E X T O X N E T
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
Publication Date: 9/93
TRADE OR OTHER NAMES
Some trade names include Vydate, DPX 1410, Oxamimidic Acid, Thioxamyl
The U.S. Environmental Protection Agency (EPA) has classified most
products containing oxamyl as Restricted Use Pesticides (RUP) due to oxamyl's
acute toxicity to humans and its toxicity to birds and mammals (21).
Restricted Use Pesticides may be purchased and used only by certified
applicators. Granular formulations of oxamyl are banned in the United States,
where this pesticide is available only in liquid formulations (22).
Containers of oxamyl and/or its formulated products should bear labels with
the signal words "DANGER-POISON" (1).
Oxamyl is used as an insecticide to kill and control a broad spectrum of
insects, as an acaricide to control mites and ticks, and as a nematicide
against roundworms. Its action is both systemic and contact. Oxamyl is used
on field crops, vegetables, fruits, and ornamental plants (20). Oxamyl may be
applied directly on plants or on the soil surface (15).
Oxamyl belongs to a family of pesticides called carbamates (7). These
insecticides work by blocking the normal functioning of cholinesterase, an
essential nervous system enzyme. Please refer to the Toxicology Information
Brief on cholinesterase-inhibition for more information.
Oxamyl has been rated as extremely poisonous to humans. Oxamyl can enter
the body by three routes of exposure: inhalation, ingestion, or skin
absorption (4, 7, 10). Acute oral exposure to oxamyl has caused human deaths
(7). Oral, skin ('dermal'), and eye ('ocular') exposure may cause poisoning,
although absorption through the skin is slow (4). Exposure of rabbit's eyes
to technical oxamyl caused decreased pupil size and congestion of the iris,
the colored portion of the eye; the cornea was not damaged (3).
As with other carbamate compounds, oxamyl's cholinesterase-inhibiting
effect is short-term and reversible (7). Symptoms of oxamyl poisoning include
nausea, vomiting, abdominal cramps, sweating, diarrhea, excessive salivation,
weakness, imbalance, blurring of vision, breathing difficulty, increased blood
pressure or 'hypertension,' and lack of control of urine or feces release.
Death may result from respiratory system failure associated with oxamyl
exposure (4). Complete recovery from an acute poisoning by oxamyl, with no
long term health effects, is possible if exposure ceases and the victim has
time to reform their normal level of cholinesterase and to recover from
symptoms (7, 19).
Carbamates generally are excreted rapidly and do not accumulate in
mammalian tissue. If exposure does not continue, cholinesterase inhibition
reverses rapidly. In non-fatal cases, the illness generally lasts less than
24 hours (26).
The amount of a chemical that is lethal to one-half (50%) of experimental
animals fed the material is referred to as its acute oral lethal dose fifty,
or LD50. In rats the oral LD50 of technical oxamyl is 5.4 mg/kg. A 24%
liquid formulation of this insecticide has an acute oral LD50 of 37 mg/kg in
rats. The dermal LD50 for technical oxamyl is 2,960 mg/kg in rabbits (1, 20).
Prolonged or repeated exposure to oxamyl may cause symptoms similar to
the pesticide's acute effects.
In a two-year rat feeding study, the no-observable effect level (NOEL)
was 2.5 mg/kg. At 5 and 7.5 mg/kg, the average body weights of the animals
were decreased. In a two-year mouse feeding study, the NOEL was 1.25 mg/kg.
At 2.5 and 3.75 mg/kg there was decreased body weight and changed nutritional
performance (3). No cumulative toxicity was seen when rats were given twice
the LD50 in divided doses over a two-week period (4).
The EPA's Lifetime Health Advisory (LHA) level for oxamyl is 200
micrograms/liter. Water containing oxamyl at or below this level is
acceptable for drinking every day over the course of one's life with no health
Litter size, viability, lactation and body weights of offspring were
decreased in a three-generation, six litter reproduction study in rats fed 100
and 150 ppm of technical oxamyl. (There were two litters per generation).
The body weights of rats fed 5 or 7.5 mg/kg/day were also lowered (23).
