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in 1996. EXTOXNET no longer updates this information, but it may be useful
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E X T O X N E T
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EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Trade names for products containing fenamiphos include Bay 68138,
Nemacur and Phenamiphos. It may also be found in formulations
with other pesticides such as isofenphos, carbofuran and
Fenamiphos is an highly toxic compound in EPA toxicity class I.
It is a Restricted Use Pesticide (RUP). RUPs may be purchased and
applied only by a certified applicator. Labels for products
containing fenamiphos must carry the Signal Word DANGER.
Fenamiphos is an organophosphate nematicide used to control a
wide variety of nematode (roundworm) pests. Nematodes can live as
parasites on the outside or the inside of a plant. They may be
free living or associated with cyst and root-knot formations in
plants. Fenamiphos is used on a variety of plants including
tobacco, turf, bananas, pineapples, citrus and other fruit vines,
some vegetables, and grains. The compound is absorbed by roots
and is then translocated throughout the plant. Fenamiphos, as is
typical of other organophosphates, blocks the enzyme
acetylcholinesterase in the target pest. The pesticide also has
secondary activity against other invertebrates such as sucking
insects and spider mites. It is available in emulsifiable
concentrate, granular, or emulsion formulations.
Formulation: It is
available in emulsifiable concentrate, granular, or emulsion
- Acute toxicity: Fenamiphos is highly
toxic via the oral route, with reported LD50 values of 2
to 19 mg/kg in the rat and 56 to 100 mg/kg in guinea
pigs. It is also highly toxic to dogs and rabbits [8,13].
The acute dermal toxicity of the compound is also high,
with reported dermal LD50 values of 72 to 154 mg/kg in
rats [8,13]. The inhalation toxicity of the compound is
also high, with reported inhalation LC50 values in rats
of 0.11 to 0.17 mg/L [8,13]. Longer exposures at
moderately lower concentrations also caused rat mortality
. The compound has the potential to cause significant
eye damage at acute exposure levels. It is nonirritating
to the skin . Symptoms of acute toxic exposure to the
nematicide are consistent with those of other
organophosphate compounds and include difficulty in
breathing, diarrhea, urination, and slowness of the
heart. Other symptoms include muscle twitching and
- Chronic toxicity: A number of long-term
feeding studies have been conducted with this compound on
several different species of animals. In dogs, dietary
doses of 0.0125 to 0.25 mg/kg/day over 2 years produced
depressions in cholinesterase activity at middle doses
and above. No effects were noted in the liver or in blood
chemistry even at the highest dose . Rats exposed to
1.5 mg/kg/day over 2 years experienced increases in
thyroid gland and lung weights in females, and increased
heart weight in males. There were no organ weight changes
noted in the rats at doses below 0.5 mg/kg/day .
Brain weights have also been affected by exposure to
moderate amounts of the compound . Two studies have
been conducted on the potential risk to pesticide workers
(loaders and applicators) from the use of Nemacur. One
study concluded that occupational exposure levels were
more than 100 times lower than the level which causes
cholinesterase inhibition in animals and thus the use of
the compound did not pose a significant risk to the users
. Another study concluded that the main threat to
applicators was through the skin on the hands. However,
the levels of exposure on the hands were significantly
below the level that had caused chronic toxicity in mice.
It was concluded that the pesticide could be used safely
- Reproductive effects: Both male and
female rats fed moderate to high doses of fenamiphos
(0.15 to 1.5 mg/kg/day) over three generations showed no
compound-related reproductive effects at the middle doses
tested (0.5 mg/kg/day). At the higher doses the second
generation of pups showed a decrease in body weight gain.
This effect was not seen in the third generation . It
is unlikely that this compound would cause reproductive
effects in humans.
- Teratogenic effects: A single study of
pregnant rats fed fenamiphos during gestation over a
range of doses (up to 1 mg/kg/day) showed a decrease in
the maternal weight at doses of 0.3 mg/kg/day and above.
At the highest dose a higher number of the pups from the
exposed group had died relative to the unexposed
controls, and the pups which survived had decreased
weights . In tests with pregnant rabbits fed up to
0.4 mg/kg, no birth defects were noted . However,
another reference stated that teratogenic studies were
positive in rabbits, though the effects in the offspring
were induced at doses much higher than those that cause
maternal toxicity . The results from these studies
suggest that teratogenic effects in humans are unlikely.
