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The information in this profile may be out-of-date.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

Coumaphos

Trade and Other Names: Trade names include Agridip, Asunthol, Bay 21, Baymix, Co-Ral, Dilice, Meldame, Muscatox, Negashunt, Resistox, Suntol, and Umbethion.

Regulatory Status: The U.S. Environmental Protection Agency (EPA) classifies most formulations of coumaphos as General Use Pesticides (GUPs). The formulations 11.6% EC and 42% flowable concentrate end-use products have been classified as Restricted Use Pesticides (RUPs) because they pose a hazard of acute poisoning from ingestion. RUPs may be purchased and used only by certified applicators. Coumaphos is classified as toxicity class II - moderately toxic. Products containing coumaphos bear the Signal Word WARNING.

Chemical Class: organophosphate

Introduction: Coumaphos is an organophosphate insecticide used for control of a wide variety of livestock insects, including cattle grubs, screw worms, lice, scabies, flies, and ticks. It is used against ectoparasites, which are insects that live on the outside of host animals such as sheep, goats, horses, pigs, and poultry. It is added to cattle and poultry feed to control the development of fly larvae that breed in manure. It is also used as a dust, dip, or spray to control mange, horn flies, and face flies of cattle. Because of its low toxicity to fish, it is also used in water as an agent to control mosquito larvae. Coumaphos is considered a selective insecticide because it kills specific insect species while sparing other non-target organisms.

Formulation: It is added to catte and poultry feed to control the development of fly larvae that breed in manure. It is also used as a dust, dip, or spray to control mange, horn flies, and face flies of cattle. Because of its low toxicity to fish, it is also used in water as an agent to control mosquito larvae.

Toxicological Effects:

• Acute toxicity: Coumaphos is highly toxic by ingestion, and moderately toxic by inhalation and dermal absorption [8]. As with all organophosphates, coumaphos is readily absorbed through the skin. Skin and eye contact with this insecticide may cause mild irritation, as well as cholinesterase inhibition. Coumaphos does not cause skin sensitization allergies [18]. Toxic symptoms in humans are largely caused by the inhibition of cholinesterase. Individuals with respiratory ailments, impaired cholinesterase production, or with liver malfunction may be at increased risk from exposure to coumaphos. High ambient temperatures or exposure to UV light may increase the toxicity of coumaphos [8]. Signs of poisoning include diarrhea, drooling, difficulty in breathing, and leg and neck stiffness [41]. Some of the symptoms of acute inhalation of coumaphos include headaches, dizziness and incoordination. Moderate poisoning is characterized by muscle twitching and vomiting. Severe poisoning is indicated by diarrhea, fever, toxic psychosis, fluid retention (edema) of the lungs, and high blood pressure. Symptoms of sublethal poisoning may continue for 2 to 6 weeks [8]. Some organophosphates may cause delayed symptoms beginning 1 to 4 weeks after an acute exposure that may or may not have produced immediate symptoms. In such cases, numbness, tingling, weakness, and cramping may appear in the lower limbs and progress to incoordination and paralysis. Improvement may occur over months or years, and in some cases residual impairment will remain [8]. The oral LD50 for coumaphos is 13 41 mg/kg in rats, 28 to 55 mg/kg in mice, 58 mg/kg in guinea pigs, and 80 mg/kg in rabbits [8,2]. The dermal LD50 is 860 mg/kg in rats, and 500 to 2400 mg/kg in rabbits [18]. The 1-hour inhalation LC50 for coumaphos is 0.34 mg/L in female and 1.1 mg/L in male rats [18].
• Chronic toxicity: Repeated or prolonged exposure to organophosphates may result in the same effects as acute exposure, including the delayed symptoms. Other effects reported in workers repeatedly exposed include impaired memory and concentration, disorientation, severe depressions, irritability, confusion, headache, speech difficulties, delayed reaction times, nightmares, sleepwalking, and drowsiness or insomnia. An influenza-like condition with headache, nausea, weakness, loss of appetite, and malaise has also been reported [8].
• Reproductive effects: Once in the bloodstream, coumaphos may cross the placenta. Mice fed coumaphos at a dietary level of 100 mg/kg/day exhibited a decrease in the number of pregnancies, litter size, and surviving offspring. No reproductive effects were observed in three generations of mice fed dietary doses of 1.25 mg/kg/day [8]. Coumaphos is unlikely to cause reproductive effects in humans at expected exposure levels.
• Teratogenic effects: Based on studies with rats and rabbits, coumaphos does not appear to be teratogenic [18]. No developmental effects occurred in rat offspring at maternal doses up to 25 mg/kg/day. Similar results were observed when pregnant rabbits were given doses of up to 18 mg/kg/day on days 7 to 19 of pregnancy [54]. No increase in embryonic deaths or teratogenesis was observed in heifers given dermal applications of coumaphos during various stages of gestation [8].
• Mutagenic effects: Gene mutations and DNA damage studies performed on bacterial cultures showed no evidence of mutagenicity [18,54].
• Carcinogenic effects: Coumaphos was not found to be carcinogenic in tests done on mice and rats. There was no increase in the number of tumors reported in rats given doses of 1.25 or 5 mg/kg/day of coumaphos in a 2-year chronic feeding study [55].
• Organ toxicity: Coumaphos primarily affects the nervous system through cholinesterase inhibition, the blockage of an enzyme required for proper nerve functioning. No organ effects were seen in acute or chronic studies of coumaphos.

