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Trifluralin

Publication Date: 9/93

TRADE OR OTHER NAMES

Some trade names include Flurene SE, Treflan, Tri-4, Trust, M.T.F., Trifluralina 600, Elancolan, Su Seguro Carpidor, Trefanocide, Treficon, Trim, L-36352, Crisalin, TR-10, Triflurex and Ipersan.

REGULATORY STATUS

In August, 1979, trifluralin was brought under Special Review by the EPA because of the presence of a N-nitrosamine contaminant which had been shown to cause tumors and to have mutagenic effects in animals. The principle manufacturer of trifluralin had already instituted manufacturing methods to reduce N-nitrosamine contaminant levels. The Special Review was concluded in 1982, with the requirement that N-nitrosamine contaminant levels in trifluralin not exceed 0.5 ppm, a level which EPA believes will have no toxic effects (12, 13).

Products containing trifluralin must bear one of the signal words "Caution" or "Warning," depending on the type of formulation (3).

INTRODUCTION

Trifluralin is a selective, preemergence dinitroaniline herbicide used to control many annual grasses and broadleaf weeds in a large variety of tree fruit, nut, vegetable, and grain crops. Preemergence herbicides are applied before weed seedlings sprout. Trifluralin should be incorporated into the soil by mechanical means within 24 hours of application. Granular formulations may be incorporated by overhead irrigation. Trifluralin is available in granular and emulsifiable concentrate formulations (2, 3, 8, 9).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Trifluralin is not acutely toxic to test animals by oral, dermal or inhalation routes of exposure (12). Pesticide products containing trifluralin may be moderately toxic to relatively non-toxic, depending on the type of formulation (3). Nausea and severe gastrointestinal discomfort may occur after eating trifluralin.

Trifluralin does not cause skin irritation. When applied to the eyes of rabbits, trifluralin produced slight irritation which cleared within 7 days (7). Skin sensitization (allergies) may occur in some individuals (1, 9). Inhalation may cause irritation of the lining of the mouth, throat or lungs (7). The solvent in emulsifiable concentrates of trifluralin may cause irritation to the skin. Most cases of poisoning result from the carrier or solvent in formulated trifluralin products, rather than from the trifluralin itself (NRC Drinking Water and Health. 1977).

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 technical trifluralin in rats is greater than 10,000 mg/kg, in mice is greater than 5,000 mg/kg, and in dogs, rabbits and chickens is greater than 2,000 mg/kg. However, certain formulated products which contain trifluralin may be more toxic than the technical material itself. For example, the oral LD50 for Treflan TR-10 in rats is >500 mg/kg. The dermal LD50 for technical trifluralin in rabbits is >2,000 mg/kg.

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. The 1-hour LC50 for technical trifluralin in rats is >2.8 mg/l (2, 3).

CHRONIC TOXICITY

Prolonged or repeated skin contact with trifluralin may cause allergic dermatitis (7). The administration of 25 mg/kg to dogs for 2 years resulted in no toxicological effects (2).

The EPA has established a Lifetime Health Advisory (LHA) level of 5 micrograms per liter (ug/l) for trifluralin in drinking water. This means that EPA believes that water containing trifluralin 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. However, consumption of trifluralin at high levels well above the LHA level over a long period of time has been shown to cause liver and kidney damage, decreased fetal weight and size, and increased miscarriages in animal studies (11).

Reproductive Effects

The reproductive capacity of rats fed dietary concentrations of trifluralin as high as 10 mg/kg was unimpaired through 4 successive generations, and no abnormalities were detected in the parents or the offspring. Trifluralin administered to pregnant rabbits at doses as high as 100 mg/kg, and to rats at doses as high as 225 mg/kg, produced no adverse effect on either the mothers or offspring (2).

Loss of appetite and weight loss followed by miscarriages were observed when pregnant rabbits were fed 224 or 500 mg/kg/day. Fetal weight decreased and there was an increase in the number of fetal runts at the 500 mg/kg/day dosage (7).

Teratogenic Effects

No abnormalities were observed the offspring of rats fed doses as high as 10 mg/kg for 4-generations (2). Studies in the rat and rabbit show no evidence that trifluralin is teratogenic. The highest doses tested in these studies were 1,000 mg/kg/day in rats and 500 mg/kg/day in rabbits (12).

