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The information in this profile may be out-of-date.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

Phosmet

Trade and Other Names: Trade names for products containing the compound include Appa, Decemthion, Fesdan, Imidan, Kemolate, Prolate, PMC and Safidon. It is also found in combination with other insecticides such as carbophenothion.

Regulatory Status: Phosmet is a moderately toxic compound, falling in EPA toxicity class II. It is a General Use Pesticide (GUP). Products containing phosmet must bear the Signal Word WARNING on the label. Some tolerances for phosmet in processed foods were revoked by EPA in 1994.

Chemical Class: organophosphate

Introduction: Phosmet is a non-systemic, organophosphate insecticide used on both plants and animals. It is mainly used on apple trees for control of coddling moth, though it is also used on a wide range of fruit crops, ornamentals, and vines for the control of aphids, suckers, mites, and fruit flies. The compound is also an active ingredient in some dog collars. Phosmet is used on approximately 1.1 million acres in the U.S. each year.

Formulation: Not Available

Toxicological Effects:

• Acute toxicity: Phosmet is moderately toxic via the oral route, with a reported acute oral LD50 of 113 to 160 mg/kg in rats [6,13]. It is slightly toxic via the dermal route, with a dermal LD50 of 3160 to greater than 4640 mg/kg in rabbits [6,13]. Phosmet is a mild irritant to the eyes, and only mildly irritating to the skin of rabbits [13]. Via the inhalation route it is slightly toxic as well, with a reported 1-hour inhalation LC50 value of 2.76 mg/L [8,13]. Signs of acute poisoning are rapid, generally occurring within 30 minutes after exposure. The principal effects due to acute exposure to phosmet are similar to those caused by acute effects of other organophosphate pesticides (e.g., inhibition of cholinesterase) [90]. 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.
• Chronic toxicity: Rats fed phosmet for 16 weeks at 22.5 to 300 mg/kg/day suffered some mortality and exhibited a number of toxic effects [90]. Over a 6-month period, doses of phosmet of 1 mg/kg/day in the diets of rats produced no observable chronic effects [8,90]. Doses of 1 mg/kg/day in a 2-year feeding study also produced no effects [8,90]. Rabbits which had phosmet applied to their skin for 5 days a week for 3 weeks suffered high mortality rates at doses of 300 to 600 mg/kg/day. At 50 mg/kg/day there was significant brain enzyme (cholinesterase) depression [8]. The signs and symptoms of chronic toxicity are generally consistent with those for the class of organophosphate insecticides.
• Reproductive effects: A three-generation study with rats indicated that there were no reproductive effects when the animals were fed phosmet at a dose of 2.0 mg/kg/day during gestation days for the first generation, and a dose of 4 mg/kg/day for the second and third generations [8]. Female rabbits given phosmet both dermally and orally for 3 weeks prior to mating and for 18 consecutive days of gestation showed no effects on reproductive parameters. The doses tested ranged from 10 to 60 mg/kg/day for both routes of exposure [91]. These data indicate that phosmet does not cause reproductive toxicity.
• Teratogenic effects: No birth defects were noted in studies with pregnant rabbits fed 10 to 60 mg/kg/day for 3 weeks during pregnancy or in monkeys given 8 to 12 mg/kg/day on days 22 to 32 of gestation. Offspring from rats fed 10 to 30 mg/kg/day on days 6 through 15 of gestation showed no abnormalities. In another study, however, doses of 30 mg/kg/day administered to rats between day 9 and 13 of gestation, produced a dose-dependent increase in brain damage (hydrocephaly) in 33 of the 55 embryos examined [91]. These data suggest that phosmet is not likely to cause teratogenic effects.
• Mutagenic effects: Almost all tests of phosmet on bacteria indicate that it does not cause any mutations [90]. However, there is a suggestion that workers producing the compound Safidon show some changes in their chromosomes [8]. A definite conclusion cannot be drawn from current evidence.
• Carcinogenic effects: Rats fed diets containing 1 to 20 mg/kg/day of phosmet for 2 years showed no increase in cancer. However, a 2-year mouse study showed that phosmet is associated with a significant increase in liver tumors in male mice [90]. In female mice, there was a positive dose-related trend for liver tumors and carcinomas [90]. The available data are not sufficient to draw a firm conclusion about the carcinogenicity of phosmet.
• Organ toxicity: The primary target organ for phosmet is the nervous system.

