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
by the USDA/Extension Service/National Agricultural Pesticide Impact
Assessment Program.
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Pesticide
Information
Profile
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Diflubenzuron
Publication Date: 9/93
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TRADE OR OTHER NAMES
Diflubenzuron is sold under the trade name Dimilin. It is used
world wide for a variety of applications.
INTRODUCTION
Diflubenzuron is a benzamide insecticide used on forest and field
crops to selectively control insects and parasites. Principle target
insect species are the gypsy moth, forest tent caterpiller, several
evergreen eating moths and the boll weevil. Diflubenzuron is a stomach
and contact poison which acts by inhibiting the production of chitin (a
compound that makes the outer covering of the insect hard) and so
interferes with the formation of the insect's cuticle or shell. It is
also used as a larvae control chemical in mushroom operations and animal
houses.
Diflubenzuron is classified as a Restricted Use Pesticide (RUP) in
the United States. Restricted Use Pesticides may be purchased and used
only by certified applicators.
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
Diflurobenzuron is slightly toxic pesticide and carries the signal
word CAUTION. No overt signs of toxicity were observed in any of the
acute studies conducted (3). The oral LD50 for rats and mice is greater
than 4,640 mg/kg and the rat dermal LD50 is greater than 10,000 mg/kg
and greater than 4000 mg/kg for rabbits. The inhalation LD50 for rats
and rabbits was >35 and >30 mg/l, respectively. The breakdown products
formed in sheep, swine, and chickens, are also slightly toxic. The rat
oral LD50 is between 1080 and 4640 mg/kg.
CHRONIC TOXICITY
No measurable pathological changes were observed at very low, long
term exposure to diflurobenzuron (3).
In a study with cats fed over a wide range of doses for 21 days,
all of the females had dose-related blood chemistry changes at low doses
and the males exhibited changes at dose levels that were slightly higher
(3). The chemistry changes were associated with the formation of
methemoglobin. This is a form of hemoglobin that is unable to carry
oxygen. Methemoglobin formation is reversible however.
Reproductive Effects
Day-old ducks and turkeys fed moderate amounts of the pesticide in
their diets for 90 days had decreased testosterone levels after 42 days,
but this did not occur in chickens and pheasants in the same study.
Combs and wattles, which reflect hormone activity, appeared unaffected.
Other studies showed some comb abnormalities. Some were underdeveloped
and others more developed compared to controls.
Testosterone levels in rats and bull calves was studied and a short
term decrease was shown in the sexually immature rats but no clear cut
change was shown in the young bulls (3).
When female rats were fed very high levels of diflurobenzuron over
one generation (through one-litter), dose-related effects on liver
weight were seen in the parents and offspring. A three-generation study
on rats at much lower doses, showed no effect on mating performance. It
does not appear that diflurobenzuron has a significant effect on
reproduction at low exposure levels in test animals and similar results
may be expected in humans.
Teratogenic Effects
Newborn rats and rabbits did not develop any birth defects after
their mothers were exposed to low levels of diflurobenzuron (1 to 4
mg/kg) on days 6 to 18 of gestation.
Mutagenic Effects
Extensive testing on mamalian cells and on bacterial cells have
shown that diflurobenzuron is not mutagenic.
Carcinogenic Effects
Rats fed diets containing low to moderate amounts of diflubenzuron
daily for two years had no increase in the number of new or abnormal
tissue growths or lesions. Mice fed low doses for eighty weeks showed
no significant tumor development. Other studies on both species at
higher levels were also negative for malignant tumors (3). It does not
appear that diflurobenzuron would pose a cancer threat to humans at low
levels of exposure.
Organ Toxicity
Rats given moderate amounts of the compound for two years had
enlarged spleens while mice in a similer study had liver and spleen
enlargement at slightly lower levels of exposure. This suggests that
moderate levels of exposure over a lifetime might pose a risk to humans.
Fate in Humans and Animals
Intestinal absorption in mammals decreases with increasing dose
levels (5). For example, in rats the total excretion in urine and bile
decreased from about fifty percent of the dose at 4 mg/kg to only four
percent at 900 mg/kg. Mice showed similar results.
A cow given 10 mg/kg orally, eliminated almost all of the product
over a four-day period. There were only minute amounts of the pesticide
in the milk. The chemical is not degraded in the digestive tract, but
that which is absorbed by the gut is completely broken down before
excretion (3). Rabbits' skin absorbed only very small amounts, all of
which was recovered in the urine.
Chickens excreted almost all of an oral dose in 13 days. Their
eggs had low levels of pesticide residues (0.3 to 0.6 mg/kg) from day
nine to the end of the nine-week study. The test animals were fed with
10 mg/kg diflubenzuron in their feed. A 28-day study at very low doses
produced no residues in the eggs and only minute amounts of the compound
were deposited in the fat. Body tissues (non-fatty) do not retain
diflubenzuron.