Mutagenic Effects

No evidence of mutagenicity was observed when trifluralin was tested in live animals, and in assays using bacterial and mammalian cell cultures (12).

Carcinogenic Effects

EPA considers trifluralin to be a possible human carcinogen (11). This classification is used when there is limited or uncertain information indicating that a chemical may cause cancer in animals receiving high doses of the chemical over the course of their lifetimes. In a 2-year study of rats fed 325 mg/kg/day, the highest dose tested, malignant tumors developed in the kidneys, bladder and thyroid (7, 12). Because there is a possible increase in the risk of cancer to humans, EPA's Lifetime Health Advisory level for trifluralin drinking water includes an additional safety margin (11).

Organ Toxicity

Consumption of trifluralin at high levels well above the EPA's Lifetime Health Advisory level for drinking water (5 ug/l) over a long period of time has been shown to cause liver and kidney damage, in animal studies (11).

Fate in Humans and Animals

Trifluralin is not readily absorbed into the bloodstream from the gastrointestinal tract. 80% of single oral doses administered to rats and dogs was excreted in the feces (7).

ECOLOGICAL EFFECTS

Effects on Birds

Trifluralin is not hazardous to birds (2, 4). The LD50 for bobwhite quail was greater than 2000 mg/kg. The 5-day LC50 in both quail and ducks was greater than 5,000 mg/kg (2).

Effects on Aquatic Organisms

Trifluralin is toxic to fish and other aquatic organisms. However, its strong adsorption to soil and the usual practice of incorporating trifluralin into the soil at the time of application may prevent exposure of fish to this herbicide. Run-off from fields should be avoided. Contamination of open waters during mixing and loading operations by rinseate from the cleaning of application equipment or by accidental spills should be avoided (2). Trifluralin is toxic to Daphnia, a small freshwater crustacean (Hdbk. Acute Tox. Chem. Fish and Aqua. Invert. 1986).

Effects on Other Animals (Nontarget species)

At exposure levels well above permissible application rates (100 ppm), trifluralin has been shown to be toxic to earthworms. However, permitted application rates will result in soil residues of approximately 1 ppm trifluralin, a level that had no adverse effects on earthworms. (10, Proc. NZ. Weed Pest. Control Conf. 35th: 328. 1982). In general, trifluralin is not very toxic to higher animals (except fish) (8). Birds are very resistant to trifluralin (4, 8). It is non-toxic to bees (3, 8).

ENVIRONMENTAL FATE

Breakdown of Chemical in Soil and Groundwater

The substituted dinitroanilines do not move much in the soil, but remain where they are placed at application (Casarett & Doull's Tox. 2nd Ed. 1980). Trifluralin is strongly absorbed on soils (Koc = 7,000 g/ml) and nearly insoluble in water (6). Therefore leaching and groundwater contamination by trifluralin is not expected to occur. Because adsorption is highest in soils high in organic matter or clay content and adsorbed herbicide is inactive, higher application rates may be required for effective weed control on such soils (5, 2).

Trifluralin is subject to degradation by soil microorganisms. Trifluralin remaining on the soil surface after application may be decomposed by UV light or may volatilize. Recommended application rates give season long weed control, but fall-seeded grain crops planted in soil treated with trifluralin during the preceding spring were not injured under warm, moist conditions (2). The half-life of trifluralin in the soil is 45 to 60 days (6) or about 6-8 months (2.5 kg/ha) (8). After six months to one year, 80- 90% of its activity will be gone (5).

Breakdown of Chemical in Water

Trifluralin is nearly insoluble in water (8). Contamination of lakes and streams should be avoided because fish are sensitive to trifluralin.

Breakdown of Chemical in Vegetation

Trifluralin inhibits the growth of roots and shoots when it is absorbed by the roots of newly germinated weed seedlings (2, 8, 12). There is no significant absorption or translocation of trifluralin in crops grown in soil treated with trifluralin. Trifluralin residues in crop plants will occur only on root tissues which are in direct contact with contaminated soil. Trifluralin is not translocated into the leaves, seeds or fruit of most plants. On most crops, trifluralin applied to the leaves has no effect, but on certain crops, such as tobacco and summer squash, leaf distortion may occur (2).

