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The information in this profile may be out-of-date.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

Phorate

Trade and Other Names: Trade names include AC 8911, Agrimet, Geomet, Granutox, Phorate 10G, Rampart, Terrathion, Thimenox, Thimet, Timet, Vegfru, and Vegfru Foratox.

Regulatory Status: Phorate is a highly toxic compound in EPA toxicity class I. Labels for products containing it must bear the Signal Words DANGER - POISON. It is a Restricted Use Pesticide (RUP). RUPs may be purchased and used only by certified applicators.

Chemical Class: organophosphate

Introduction: Phorate is an organophosphorus insecticide and acaricide used to control sucking and chewing insects, leafhoppers, leafminers, mites, some nematodes, and rootworms [1,2]. Phorate is used in pine forests and on root and field crops, including corn, cotton, coffee, some ornamental and herbaceous plants, and bulbs. It is available in granular and emulsifiable concentrate formulations.

Formulation: It is available in granular and emusifiable concentrate formulations.

Toxicological Effects:

• Acute toxicity: Phorate is highly toxic via the oral route with reported oral LD50 values of 1.1 to 3.7 mg/kg in rats [2,13], and 2.25 to 6.59 mg/kg in mice [2,87]. It is highly toxic via the dermal route as well, with reported dermal LD50 values of 2.5 to 6.2 mg/kg in rats [2,13], and 5.2 mg/kg in rabbits [2,87]. Guinea pigs reportedly have a dermal LD50 of 20 to 30 mg/kg during a 24-hour exposure [13,87]. The acute 1-hour inhalation LC50 for rats is reported as 0.06 mg/L [13]. Symptoms of acute exposure to phorate are similar to those caused by exposure to other organophosphate pesticides, except that they may occur at lower doses. Symptoms of acute exposure to organophosphate or cholinesterase-inhibiting compounds may include the following: numbness, tingling sensations, incoordination, headache, dizziness, tremor, nausea, abdominal cramps, sweating, blurred vision, difficulty breathing or respiratory depression, and slow heartbeat. Very high doses may result in unconsciousness, incontinence, and convulsions or fatality. Toxicity appears to vary with age, with the young being more susceptible [8]. Several poisoning cases involved workers from 16 to 18 years old, wearing inadequate protection while applying phorate to crops, or working around machines used to apply phorate [2,8]. Studies indicate that direct eye exposure may cause blurring, tearing, and ocular pain [2].
• Chronic toxicity: Repeated low-level exposures may result in cholinesterase inhibition and the associated neurological and neuromuscular effects [2]. A survey of workers exposed to phorate revealed toxic effects in 60% of the males tested (after a 2-week exposure). Symptoms included a lowering of the heart rate. Effects on cholinesterase in the blood of the workers were also noted in this study [2,8]. In a study on dogs, moderate to high doses of phorate 6 days each week for 13 to 15 weeks lowered cholinesterase activity, but produced no tissue damage [87].
• Reproductive effects: Long-term studies of mice fed high doses of 98.7% pure phorate showed no effects on fertility, gestation, or viability [87]. Maternal and embryo toxicity occurred at dietary doses of 0.5 mg/kg/day fed to rats [88]. Available data suggest that phorate is unlikely to cause reproductive effects.
• Teratogenic effects: No birth defects were found in two studies on the rat [87,88]. Available data suggest that phorate does not cause birth defects.
• Mutagenic effects: Studies of phorate in both bacterial systems or in mice indicate that it is nonmutagenic [2].
• Carcinogenic effects: Studies in both rats and mice produced no evidence of carcinogenicity [88].
• Organ toxicity: Phorate's main target organ, as determined by animal testing and human use experience, is the nervous system.
• Fate in humans and animals: Phorate is readily absorbed by the skin and the gastrointestinal tract. The major breakdown products of phorate in mammals are more toxic and have greater anticholinesterase activity than phorate [2]. Phorate may have a long residence time in mammalian systems; for example, rats given a high oral dose excreted less than 40% in 6 days. The liver, kidney, lung, brain, and glandular tissue held the remaining residues [89].