ECOLOGICAL EFFECTS
Diflurobenzuron is practically non toxic to wild birds. Bobwhite
quail and mallard ducks both have an eight-day dietary LC50 of greater
than 4640 ppm. The 96-hour LC50 for diflurobenzuron in various fish
were: bluegill sunfish, 660 ppm; rainbow trout, 240 ppm; saltwater
minnow 255 ppm; channel catfish 180 ppm. Oyster larvae and juveniles
had EC50s of 130 and 250 ppm, respectively. These values indicate the
the compound is practically non-toxic to aquatic invertebrates and to
fish. Fish tissue can show some traces of the metabolites when water is
contaminated with diflubenzuron, however, tissue concentrations decline
steadily with time in clean water.
Insects and other arthropods are most susceptible in the pre-
molting stage. For instance, fiddler crabs, exposed for as little as
one week at levels up to 50 ppb exhibited limb regeneration effects (7).
ENVIRONMENTAL FATE
The rate of degradation in soil is strongly dependent on the
particle size of the diflubenzuron (5). For larger particles (10
microns) the half-life is 8 to 16 weeks and for smaller particles (2
microns) it is 0.5 to 1 week. Almost all of the parent compound breaks
down to form DFBA and CPU. A very minor amount forms 4-chloroaniline
(PCA) which rapidly binds to the soil. Under field conditions
diflubenzuron has very low mobility.
In sterilized water (no microbes), there appears to be little
degradation under neutral or acidic conditions. However, under field
conditions it is degraded rapidly, with CPU being the major metabolite.
Residues could not be detected 72 hours after an application of 110
g/hectare of field water. Other studies suggest half-lives of one to
three weeks.
Very little diflubenzuron is absorbed, metabolized, or translocated
in plants. It also is not readily taken up from treated soil. Although
very persistent in greenhouse studies (5), residues on crops such as
apples have a half-life of five to ten weeks. The half-life in oak leaf
litter is six to nine months.
Exposure Guidelines:
| NOEL: |
dog: 2 mg/kg (ppm), based on changes in met- and sulfhemoglobin
mouse: 2.4 mg/kg (ppm), based on changes in met- and sulfhemoglobin
rat: 2 mg/kg (ppm), based on toxic effects |
| ADI: | 0.02mg/kg/day (WHO) |
| RfD: | 0.02mg/kg/day |
| LEL: | 10 mg/kg/day (rat) |
Physical Properties:
| CAS #: | 35367-38-5 |
| Chemical name: | N-[{(4-chlorophenyl) amino}carbonyl]-2,6-difluorobenzamide |
| Chemical class/use: | benzamide insecticide |
| Solubility in water: | 0.08 mg/l |
| Solubility in other solvents: | DMSO 12 g/100 g; acetone 0.615 g/100 g; methanol 0.09 g/100 g |
| Melting Point: | 230-232 degrees C |
| Vapor Pressure: | 9 x 10 to the minus 10 power mm Hg |
| Partition Coefficient: | 5,000 (octanol/water) |
BASIC MANUFACTURER
Duphar BV
Crop Protection Div.
PO Box 4
1243 ZG-s-Graveland,
THE NETHERLANDS
Telex: DUBOE 730 NL
U. S. DISTRIBUTOR
Uniroyal
World Headquarters
Middlebury, CT 06749
Telephone: 203/575-2000
Review by Basic Manufacturer - Duphar BV:
Comments solicited: October, 1992
Comments received:
REFERENCES
Thompson - Hayward Chemical Company (1975). Dimilin Forest Insect
Control. North American Philips Company.
Friel, John P., Editor (1981). Dorland's Illustrated Medical
Dictionary. W. B. Saunders Company, Philadelphia, PA.
Food and Agriculture Organization of the United Nations, (1981).
Pesticide Residues in Food - 1981. FAO Plant Production and Protection
Paper 42.
Food and Drug Administration (1986). The FDA Surveillance Index.
Bureau of Foods, Dept of Commerce, National Technical Information
Service, Springfield, VA.
Dost, F.N., S.L. Wagner, J.M. Witt, and M. Heumann (1985).
Toxicological Evaluation of Dimilin (Diflubenzuron). Oregon State
University, Extension Service Toxicology Information Program, Department
of Agricultural Chemistry, Corvallis, OR.
Food and Agriculture Organization of the United Nations, (1985).
Pesticide Residues in Food - 1985: Evaluations, Part I Residues, FAO
Plant Production and Protection Paper 72/1.
Weis, J.S., S.R. Cohen and J.K. Kwiathowsi (1987). Effects of
Diflubenzuron on Limb Regeneration and Molting in the Fiddler Crab, Uca
pugilator, Aquatic Toxicology 10:279-290.
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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