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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Hexazinone
Publication Date: 9/93
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TRADE OR OTHER NAMES
Trade names for products containing hexazinone are DPX 3674 and
Velpar. It may be used in combination with other herbicides such as
bromacil and diuron.
INTRODUCTION
Hexazinone is a triazine herbicide used against many annual,
biennial and perennial weeds as well as some woody plants. It is mostly
used on non-crop areas; however, it is used selectively for the control
of weeds among sugar cane, pineapples, and lucerne. Hexazinone is a
systemic herbicide that works by inhibiting photosynthesis in the target
plants. Rainfall or irrigation water is needed before it becomes
activated.
Hexazinone is a general use pesticide.
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
Hexazinone has a very low acute toxicity. However, it carries the
signal word DANGER-WARNING due its ability to cause serious and
irreversible eye irritation. In rats, the oral LD50 of hexazinone is
1,690 mg/kg and in male guinea pigs is 860 mg/kg. The lethal dose in
beagle dogs is greater than 3,400 mg/kg. The dermal LD50 for rabbits is
greater than 5,278 mg/kg. Hexazinone is not a significant skin irritant
nor does it cause skin sensitization in guinea pigs. It may irritate
the eyes, nose and throat, in humans. Another symptom of acute toxicity
noted for humans is vomiting (7).
Rats exposed to hexazinone at very high concentrations in air for
one hour experienced no mortality.
CHRONIC TOXICITY
Over a two-week period rats given moderate doses of hexazinone in
their food showed no evidence of cumulative toxicity. Rats and dogs fed
high doses of the compound for 90 days showed decreased body weight.
The highest dose that resulted in no toxicity is about 50 mg/kg for
dogs. Very high doses for eight weeks did not affect hamsters and
caused only increased liver weights in mice.
Reproductive Effects
Female rats, fed moderate to high doses (up to 150 mg/kg) over
three generations, showed no effects on reproduction or milk production.
The weight of the pups was reduced only at the highest dose
administered.
Teratogenic Effects
Female rats receiving low to moderate doses (10 to 250 mg/kg/day)
during gestation produced no malformations in the fetuses. Fetal weight
was significantly lower only at the highest dose. Pregnant rabbits fed
hexazinone within this same range of doses on days 6 through 19 of
gestation showed no significant differences from the controls. The
fetus was also unaffected (2). It is unlikely that hexazinone would
pose a serious threat to a developing fetus.
Mutagenic Effects
Hexazinone is not mutagenic as indicated by a variety of tests on
bacteria and mammalian cells. Thus, it is not likely to pose a
mutagenic threat to humans.
Carcinogenic Effects
Rats and mice were tested for two years on diets containing up to
500 mg/kg (10,000 ppm). Hexazinone was not carcinogenic in either
species in either of two studies. These studies suggest that hexazinone
is unlikely to be carcinogenic to humans though the EPA has not
classified the carcinogenicity of the compound.
Organ Toxicity
A single moderate dose of hexazinone in rabbit eyes caused severe
irritation. It took nearly a month for the eyes to return to normal.
With lower doses, the eyes were irritated but returned to normal in 3
days.
Fate in Humans and Animals
Almost all of a 14 mg/kg oral dose administered to rats was
excreted in three to six days, with the majority in urine. In another
study, animals fed 125 mg/kg for two weeks then given a small single
dose, excreted almost all of the product within three days. Less than
1% of the parent hexazinone was detected in urine and feces. There does
not appear to be any significant tissue accumulation (2).
Dairy cows given small amounts of hexazinone in their diets for 30
days had no detectable residues in milk, fat, liver, kidney, or lean
muscle but did have minute amounts of a hexazinone metabolite in their
milk. Lactating goats given small amounts of hexazinone for five days
also had small amounts of the compound in their milk. The goats had a
small amount of the parent compound in their liver (1). Hens fed very
low doses for four weeks had no residues in eggs, skin, muscle, fat or
liver.