PHYSICAL PROPERTIES AND GUIDELINES

Trifluralin is an odorless, yellow-orange crystalline solid (2). Trifluralin will decompose in both sunlight and artificial light (7). Trifluralin is stable under normal temperatures and pressures, but it may pose a slight fire hazard if exposed to heat or flame. It poses a fire and explosion hazard in the presence of strong oxidizers. Thermal decomposition of trifluralin will release corrosive fumes of hydrogen fluoride and toxic oxides of nitrogen (7).

Technical trifluralin is not flammable, but emulsifiable concentrate formulations containing trifluralin may be flammable. The product Treflan EC is classified as a combustible liquid. Closed containers of this product may explode if exposed to excessive heat or intense fire (2).

It is recommended that applicators wear full protective clothing when spraying trifluralin. This gear should include neoprene gloves, rubber workshoes, rubber apron, goggles to protect the eyes and a respirator to prevent inhalation of fumes or mists (1).

Occupational Exposure Limits:

No occupational exposure limits have been established for trifluralin by OSHA, NIOSH or ACGIH (7).

Physical Properties:

CAS#: 1582-09-8
Specific gravity: 1.294 at 25 degrees C (7)
Solubility in water: practically insoluble; 0.0024% at 27 degrees C (7)
Solubility: readily soluble in organic solvents such as xylene, acetone and aromatic napthas (3).
Solvent Solubility at 25 degrees C
Acetone > 50 g/100 ml (2)
Methanol 2 g/100 ml (2)
Xylene 81 g/100 ml (2)
Boiling point: 139-140 degrees C (282-284 degrees F) at 4.2 mm Hg (2, 15); 96-97 degrees C at 0.18 mm Hg (2)
Melting point: 46-47 degrees C (115-117 degrees F) (7)
Flash point: Technical material is not flammable. However, emulsifiable concentrate formulations may be flammable.
Vapor pressure: 1.99 x 10 to the minus 4 mm Hg at 29.5 degrees C (2)
pH: 7.0 (50% suspension) (7)
Koc: 7000 g/ml (6)
Soil half-life: 60 days (6)
ADI: 0.1 mg/kg/day (14)

BASIC MANUFACTURER

DowElanco
9002 Purdue Rd.
Indianapolis, IN 46268-1189

Review by Basic Manufacturer:

Comments solicited: November, 1992
Comments received: December, 1992

REFERENCES

  1. Meister, R.T. (ed.). 1987. Farm Chemicals Handbook. Meister Publishing Co., Willoughby, OH.
  2. WSSA Herbicide Handbook Committee. Herbicide Handbook of the Weed Science Society of America, 6th Ed. WSSA, Champaign, IL. 1989.
  3. Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister Publishing Company, Willoughby, OH.
  4. Tucker, Richard. 1970. Handbook of Toxicity of Pesticides to Wildlife. USDI Fish and Wildlife Service.
  5. Worthing, C.R. (ed.). 1987. The Pesticide Manual. 8th Ed. British Crop Protection Council.
  6. 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.
  7. Occupational Health Services, Inc. 1991. MSDS for Trifluralin. OHS Inc., Secaucus, NJ.
  8. The Agrochemicals Handbook. 1983. The Royal Society of Chemistry.
  9. Crop Protection Chemicals Reference. 1986. 2nd Ed. Chemical and Pharmaceutical Press.
  10. Barber, Daniel T., Manager, State Regulatory Affairs. Letter of Dec. 3, 1991. DowElanco, Indianapolis, IN.
  11. US Environmental Protection Agency. 1989 (Jan.). Health Advisory Summary: Trifluralin. US EPA, Washington, DC.
  12. _____. 1987 (Aug.). Guidance for the reregistration of pesticide products containing trifluralin as the active ingredient. Office of Pesticides and Toxic Substances, US EPA, Washington, DC.
  13. _____. 1982 (Aug. 4). Trifluralin; Determination concluding the Rebuttable Presumption Against Registration; Notice of availability of position documents. Federal Register 47 (150): 33777-84.
  14. _____. 1982 (Feb. 10). Trifluralin: proposed tolerances. Federal Register 47 (28): 6033-4.
  15. Merck Index. 1976. 9th Ed.