppm (or 12.5 mg/kg/day) of fenthion, rats
showed weight loss without change in food intake, and inhibition of
brain cholinesterase activity to about 15% of normal. A dose of 1 mg/kg
caused inhibition of 60-70% of normal brain cholinesterase activity. A
dose of 0.25 mg/kg caused slight brain cholinesterase-inhibition (8).
Fate in Humans and Animals
In animals, fenthion is quickly absorbed into the bloodstream
through the digestive tract, lungs, and skin, and then broken down. Its
breakdown products are eliminated through the urine and the feces in a
three-day period (1, 7). A single dose of the insecticide has prolonged
action, suggesting that much of it is stored and later released for
metabolism (8). Fenthion has fat-loving, or 'lipophilic,' properties
and tends to be deposited in fatty tissue (19). Fenthion and its
metabolites were found in the fat of steers slaughtered 3 days after
dermal application of fenthion (25).
When cows were given a dermal application of 9 mg radio-labeled
fenthion per kg, 45-55% of the dose was excreted in the urine, 2.0 to
2.5% in the feces, and 1.5 to 2.0% was recovered in the milk (25).
Effects on Birds
Fenthion is highly toxic to birds (10). It is more toxic to fowl
than to mammals (5). Acute symptoms of fenthion poisoning in birds
include tearing of the eyes, foamy salivation, lack of movement,
tremors, congestion of the windpipe, lack of coordination in walking,
and an abnormally rapid rate of breathing or difficult breathing (20).
Chickens developed leg weakness when they were fed 25 mg/kg doses of
fenthion (15). The acute oral LD50 in poultry is 15 to 30 mg/kg (7,
The LC50 for fenthion in mallards is 250 to 299 ppm, 180 to 220 ppm
in pheasants, and 25 to 35 ppm or 60 mg/kg in bobwhites. In these
tests, fenthion was included in diets of two-week-old birds for five
days and was followed by untreated feed for three days (15, 26).
Effects on Aquatic Organisms
Fenthion is moderately toxic to fish (19). The 96-hour LC50 for
fenthion in rainbow trout is 0.930 ppm or 0.83 mg/l, 1.160 ppm in carp,
1.540 ppm in largemouth bass, 2.404 ppm in fathead minnow, and 3.404 ppm
in goldfish. Brown bullheads were not affected by the insecticide when
it was applied to a California refuge at 0.01 pounds per acre (15, 26).
Fenthion should not be applied for mosquito control in areas containing
fish, shrimp, crabs, or crayfish (18).
Effects on Other Animals (Nontarget species)
Because fenthion is toxic to bees, flowering crops must not be
sprayed (7, 18). The LD50 in domestic farm animals given fenthion by
injection through the skin is 98 mg/kg. The intramuscular LD50 of
domestic farm animals is 46 mg/kg (13).
Organophosphates tend to be persistent and to bioconcentrate in
environmental systems (23).
Breakdown of Chemical in Soil
Fenthion adsorbs strongly to soil particles. This adsorption makes
fenthion less likely to move, or leach, through the soil with water
percolating through the ground (23). In soil, residues of fenthion
persist for approximately 4 to 6 weeks (6).
Breakdown of Chemical in Water
This material should be kept out of lakes, streams, or ponds, and
it should not be applied where runoff is likely to occur. Care should
be taken not to contaminate water by cleaning fenthion application
equipment or disposal of related wastes. In one study of its
persistence in water, 50% of applied fenthion remained in river water 2
weeks later, while 10% remained after 4 weeks (9). Residue levels of 16
micrograms per liter (ug/l) of fenthion were found in the water from
which dead birds were retrieved, in an area that had been sprayed 2 days
earlier with recommended mosquito control levels of the insecticide
Breakdown of Chemical in Vegetation
Fenthion is phytotoxic (or poisonous to plant material) to American
linden, Hawthorn and sugar maple trees, and to certain rose varieties
(19). It is not considered phytotoxic when used at recommended rates,
although injury has occurred in certain varieties of apples and cotton.
Plant foliage should not be sprayed when temperatures exceed 90 degrees
F (18). Only about 10% of applied fenthion remained on rice plants
after 6 hours. Almost half of the activity was found in the rice bran,
6.5% was in the husk, and 14.7% was in polished rice. Water soluble
metabolites were found 14 days after fenthion application to rice plants
PHYSICAL PROPERTIES AND GUIDELINES
Pure fenthion is a colorless liquid. Technical fenthion is a
yellow or brown oily liquid with a weak garlic odor (1, 25).
Fenthion is subject to hydrolysis (1), and it is not compatible
with highly alkaline materials (18). Fenthion is stable under normal
temperatures and pressures, but may pose a moderate fire hazard if
exposed to heat or flame. Containers may explode in the heat of a fire.
In the presence of strong oxidizers, fenthion may pose a fire and
explosion hazard. Thermal decomposition may release toxic oxides of
carbon, sulfur and phosphorus (27).
Fenthion is sometimes mixed with paints (18). Fenthion must be
stored in sealed, original containers, and kept in well-ventilated dry
storage areas. It should be kept away from heat sources, flames, or
sparking equipment, as its temperature must not exceed 25-30 degrees C.
Containers should be stacked in a way that permits air circulation at
the bottom and insides of piles. Storage areas should be an appropriate
distance from inhabited buildings, animal shelters, and food storage.
Fenthion containers must also be kept out of reach of unauthorized
persons, children, and domestic animals (19). Household use of fenthion
should be limited to trained personnel. Excessive wetting of plastic,
tile, or rubber should be avoided. It should not be applied to young,
stressed, or sick animals (18).
Persons who work with organophosphate materials for long periods of
time should have frequent blood tests of their cholinesterase levels.
If the cholinesterase level falls below a critical point, no further
exposure should be allowed until it returns to normal (28).
Protective clothing must be worn when handling fenthion. Before
removing gloves, wash them with soap and water. Always wash hands, face
and arms with soap and water before smoking, eating or drinking.
After work, remove all work clothes and shoes. Shower with soap
and water. Wear only clean clothes when leaving the job. Wash
contaminated clothing and equipment with soap and water after each use.
Keep contaminated work clothes separate from regular laundry.
|TLV-TWA: ||0.2 mg/m3 (skin) (1)
|OSHA TWA: ||0.2 mg/m3 (skin) (27)
|ACGIH TWA: ||0.2 mg/m3 (skin) (27)
|CAS #: ||55-38-9
|Specific gravity: ||1.25 at 20 degrees C (26)
|H20 solubility: ||54-56 mg/L (1); nearly insoluble in water (26)
|Solubility in other solvents:
||highly soluble in most organic solvents, including alcohols, ethers, esters, halogenated aromatic.
Soluble in petroleum ether (11).
Readily soluble in dichloromethane, 2-propanol, and toluene (26).
|Melting point: ||7.5 degrees C (26)
|Boiling point: ||87 degrees C (189 degrees F) at 0.01 mm Hg (pure) (8, 25)
|Flash point: ||>180 degrees F (>82 degrees C) (27)
|Vapor pressure: ||3.7 x 10 to the minus 5 power mmHg at 20 degrees C (26); Negligible (27)
|Kow: ||4.091 (19)
|Chemical Class/Use: ||Organophosphate insecticide
Crop Protection and Animal Health Div.
PO Box 4913
Kansas City, MO 64120
Review by Basic Manufacturer:
Comments solicited: November, 1992
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