When pregnant rats were fed oxamyl, there was a dose related decrease in
the maternal body weight and in food consumption rates in rats fed doses of 5,
7.5 or 15 mg/kg/day on days 6 through 15 of pregnancy, but not in rats fed
doses of 0 and 2.5 mg/kg/day. No effects were observed on the number of
implantation sites, resorptions and live fetuses. The NOEL was calculated at
2.5 mg/kg/day (23).
No teratogenic effects were observed in the offspring of rabbits fed 2
and 4 mg/kg during days 6 through 19 of gestation (23).
Oxamyl was not teratogenic or embryotoxic in the offspring of pregnant
rats fed up to 15 mg/kg/day of the insecticide (3, 23). However, embryotoxic
effects were produced in rabbits at 4 mg/kg/day. No teratogenic effects were
observed in rabbits given oxamyl levels approximately equal to 130 ppm in the
Oxamyl was not reported to be mutagenic after several tests (3, 23).
Sufficient data is available from animal studies to indicate that oxamyl
does not increase the risk of cancer in humans (25). No evidence of
carcinogenic potential has been seen following long-term dietary exposure in
rats and mice (23).
Liver impairment was suggested by a slight biochemical change seen in
dogs that were fed 3.75 mg/kg/day as a part of a two-year feeding study (3).
In a two-year study, male rats fed 7.5 mg/kg/day oxamyl for two years had
decreased organ weight of the heart, testes and adrenals. In females, there
was an increase in the relative weights of the brain, heart, lungs and
Fate in Humans and Animals
When oxamyl was administered to rats, most of the dose was rapidly
eliminated in the urine and feces as breakdown byproducts, or metabolites (4).
Carbamates generally are excreted rapidly and do not accumulate in mammalian
Oxamyl is toxic to fish, birds, and other wildlife (3). It does not
bioaccumulate to any great extent (23).
Effects on Birds
Oxamyl is extremely toxic to birds (3). The acute oral LD50 for oxamyl
in quail is 4.18 mg/kg (6). Hens given single oral doses of oxamyl at 20 to
40 mg/kg of body weight followed by intramuscular injections of 0.5 mg of
atropine, an antidote, exhibited early symptoms of cholinesterase inhibition
with full recovery after 12 hours. No signs of delayed neurotoxicity were
observed in these same hens (23). The oral LD50 for oxamyl is 3.83 mg/kg in
male mallard ducks and 2.61 mg/kg in female mallard ducks (3). Egg production
was decreased in mallard ducks to which oxamyl was fed at 50 ppm dietary
levels over a 28-week period (3).
Effects on Aquatic Organisms
Oxamyl is moderately toxic to fish (3). The lethal concentration fifty,
or LC50, is that concentration of a chemical in air or water that kills half
of the experimental animals exposed to it for a set time period. The 96-hour
LC50, for oxamyl in bluegill sunfish is 5.6 mg/l, 27.5 mg/l in goldfish, and
42 mg/l in rainbow trout (6).
Effects on Other Animals (Nontarget species)
Oxamyl is highly toxic to bees (22).
Breakdown of Chemical in Soil and Groundwater
Oxamyl does not readily bind, or 'adsorb,' to soil or sediments and has
been shown to leach in soil (23). No single soil property appears to
influence the tendency of this insecticide to adsorb. Its adsorption is
strongest in soils of high organic matter. Its adsorption on sandy loam is
fairly weak. An increase in temperature causes a decrease in adsorption. The
effectiveness of this material is affected by how deeply it is incorporated in
treated soil (17).
Oxamyl is a nonpersistent pesticide which rapidly degrades in the soil
(20, 23). Loss is due to decomposition by aerobic and anaerobic bacteria
(17, 23). Its soil/field dissipation half-life is one to eight weeks (16). Its
soil half-life is one to five weeks, with residual levels found for up to six
to 12 months later (23). Oxamyl is hydrolyzed rapidly in neutral and alkaline
soils and more slowly in acid soils (23).
Rain readily leaches oxamyl from soil (17). Oxamyl is highly soluble in
water (280 g/liter at 25 degrees C). Generally, high solubility promotes
groundwater contamination. However, oxamyl is rapidly broken down by plants
after application and by both aerobic and anaerobic bacteria in the soil.
