E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
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University of California at Davis. Major support and funding was provided
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Pesticide
Information
Profile
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Diazinon
Publication Date: 9/93
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TRADE OR OTHER NAMES
Trade names of this product include Knox Out, Spectracide and
Basudin. Diazinon may be found in formulations with a variety of other
pesticides such as pyrethrins, lindane and disulfoton.
INTRODUCTION
Diazinon is a non-systemic organo-phosphate insecticide used on
home gardens and farms to control a wide variety of sucking and leaf
eating insects. It is used on rice, fruit trees, sugarcane, corn,
tobacco, potatoes and on horticultural plants. It is also an ingredient
in pest strips. Diazinon has veterinary uses against fleas and ticks.
Nearly 2.6 million pounds of diazinon were used each year prior to 1983
(6).
Some of the older formulations of diazinon were unstable and
contained a number of potent impurities such as sulfotepp and
monothiono-TEEP (6). Newer products do not contain impurities which
increase the risk associated with diazinon use. In 1988 EPA cancelled
the registration of diazinon for use on golf courses and sod farms.
They cited die-offs of birds which often congregate in these areas.
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
Diazinon is classified as slightly toxic to moderately toxic,
depending on the formulation. It carries the signal words CAUTION or
WARNING. Toxic effects of diazinon are due to the inhibition of
acetylcholinesterase. The range of doses that results in toxic effects
varies widely with formulation and with the individual species being
exposed. The toxicity of encapsulated formulations is relatively low
because diazinon is not released readily while in the digestive tract.
Some formulations of the compound can be degraded to more toxic forms.
This transformation may occur in air, particularly in the presence of
moisture, and by ultraviolet radiation. Most modern diazinon
formulations in the United States are now stable.
Several independently documented cases of diazinon poisoning have
occurred among agricultural applicators and among household residents.
In the latter case, poisoning followed indoor spraying of a relatively
concentrated (25%) solution of diazinon.
The symptoms associated with diazinon poisoning in humans include
weakness, headaches, tightness in the chest, blurred vision, non-
reactive pinpoint pupils, salivation, sweating, nausea, vomiting,
diarrhea, abdominal cramps, and slurred speech. Death has occurred in
some instances from both dermal and oral exposures at very high levels.
Repeated single dose LD50s range from 2.75 mg/kg/day to nearly 450
mg/kg/day for rats (8). Still others have reported LD50s as high as 720
mg/kg/day (4).
CHRONIC TOXICITY
Chronic effects have been observed at doses ranging from 10
mg/kg/day for swine to 1,000 mg/kg/day for rats. These effects included
only visibly recognizable symptoms of toxicity (gross toxicities).
Certain effects such as the inhibition of red blood cell cholinesterase,
and enzyme response occurred at much lower doses in the rats. No-effect
doses have ranged from 0.02 mg/kg/day in humans to 0.1 mg/kg/day in
rats. These values are based on inhibition of the enzyme
acetylcholinesterase. Enzyme inhibition has been documented in red
blood cells, in blood plasma, and in brain cells at varying doses and
with different species.
Reproductive and Teratogenic Effects
The data on reproductive and developmental effects due to chronic
exposure is limited. One study has shown that injection of diazinon
into chicken eggs resulted in skeletal and spinal deformities in the
chicks. Bobwhite quail born from eggs treated in a similar manner
showed skeletal deformities but no spinal abnormalities. Acetylcholine
was significantly affected in this latter study (3). Tests with
hamsters and rabbits at low doses (0.125-0.25 mg kg) showed no
developmental effects while tests with dogs and pigs at higher levels
(1.0-10.0 mg/kg) revealed gross abnormalities (2).
Mutagenic Effects
Tests have revealed the potential for diazinon to be mutagenic, but
no fully conclusive evidence exists to support this notion (7). The
mutagenicity in humans remains unevaluated.
Carcinogenic Effects
Diazinon is not considered carcinogenic. Test on rats over a two
year period at moderate doses (about 45 mg/kg) did not cause tumor
development in the test animals.
Organ Toxicity
Diazinon itself is not a potent cholinesterase inhibitor. However,
in animals it is converted to diazoxon (a substitution of oxygen for the
sulfur molecule), a compound that is a strong enzyme inhibitor.
Fate in Humans and Animals
Metabolism and excretion rates for diazinon are rapid. The half
life of the pesticide in animals is about 12 hours. The product is
passed out of the body through urine and in the feces. The metabolites
account for around 70% of the total amount excreted. Cattle exposed to
diazinon may store the compound in their fat over the short term. One
study showed that the compound cleared the cows within two weeks after
spraying stopped. Application of diazinon to the skin of cows resulted
in trace amounts in milk 24 hours after the application.
ECOLOGICAL EFFECTS
Birds are quite susceptible to diazinon poisoning and therefore
regulations are in place to protect them from hazards posed by turf and
golf course treatments. The EPA in 1988 concluded that the use of
diazinon in these areas poses a "widespread and continuous hazard" to
birds. Bird kills associated with diazinon use have been reported in
every area of the country and at all times of the year. The EPA further
concluded that Canadian geese and mallard ducks would be exposed to LC50
concentrations in very short periods of time after application (from 15
to 80 minutes depending on the application rate of the pesticide).
