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Chemical Fact Sheet

Chemical Abstract Number (CAS #) 1689845
CASRN 1689-84-5
SynonymsBromoxynil
3,5-Dibromo-4-hydroxybenzonitrile
Benzonitrile, 3,5-dibromo-4-hydroxy-
Molecular FormulaC7H3Br2NO

Link to the National Library of Medicine's Hazardous Substances
Database for more details on this compound.

Use Selective contact herbicide with some systemic activity . Post-emergence control of annual broad-leaved weeds, especially young seedlings of the Polygonaceae, Compositae, and certain Boraginaceae, in cereals, maize, sorghum, flax, onions, garlic, mint, grass-seed crops, turf, and non-crop land. Often used in combination with other herbicides, in order to extend the spectrum of control. Contact herbicide with some systemic activity. For mint, barley, flax forage grasses and alfalfa on Conservation Reserve acres, seedling alfalfa, field corn, popcorn, grass for sod and seed protection, oats, onions, rye, sorghum, triticale, wheat. Post-emergent control of common cocklebur, common ragweed; seedling broadleaf weeds such as blue (purple) mustard, corn gromwell, cowcockle, fiddleneck, field pennycress, green smartweed, groundsel, jimsonweed, lambsquarters, London rocket, nightshade, shepherdspurse, tartary buckwheat, tarweed, tumble mustard, velvetleaf, volunteer sunflower, wild buckwheat, and wild mustard.
Apparent Color WHITE CRYSTALLINE SOLID; LIGHT BUFF TO CREAMY POWDER; Colorless solid; Colorless crystals
Odor ODORLESS WHEN PURE
Melting Point 194-195 DEG C
Molecular Weight 276.93
Environmental Impact Bromoxynil is released to the environment in its use as a post-emergent herbicide for controlling broadleaf weeds in small grains and other crops. Although it is usually applied as the octanoate ester, the ester hydrolyzes rapidly to bromoxynil. Bromoxynil may also be released as runoff from fields treated with bromoxynil and enter waterways. However, high concentrations appear to occur during rain events within two months of application. Bromoxynil is discharged into the atmosphere as an aerosol during spraying operations and will be removed by gravitational settling and photolysis. If sprayed on fields, bromoxynil will photolyze on the soil surface and biodegrade. It is expected to adsorb moderately to soil at neutral and alkaline pHs. In field studies, bromoxynil was completely dissipated from soil in 10 wks when applied in May and 15 wks when applied in December. No bromoxynil residues were found in lower layers of soil. If released into water, bromoxynil will photolyze in surface layers of water and biodegrade. In test ponds, bromoxynil did not persist in sediment beyond 15 days after treatment. It should not bioconcentrate in aquatic organisms. Exposure to bromoxynil will be primarily occupational. Agricultural workers may be exposed by inhalation and dermal contact during spraying, mixing, and cleanup operations and by touching soil and plants to which bromoxynil was applied.
Environmental Fate AT 25 DEG C, 50% OF BROMOXYNIL APPLIED TO REGINA HEAVY CLAY WAS DEGRADED IN 2 WK. AMIDE & ACID WERE DETECTED . BROMOXYNIL IS EXTREMELY EFFECTIVE INHIBITOR OF NITRIFICATION IN SOILS. 50%INHIBITION WAS OBSERVED @ CONCN BELOW 50 PPM. No evidence of residual problems when applied at the rate of 0.5-1.0 lb/acre. TERRESTRIAL FATE: If sprayed on fields bromoxynil will photolyze on the surface and biodegrade. It should adsorb moderately to soil at low pHs, not at neutral or higher pHs. Commercial formulations of bromoxynil were applied to field plots containing heavy clay or sandy loam soil in May for two consecutive years and the soil sampled 10 weeks after application . No bromoxynil residues were found at either the 0-5 or 5-10 cm soil depths . On test winter wheat field plots treated with bromoxynil octanoate in December, concn of bromoxynil and bromoxynil octanoate averaged 0.46 and 0.91 umol/kg, respectively 24 hr after treatment . After 107 days, trace amounts of bromoxynil and no ester remained in the upper 7 cm of soil and neither substance was detected between 7 and 21 cm . AQUATIC FATE: If released into water, bromoxynil will be partially dissociated at neutral or basic environmental pHs. It will adsorb moderately to sediment and particulate matter at acid pHs. It will photolyze in surface water and biodegrade. In four test ponds sprayed with equal proportions of bromoxynil butyrate and octanoate, bromoxynil was initially detected in the surface (0-2 cm) sediment but did not persist there beyond 15 days after treatment . In the pond water the concentration of the photolysis product of bromoxynil was at similar levels as bromoxynil between 5 and 120 days post-treatment . This suggests that the photolysis half-life