Isoxaflutole

SRP: The most favorable course of action is to use an alternative chemical product with less inherent propensity for occupational exposure or environmental contamination. Recycle any unused portion of the material for its approved use or return it to the manufacturer or supplier. Ultimate disposal of the chemical must consider: the material's impact on air quality; potential migration in soil or water; effects on animal, aquatic, and plant life; and conformance with environmental and public health regulations.

Tolerances are established for combined residues of the herbicide isoxaflutole [5-cyclopropyl-4-(2-methylsulfonyl-4-trifluoromethyl benzoyl) isoxazole] and its metabolites 1-(2-methylsulfonyl-4-trifluoromethylphenyl)-2-cyano-3-cyclopropyl propan-1,3-dione (RPA 202248) and 2-methylsulphonyl-4-trifluoromethyl benzoic acid (RPA 203328), calculated as the parent compound, in or on the following raw agricultural commodities: corn, field, forage 1.0 ppm; corn, field, grain 0.20 ppm; and corn, field, stover 0.50 ppm.

Tolerances are established for combined residues of the herbicide isoxaflutole [5-cyclopropyl-4-(2-methylsulfonyl-4-trifluoromethyl benzoyl) isoxazole] and its metabolite 1-(2-methylsulfonyl-4-trifluoromethylphenyl)-2-cyano-3-cyclopropyl propan-1,3-dione (RPA 202248), calculated as the parent compound, in or on the following raw agricultural commodities: cattle, fat 0.20 ppm; cattle, liver 0.50 ppm; cattle, meat 0.20 ppm; cattle, meat byproducts, except liver 0.10 ppm; egg 0.01 ppm; goat, fat 0.20 ppm; goat, liver 0.50 ppm; goat, meat 0.20 ppm; goat, meat byproducts, except liver 0.10 ppm; hog, fat 0.20 ppm; hog, liver 0.50 ppm; hog, meat 0.20 ppm; hog, meat byproducts, except liver 0.10 ppm; horse, fat 0.20 ppm; horse, liver 0.50 ppm; horse, meat 0.20 ppm; horse, meat byproducts, except liver 0.10 ppm; milk 0.02 ppm; poultry, fat 0.20 ppm; poultry, liver 0.30 ppm; poultry, meat 0.20 ppm; sheep, fat 0.20 ppm; sheep, liver 0.50 ppm; sheep, meat 0.20 ppm; and sheep, meat byproducts, except liver 0.10 ppm.

LD50 Bee contact >100 ug/bee

LC50 Anas platyrhynchos (Mallard duck, age 5 days) dietary >4255 ppm (8 days)[USEPA, Office of Pesticide Programs; Pesticide Ecotoxicity Database (2000) on (5-Cyclopropyl-4-isoxazolyl)

LD50 Anas platyrhynchos (Mallard duck, age 2 wk) oral >2150 mg/kg[USEPA, Office of Pesticide Programs; Pesticide Ecotoxicity Database (2000) on (5-Cyclopropyl-4-isoxazolyl)

LD50 Colinus virginianus (Northern bobwhite, age 26 wk) oral >2150 mg/kg[USEPA, Office of Pesticide Programs; Pesticide Ecotoxicity Database (2000) on (5-Cyclopropyl-4-isoxazolyl)

For more Ecotoxicity Values (Complete) data for ISOXAFLUTOLE (9 total), please visit the HSDB record page.

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 440(SRC), determined from a log Kow of 2.32(2) and a regression-derived equation(3), indicates that isoxaflutole is expected to have moderate mobility in soil(SRC). Neither isoxaflutole nor any of its metabolites were detected in the soil below 10 cm during a field dissipation study(4). Volatilization of isoxaflutole from moist soil surfaces is not expected to be an important fate process(SRC) given a Henry's Law constant of 1.85X10-10 atm-cu m/mole(2). Isoxaflutole is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 7.50X10-9 mm Hg(2). The half-life for the photolysis of isoxaflutole has been reported as 23 hours in soil(5). Half-lives of isoxaflutole in laboratory soil degradation studies range from 12 hours to 13.9 days(6,7,8). The effects of moisture and temperature on isoxaflutole degradation and the similarity of the degradation patterns between sterile and non-sterile samples indicate that chemical hydrolysis to the active product (2-cyano-3-cyclopropyl-1-(2-methylsulfonyl-4-trifluoromethylphenyl)-propane-1,3-dione) is the primary route of isoxaflutole degradation in soil(6-8). The half-lives for the conversion of isoxaflutole into its primary metabolite in the 0-10 cm surface soil layer of corn crops were between 9 and 18 days during a soil field dissipation study(4). The sum of isoxaflutole and this metabolite disappeared in the 0-10 cm layer with half-lives of 45-65 days(4).

AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 440(SRC), determined from a log Kow of 2.32(2) and a regression-derived equation(3), indicates that isoxaflutole may adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is not expected(3) based upon a Henry's Law constant of 1.85X10-10 atm-cu m/mole(2). According to a classification scheme(4), an estimated BCF of 34(SRC), from its log Kow(2) and a regression-derived equation(5), suggests the potential for bioconcentration in aquatic organisms is moderate(SRC). The half-lives reported for the hydrolysis of isoxaflutole in aqueous mineral buffered solutions were 433, 241, 95, 43, 65, and 5 hours at pH values of 5.2, 6.0, 7.2, 8.0, 8.3, and 9.3, respectively, at 22 °C(1). The half-lives at these same pH values were 182, 87, 18, 8, 9, and 1.2 hours, respectively, at 35 °C(6). The half-life for the photolysis of isoxaflutole has been reported as 6.7 days in water(7). Half-lives of isoxaflutole in laboratory soil degradation studies range from 12 hours to 13.9 days(8-10). The effects of moisture and temperature on isoxaflutole degradation and the similarity of the degradation patterns between sterile and non-sterile samples indicate that chemical hydrolysis to the active product (2-cyano-3-cyclopropyl-1-(2-methylsulfonyl-4-trifluoromethylphenyl)-propane-1,3-dione) is the primary route of isoxaflutole degradation in soil(8-10) and may also true for water(SRC).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), isoxaflutole, which has a vapor pressure of 7.50X10-9 mm Hg at 25 °C(2), is expected to exist solely in the particulate phase in the ambient atmosphere. Particulate-phase isoxaflutole may be removed from the air by wet and dry deposition(SRC).

