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

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Bromacil

Publication Date: 9/93

TRADE OR OTHER NAMES

Borea, Bromax 4G, Bromax 4L, Borocil, Rout, Cynogan, Uragan, Isocil, Hyvar X, Hyvar XL, Urox B, Urox HX, Krovar.

REGULATORY STATUS

Bromacil is classified by the U. S. Environmental Protection Agency (EPA) as a general use herbicide. Dry formulations containing bromacil must bear the signal word "Caution" and liquid formulations must bear the signal word "Warning" (29).

INTRODUCTION

Bromacil is an herbicide used for brush control on non-cropland areas. It is especially useful against perennial grasses. It is also used for selective weed control in pineapple and citrus crops. It works by interfering with photosynthesis, the process by which plants use sunlight to produce energy. Bromacil is available in granular, liquid, water soluble liquid, and wettable powder formulations (5, 29).

Bromacil is one of a group of compounds called substituted uracils. These materials are broad spectrum herbicides used for nonselective weed and brush control on non-cropland, as well as for selective weed control on a limited number of crops, such as citrus fruit and pineapple (3). The herbicide is preferably sprayed or spread dry on the soil surface just before, or during, a period of active weed growth (19).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Liquid formulations of bromacil are moderately toxic, while dry formulations are relatively non-toxic (29). Hyvar X-L formulation can be harmful or fatal if swallowed (5, 6, 29). Industrial and agricultural workers are exposed to the wettable powders and aqueous emulsions of bromacil through two primary routes of exposure: inhalation of dusts and sprays, and skin contact with dusts, emulsions and sprays (3). The herbicide is irritating to the skin, eyes and respiratory tract (12).

When as little as 100 mg/kg of the herbicide was fed to dogs, it caused vomiting, watering of the mouth, muscular weakness, excitability, diarrhea, and dilation of the pupils of the eyes. Rats that were fed single doses of bromacil experienced initial weight loss, paleness, exhaustion, and rapid breathing (15). Within four hours of being given 250 mg/kg of this, or a related material (isocil), sheep became bloated and walked with stilted gaits (5). Bromacil caused mild dermal irritation when it was applied to the skin of guinea pigs. Rabbits did not show clinical signs of poisoning, or toxicity, in response to skin applications of 5,000 mg/kg of the herbicide (1, 5). When bromacil was put in the eyes of rabbits, there was irritation in the conjunctiva, the mucous membrane lining of the eye, but there was no injury to the cornea, the transparent portion of the eyeball (5).

Because bromacil has a low vapor pressure, it is unlikely to produce vapors which can be inhaled. No deaths occurred when rats were exposed to approximately 4.8 milligrams of bromacil per liter of air (mg/l) for four-hours (1, 15).

Bromacil poses a moderate threat when it is ingested by animals (18). The amount of bromacil that is lethal to one-half (50%) of the test animals, when it is given orally, is called its acute oral lethal dose fifty, or LD50. The oral LD50 for bromacil in rats is 5,200 mg/kg, and in mice is 3040 mg/kg (5, 12, 15).

CHRONIC TOXICITY

Sheep died after being given 250 mg/kg doses of bromacil on four successive days. One dog survived a single dose of five grams per kilogram (gm/kg), but rats died after five days of being given repeated daily doses of 1,500 mg/kg (5). Autopsy revealed enlarged livers in the rats (5). In another study, rats were fed 0, 2.5, 12.5 or 62.5 mg/kg/day for 2 years. Female rats at the highest dose level exhibited decreased weight gain. No other toxic effects were observed and a NOAEL of 12.5 mg/kg/day was established (32). No evidence of toxicity was detected in dogs fed up to 31.2 mg/kg/day for 2 years (32). In an 18- month study in which mice were given dietary doses of 12.5, 62.5 or 250 mg/kg/day, changes in the liver and testes were observed at the 62.5 mg/kg dosage (24, 32). Even though chickens appeared to tolerate one 500 mg/kg dose of bromacil, they did show a decrease in weight gain (23).

The EPA has established a Lifetime Health Advisory (LHA) level of 90 micrograms per liter (ug/l) for bromacil in drinking water. This means that EPA believes that water containing bromacil 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 bromacil at high levels well above the LHA level over a long period of time has been shown to cause damage to the testes, liver and thyroid of laboratory animals (31).

Reproductive Effects

Bromacil did not affect the reproduction and lactation performance of rats fed 0 or 12.5 mg/kg/day for 3 generations (19, 32). Toxic effects and developmental abnormalities of the musculoskeletal system were seen in the embryos or fetuses of female rats which inhaled 38 mg/m3 of bromacil for two hours daily, during the 7th to 14th day of pregnancy (13).