ECOLOGICAL EFFECTS
The LD50 of hexazinone in bobwhite quail is 2258 mg/kg. The LC50
of hexazinone in bobwhite quail and mallard ducklings is greater than
10,000 ppm. This indicates that hexazinone is practically non-toxic to
birds.
Hexazinone is only slightly toxic to fish and other freshwater
organisms. Some of the aquatic 96-hour LC50 values include: rainbow
trout 320 ppm, bluegill 370 ppm, fathead minnow 274 ppm. The LC50 for
hexazinone in the water flea, Daphnia magna, is 151. The compound is
non-toxic to bees. It is not expected to bioaccululate in aquatic
systems.
The herbicide is toxic to larch trees (Larix spp.) and should not
be used for weed control in forested areas (6).
ENVIRONMENTAL FATE
Half of the applied herbicide is lost in soil after one to six
months depending on the climate and soil type. Hexazinone is broken down
by soil microbes. They break apart the ring structure of the compound
and release carbon dioxide in the process. Sunlight can also break down
the compound (photodegradation) (4). The rate of photodegradation under
natural field conditions depends on factors like light intensity and
depth of incorporation into the soil.
Hexazinone does not evaporate to any appreciable extent from soil.
It can leach through the soil to the root zone. It has been detected in
ground water and in well water in several states at concentrations as
high as nine parts per billion.
Photodecomposition, biodegradation and dilution are the prime
mechanisms for loss of hexazinone activity in aquatic systems (1).
An alfalfa plot treated with hexazinone at one pound/acre had a
small amount of hexazinone residue after two months. At three and six
months no hexazinone or its metabolites were detected. Pineapple plants
treated with hexazinone were shown to have some residue present with a
half life of three months. The metabolites appeared in the bound form
in pineapple, alfalfa, onions, and sorghum (4).
Exposure Guidelines:
| NOEL (rat): | 10 mg/kg/day |
| DWEL: | 1.05 mg/day |
| HA: | 0.20 mg/l (lifetime) |
| LEL: | 50 mg/kg/day (rat) |
Physical Properties:
| CAS #: | 51235-04-2 |
| Chemical name: | 3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione |
| Chemical class/use: | trianzine herbicide |
| Solubility in water: | 33,000 mg/l at 25 degrees C |
| Solubility in other solvents: | acetone 70.9 g/100 g; hexane 0.3 g/100 g; methanol 0.265 g/100 g |
| Melting Point: | 115-117 degrees C |
| Vapor Pressure: | 2 x 10 to the minus 7 power mm Hg |
| Partition Coefficient: | |
BASIC MANUFACTURER
Du Pont Agricultural Products
Walker's Mill, Barley Mill Plaza
PO Box 80038
Wilmington, DE 19880-0030
Toll free: 800-441-3637
Emergency: 800-441-7515
Review by Basic Manufacturer:
Comments solicited: October, 1992
Comments received: November, 1992
REFERENCES
Food and Drug Administration (1986). The FDA Surveillance Index.
Bureau of Foods, Dept of Commerce, National Technical Information
Service, Springfield, VA.
U. S. Environmental Protection Agency (1987). Health Advisory,
Office of Drinking Water.
Beste, C.E., Chairman (1983). Herbicide Handbook of the Weed
Science Society of America. Weed Science Society of America, Champaign,
IL.
Forest Service, (1984). Pesticide Background Statements, Vol. I
Herbicides. United States Department of Agriculture, Agriculture
Handbook No. 633.
Worthing, Charles R., Editor (1983). The Pesticide Manual, A World
Compendium. The British Crop Protection Council, The Ravenham Press
Limited, Ravenham, Suffolk, England.
The Agrichemicals Handbook. 1991. The Royal Society of Chemistry.
Cambridge, England.
U.S. Environmental Protection Agency. (1987). Hexazinone Health
Advisory. Office of Drinking Water. August.
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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