Oxamyl is therefore considered to be a non-persistent pesticide with a low
potential for groundwater contamination under most soil-water conditions.
Wherever conditions favor very rapid movement of leachate, oxamyl dissolved in
the soil-water may reach the groundwater. Sites where the water table is very
close to the surface, where large volumes of water are applied to the site (as
irrigation or precipitation), or where there are sandy soils low in organic
matter, are sites where oxamyl contamination of the groundwater may occur
Oxamyl is rapidly hydrolyzed, or broken down by groundwater in neutral
and alkaline soil. This occurs more slowly in acid soil. Since oxamyl
degrades relatively quickly in the presence of bacteria, it is more likely to
be found in groundwater than in surface water. It has been found in parts per
billion (ppb) levels in the states of New York (1-60 ppb) and Rhode Island (1
ppb) (2, 8, 23).
Breakdown of Chemical in Water
In a river water study, oxamyl had a half-life of one to two days (23).
Another study indicates that its hydrolysis half-life is from less than one
week to a few weeks (16). This insecticide should not be applied directly to
water, nor where runoff is likely to occur. Cleaning of equipment or disposal
of wastes can also contaminate water, so precautions should be taken to avoid
such contamination (3).
Breakdown of Chemical in Vegetation
Oxamyl has a residual period in plants of approximately one to two weeks.
It is considered non-toxic to plants (5). Plants take oxamyl up through both
leaves and roots; it is transported downward to the roots in treated plants
(6). Oxamyl is metabolized rapidly by plants (23).
PHYSICAL PROPERTIES AND GUIDELINES
Oxamyl is an off-white crystalline powder (23) or a white crystalline
solid with a slight sulfurous odor (1, 7, 19).
As a carbamate, it tends to
have poor stability (18). While oxamyl is stable in solid form and in most
solutions, it decomposes to innocuous materials in natural waters and in
soils. Aeration, sunlight, alkalinity, and higher temperatures increase its
rate of decomposition (7). Toxic fumes of nitrogen oxides and sulfur oxides
are emitted if oxamyl is heated to decomposition (10). It is noncorrosive
(6). Oxamyl is available in a variety of formulations, such as a 24% water-
soluble liquid and 10% granules (7).
Protective clothing and respirators should be worn by applicators so that
skin, eye and clothing contact can be carefully avoided. Oxamyl should be
kept away from children, unauthorized persons, domestic and other animals,
food, and feedstuffs (6).
Occupational Exposure Limits:
No occupational exposure limits have been established for oxamyl by OSHA,
ACGIH or NIOSH.
|CAS #: ||23135-22-0
|H20 solubility: ||280 g/l at 25 degrees C (15); 280,000 ppm (16)
|Solubility in other solvents: ||(per 100 g. solvent at 25 degrees C): 67 g in acetone, 33 g in ethanol, 11 g in 2-propanol, 144 g in methanol, 1 g in toluene (7)
|Melting Point: ||100 - 102 degrees C (15); at this point it changes to a different crystalline form with a melting point of 108 degrees C to 10 degrees C (7, 19, 20)
|Vapor pressure: ||2.3 x 104 mm Hg at 25 degrees C (19)
|Partitioning Model: ||PCMC1 (mole fraction): 0.023
PCMC2 (mg/l): 2.8 x 10 to the minus 5
PCMC3 (ug/l): 1,280,000 (16)
|Kow: ||0.3 (14)
|Koc: ||0.2 - 8.6; 4.4 (calc) (16)
|Kd: ||0.02-0.3 (16)
|pH: ||2.37 x 10 to the minus 7 atm x m/3 mole, suggesting that aeration is not likely to be a suitable water treatment technique for oxamyl removal (15).
|Chemical Class/Use: ||Carbamate insecticide, nematicide, acaricide.
|ADI: ||a temporary ADI of 0.01 mg/kg/day was calculated by WHO using a two-year dog feeding study (15).
Du Pont Agricultural Products
Walker's Mill, Barley Mill Plaza
PO Box 80038
Wilmington, DE 19880-0038
Review by Basic Manufacturer:
Comments solicited: October, 1992
Comments received: November, 1992
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