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Bromoxynil

Publication Date: 5/94

TRADE OR OTHER NAMES

Trade names for commercial products containing bromoxynil include Brominal, Bromotril, Buctril, Bronate, Certrol B, Litarol, M&B 10064, Merit, Pardner, and Sabre. Discontinued products include Chipco, Buctril, Harness and Torch. This compound may also be found in mixed formulations with a wide variety of other herbicides including MCPA, linuron, dicamba, mecoprop, and 2,4-D.

INTRODUCTION

Bromoxynil is a nitrile herbicide that is used for post-emergent control of annual broadleaved weeds. It is especially effective in the control of weeds in cereal, corn, sorghum, onions, flax, mint, turf, and on non-cropland. The compound works by inhibiting photosynthesis in the target plants.

Bromoxynil is a Restricted Use Pesticide (RUP), and is not registered for homeowner use. RUPs may be purchased and used only by certified applicators.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Bromoxynil is a moderately toxic compound and carries the signal word WARNING on the label.

The compound has an oral acute LD50 of 779 mg/kg in the rat (specifically for the product Buctril) and a LD50 of 691 mg/kg in the rat for Bronate. The technical material has an acute oral LD50 of 190 mg/kg in rats (1), an LD50 of 260 mg/kg in rabbits, and an LD50 of 63 mg/kg in guinea pigs (4). Dermal acute toxicity of bromoxynil is greater than 2,000 mg/kg for rabbits. The compound is a slight eye irritant (1) and it is not a skin irritant in rabbits (2). However, when in contact with abraded skin, bromoxynil may produce a mild irritation (3).

CHRONIC TOXICITY

Dogs fed bromoxynil for 90 days at low doses showed unspecified adverse effects at and above 5 mg/kg. In the same type of test, the compound had no observable effect on rats at or below a 16.6 mg/kg/day dose (1). In another study at low doses (up to 50 mg/kg), rats developed no significant abnormalities (3). In other tests with rats administered low doses (up to 5 mg/kg) for up to two years, there were no significant changes in blood chemistry or in urine (3).

In one documented case of chronic exposure of humans, workers showed symptoms of weight loss, fever, vomiting, headache and urinary problems (3). Chronic exposure for these four individuals had lasted for about one year.

Reproductive Effects

No changes in reproduction were noted in female rats fed low amounts of bromoxynil (15 mg/kg/day) over three generations of litters (3).

Teratogenic Effects

Bromoxynil is a suspected teratogen. The compound produced birth defects in rats at low oral doses (above 35 mg/kg). The compound was toxic to the mother and to the fetus at these low doses as well. Toxic effects included abnormal rib formation, and reduced fetal weight. Newborn rabbits had birth defects when bromoxynil was administered to pregnant mothers at doses above 30 mg/kg (3). In the rabbit, birth defects included changes in bone formation in the skull and hydrocephaly. The available evidence indicates that bromoxynil may pose a teratogenic risk to humans.

Mutagenic Effects

No information is currently available.

Carcinogenic Effects

Rats fed bromoxynil in their diets at low levels of 5 mg/kg and below did not develop any cancer related effects (3).

Organ Toxicity

No information is currently available.

Fate in Animals and Humans

No bromoxynil was present in the milk or feces of cows nine days after exposure to low doses of the herbicide. Less than twenty percent of the compound was excreted in urine as the parent compound (3). No other information on the breakdown of bromoxynil in humans or animals is currently available.

ECOLOGICAL EFFECTS

Bromoxynil is highly toxic to pheasants (LC50 of 50 mg/kg) and is moderately toxic to hens (LC50 of 240 mg/kg), quail (LC50 of 100 mg/kg), and mallard ducks (LC50 of 200 mg/kg) (2). The compound is very highly toxic to moderately toxic to freshwater fish. The toxicity level is dependent on the species tested. Bromoxynil has an LC50 of 5.0 mg/l in harlequin fish (potassium salt), 0.15 mg/l in rainbow trout (octanoate), 0.46 in goldfish, and 0.063 in catfish (1).

Bromoxynil is not toxic to bees (2).

ENVIRONMENTAL FATE

In sandy soil, the half-life of bromoxynil is about ten days (2). During that time bromoxynil is broken down to less toxic compounds. Degradation in clay was slower, with half of the bromoxynil degraded to its metabolites in about a two week period at 25 degrees C (3). The persistence of the compound is also a bit longer in peat field soils than in the sandy soils (5). The evidence suggests that, while bromoxynil is broken down by some soil bacteria, it may inhibit the action of other bacteria. More specifically, it inhibits the bacteria that promote the formation of nitrite (NO3), by a process called nitrification (3).

In plants, the herbicide works by disrupting the plants ability to produce energy for cell related activities. The herbicide is not readily translocated throughout the plant once it has been absorbed (3).

Information about the movement of bromoxynil or its presence or absence in water and groundwater is currently unavailable.

Exposure Guidelines:

NOEL: 5 mg/kg (dog); 16.6 mg/kg (rat)
ADI: not available
RfD: 0.02 mg/kg/day (3)

Physical Properties:

CAS #: 1689-84-5
Chemical name: 3,5-dibomo-4-hydroxybenzonitrile
Chemical class/use: nitrile herbicide
Solubility in water: 130 mg/l at 25 degrees C
Solubility in other solvents: 90 g/l methanol; 70 g/l ethanol; 170 g/l acetone; 170 g/l cyclohexane; 410 g/l tetrahydofuran, all at 25 degrees C.
Melting Point: 194-195 degrees C
Vapor pressure: less than 1 mPa at 20 degrees C

BASIC MANUFACTURER

Rhone Poulenc
P.O. Box 12014
2 T.W. Alexander Drive
Research Triangle Park, N.C. 27709
Telephone 919-334-7577

Review by Basic Manufacturer:

Comments solicited: November, 1991
Comments received:

REFERENCES

  1. Worthing, Charles R. 1991. The Pesticide Manual: A World Compendium. Ninth Edition. The British Crop Protection Council.
  2. The Agrochemicals Handbook. 1991. The Royal Society of Chemistry. Cambridge, England.
  3. Hazardous Substance Data Base. 1992. National Library of Medicine. Toxnet. Bromoxynil.
  4. Registry of Toxic Effects of Chemicals. 1981-1982. pg. 639.
  5. Smith, Allan. E. 1980. An Analytical Procedure for Bromoxynil and its Octanoate in Soils; Persistence Studies with Bromoxynil Octanoate in Combination with Other Herbicides in Soil. Pesticide Science. 11, 341-346.