• Fate in humans and animals: Phosmet is rapidly absorbed, distributed, and eliminated in mammals; rats given single doses of 23 to 35 mg/kg phosmet excreted greater than 75% of the dose in urine and about 15% in the feces. Less than 3% was found in body tissues after 2 days [91]. Other studies show nearly 80% eliminated in the urine and 20% eliminated in the feces after 3 days [90]. Rat studies indicate that phosmet crosses the placenta [8]. Phosmet's breakdown products in steers include phthalamic and phthalic acids [8]. The situation is similar in other other animal systems as well; the major metabolite is phthalamic acid with phthalic acid produced in smaller quantities [13].

Ecological Effects:

• Effects on birds: Phosmet is variable in its toxicity to birds. In red-wing blackbirds it is highly toxic, with a reported acute oral LD50 of 18 mg/kg. In starlings and pheasants, it is moderately toxic with reported acute oral LD50 values of greater than 100 mg/kg and 237 mg/kg, respectively. In mallards, it is only slightly toxic with a reported acute oral LD50 of 1830 mg/kg. The 5- to 8-day dietary LC50 values (greater than 2000 ppm) indicate slight toxicity in Japanese quail, mallard, and ring-neck pheasant [6]. Phosmet may be moderately toxic to northern bobwhite quail, with a reported dietary LC50 of 501 ppm [6]. Phosmet can cause reproductive difficulties in birds whose feed contains phosmet residues [92]. No delayed neurotoxic effects were noted in chickens fed diets containing moderate levels of phosmet for 6 weeks [92].
• Effects on aquatic organisms: Phosmet's toxicity to aquatic organisms is species-specific, varying from highly to very highly toxic. The reported 96-hour LC50 values for phosmet are less than 1 mg/L in bluegill sunfish, small- and largemouth bass, rainbow trout, and chinook salmon, and are less than 10 mg/L in fathead minnow and channel catfish [16]. The reported 96-hour LC50 values in aquatic invertebrates and crustaceans such as Daphnia spp., scuds, and sideswimmers indicate very high toxicity [16]. Phosmet has a reported bioconcentration factor of 6 to 37 in fish [90], indicating it has very little potential for accumulation in aquatic organisms.
• Effects on other organisms: Phosmet is very toxic to honeybees; the contact LD50 for the compound is 0.0001 mg per bee [13].

Environmental Fate:

• Breakdown in soil and groundwater: Phosmet is of low persistence in the soil environment, with reported field half-lives of 4 to 20 days. A representative half-life may be about 19 days [19]. Phosmet is rapidly broken down in soil to nontoxic products [6,13]. Degradation is by hydrolysis (the chemical action of water) and microbial action, and may be faster under wet, basic conditions [6]. It is moderately bound by soils, and not highly soluble in water [19], and thus is not expected to be highly mobile or a significant risk to groundwater. There is little leaching or runoff associated with the compound, even after repeated applications [8].
• Breakdown in water: In water, phosmet is rapidly broken down by the chemical action of the water (hydrolysis) and by sunlight (photolysis) [90]. Under moderately acidic conditions (pH 5), half of the compound degrades within 9 days, but in neutral solution (pH 7), its half-life is 18 hours. Under alkaline conditions (pH 9), the half-life is reported as 16 hours [8,90].
• Breakdown in vegetation: Phosmet breaks down rapidly in plant systems, primarily due to passive oxidation and hydrolysis due to air contact [90]. The breakdown products are much less toxic than the parent compound [13]. On apricots and nectarines treated at an unknown rates, there were residues of less than 5 mg/kg 7 days after treatment and less than 1 mg/kg 21 days after treatment [8]. Maize used for silage showed a rapid decline in residues before being made into silage, but the half-life of the silage residue was about 92 days [8]. Washing and blanching of fruits and vegetables can reduce residue levels by 50 to 80% and thus reduce the potential human exposure to the pesticide [91].

Physical Properties:

• Appearance: Technical phosmet is an off-white to pink solid at room temperature [13].
• Chemical Name: O,O-dimethyl S-phthalimidomethyl phosphorodithioate [13]
• CAS Number: 732-11-6
• Molecular Weight: 317.33
• Water Solubility: 25 mg/L @ 25 C [13]
• Solubility in Other Solvents: v.s. in acetone, xylene, methanol, benzene, toluene, and methyl isobutyl ketone; s. in kerosene
• Melting Point: 66-69 C (technical) [13]
• Vapor Pressure: 133 m Pa @ 50 C [13]
• Partition Coefficient: 3.0414 [13]
• Adsorption Coefficient: 820 [19]

Exposure Guidelines:

• ADI: 0.02 mg/kg/day [38]
• MCL: Not Available
• RfD: 0.02 mg/kg/day [53]
• PEL: Not Available
• HA: Not Available
• 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.