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The information in this profile may be out-of-date.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

Fenamiphos

Trade and Other Names: Trade names for products containing fenamiphos include Bay 68138, Nemacur and Phenamiphos. It may also be found in formulations with other pesticides such as isofenphos, carbofuran and disulfoton.

Regulatory Status: Fenamiphos is an highly toxic compound in EPA toxicity class I. It is a Restricted Use Pesticide (RUP). RUPs may be purchased and applied only by a certified applicator. Labels for products containing fenamiphos must carry the Signal Word DANGER.

Chemical Class: organophosphate

Introduction: Fenamiphos is an organophosphate nematicide used to control a wide variety of nematode (roundworm) pests. Nematodes can live as parasites on the outside or the inside of a plant. They may be free living or associated with cyst and root-knot formations in plants. Fenamiphos is used on a variety of plants including tobacco, turf, bananas, pineapples, citrus and other fruit vines, some vegetables, and grains. The compound is absorbed by roots and is then translocated throughout the plant. Fenamiphos, as is typical of other organophosphates, blocks the enzyme acetylcholinesterase in the target pest. The pesticide also has secondary activity against other invertebrates such as sucking insects and spider mites. It is available in emulsifiable concentrate, granular, or emulsion formulations.

Formulation: It is available in emulsifiable concentrate, granular, or emulsion formulations.

Toxicological Effects:

• Acute toxicity: Fenamiphos is highly toxic via the oral route, with reported LD50 values of 2 to 19 mg/kg in the rat and 56 to 100 mg/kg in guinea pigs. It is also highly toxic to dogs and rabbits [8,13]. The acute dermal toxicity of the compound is also high, with reported dermal LD50 values of 72 to 154 mg/kg in rats [8,13]. The inhalation toxicity of the compound is also high, with reported inhalation LC50 values in rats of 0.11 to 0.17 mg/L [8,13]. Longer exposures at moderately lower concentrations also caused rat mortality [8]. The compound has the potential to cause significant eye damage at acute exposure levels. It is nonirritating to the skin [13]. Symptoms of acute toxic exposure to the nematicide are consistent with those of other organophosphate compounds and include difficulty in breathing, diarrhea, urination, and slowness of the heart. Other symptoms include muscle twitching and tremors [8,13].
• Chronic toxicity: A number of long-term feeding studies have been conducted with this compound on several different species of animals. In dogs, dietary doses of 0.0125 to 0.25 mg/kg/day over 2 years produced depressions in cholinesterase activity at middle doses and above. No effects were noted in the liver or in blood chemistry even at the highest dose [8]. Rats exposed to 1.5 mg/kg/day over 2 years experienced increases in thyroid gland and lung weights in females, and increased heart weight in males. There were no organ weight changes noted in the rats at doses below 0.5 mg/kg/day [64]. Brain weights have also been affected by exposure to moderate amounts of the compound [8]. Two studies have been conducted on the potential risk to pesticide workers (loaders and applicators) from the use of Nemacur. One study concluded that occupational exposure levels were more than 100 times lower than the level which causes cholinesterase inhibition in animals and thus the use of the compound did not pose a significant risk to the users [8]. Another study concluded that the main threat to applicators was through the skin on the hands. However, the levels of exposure on the hands were significantly below the level that had caused chronic toxicity in mice. It was concluded that the pesticide could be used safely [65].
• Reproductive effects: Both male and female rats fed moderate to high doses of fenamiphos (0.15 to 1.5 mg/kg/day) over three generations showed no compound-related reproductive effects at the middle doses tested (0.5 mg/kg/day). At the higher doses the second generation of pups showed a decrease in body weight gain. This effect was not seen in the third generation [64]. It is unlikely that this compound would cause reproductive effects in humans.
• Teratogenic effects: A single study of pregnant rats fed fenamiphos during gestation over a range of doses (up to 1 mg/kg/day) showed a decrease in the maternal weight at doses of 0.3 mg/kg/day and above. At the highest dose a higher number of the pups from the exposed group had died relative to the unexposed controls, and the pups which survived had decreased weights [64]. In tests with pregnant rabbits fed up to 0.4 mg/kg, no birth defects were noted [8]. However, another reference stated that teratogenic studies were positive in rabbits, though the effects in the offspring were induced at doses much higher than those that cause maternal toxicity [8]. The results from these studies suggest that teratogenic effects in humans are unlikely.
• Mutagenic effects: A number of studies evaluating the mutagenic potential of fenamiphos have all shown the compound to be nonmutagenic. The test subjects included bacterial cells and male mice [8,64].
• Carcinogenic effects: Two studies, one conducted with mice and the other with rats, indicated that fenamiphos is not carcinogenic [8,64]. One study was conducted for 1 1/2 years at very high levels (up to 7.5 mg/kg/day in mice) and the other study was conducted over 2 years (up to 1.5 mg/kg/day in rats) [64].
• Organ toxicity: Target organs identified in studies of test animals and exposed workers are the central nervous system, heart, lungs, and thyroid.

