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The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

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E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Hexazinone

Trade and Other Names: Trade names for products containing hexazinone are DPX 3674, Pronone, and Velpar. It may be used in combination with other herbicides such as bromacil and diuron.

Regulatory Status: Hexazinone is a slightly toxic compound in EPA toxicity class I. Labels for products containing hexazinone bear the Signal Word DANGER - POISON due its ability to cause serious and irreversible eye irritation. It is a General Use Pesticide (GUP).

Chemical Class: triazine

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. It is available in soluble concentrate, water-soluble powder, or granular formulations.

Formulation: It is available in soluble concentrate, water-soluble powder, or granular formulations.

Toxicological Effects:

• Acute toxicity: Hexazinone is slightly toxic via the oral route, with a reported LD50 of 1690 mg/kg in rats, and 860 mg/kg in male guinea pigs [6,15]. Via the dermal route, it is practically nontoxic, with a reported dermal LD50 in rabbits of greater than 5278 mg/kg [6,15]. Hexazinone does not cause significant skin irritation or sensitization in guinea pigs or rabbits, but it does cause severe eye irritation in rabbits [15]. Hexazinone's inhalation toxicity is very low, its 1-hour inhalation LC50 is greater than 7.48 mg/L in rats [15]. Effects due to acute exposure may include irritatation the eyes, nose and throat, as well as nausea and vomiting [29].
• Chronic toxicity: Over a 2-week period, male rats receiving dietary doses of 300 mg/kg/day showed no evidence of cumulative toxicity [15]. Male rats receiving doses of 50 mg/kg/day over 90 days showed no effects, but higher doses caused decreased body weights. Body weight gain was seen in dogs at doses of about 35 mg/kg/day and higher over 1 year [15]. Very high doses for 8 weeks did not affect hamsters and caused only increased liver weights in mice [29].
• Reproductive effects: Female rats, fed moderate to high doses (up to 150 mg/kg) over two generations, showed no effects on reproduction or milk production, but only reduced offspring weight [15,29]. Available evidence suggests that hexazinone is unlikely to cause reproductive effects in humans.
• Teratogenic effects: Pregnant female rats receiving doses up to 100 mg/kg/day during gestation, and rabbits receiving up to 125 mg/kg/day, evidenced no fetal abnormalities [15]. Teratogenic effects were observed in rats only at maternal doses greater than 400 mg/kg/day during gestation [15]. It is unlikely that hexazinone would pose a teratogenic effects in humans under normal conditions.
• Mutagenic effects: Hexazinone showed no mutagenic activity in the Ames assay and tests using Chinese hamster ovary cell cultures [15]. In living animal tests, no changes in chromosomal structure occurred. In other laboratory analyses of its capacity to induce genetic disruption, results were inconclusive [15]. The evidence suggests hexazinone is either slightly or nonmutagenic.
• Carcinogenic effects: Rats, mice, and dogs have been tested for 1 to 2 years on diets containing up to 500 mg/kg. Hexazinone was not carcinogenic in rats, and was only carcinogenic in mice at dietary levels of over 300 mg/kg. At these levels in mice, liver adenomas were observed [15]. These studies suggest that hexazinone is unlikely to be carcinogenic to humans under normal circumstances.
• Organ toxicity: Target organs affected in lab animals by chronic hexazinone exposure include the liver.

• Fate in humans and animals: Hexazinone is fairly rapidly processed and excreted by animal systems. Rats typically excrete hexazinone almost completely within 3 to 6 days, the majority in urine [30]. Long-term exposure does not diminish this rapid processing and elimination; rats given prior exposure for 2 weeks excreted almost all of the product within 3 days [30]. Less than 1% of the parent hexazinone was detected in urine and feces. There does not appear to be any significant tissue accumulation [30]. 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 [30]. Lactating goats given small amounts of hexazinone for 5 days also had small amounts of the compound in their milk and livers [30].

Ecological Effects:

• Effects on birds: Hexazinone is slightly to practically nontoxic to birds. The acute oral LD50 of hexazinone in bobwhite quail is 2258 mg/kg [15]. The 5- to 8-day dietary LC50 in bobwhite quail and mallard ducklings is greater than 10,000 ppm [15].
• Effects on aquatic organisms: Hexazinone is slightly toxic to fish and other freshwater organisms. Some of the reported 96-hour LC50 values include: rainbow trout, 320 mg/L; bluegill, 370 mg/L; fathead minnow, 274 mg/L [6,15]. The 48-hour LC50 for hexazinone in the water flea, Daphnia magna, is 151 mg/L [15]. The bioconcentration factor in bluegill sunfish is only seven times the ambient water concentration, indicating very low bioaccumulation in fish [30].
• Effects on other organisms: Hexazinone is nontoxic to honey bees. The herbicide is toxic to larch trees (Larix spp.), and should not be used for weed control in forested areas [6].

Environmental Fate:

• Breakdown in soil and groundwater: Hexazinone is of moderate to high persistence in the soil environment. Measured field half-lives range from less than 30 to 180 days, with a representative value of about 90 days [31]. Hexazinone is broken down by soil microbes, which release carbon dioxide in the process [15]. Sunlight may also break down the compound via photodegradation [31]. The rate of breakdown under natural field conditions will depend on many site-specific variables, including sunlight, rainfall, soil type, and rate of application. Hexazinone does not evaporate to any appreciable extent from soil [31]. Hexazinone is very poorly adsorbed to soil particles, very soluble in water, and slowly degraded, so it is likely to be mobile in most soils and has the potential to contaminant groundwater.
• Breakdown in water: Photodecomposition, biodegradation, and dilution are the prime mechanisms for loss of hexazinone activity in aquatic systems [15].
• Breakdown in vegetation: Hexazinone is readily absorbed in the root zone and translocated throughout the plant. It is less mobile following uptake from the foliage. It is converted in non-susceptible plants to less phytotoxic compounds. In susceptible plants, it is more persistent and can result in disruption of photosynthesis and chloroplast damage [15].

Physical Properties:

• Appearance: Hexazinone is a colorless, odorless crystal at room temperature [6].
• Chemical Name: 3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione [6]
• CAS Number: 51235-04-2
• Molecular Weight: 252.32
• Water Solubility: 33,000 mg/L @ 25 C [6]
• Solubility in Other Solvents: v.s. in acetone, hexane, and methanol [6]
• Melting Point: 115-117 C [6]
• Vapor Pressure: 0.03 Pa @ 25 C [6]
• Partition Coefficient: -4.40 (calculated) [16]
• Adsorption Coefficient: 54 [20]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: 0.033 mg/kg/day [26]
• PEL: Not Available
• HA: 0.20 mg/L (lifetime) [29]
• TLV: Not Available

Basic Manufacturer:

DuPont Agricultural Products
Walker's Mill, Barley Mill Plaza
P.O. Box 80038
Wilmington, DE 19880-0038

• Phone: 800-441-7515
• Emergency: 800-441-3637
  

References:

References for the information in this PIP can be found in Reference List Number 8

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.