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EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Trade names for fonofos include Capfos, Cudgel, Difonate,
Dyfonate, Dyphonate, and Stauffer N 2790.
Fonofos is a highly toxic organophosphate insecticide in EPA
toxicity class I. Labels for products containing it must bear the
Signal Words DANGER - POISON. Some or all formulations of fonofos
are classified as Restricted Use Pesticides (RUPs) by the EPA.
RUPs may be purchased and used only by certified applicators.
Fonofos is a soil organophosphate insecticide primarily used on
corn. It is also used on sugar cane, peanuts, tobacco, turf, and
some vegetable crops. It controls aphids, corn borer, corn
rootworm, corn wireworm, cutworms, white grubs, and some maggots.
It is available in granular, microgranular, emusifiable
concentrate, suspension concentrate, microcapsule suspension, and
Formulation: It is
available in granular, microgranular, emulsifiable concentrate,
suspension concentrate, microcapsule suspension, and seed
- Acute toxicity: Fonofos is highly toxic
via the oral route, with reported oral LD50 values in
male rats ranging from 6.8 to 18.5 mg/kg [2,28] and from
3.2 to 7.9 mg/kg in female rats . It is also highly
toxic via the dermal route with reported dermal LD50
values of 25 mg/kg in female rabbits, 147 mg/kg in rats,
and 278 mg/kg in guinea pigs . The inhalation toxicity
is moderate with a reported 4-hour airborne LC50 of 0.9
mg/L . Symptoms of fonofos exposure may be delayed
from a few minutes to up to 12 hours after exposure.
Early symptoms include blurred vision, headache, and
dizziness. Skin contact often brings about sweating and
muscle twitching. Eye contact causes tearing, pain, and
blurring. Ingestion may cause nausea, abdominal cramps,
and diarrhea . Deaths resulting from high exposures
are often due to respiratory arrest. While these effects
are similar to those caused by other organophosphates,
fonofos may cause them at lower doses than others. A
number of human poisonings by fonofos have been recorded.
One woman exposed orally to a large amount of fonofos,
developed nausea, sweating, and respiratory arrest in
addition to muscle twitching, low blood pressure and
pulse rate, and pinpoint pupils. A pancreatic cyst
(attributed to fonofos exposure) was located and drained
externally in the course of her treatment. She recovered
after 2 months of hospitalization .
- Chronic toxicity: Chronic effects may be
similar to those observed after acute exposure, with some
delay [2,8]. In hens, administration of 90 oral doses of
8 mg/kg (at unspecified intervals) didn't produce delayed
neurotoxicity . Dietary feeding of fonofos at low
levels to dogs for 14 weeks produced no effects at or
below doses of 0.20 mg/kg .
- Reproductive effects: A long-term
reproduction test in rats showed no effects on female
reproductive ability at doses of 2.0 mg/kg/day of fonofos
[69,70]. This evidence suggests that fonofos does not
cause reproductive effects.
- Teratogenic effects: Pregnant mice were
fed very high doses of fonofos during the sensitive
period of gestation. At these levels, some abnormal bone
development and brain changes were observed in the
fetuses . Teratogenic effects in humans are not
likely under normal conditions.
- Mutagenic effects: Fonofos was not
mutagenic in five microbial assays nor in a DNA synthesis
test using human cells  suggesting that it is not
- Carcinogenic effects: Male and female
rats which ingested very high daily doses (relative to
the LD50) of fonofos for 2 years showed no cancerous
- Organ toxicity: Fonofos affects the
eyes, respiratory system, and central nervous system.
- Fate in humans and animals: Fonofos is
readily absorbed through the skin, gastrointestinal
tract, and respiratory tract . Once absorbed it is
systemically distributed. Fonofos is quickly excreted in
animals; 96 hours after rats received a single, high oral
dose of fonofos, three quarters of the dose was found in
the urine, a third in the feces, a small amount in
expired air, and only a trace in the tissues .
Virtually complete elimination occurred within 2 to 16
days after exposure . In another study, rats given
nearly pure fonofos excreted almost all of it within 4
days . A fonofos product, Dyfonate, is broken down in
rat livers into several metabolites, one of which is a
potent cholinesterase inhibitor known as an oxon .
This also is rapidly eliminated. Other than the fonofos
oxon (an anticholinesterase metabolite), fonofos'
breakdown products are less toxic than the parent
- Effects on birds: Fonofos is highly
toxic to birds, with a reported acute LD50 of 128 mg/kg
in mallards . Other reported LD50 values are 16.9
mg/kg in mallards, 12 to 14 mg/kg in northern bobwhite
and 10 mg/kg in red-winged blackbirds . It has a
reported 5-day dietary LC50 of 284 ppm in Japanese quail
. Despite its high acute toxicity and widespread use,
wildlife die-offs due to fonofos use have not been
- Effects on aquatic organisms: Fonofos is
highly toxic to freshwater fish and saltwater organisms.
Its acute freshwater 96-hour LC50 ranges from 0.028 mg/L
 to 44 mg/L  in bluegill sunfish, and 0.05 mg/L
 to 44 mg/L  in rainbow trout, perhaps reflecting
a difference in formulation. Organophosphates, such as
fonofos, do not bioaccumulate in the environment or in
- Effects on other organisms: Fonofos is
toxic to bees .
- Breakdown in soil and groundwater:
Fonofos is of moderate persistence in soils with a field
half-life of about 40 days . Field residence times
depend on variables such as soil type, organic matter,
rainfall, and sunlight. On a silty clay loam, the
half-life was 82 days after a high level of application,
while at lower application rates the half-life was 46
days . Fonofos is moderately well-bound to soils,
depending on organic matter content . It can be
transported in runoff. It is immobile in sandy loam and
silt loam soils, but is mobile in quartz sand. Soil
microbes, such as fungi, rapidly degrade fonofos .
Fonofos resists soil leaching, and has been detected only
rarely in groundwater and then at very low levels.
Fonofos has been detected in California groundwater at
0.01 to 0.03 ug/L, and in Iowa groundwater at 0.1 ug/L
- Breakdown in water: Although it is
practically insoluble in water, it is quickly broken down
by hydrolysis [8,13].
- Breakdown in vegetation: Fonofos is
rapidly metabolized in plant tissues to nontoxic
compounds . The compound is not readily absorbed by
plant foliage and it is not translocated throughout
- Appearance: Fonofos is a clear to yellow
liquid at room temperature .
- Chemical Name: O-ethyl S-phenyl
- CAS Number: 944-22-9
- Molecular Weight: 246.32
- Water Solubility: 13 mg/L 
- Solubility in Other Solvents: v.s. in
organic solvents like kerosene, xylene, and isobutyl
methyl ketone 
- Melting Point: Not Available
- Vapor Pressure: 28 mPa @ 25 C 
- Partition Coefficient: 3.9031 
- Adsorption Coefficient: 870 
- ADI: Not Available
- MCL: Not Available
- RfD: 0.002 mg/kg/day 
- PEL: 0.1 mg/m3 (8-hour) (skin) 
- HA: 0.01 mg/L 
- TLV: Not Available
Zeneca Ag Products
1800 Concord Pike
Wilmington, DE 19897
- Phone: 800-759-4500
- Emergency: 800-759-2500
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