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The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

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E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Fonofos

Trade and Other Names: Trade names for fonofos include Capfos, Cudgel, Difonate, Dyfonate, Dyphonate, and Stauffer N 2790.

Regulatory Status: 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.

Chemical Class: organophosphate

Introduction: 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 seed treatment.

Formulation: It is available in granular, microgranular, emulsifiable concentrate, suspension concentrate, microcapsule suspension, and seed treatment formulations.

Toxicological Effects:

• 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 [69]. 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 [2]. The inhalation toxicity is moderate with a reported 4-hour airborne LC50 of 0.9 mg/L [13]. 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 [47]. 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 [2].
• 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 [2]. Dietary feeding of fonofos at low levels to dogs for 14 weeks produced no effects at or below doses of 0.20 mg/kg [47].
• 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 [69]. 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 [69] suggesting that it is not mutagenic.
• Carcinogenic effects: Male and female rats which ingested very high daily doses (relative to the LD50) of fonofos for 2 years showed no cancerous effects [69].
• 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 [2]. 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 [71]. Virtually complete elimination occurred within 2 to 16 days after exposure [69]. In another study, rats given nearly pure fonofos excreted almost all of it within 4 days [69]. 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 [69]. This also is rapidly eliminated. Other than the fonofos oxon (an anticholinesterase metabolite), fonofos' breakdown products are less toxic than the parent compound [2].

Ecological Effects:

• Effects on birds: Fonofos is highly toxic to birds, with a reported acute LD50 of 128 mg/kg in mallards [13]. 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 [6]. It has a reported 5-day dietary LC50 of 284 ppm in Japanese quail [14]. Despite its high acute toxicity and widespread use, wildlife die-offs due to fonofos use have not been reported [14].
• 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 [13] to 44 mg/L [72] in bluegill sunfish, and 0.05 mg/L [13] to 44 mg/L [72] in rainbow trout, perhaps reflecting a difference in formulation. Organophosphates, such as fonofos, do not bioaccumulate in the environment or in animals [1].
• Effects on other organisms: Fonofos is toxic to bees [13].

Environmental Fate:

• Breakdown in soil and groundwater: Fonofos is of moderate persistence in soils with a field half-life of about 40 days [19]. 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 [73]. Fonofos is moderately well-bound to soils, depending on organic matter content [19]. 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 [73]. 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 [73].
• 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 [8]. The compound is not readily absorbed by plant foliage and it is not translocated throughout plants [8].

Physical Properties:

• Appearance: Fonofos is a clear to yellow liquid at room temperature [13].
• Chemical Name: O-ethyl S-phenyl (RS)-ethylphosphorodithioate [13]
• CAS Number: 944-22-9
• Molecular Weight: 246.32
• Water Solubility: 13 mg/L [13]
• Solubility in Other Solvents: v.s. in organic solvents like kerosene, xylene, and isobutyl methyl ketone [13]
• Melting Point: Not Available
• Vapor Pressure: 28 mPa @ 25 C [13]
• Partition Coefficient: 3.9031 [13]
• Adsorption Coefficient: 870 [19]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: 0.002 mg/kg/day [53]
• PEL: 0.1 mg/m3 (8-hour) (skin) [39]
• HA: 0.01 mg/L [69]
• TLV: Not Available

Basic Manufacturer:

Zeneca Ag Products
1800 Concord Pike
Wilmington, DE 19897

• Phone: 800-759-4500
• Emergency: 800-759-2500
  

References:

References for the information in this PIP can be found in Reference List Number 5

DISCLAIMER: The 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 product labeling.