Birds are significantly more susceptible to diazinon than other
wildlife. LD50s for birds range from 2.75 mg/kg to 40.8 mg/kg/day (5).
Most fish are very sensitive to diazinon. Rainbow trout have a LC50
of 90-140 ppb. In hard water, lake trout and cutthroat trout are
somewhat more resistant. Warm water fish such as fathead minnows and
goldfish are even more resistant (LC50s ranging from 0.5 ppm to 15 ppm).
There is some evidence that saltwater fish are more susceptible than are
freshwater fish. Bioconcentration ratios range from 200 in minnows to
17.5 for guppies. Howard (8) states that based on these experimental
figures, "diazinon will not be expected to significantly bioconcentrate
in aquatic systems." Other studies show that diazinon has been found to
concentrate in fish 300-600 times the ambient water concentration. This
is a relatively low bioaccumulation level as compared to a very
persistent compound like DDT which may accumulate to about 60,000 times
background levels.
ENVIRONMENTAL FATE
Diazinon seldom migrates below the top 1.3 centimeters (1/2 inch)
in soil but can stay biologically available for six months under
conditions of low temperature and low moisture. The average time for
50% degradation in soil is two to four weeks. Bacterial enzymes can
speed the breakdown of diazinon and have been used in treating emergency
situations such as spills (3). The breakdown rate is also highly
dependent on the acidity of water. At highly acidic levels, one half of
the compound disappeared within 12 hours while in a neutral solution,
the pesticide took six months to degrade to one half of the original
concentration. Diazoxon is unstable in soil. Howard (8) notes that the
pesticide was detected in 54 wells in California and in tap water in
Ottawa, Canada and in Japan. Diazinon has also been detected (but not
quantified) in Lake Erie and Lake Ontario.
In plants, a lower temperature and a high oil content tend to
increase the persistence of diazinon (5). Generally the half-life is
rapid in leafy vegetables, forage crops and grass. The range is from two
days to 14 days. In treated rice plants only 10% of the residue was
present after nine days. Diazinon is absorbed by plant roots when
applied to the soil and translocated to other parts of the plant.
Exposure Guidelines:
| NOEL: | - 0.01mg/kg/day rat
- 0.02mg/kg/day monkey
- 0.02mg/kg/day humans
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| Drinking Water: | 0.014 mg/l (ppm) |
| DWEL: | 0.003 mg/l |
| ADI: | 0.002 mg/kg/day |
| TLV-TWA: | 0.1 mg/m3 |
| RfD: | 0.00009 mg/kg/day (OPP) |
| HA: | 0.0006 mg/l lifetime |
Physical Properties:
| CAS #: | 333-41-5 |
| Solubility in water: | 60 mg/l |
| Solubility in solvent: | Petroleum ether, alcohol, benzene |
| Melting Point: | decomposes >120 degrees C |
| Vapor Pressure: | 6 x 10 to the minus 5 power mm Hg |
| Partition Coefficient: | 1.9-4.2 (log) |
| Adsorption Coefficient: | 1,000 ml/g |
BASIC MANUFACTURER
Ciba-Geigy Corp
PO BOX 18300
Greensboro, NC 27419
Telephone:919-632-6000
Review by Basic Manufacturer:
Comments solicited: January, 1992
Comments received: April, 1992
REFERENCES
The Agrochemicals Handbook. 1991. The Royal Society of Chemistry.
Cambridge, England
National Research Council (1977). Drinking Water and Health,
Advisory Center on Toxicology, Assembly of Life Sciences, Safe Drinking
Water Committee, National Academy of Sciences, Washington, DC.
Eisler, Ronald (1986). Diazinon Hazards to Fish, Wildlife and
Invertebrates: A Synoptic Review. U.S. Department of the Interior, Fish
and Wildlife Service, Contaminant Hazards Reviews, Report number 9,
Biological Report 85(1.9).
National Library of Medicine. (1992). Hazardous Substance
Databank. TOXNET, Medlars management Section, Bethesda, MD.
Bartsch, Elisabeth (1974). Diazinon II. Residue in Plants, Soil
and Water, Residue Reviews, 51:37-68.
Vettorazzi, G. (1976). II Carbamate and Organophosphorous
Pesticides Used in Agriculture and Public Health, Residue Reviews 63:1-
44.
Gallo, Michael A. and Nicholas J. Lawryk. (1991). Organic
Phosphorus Pesticides. in Handbook of Pesticide Toxicology, Volume 2,
Classes of Pesticides. Wayland J. Hayes and Edward R. Laws
editors.Academic Press, Inc., NY.
Howard, Philip H. (1991). Fate and Exposure Data for Organic
Chemicals, Volume III, Pesticides. Lewis Publishers, Chelsea, MI.
Disclaimer: Please read
the pesticide label prior to use. The information contained at this web
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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