| Chemical Abstract Number (CAS #) |
1689845
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| Synonyms | Bromoxynil |
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3,5-Dibromo-4-hydroxybenzonitrile | Benzonitrile, 3,5-dibromo-4-hydroxy- |
| Molecular Formula | C7H3Br2NO |
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| 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.
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| Apparent Color | WHITE CRYSTALLINE SOLID; LIGHT BUFF TO CREAMY POWDER;
Colorless solid; Colorless crystals
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| Odor | ODORLESS WHEN PURE
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| Melting Point | 194-195 DEG C
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| Molecular Weight | 276.93
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| 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.
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| 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.
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| 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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