Teratogenic Effects

There was no evidence of birth defects in the offspring of rats that were given dietary concentrations of 12.5 mg/kg/day nor in rabbits that were given 7.5 mg/kg/day on days 8 through 16 of pregnancy (1, 32). No prenatal or teratogenic effects were observed when pregnant rats were exposed to aerosols of bromacil (165 mg/m3) on days 7 to 14 of pregnancy (32). Toxic effects and developmental abnormalities were observed in the fetuses of pregnant rats repeatedly exposed by inhalation to bromacil (15).

Mutagenic Effects

Several mutagenic screening tests have not found bromacil to be mutagenic (3, 32).

Carcinogenic Effects

Although bromacil has not been determined to cause cancer, it is considered by the EPA to be a possible human carcinogen because there is some limited or uncertain evidence that bromacil causes cancer in animals receiving high doses of the chemical over the course of their lifetimes (31, 32).

Thirty-six male and 36 female weanling rats were fed dietary doses of 2.5, 12.5 or 62.5 mg/kg/day for 2 years. There was no evidence of carcinogenicity in rats fed 12.5 mg/kg of bromacil. At the 62.5 mg/kg dose, there was at slight increase in hyperplasia of the thyroid, and one individual developed benign liver tumors (1, 32). When mice were fed dietary doses of 0, 12.5, 62.5 or 250 mg/kg/day for 78 weeks, an increased incidence of both malignant and benign tumors was observed in the livers of male mice given 250 mg/kg of bromacil. No effect on liver tumor incidence was observed in female mice (24, 32).

Organ Toxicity

Enlarged livers were revealed in autopsies on rats that died after five days of repeated doses of bromacil at 1,500 mg/kg/day (5). Sheep that died after being given 250 mg/kg/day of bromacil on four successive days showed the following disease-related findings: inflammation of the mucous membrane that lines the stomach and intestines, or 'gastroenteritis;' congestion and enlargement of the liver; weakened appearance of the adrenal glands; bleeding of the heart; swollen and bleeding lymph nodes (5).

Fate in Humans and Animals

A number of studies show that the substituted uracils, the class of compounds to which bromacil belongs, are absorbed into the body from the gut and excreted primarily in the urine (14, 16, 32). Small amounts of bromacil were detected in the milk of lactating cows that were given five ppm in their food (5). No bromacil was found in the urine or feces of these cows (16).

ECOLOGICAL EFFECTS

Effects on Birds

The 8-day oral LD50 for bromacil is over 10,000 ppm in mallards and quail (3).

Effects on Aquatic Organisms

The median tolerance limit, or the concentration of bromacil that will kill 50% of the exposed fish after 48 hours of exposure, varies from 40 ppm to 164 ppm, depending on the type of fish tested (3). The 48-hour LC50 for bromacil in bluegill sunfish is 71 ppm, in rainbow trout is 56-75 ppm, and in carp is 164 ppm (19). The 96-hour LC50 in fathead minnows is 182 mg/l (33).

Effects on Other Animals (Nontarget Species)

Tadpoles have a 48-hour median tolerance limit of 230 ppm bromacil (3). The herbicide is not toxic to either aquatic invertebrates or honeybees (24, 29).

ENVIRONMENTAL FATE

Breakdown of Chemical in Soil and Groundwater

Bromacil binds, or adsorbs, only lightly to soil particles (Koc = 32 g/ml), is soluble in water, and has a relatively lengthy soil half- life (60 days). For these reasons, bromacil is expected to move (leach) quite readily through the soil and it can contaminate groundwater. It was weakly adsorbed by soils when it was applied at rates of 4 and 1.5 l/hr in tests conducted to study the effects of wetting and drying cycles on the herbicide. After several cycles of wetting and drying, the herbicide was completely leached from the original application sites and was concentrated at the outer edges of the wetted zones. Offsite leaching is the main route by which bromacil disappears from treated soils. The amount of leaching is dependent on the soil type and the amount of rainfall or irrigation water. The potential for bromacil to leach and contaminate groundwater is greatest in sandy soils. In regular soils, it can be expected to leach to a depth of 2-3 ft (24). Bromacil was found in Florida's groundwater at 300 parts per billion (ppb) (21, 32). Bromacil should not be used near drinking water reservoirs or in well recharge areas because of its mobility in soil. Directions and precautions listed on product labels must be followed to minimize potential bromacil movement into groundwater (24, 29, 30).

The other major mode for the disappearance of bromacil from most treated soils is microbial degradation. Tests show that at increased temperatures and long exposures to sunlight, there is very little loss of the herbicide from dry soil. It does not readily volatilize, or change into a gas, nor does it photodecompose, or break down in sunlight (19). Laboratory studies show that 5-30% of bromacil is lost six to nine weeks after application to the soil, as carbon dioxide, an odorless, colorless gas (11).

When it is applied to the soil, bromacil destroys most annual plants in the treated area (10). Field dissipation studies have shown that phytotoxic residues of bromacil have persisted in both sand and clay soils for longer than 2 years following a single application of 2.6 lb bromacil/acre (32).