• Fate in humans and animals: Following oral administration to mammals, coumaphos is rapidly broken down into nontoxic products which are eliminated in urine and feces with no evidence of bioaccumulation [18]. Some 70% of an oral dose given to rats was eliminated in 7 days. With dermal doses, 5% was eliminated. Single oral doses produced no changes in metabolism and no evidence of bioaccumulation in rats [54]. Coumaphos was found in the milk of dermally treated cows [8]. Unchanged coumaphos and other breakdown products were found in the excreta of hens that were dusted with the insecticide. Similar results were found after oral treatment of hens with coumaphos [8].

Ecological Effects:

• Effects on birds: Coumaphos is highly toxic to birds [18]. The symptoms of acute toxicity in mallards given a dietary concentration of 29.8 mg/kg include spraddle-legged walking, wing twitching, wing drop, tearing of the eyes, and spread wings. These symptoms persisted in some survivors for up to 13 days, accompanied by weight loss. Death usually occurred between 2 and 12 hours after treatment. Severe acute toxicity, and eventual death, was caused in hens after they were given daily oral doses of 10 mg/kg/day for 1 to 8 days. Hens given single oral doses of 50 mg/kg recovered from the initial effects of cholinesterase inhibition and developed signs of delayed nerve poisoning [8]. The oral LD50 for coumaphos is 3 mg/kg in wild birds, 29.4 mg/kg in mallard ducks, 7.94 mg/kg in pheasants, and 14 mg/kg in chickens [8,13].
• Effects on aquatic organisms: Coumaphos is moderately toxic to fish and highly toxic to aquatic invertebrates [8]. The LC50 (96-hour) in channel catfish is 0.8 mg/L, in largemouth bass is 1.1 mg/L, and in walleye is 0.8 mg/L [27,13]. The LC50 (96-hour) in rainbow trout is 5.9 mg/L, in bluegill sunfish is 5 mg/L, and in freshwater invertebrates (amphipods) is 0.00015 mg/L [18]. Coumaphos tends to accumulate slightly in fish. For example, bluegill sunfish showed a bioconcentration factor of 331 times the ambient water concentration; however, mortality was high among the fish at the concentrations tested (0.1 mg/L).
• Effects on other organisms: Coumaphos poses a moderate hazard to honeybees and a slight hazard to other beneficial insects [8].

Environmental Fate:

• Breakdown in soil and groundwater: Based on the general characteristics of organophosphates, coumaphos is expected to have low to moderate persistence in soil. Coumaphos was relatively immobile in a sandy loam soil and is unlikely to contaminate groundwater. A general characteristic of organophosphates such as coumaphos is that they bind fairly well to soil particles. Therefore, they do not readily move (leach) with water percolating through the soil [8].
• Breakdown in water: Coumaphos is resistant to breakdown in water (hydrolysis). It is nearly insoluble in water, and is stable over a wide pH range [8].
• Breakdown in vegetation: No data are currently available.

Physical Properties:

• Appearance: Technical coumaphos is a tan crystalline solid with a slight sulfur odor [13].
• Chemical Name: 3-chloro-7-diethoxyphosphinothioyloxy-4-methylcoumarin [13]
• CAS Number: 56-72-4
• Molecular Weight: 362.50
• Water Solubility: i.s. in water [11]; 1.5 mg/L at 20 C [13]
• Solubility in Other Solvents: acetone s.s.; chloroform s.s.; ethanol s.s. [13]
• Melting Point: 90-92 C (technical) [13]
• Vapor Pressure: 0.013m Pa @ 20 C [13]
• Partition Coefficient: Not Available
• Adsorption Coefficient: Not Available

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: Not Available
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Bayer Corporation
Animal Health
Box 390
Shawnee Mission, KS 66201

• Phone: 913-631-4800
• Emergency: Not Available
  

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.