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Butylate

Publication Date: 9/93

TRADE OR OTHER NAMES

Genate Plus, Anelda Plus, Aneldazin, Anelirox, Sutan, Sutan 6E, Butilate, Carbamic Acid, Ethyl N, N-Diisobutylthiocarbamate, R1910, Stauffer R-1, 910.

REGULATORY STATUS

Butylate belongs to the thiocarbamate chemical class. It is classified by the U.S. Environmental Protection Agency (EPA) as a general use herbicide, with applications limited to corn fields. Products containing butylate must bear the signal word "Caution" (16).

INTRODUCTION

Butylate was initially registered in 1967 as a selective herbicide. It is registered only for use in corn to control grassy weeds such as nutgrass and millet grass, as well as some broadleaf weeds. It is applied to soil immediately before corn is planted, often in combination with atrazine and/or cyanazine herbicides (11). Butylate acts selectively on seeds of weeds that are in the germination stage of development (3). It is absorbed from the soil by shoots of grass seedlings before they emerge, causing shoot growth to be slowed, and leaves to become twisted (4). Butylate breaks down relatively quickly in soil, so there are no carry over problems in treated soil that might jeopardize later plantings of crops on the same plots (13). The exact poisoning mechanism of the herbicide in plants is not yet fully understood (1, 11).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

The major routes of exposure to butylate are dermal and respiratory.

Butylate is part of a group of chemicals referred to as thiocarbamates, known for their tendency to irritate the skin and the mucous membranes of the respiratory tract. It may cause symptoms of scratchy throat, sneezing and coughing when large amounts of dusts or spray are inhaled (7, 20). Slight eye irritation can be caused by butylate, potentially leading to permanent eye damage (3, 12).

Skin irritation was observed in rabbits topically exposed to 2 g of technical butylate (85.71% pure) for 24 hours. Application of 21 doses of 20 and 40 mg/kg/day to the skin of rabbits caused no effects other than local skin irritation (19). The acute dermal LD50 for butylate is greater than 4,640 mg/kg in rabbits (13). Butylate caused irritation to the eyes of rabbits (19).

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. The oral LD50 for butylate ranges from 1,659 milligrams per kilogram (mg/kg) in male guinea pigs, to 5,431 mg/kg in female rats. 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. Butylate's 2- hour LC50 is 19 milligrams per liter (mg/l) (3, 19).

CHRONIC TOXICITY

Prolonged or repeated exposure to butylate may cause symptoms similar to the pesticide's acute effects.

In a study where dogs were fed 11, 23 or 45 mg/kg/day for 16 weeks, no remarkable effects were observed. In another study, rats fed 180 mg/kg/day for 15 weeks were not adversely affected. Rats fed 8, 16 and 32 mg/kg/day for 13 weeks were not affected (19). There were no changes in behavior, body weight, nerve or eye function, blood chemistry, nor organ appearance and weight, in dogs that were fed butylate for 13 weeks (11). Rats and dogs tolerated daily dietary doses of 40 mg/kg of the herbicide for 13 weeks (2).

When butylate was fed to rats at doses of 50, 100, 200, or 400 mg/kg/day for two years, body weights were decreased and liver to body weight ratios increased with all but the lowest dose tested. In rats fed 20, 80 or 120 mg/kg/day for 2 years, no effects were observed at the 20 mg/kg dose, but kidney and liver lesions formed at the two higher doses. Butylate fed to rats at 10, 30 and 90 mg/kg/day for 56 weeks affected blood clotting at all doses. At the two higher doses body weight and testes/body weight ratios decreased, liver to body weight ratios increased, and lesions formed on the testes. In a study of dogs fed 5, 25, or 100 mg/kg/day for 12 months, decreased body weights, increased liver weights, and increased incidence of liver lesions were observed at the highest dose (19).

The EPA has established a Lifetime Health Advisory (LHA) level for butylate in drinking water at 700 micrograms per liter. This means that the EPA believes that water containing butylate at or below this level is acceptable for drinking every day over the course of one's lifetime, and does not pose any health concerns.

Reproductive Effects

No reproductive effects were observed in test animals receiving doses of up to 24 mg/kg of butylate (11).

In a study of two generations of offspring from rats fed 0, 10, 50 or 200 mg/kg/day for 63 days before mating, decreased body weight was observed in both generations at the 50 mg/k/day dose. Decreased brain weights were observed in the first generation of offspring at the 50 mg/kg/day dose. At 200 mg/kg/day, adverse effects on the eyes and kidneys of the first generation were observed. No effects were observed at the 10 mg/kg/day dose (19).

Long-term consumption of concentrations well above the Lifetime Health Advisory level (700 ug/l) of butylate has caused damage to the testes, liver and kidneys, and to delayed fetal development in test animals (18).

Teratogenic Effects

No teratogenic effects were observed in mice ingesting 4-24 mg/kg/day of Sutan from the sixth through eighteenth days of gestation/pregnancy. No teratogenic effects were observed in the offspring of rats given up to 1,000 mg/kg/day on days 6 through 20 of gestation or in the offspring of rabbits given doses of up to 500 mg/kg/day on days 6 through 18 of gestation (11, 19).