was comparable to that of the hydrolysis of the bromoxynil esters, 12-25 hr . ATMOSPHERIC FATE: Bromoxynil is discharged into the atmosphere as an aerosol during spraying operations. It will be removed from theair by gravitational settling. Due to its very low vapor pressure, bromoxynil should not occur as a vapor in the atmosphere . Bromoxynil-containing aerosols will undergo photolysis, the rate of which will depend on the solar irradiance and cloud cover. In the laboratory, the photolysis half-life of bromoxynil solutions irradiated with a 100 watt xenon-mercury lamp that was filtered to remove radiation less than 300 nm, was less than 40 min . AQUATIC FATE: Commercial bromoxynil is usually formulated as the octanoate ester, potassium salt or butyrate ester(3-4). After 72 hr at room temperature in the dark, 88% of a 30 ppb sample of bromoxynil octanoate in runoff water was converted to bromoxynil . The chemical nature of the hydrolysis was apparent from the fact that sodium azide did not impede degradation . In field experiments where bromoxynil butyrate and octanoate esters (BB and BO) were sprayed on ponds, the half-life of these esters in the surface microlayer was 0.28 - 0.91 hr for BB and 0.84-0.98 for BO; higher application rates give rise to longer half-lives . One hour afte test ponds with BO and BB, bromoxynil-phenol was the predominant f bromoxynil in subsurface pond water . The half-life of BB and BO 0.58-0.93 days and 0.51-0.85 days, respectively . Laboratory-der hydrolysis half-lives for the butyrate and octanoate in unsterile 8.2) at 25 deg C are 25 hours and 12 hours, respectively . Since hydrolysis of the BB and BO esters are 16 and 62 hr, respectively very slow at pH 7, chemical hydrolysis may contribute to the disappearance of the esters in the pond water. When bromoxynil octanoate was added to clay loam, fen peat, and sand soils, residues declined to below the level of detection after 28, 44 and 14 days, respectively. The partitioning and degradation of a single spray application of a 1:1 mixture of bromoxynil octanoate and bromoxynil butyrate were studied in fifteen 0.01 ha ponds located in the Delta marsh area of Manitoba. Intensive sampling of two ponds treated at 2.5 ug/l and two treated at 50 ug/l (nominal concn) showed that bromoxynil octanoate and bromoxynil butyrate persisted in the surface microlayer (0-1 mm) of the water at levels 50 to 100 fold higher than the intended treatment level, with half-lives of 0.8 to 2.5 hr. In subsurface waters (10-20 cm depth) the major forms of the herbicide were bromoxynil phenol and its monobromo analog (3-bromo-4-hydroxybenzonitrile. Half-lives of the phenol averaged 9.2 d in pondstreated at 50 ug/l and 14.5 d in those receiving 2.5 ug/l. Low ng/g (dry wt) levels of bromoxynil octanoate, bromoxynil butyrate, 3-bromo-4-hydroxybenzonitrile and bromoxynil phenol were present in bottom sediments (0-2 cm depth) during the first 15 days post treatment and declined to near detection limits (< 0.5 ng/g) by 120 days after spray application.
Drinking Water Impact GROUNDWATER: In a survey of farm wells in Ontario, Canada, 103 in 1986 and 76 in 1987, bromoxynil was not detected in any wells at a detection limit of 0.1 ug/l . However, bromoxynil was only used on crops in only 15 farms in 1986 and 6 in 1987 . SURFACE WATER: Levels of major herbicides were monitored in two rivers draining prairie agricultural watershed in Manitoba, Canada, the Ochre and Turtle, during 1984 . The Ochre drains mostly non-cropped land and forest and the Turtle drains mainly agricultural land . Bromoxynil residues were observed in the Turtle river following the major high water event in late June 1984, but only at very low levels at other times. The monthly avg concn of bromoxynil in the Ochre River from April to December ranged from <0.5 to 1.63 ug/cu m with high in June. For the Turtle River, the concn ranged from 0.3 to 37.2 ug/cu m with the high in July, although the concn in June was close to that observed in July. This pattern indicates that the source of bromoxynil is field runoff. EFFL: The yearly surface lossesof bromoxynil through runoff of 1.0 cm of water from winter wheat plots that were planted in December and managed under various management systems ranged from below detection to 3.01 g/ha . Although the herbicide was applied as the octanoate ester, no ester was detected in the runoff. The concn of a herbicide in runoff water will depend on how soon after application it rained and how much rain fell. In test plots on which rain fell six days after application, the concn of bromoxynil ranged from 0.256 to 0.594 umol/L and no bromoxynil octanoate was detected .

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