Ecological Effects:

• Effects on birds: Phorate is very highly toxic to highly toxic to birds. The reported acute oral LD50 values are 12.8 mg/kg in chukar, 7.5 mg/kg in starlings, 0.6 to 2.5 mg/kg in mallards, 7 to 21 mg/kg in northern bobwhite quail, 1 mg/kg in red-winged blackbirds, and 7 mg/kg in ring-neck pheasants [6]. The 5- to 8-day dietary LC50 values are reported as 370 to 580 ppm in Japanese quail, mallard, northern bobwhite quail, and ring-neck pheasant [6].
• Effects on aquatic organisms: Phorate is very highly toxic to fish. Reported 96-hour LC50 values range from 2 to 13 ug/L in cutthroat trout, bluegill sunfish and largemouth bass. Other 96-hour LC50 values are 110 ug/L in northern pike and 280 ug/L in channel catfish [16]. Reported 96-hour LC50 values for the compound in freshwater invertebrates such as stoneflies and scuds are 4 ug/L, also indicating very high toxicity. Other LC50 values are 0.006 ug/L for amphipods and 0.11 to 1.9 ug/L in other freshwater invertebrates [88]. The acute oral LD50 of phorate is 85 mg/kg in bullfrogs [6].
• Effects on other organisms: Phorate is toxic to bees, with a reported topical application LD50 of 10 ug per bee [13].

Environmental Fate:

• Breakdown in soil and groundwater: Phorate is of moderate persistence in the soil environment, with reported field half-lives of 2 to 173 days. A representative value may be approximately 60 days [19]. Actual residence times may be influenced by soil clay and organic matter content, rainfall, and soil pH [8]. Soil treatments often leave more residues in plants than foliar treatments, because the compound persists in the soil and is readily taken up by plant roots [13,8]. Phorate binds moderately well to most soils and is slightly soluble in water [19]. It should therefore not be highly mobile in most soils, and should mainly be transported with runoff via sediment and water. Phorate has minimal potential to leach through the soil and contaminate groundwater. This is most likely where soils are sandy and aquifers are shallow. Field studies indicate that leaching is very low in soils high in clay and organic matter content, and lower in sandy soils [8].
• Breakdown in water: The half-life of phorate in acidic water solutions is between a few days and a few weeks, depending on temperature; the half-life in alkaline (basic) water may be much shorter [8,88]. Phorate is degraded by waterborne microorganisms and hydrolysis [8,88]. As it breaks down in water, nontoxic, water-soluble products are formed.
• Breakdown in vegetation: Phorate itself is not persistent in plants, but plants metabolize phorate to very potent anticholinesterase agents such as the sulfoxide and sulfone derivatives of the compound [2]. This activity will usually peak several days following application before decreasing [8]. Phorate and its soil metabolites are absorbed from the soil by plant roots and are translocated to above-ground portions of the plant. Following treatment with a 10% granular formulation at 1 pound a.i./acre, phorate residues persisted at very low levels for 28 days in the kernels, cobs, or husks. After 83 days, there were no detectable residues of phorate or breakdown products [8].

Physical Properties:

• Appearance: Technical phorate is a clear liquid at room temperature [13].
• Chemical Name: O,O-diethyl S-ethylthiomethyl phosphorodithioate [13]
• CAS Number: 298-02-2
• Molecular Weight: 260.38
• Water Solubility: 50 mg/L @ 25 C [13]
• Solubility in Other Solvents: v.s. in xylene, carbon tetrachloride, dioxane, methyl cellosolve, dibutylphthalate vegetable oils, ethanol, ether, and aliphatic hydrocarbons [13]
• Melting Point: Less than -15 C [13]
• Vapor Pressure: 110 mPa @ 20 C [13]
• Partition Coefficient: 3.9248 [13]
• Adsorption Coefficient: 1000 (estimated) [19]

Exposure Guidelines:

• ADI: 0.0002 mg/kg/day [38]
• MCL: Not Available
• RfD: Not Available
• PEL: Not Available
• HA: Not Available
• TLV: 0.05 mg/m3 (8-hour) (skin) [47]

Basic Manufacturer:

American Cyanamid Co.
One Cyanamid Plaza
Wayne, NJ 07470-8426

• Phone: 201-831-2000
• Emergency: 201-835-3100
  

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.