Mutagenic Effects

Mutation was seen in mice given oral doses of one gram per kilogram (g/kg) of the herbicide (6). It was not mutagenic in the Ames test, performed on Salmonella bacteria (8, 19).

Carcinogenic Effects

There was no tumor formation related to doses of up to 320 mg/kg/day of the herbicide in a 24-month study of rats. The EPA has determined that there is no evidence that butylate produces cancers in humans or in animals (11, 19).

Organ Toxicity

Liver changes were produced by 180 mg/kg dietary doses in a 56-week rat study with butylate. Blood clotting was affected by ten mg/kg/day in the same experiment (11). Several studies have shown that long-term exposure to high doses of butylate have caused increases in liver weights in test animals (19).

Fate in Humans and Animals

Butylate is rapidly metabolized and excreted in animals (11). Within 48 hours after administration of radio-labeled butylate to rats by gavage, 27.3 to 31.5% of the radioactivity was eliminated through the urine, 60.9 to 64 % was expired as carbon dioxide, and 3.3 to 4.7% was excreted in the feces. Only 2.2 to 2.4% of the administered radioactivity was retained in the body, with most of this located in the blood, kidneys and liver. The same pattern of rapid elimination was exhibited in two other studies with rats (19).

ECOLOGICAL EFFECTS

Effects on Birds

Given its low toxicity and low exposure rates, butylate is considered a minimal hazard to birds by the EPA (11). Technical butylate has an acute oral LD50 greater than 4,640 mg/kg in mallard ducks. Its 8-day dietary LC50 in bobwhite quail is estimated at 40,000 parts per million (ppm) (12).

Effects on Aquatic Organisms

Butylate is moderately toxic to fish (3). It has a low to moderate potential for bioaccumulation in fish (19). With the low exposure rates expected from registered use and proper disposal practices, there should not be any risk posed by this material to aquatic invertebrates (11). The LC50 for a 96-hour exposure to technical Sutan ranges from 4.2 ppm in rainbow trout, to 6.9 ppm in bluegill sunfish (8).

Effects on Other Animals (Nontarget Species)

Butylate is not harmful to bees if it is used appropriately (3). The herbicide appears to pose few, if any, acute toxicological hazards to nontarget wildlife (11).

ENVIRONMENTAL FATE

Reportedly, butylate does not pose very much risk to the environment because its residues are short-lived (8).

Breakdown of Chemical in Soil and Groundwater

Butylate is one of the pesticide compounds considered by the US EPA to have the greatest potential for leaching into groundwater (9). Butylate is only slightly soluble in water (46 micrograms/ml). It degrades fairly rapidly with a soil half life of 3 to 10 weeks in moist soils under aerobic conditions. Under anaerobic conditions, butylate degrades with a half-life of 13 weeks (19). In loamy soil, at 70-80 degrees F, its half-life is three weeks (13). Soil half-lives of 12 days and 1.5 to 3 weeks have also been reported (13, 17). Butylate does not strongly adsorb to soil particles (Koc = 126 g/ml) and is considered to be slightly to highly mobile in soils, depending on the soil type (17, 19). Leaching is more likely to occur in sandy, dry soils, while leaching is less likely to occur in soil with higher amounts of organic matter and clay. A study conducted by the EPA in the United States did not find butylate in groundwater samples (10). Another study found butylate in 2 out of 152 groundwater samples analyzed (19).

Butylate degrades to sulfoxide in soil (5). Butylate has a residual activity in soil of approximately four months, when it is applied at five to six kilograms per hectare (kg/her) (3). It is broken down primarily by soil organisms (microbes) in a process called microbial degradation. When applied to dry soil surfaces, very little butylate is lost through vaporization. However, it can be lost by vaporization when applied to the surface of wet soils without being sufficiently incorporated (13). 45 to 50% of butylate applied to a clay loam soil was recovered as volatilized gas during the three weeks following application (19).

Breakdown of Chemical in Water

Butylate should not be applied directly to water or wetlands, and water should not be contaminated by cleaning of butylate application equipment or disposal of related wastes (11). Very low concentrations of butylate (maximum of 4.70 micrograms/liter) were found in 91 of 836 surface water samples analyzed (19).

Breakdown of Chemical in Vegetation

Butylate is readily adsorbed by plant leaves, but as it is normally applied to soil, it does not usually come in contact with foliage. Once it is applied to the soil, butylate is rapidly taken up by the roots of corn plants and moved upward throughout the entire plant (13). Butylate is rapidly metabolized in corn roots and leaves, to carbon dioxide, fatty acids and certain natural plant constituents (12, 13).

The herbicide is not thought to persist in plants since it disappeared from the stems and leaves of corn plants seven to 14 days after treatment. It does not have contact activity, that is, the injury that it causes is not limited to that part of the plant to which it is applied (7).