• Fate in humans and animals: Fenamiphos is readily absorbed through the digestive tract and lungs. One study placed the amount absorbed near 95% of the ingested dose. The compound is rapidly broken down within the organism, and the by-products are excreted in the urine. The majority of a dose was recovered in urine within 15 hours after treatment [65].

Ecological Effects:

• Effects on birds: Fenamiphos is very highly toxic to birds, with a reported acute oral LD50 for the most sensitive species tested, the ring-necked pheasant, of 0.5 mg/kg [6]. LD50 values for other species range from 1.0 to 2.4 mg/kg, all of which indicate that this is a very highly toxic compound [6]. In a controlled experiment, fenamiphos was determined to be the most toxic of thirteen different cholinesterase inhibitors [66]. In tests with wild songbirds (red-winged blackbirds and house sparrows) an unspecified dose of Nemacur was highly toxic to these species, with death of the birds occurring within an hour of eating the granules [66].
• Effects on aquatic organisms: The toxicity of fenamiphos to aquatic species varies from moderate to high. Bluegill sunfish are extremely sensitive to the presence of the compound. The LC50 for fenamiphos is 9.6 mg/L in this species. Other species tested include the rainbow trout (LC50 is 0.11 mg/L) and the goldfish (LC50 is 3.2 mg/L) [8]. The compound is not expected to bioaccumulate appreciably in aquatic organisms [6].
• Effects on other organisms: Fenamiphos is practically nontoxic to honeybees [8].

Environmental Fate:

• Breakdown in soil and groundwater: Fenamiphos is of moderate persistence in the soil environment, with a reported soil half-life of about 50 days [19]. The compound appears to have no effect on the activity of soil bacteria [8]. Aerobic processes are most important for breakdown of the compound. Fenamiphos is not strongly adsorbed to soils [19], but neither it nor its breakdown products have been found in over 1200 wells tested in six states.
• Breakdown in water: Fenamiphos disappears quickly from water in acidic and alkaline water, but it is stable in neutral water when held in the dark. The compound, when in the presence of artificial light, disappears very rapidly. In a neutral solution, half of the initial amount of the compound degraded within 4 hours.
• Breakdown in vegetation: In plants, the compound is absorbed through the roots and translocated to the leaves. It is broken down within the plant. The products of its breakdown are relatively persistent and can also inhibit cholinesterase [6].

Physical Properties:

• Appearance: Fenamiphos is a colorless crystal in its pure form, or a tan waxy solid in the technical form [13].
• Chemical Name: ethyl 4-methylthio-m-tolyl isopropylphosphoramidate [13]
• CAS Number: 22224-92-6
• Molecular Weight: 303.40
• Water Solubility: 700 mg/L @ 20 C [13]
• Solubility in Other Solvents: s. in dichloromethane, isopropanol, and toluene [13]
• Melting Point: 46 C (technical) [13]
• Vapor Pressure: 0.12 mPa @ 20 C [13]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 100 [19]

Exposure Guidelines:

• ADI: 0.005 mg/kg/day [38]
• MCL: Not Available
• RfD: 0.00025 mg/kg/day [53]
• PEL: Not Available
• HA: 0.002 mg/L (lifetime) [64]
• TLV: 0.1 mg/m3 (8-hour) (skin) [47]

Basic Manufacturer:

Miles, Inc.
P.O. Box 4913
8400 Hawthorn Road
Kansas City, MO 64120

• Phone: 816-242-2429
• Emergency: 816-242-2582
  

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.