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Extension Toxicology Network

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


Publication Date: 5/94


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


Fenamiphos is a Restricted Use Pesticide (RUP). Restricted Use Pesticides may be purchased and applied only by a certified applicator.


Fenamiphos is an organophosphate insecticide (nematicide) which is used to control a wide variety of nematode (round worm) pests. Nematodes can live as parasites on or within 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, cocoa, turf, bananas, pineapples, citrus and other fruit vines, and on some vegetables and grains.

The compound is absorbed by the roots and is then transported throughout the plant. Fenamiphos, similar to other organophosphates, blocks the enzyme acetyl cholinesterase in the target pest. The enzyme regulates inter-cellular activity. The pesticide is also active against non-target invertebrates such as sucking insects and spider mites (1).



Fenamiphos is a highly toxic poison that carries the signal word DANGER- POISON on its label. The symptoms of acute toxic exposure are consistent with those of other organophosphate compounds and include breathing difficulty, diarrhea, urination, and slowness of the heart. Other symptoms include muscle twitching and tremors.

The compound can cause acute toxic symptoms and death in rats at low doses. The LD50 of the compound ranges from 2 to 19 mg/kg/day in the rat and from 56 to 100 mg/kg/day in guinea pigs. It is also highly toxic to dogs and rabbits (2).

The acute toxicity of the compound, when applied to the skin of rats and mice, is also very high. Between 72 and 154 mg/kg/day caused the death of half of the rats (LD50). Breathing high concentrations of the compound has also resulted in mortality in rats (LC50 of 110 to 175 mg/m3). Extended exposure at moderately lower concentrations also caused rat mortality (2). The compound has the potential to cause significant eye damage at acute exposure levels. It is non-irritating to the skin (1).


A number of long-term feeding studies have been conducted with this compound on several different species of animals. Dogs fed low doses (from 0.0125 to 0.25 mg/kg/day) of fenamiphos for two years experienced a depression in their cholinesterase activity at the middle doses and above. No effects were noted in the liver or in blood chemistry even at the highest dose (3). Rats fed low amounts of fenamiphos over a two year period showed no effects at or below the 0.5 mg/kg/day dose level (3). The evidence that even small amounts of fenamiphos can cause cholinesterase inhibition in animals suggests that there is the potential for effects in humans exposed to small amounts of the compound over time.

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 (4). Another study concluded that the main threat to applicators was through the skin of the hands. However, the levels of exposure on the hands were significantly below the level that caused chronic toxicity in mice. It was concluded that the pesticide could be used safely (5).

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 0.5 mg/kg dose. 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. The no effect level for reproductive effects was therefore set at the top dose of 1.5 mg/kg, which is close to the lethal dose (6).

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 number of the pups had died and the pups which survived had decreased weights (6).

No birth defects were noted when pregnant rabbits were fed up to 0.4 mg/kg (2). However, another study indicated that teratogenic studies were positive in rabbits, though birth defects in the offspring were induced at doses much higher than doses that caused maternal toxicity (3).

In another study pregnant rats which were fed fenamiphos during gestation over a range of doses (0.25 to 3.0 mg/kg/day) showed maternal tremors and mortality at 3.0 mg/kg/day. No developmental toxicity was observed at any dose (11).

The results from the studies on reproductive and teratogenic effects indicate that such effects occurred only at levels that caused overt maternal toxicity and are likely indirect consequences of this toxicity.

Mutagenic Effects

A number of studies evaluating the mutagenic potential of fenamiphos have all shown the compound to be non-mutagenic. The tests were conducted on bacterial cells and with male mice (2, 6).

Carcinogenic Effects

Two studies, one conducted with mice and the other with rats, produced no compound-related carcinogenicity (2, 6). In one eighteen month study, mice were fed very high levels of fenamiphos, up to 7.5 mg/kg/day. In a two year study, rats were fed up to 1.5 mg/kg/day of fenamiphos. Thus, there is no evidence suggesting that fenamiphos is a carcinogen (6).

Organ Toxicity

In a two year study, rats exposed to moderate or high levels of the compound (up to 1.5 mg/kg) experienced increases in 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 (6). Brain weights have also been affected by exposure to moderate amounts of the compound (7). The data suggests that humans are unlikely to experience significant risk of organ toxicity from this compound.

Fate in Humans and Animals

Fenamiphos is readily absorbed through the digestive tract and lungs. In a rat study, nearly 95% of the ingested dose was absorbed through the digestive tract. The compound is rapidly broken down within the organism and the byproducts are excreted in the urine. In rats over 50% of the dose was recovered in the urine within 15 hours after treatment (6).


Effects on Birds

Fenamiphos is acutely toxic to birds (8). The acute LD50 for the most sensitive species tested, the ring-necked pheasant, is 0.5 mg/kg. LD50 values for other bird species range from 1.0 to 2.4 mg/kg which indicates that fenamiphos is a very highly toxic compound (8). In studies of wild songbirds, red-winged blackbirds and house sparrows were fed granules containing 15% active ingredient of fenamiphos. Forty percent of the red- winged blackbirds died after eating 5 granules and 60% died after eating 10 granules containing fenamiphos. Forty percent of the house sparrows died after eating 5 granules and 80% died after eating 10 granules containing fenamiphos. Fenamiphos, as compared to other pesticides, is very toxic to birds because on average, the house sparrows died 27 minutes after eating the granules (10). When fenamiphos was applied to an area to control nematodes within ornamental bushes, an estimated 400-500 cedar waxwings died after they fed on the bushes' berries and blossoms. Fenamiphos was found in the birds' digestive tracts. No estimate of the total amount of the compound ingested was made (8).