PHYSICAL PROPERTIES AND GUIDELINES

Technical butylate is a clear amber to yellow liquid with an aromatic odor (1, 14, 16). Precautions should be taken to avoid skin and eye contact, and inhalation or drift exposure to butylate (3). Under normal ambient conditions, butylate reportedly has an indefinite storage life (13). It is noncorrosive, but it is hydrolyzed by strong acids and bases (3). Thermal decomposition may release toxic oxides of nitrogen and sulfur (20).

Occupational Exposure Limits:

No occupational exposure limits for butylate have been established by OSHA, ACGIH or NIOSH (20).

Exposure Guidelines:

NOEL: A NOEL of 32 mg/kg/day was set based on a 90-day dietary feeding study of rats.
A NOEL of 40 mg/kg/day was set based on a 90-day dietary study in dogs (13).

Physical Properties:

CAS #: 2008-41-5
H2O solubility: 44 ppm in water at 20 degrees C (8); 45 ppm (10)
  • 0.03% in water at room temperature (3)
Solubility in other solvents: miscible with kerosene, xylene, acetone, ethyl-alcohol and other organic solvents (8, 20)
Boiling point: 160 degrees F (71 degrees C) at 10 mmHg (20)
Specific gravity: 0.9402 at 20 degrees C (20)
Vapor pressure: 13 x 10 to the minus 3 power mm at Hg at 25 degrees C (13)
Koc: 540 (soil-water distribution coefficient divided by the organic carbon content and calculated by log Koc = 3.64-0.55 [log water solubility in ppm] + 1.23) (11)
Kd: 1.4-5.0; 2.5-8.9 (11). Soil-water distribution coefficient or adsorption constant from column leaching or TLC studies.
  • Soil/field dissipation of ambient pH and temperature from lab studies showed three to ten week half-life (11)
Chemical Class/Use: Thiocarbamate fungicide

BASIC MANUFACTURER

Zeneca Ag Products
Wilmington, DE 19897
Telephone: (302) 886-1000

Review by Basic Manufacturer:

Comments solicited: November, 1992
Comments received:

REFERENCES

  1. Berg, G. L., ed. 1986. Farm chemicals handbook. Willoughby, OH: Meister Publishing Company.
  2. Gosselin, R. E., et al. 1984. Clinical toxicology of commercial products. Fifth edition. Baltimore, MD: Williams and Wilkins.
  3. Hartley, D. and H. Kidd. (eds.) 1983. The agrochemicals handbook. Nottingham, England: Royal Society of Chemistry.
  4. McEwen, F. L. and G. R. Stephenson. 1979. The use and significance of pesticides in the environment. NY: John Wiley and Sons, Inc.
  5. Menzie, C. M. 1980. Metabolism of pesticides. Update III. U.S. Department of the Interior. Fish and Wildlife Service. Special Scientific Report. Wildlife No. 232. Washington, DC: U.S. Government Printing Office.
  6. National Institute for Occupational Safety and Health (NIOSH). 1981-1986. Registry of toxic effects of chemical substances (RTECS). Cincinnati, OH: NIOSH.
  7. Thomson, W. T. 1986. Herbicides. Agricultural Chemicals, Book II. Fresno, CA: Thomson Publications.
  8. TOXNET. 1975-1986. National library of medicine's toxicology data network. Hazardous Substances Data Bank (HSDB). Public Health Service. National Institute of Health, U. S. Department of Health and Human Services. Bethesda, MD: NLM.
  9. U. S. Environmental Protection Agency. 1987 (Feb. 4). EPA's Environmental News.
  10. _____. 1984. Memorandum from Stuart Z. Cohen. List of potential groundwater contaminants. Office of Pesticides and Toxic Substances. Washington, DC. Photocopy.
  11. _____. 1984 (Mar.). Chemical fact sheet for butylate. Fact sheet number 7. Office of Pesticide Programs. Washington, DC.
  12. _____. 1983 (Sept. 30). Guidance for the reregistration of pesticide products containing butylate as the active ingredient. Washington, DC.
  13. Weed Science Society of America. 1983. Herbicide handbook. Fifth edition. Champaign, IL: WSSA, Herbicide Handbook Committee.
  14. Worthing, C. R., ed. 1983. The pesticide manual: a world compendium. Croyden, England: The British Crop Protection Council.
  15. Hayes, W.J. and E.R. Laws (ed.). 1990. Handbook of Pesticide Toxicology, Vol. 3, Classes of Pesticides. Academic Press, Inc., New York.
  16. Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister Publishing Company, Willoughby, Ohio.
  17. U.S. Department of Agriculture, Soil Conservation Service. 1990 (Nov). SCS/ARS/CES Pesticide Properties Database: Version 2.0 (Summary). USDA - Soil Conservation Service, Syracuse, NY.
  18. U.S. Environmental Protection Agency. 1989 (Jan.). Health Advisory Summary: Butylate. US EPA, Washington, DC.
  19. U.S. Environmental Protection Agency. 1989 (Feb.). Butylate: Health Advisory. Office of Drinking Water, US EPA, Washington, DC.
  20. Occupational Health Services, Inc. 1991 (Feb. 21). MSDS for Butylate. OHS Inc., Secaucus, NJ.