- Mutagenic effects: A number of studies
evaluating the mutagenic potential of fenamiphos have all
shown the compound to be nonmutagenic. The test subjects
included bacterial cells and male mice [8,64].
- Carcinogenic effects: Two studies, one
conducted with mice and the other with rats, indicated
that fenamiphos is not carcinogenic [8,64]. One study was
conducted for 1 1/2 years at very high levels (up to 7.5
mg/kg/day in mice) and the other study was conducted over
2 years (up to 1.5 mg/kg/day in rats) .
- Organ toxicity: Target organs identified
in studies of test animals and exposed workers are the
central nervous system, heart, lungs, and thyroid.
- Fate in humans and animals: Fenamiphos
is readily absorbed through the digestive tract and
lungs. One study placed the amount absorbed near 95% of
the ingested dose. The compound is rapidly broken down
within the organism, and the by-products are excreted in
the urine. The majority of a dose was recovered in urine
within 15 hours after treatment .
- Effects on birds: Fenamiphos is very
highly toxic to birds, with a reported acute oral LD50
for the most sensitive species tested, the ring-necked
pheasant, of 0.5 mg/kg . LD50 values for other species
range from 1.0 to 2.4 mg/kg, all of which indicate that
this is a very highly toxic compound . In a controlled
experiment, fenamiphos was determined to be the most
toxic of thirteen different cholinesterase inhibitors
. In tests with wild songbirds (red-winged blackbirds
and house sparrows) an unspecified dose of Nemacur was
highly toxic to these species, with death of the birds
occurring within an hour of eating the granules .
- Effects on aquatic organisms: The
toxicity of fenamiphos to aquatic species varies from
moderate to high. Bluegill sunfish are extremely
sensitive to the presence of the compound. The LC50 for
fenamiphos is 9.6 mg/L in this species. Other species
tested include the rainbow trout (LC50 is 0.11 mg/L) and
the goldfish (LC50 is 3.2 mg/L) . The compound is not
expected to bioaccumulate appreciably in aquatic
- Effects on other organisms: Fenamiphos
is practically nontoxic to honeybees .
- Breakdown in soil and groundwater:
Fenamiphos is of moderate persistence in the soil
environment, with a reported soil half-life of about 50
days . The compound appears to have no effect on the
activity of soil bacteria . Aerobic processes are most
important for breakdown of the compound. Fenamiphos is
not strongly adsorbed to soils , but neither it nor
its breakdown products have been found in over 1200 wells
tested in six states.
- Breakdown in water: Fenamiphos
disappears quickly from water in acidic and alkaline
water, but it is stable in neutral water when held in the
dark. The compound, when in the presence of artificial
light, disappears very rapidly. In a neutral solution,
half of the initial amount of the compound degraded
within 4 hours.
- Breakdown in vegetation: In plants, the
compound is absorbed through the roots and translocated
to the leaves. It is broken down within the plant. The
products of its breakdown are relatively persistent and
can also inhibit cholinesterase .
- Appearance: Fenamiphos is a colorless
crystal in its pure form, or a tan waxy solid in the
technical form .
- Chemical Name: ethyl
4-methylthio-m-tolyl isopropylphosphoramidate 
- CAS Number: 22224-92-6
- Molecular Weight: 303.40
- Water Solubility: 700 mg/L @ 20 C 
- Solubility in Other Solvents: s. in
dichloromethane, isopropanol, and toluene 
- Melting Point: 46 C (technical) 
- Vapor Pressure: 0.12 mPa @ 20 C 
- Partition Coefficient: Not Available
- Adsorption Coefficient: 100 
- ADI: 0.005 mg/kg/day 
- MCL: Not Available
- RfD: 0.00025 mg/kg/day 
- PEL: Not Available
- HA: 0.002 mg/L (lifetime) 
- TLV: 0.1 mg/m3 (8-hour) (skin) 
P.O. Box 4913
8400 Hawthorn Road
Kansas City, MO 64120
- Phone: 816-242-2429
- Emergency: 816-242-2582
References for the information in this PIP can be found in
Reference List Number 5
information in this profile does not in any way replace or
supersede the information on the pesticide product labeling or
other regulatory requirements. Please refer to the pesticide