E X T O X N E T
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A Pesticide Information Project of Cooperative Extension Offices of
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Pesticide
Information
Profile
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Fenamiphos
Publication Date: 5/94
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TRADE OR OTHER NAMES
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.
REGULATORY STATUS
Fenamiphos is a Restricted Use Pesticide (RUP). Restricted Use
Pesticides may be purchased and applied only by a certified applicator.
INTRODUCTION
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).
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
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).
CHRONIC TOXICITY
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).
ECOLOGICAL EFFECTS
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).
ENVIRONMENTAL FATE
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).
PHYSICAL PROPERTIES AND GUIDELINES
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 |
BASIC MANUFACTURER
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
REFERENCES
The Agrochemicals Handbook: Third Edition. (1991). Royal Society of
Chemistry, Unwin Brothers Ltd., Surrey, England.
American Conference of Governmental Industrial Hygienists, Inc. (1991).
Documentation of the Threshold Limit Values and Biological Exposure Indices:
Sixth Edition, Volume I.
Integrated Risk Information System. (1993). National Library of
Medicine. Medlars. Bethesda, MD.
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.
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.
U.S. Environmental Protection Agency. (1988). Health Advisories for
50 Pesticides. Fenamiphos. Office of Drinking Water.
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.
Smith, Gregory J. (1993). Toxicology & Pesticide Use in Relation to
Wildlife: Organophosphorus & Carbamate Compounds. C.K. Smoley. Boca Raton,
FL.
The Farm Chemicals Handbook. (1992). Meister Publishing Company.
Willoughby, OH.
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.
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.
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site is not a substitute for a pesticide label. Trade names used herein
are for convenience only; no endorsement of products is intended, nor is
criticism of unnamed products implied. Most of this information is historical
in nature and may no longer be applicable.
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