Bromacil is long lasting, or persistent, and its half-life, or the time that it takes for half of it to break down by natural processes, is greater than 100 days (17). The herbicide had trace (residual) activity in soil for seven months after being applied at 7.5 kilogram per hectare (6). On silt loam soils, bromacil has a half-life of five to six months and can have toxic effects on susceptible crops for up to one year. Soils with moderate to high organic matter content may retain residues for one to two years, but a soil half-life of three to seven months is more likely. An even shorter half-life is possible in sandy soils treated with bromacil due to its movement out of the soil and into groundwater via leaching (23, 24). Eighteen months after 22.4 kg of bromacil was sprayed on abandoned field sites, residues of the herbicide were detectable, in decreasing amounts, in loamy sand, silt loam, silty clay loam and light silty clay loam soils. In all four soil types, organic matter content, cation-exchange capacity, total nitrogen and soluble salt concentrations were significantly correlated with residue persistence (19).

Breakdown of Chemical in Water

There is little information available on the breakdown rate of bromacil in water, although a two-month half-life is suggested for this herbicide in clean river water which is low in sediment (24).

Breakdown of Chemical in Vegetation

In plants, bromacil is taken up rapidly by the roots and slightly absorbed through the leaves (11, 25). When it is applied at 10 ppm, some types of algae have slowed growth, but most strains are unaffected (23). Improper application of bromacil will destroy shade trees and other desirable vegetation. Label instructions should be followed carefully. Equipment and containers should not be emptied or rinsed out near desirable trees or shrubs (24). No breakdown products (metabolites) of bromacil were found in tests done on maize (corn) and beans (19).

PHYSICAL PROPERTIES AND GUIDELINES

Bromacil is an odorless, white crystalline solid (1, 3). It is chemically stable under normal storage conditions, but may pose a slight fire hazard when exposed to heat or flame. It slowly decomposes in the presence of strong acids and poses a fire and explosion hazard in the presence of strong oxidizers (15). Technical bromacil and its dry formulations are non-flammable, but some liquid formulations are combustible (25). When heated to decomposition, bromacil emits highly toxic and corrosive fumes of bromides and toxic oxides of nitrogen and carbon (15, 18). Airborne bromacil dust may ignite (5).

Bromacil formulations are compatible with most herbicides with which they might be mixed. However, water-soluble formulations are not compatible with products that greatly reduce the spray of suspensions (e.g., AMS, amitrole, etc.) and may be precipitated by pesticides containing soluble calcium salts (19). When used with water-soluble formulations of bromacil, weed killers that contain soluble calcium salts can form precipitates (25). This herbicide should be stored in a cool, dry place (2).

Breathing of bromacil spray mist, as well as eye, skin and clothing contact with this herbicide, should be avoided. A thorough washing after handling is advised (2).

Occupational Exposure Limits:

1 ppm (10 mg/m3) OSHA TWA (15)
1 ppm (10 mg/m3) ACGIH TWA (15)
2 ppm ACGIH STEL (32)
1 ppm (10 mg/m3) NIOSH
Recommended TWA (15)

Physical Properties:

CAS#: 314-40-9
Specific gravity: 1.55 at 25 degrees C (25)
H2O solubility: 813 - 815 ppm (0.0815%) at 25 degrees C (21, 27, 29)
Solubility in other solvents: moderately soluble in acetone, strong aqueous bases, acetonitrile, and ethyl alcohol. Only slightly soluble in hydrocarbons (29).
  • Xylene: 3.2 g/100 ml (3, 25)
  • Acetone: 16.7 g/100 ml (3, 25)
  • acetonitrile: 7.1 g/100 ml (25)
  • strong base: 8.8 g/100 ml (3)
  • ethyl alcohol: 13.4 g/100 ml (3)
  • sodium hydroxide(3% aqueous): 8.8 g/100 ml (25)
Melting point: 157.5-160 degrees C (316-320 degrees F) (3, 1, 29)
Flash point: Combustible (29)
Decomposition temperature:
Vapor Pressure: 8 x 10 to the minus 4 power Torr at 100 degrees C (1, 3)
Kow: log Kow = 2.61 (9); 1.33 (8, 26); 2.02 (20)
Koc: 109 (calculated); 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 (21); 210 (8, 26); 1.2/2.1 (4); 72 (7); 32 g/ml (30)
Kd/mobility: 0.2-1.8 (soil-water distribution coefficient or adsorption constant from column leaching or TLC studies) (21)
Chemical Class/Use: Substituted uracil herbicide
NOEL: in two-year feeding studies, greater than 250 ppm and less than 1,250 ppm in rats; 1,250 ppm in dogs (1)
ADI: 130 ug/kg/day, based on a 2-year rat feeding study using a NOAEL of 12.5 and a 100-fold uncertainty factor (32).

BASIC MANUFACTURER

Du Pont Agricultural Products
Walker's Mill, Barley Mill Plaza
PO Box 80038
Wilmington, DE 19880-0038

Review by Basic Manufacturer:

Comments solicited: October, 1992
Comments received: November, 1992

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