Effects on Aquatic Organisms

The toxicity of fenamiphos to fish species varies from moderate to high. Bluegill sunfish are extremely sensitive to the presence of the compound. The LC50 of fenamiphos is 0.0096 mg/l for this species. Other species tested include rainbow trout (LC50 of 0.11 mg/l) and goldfish (LC50 of 3.2 mg/l) (1). No information was available about the effect of fenamiphos on aquatic invertebrates or other aquatic species.

The compound is not expected to bioaccumulate appreciably in aquatic organisms (8).

Effects on Other Organisms (Non-target species)

It is practically non-toxic to honey bees (9).


Breakdown of Chemical in Soil and Groundwater

The fate of fenamiphos in soil and in water is well documented. In a clay-loam soil with 3 ppm containing fenamiphos, half of the initial amount of the compound was breaks down within four days and only 17% of the compound remained 55 days later. When sandy loam soil containing 20 ppm fenamiphos was irradiated with artificial light, 6% of the compound remained after two days. Therefore, if the compound is incorporated into the soil where light cannot reach it, decomposition will be slower.

Sandy loam soil was leached with 22.5 inches of water 30 days after fenamiphos was applied (4 lbs./acre). Approximately 2.3% of the compound leached from the 12 inch column of soil sample and about 91% of the applied fenamiphos remained in the top five inches of the soil column (6).

The compound appears to have no effect on the activity of soil bacteria (1).

Fenamiphos has been found in only two ground water samples out of 452 analyzed. Both locations were in California with the highest concentration found being 0.005 mg/l. No surface water locations were tested (6).

Breakdown of Chemical in Surface Water

Fenamiphos degrades in acidic and alkaline water more quickly than in neutral water when held in the dark. In the presence of artificial light, the compound disappears very rapidly. In a neutral solution, half of the initial amount of the compound degraded within four hours.

Breakdown in Vegetation

In plants, the compound is absorbed through the roots and distributed to the leaves. It is broken down within the plant. The products of its breakdown are relatively persistent and can also inhibit cholinesterase, an enzyme which regulates inter-cellular activity (8).


Fenamiphos is a colorless crystal or a tan, waxy solid. It is non- corrosive to metals and breaks down readily in strong acids and bases.

Exposure Guidelines:

RfD: 0.00025mg/kg/day
HA: 0.002 mg/l (lifetime)
ADI: 0.0005 mg/kg
PEL: 0.1 mg/m3

Physical Properties:

Common name: fenamiphos
CAS#: 22224-92-6
Chemical name: ethyl 4-methylthio-m-tolyl isopropylphosphoramidate
Molecular Weight: 303.40 g/mol
Solubility in water: 700 mg/l @ 20 degrees C
Solubility in Solvents: Readily soluble in dichloromethane, isopropanol and toluene
Vapor pressure: 0.12 mPa at 20 degrees C
Partition coefficient (octanol/water) (log): N/A
Adsorption coefficient: 200
Chemical class/use: Organophosphate pesticide


Miles Inc.
Agricultural Chemicals Division
8400 Hawthorn Road
P.O. Box 4913
Kansas City, MO 64120
Emergency: (816) 242-2582
Telephone: (816) 242-2000
Fax: (816) 242-2592

Review by Basic Manufacturer:

Comments solicited: April, 1993
Comments received: June, 1993


  1. The Agrochemicals Handbook: Third Edition. (1991). Royal Society of Chemistry, Unwin Brothers Ltd., Surrey, England.
  2. American Conference of Governmental Industrial Hygienists, Inc. (1991). Documentation of the Threshold Limit Values and Biological Exposure Indices: Sixth Edition, Volume I.
  3. Integrated Risk Information System. (1993). National Library of Medicine. Medlars. Bethesda, MD.
  4. Wang, R.G., K.C. Jacobs and S. Frederickson. (1983). A Study of Dermal and Inhalation Exposure of Mixer-Loaders and Applicators to Nemacur in Fresno and Tulare Counties of California. Worker Health and Safety Unit, Division of Pest Management. Environmental Protection and Worker Safety, California Department of Food and Agriculture.
  5. Knaak, J.B., K.C. Jacobs and G.M. Wang. (1986). Estimating the hazard to Humans Applying Nemacur 3EC With Rat Dermal-Dose ChE Response Data. Bulletin of Environmental Contamination and Toxicology, 37: 159-163.
  6. U.S. Environmental Protection Agency. (1988). Health Advisories for 50 Pesticides. Fenamiphos. Office of Drinking Water.
  7. Hayes, R.H., D.W. Lamb and D.R. Mallicoat. (1982). Technical Fenamiphos Oncogenicity Study in Mice. Report No. 3037. MRID 00098614. In Health Advisories for 50 Pesticides. U.S. EPA. 1988.
  8. Smith, Gregory J. (1993). Toxicology & Pesticide Use in Relation to Wildlife: Organophosphorus & Carbamate Compounds. C.K. Smoley. Boca Raton, FL.
  9. The Farm Chemicals Handbook. (1992). Meister Publishing Company. Willoughby, OH.
  10. Balcomb, R., R. Stevens and C. Bowen, II. (1984). Toxicity of 16 Granular Insecticides to Wild-Caught Songbirds. Bulletin of Environmental Contamination and Toxicology, 33: 302-307.
  11. Clemens, G.R., C.M. Troup, and R.E. Hartnagel, Jr. (1989). Teratology Study in the Rat with Nemacur Technical. Miles Inc. Agriculture Division Report No. 99650, Elkhart, IN, Unpublished report.