The goats were dosed (balling gun) at a dietary burden of 10 ppm for seven days. The administered radioactivity was mainly eliminated via the urine and feces with the remaining radioactivity found in tissues, milk and cage wash and debris. Isoxaflutole was not identified in any of the tissues and milk. RPA 202248 was identified as a major component in all tissues, including milk. RPA 207048 was identified as a minor component in tissues and milk.

The Koc of isoxaflutole is estimated as 440(SRC), using a log Kow of 2.32(1) and a regression-derived equation(2). According to a classification scheme(3), this estimated Koc value suggests that isoxaflutole is expected to have moderate mobility in soil. Neither isoxaflutole nor any of its metabolites were detected in the soil below 10 cm during a soil field dissipation study(4).

AEROBIC: The half-life for the aerobic soil metabolism of isoxaflutole has been reported as 2.4 days(1). Half-lives for the terrestrial field dissipation of this compound have been reported to range from 1.4 to 3.0 days(1). Additional information regarding these values were not provided(1). The effects of temperature and moisture on isoxaflutole degradation have been studied(2-4). During a controlled laboratory soil degradation study, half-lives of 1.5 and 2.4 days were measured at moisture contents of -100 kPa (25%) and -1500 kPa (13%), respectively, while the half-life in air-dry soil (3% moisture content) was reported as 9.6 days(2). No mineralization was observed in the air-dry soil, although degradation was rapid after water was added (-100 kPa) to an air dry soil sample on day 14(2). Half-lives reported in a similar study were 67, 49, and 33 hours at moisture contents of 17, 29, and 45%, respectively(3). A third laboratory study reported half-lives of 24, 24, 22, and 19 hours in sandy loam at moisture content 5, 10, 20, and 30%, respectively, and an application rate of 100 g/ha(4). Half-lives in sandy loam at these moisture contents were 41, 36, 32, and 29 hours, respectively, for a 750 g/ha application rate using a water dispersible granule formulation(4). Half-lives in clay loam at moisture contents <2, 10, 20, and 30% were 144, 33, 20, and 12 hours, respectively, for a 250 g/ha application rate(4). Isoxaflutole degradation was inversely affected by changes in temperature. Half-lives were 13.9 days at 5 °C, 3.3 days at 15 °C, 1.3 days at 25 °C, and 0.8 days at 35 °C(2). The activation energy calculated from the rate constants at these temperatures was 67 kJ/mol(2). The authors reported that an activation energy above 60 kJ/mol and responsiveness to changes in temperature such as was observed with isoxaflutole are indicative of a chemically controlled process as opposed to an enzyme-mediated biological process(2).

AEROBIC: Half-lives observed in sterile and non-sterile soils were similar (1.8 days and 1.4 days, respectively)(1). Four percent mineralization was observed in the non-sterile soil by day 56 while no mineralization was observed in the sterile soil throughout the experiment(1). Based on the data from these tests, the authors concluded that chemical hydrolysis to the active product (2-cyano-3-cyclopropyl-1-(2-methylsulfonyl-4-trifluoromethylphenyl)-propane-1,3-dione) is the primary route of isoxaflutole degradation in the environment(1-3). Any mineralization observed was considered to be from the degradation of this active product while forming inactive metabolites through biological processes(1). An activation energy of 81.2 kJ/mol, calculated using isoxaflutole degradation rate constants measured at various temperatures in non-sterile soil, was similar to a value of 82.4, calculated from degradation rates in sterile aqueous solutions(2). The half-lives for the conversion of isoxaflutole into its primary metabolite in the 0-10 cm surface soil layer of corn crops were between 9 and 18 days during a soil field dissipation study(4). The sum of isoxaflutole and this metabolite disappeared in the 0-10 cm layer with half-lives of 45-65 days(4).

An estimated BCF of 34 was calculated for isoxaflutole(SRC), using a log Kow of 2.32(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is moderate(SRC), provided the compound is not altered physically or chemically once released into the environment.

The Henry's Law constant for isoxaflutole is 1.85X10-10 atm-cu m/mole(1). This Henry's Law constant indicates that isoxaflutole is expected to be essentially nonvolatile from moist soil or water surfaces(2). Isoxaflutole is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 7.50X10-9 mm Hg(1).

/LABORATORY ANIMALS: Acute Exposure/ Not a skin irritant; minimal eye irritation (rabbits). Not a skin sensitiser.

/LABORATORY ANIMALS: Subchronic or Prechronic Exposure/ In a 90-day dietary study, groups of 10 CD rats/sex/dose received either 0, 1.0, 3.0, 10 or 100 mg/kg bw/day isoxaflutole (purity 99.4%) via dietary administration daily for 13 weeks and three days. There were no treatment-related mortalities and no treatment-related effects on body weight, body-weight gain, food consumption or food efficiency. There were no significant treatment-related effects on hematological, clinical chemistry or urinalysis parameters examined. Treatment-related findings in males at 100 mg/kg bw/day included increased absolute and relative liver weights, with an associated increased incidence of periacinar hepatocytic hypertrophy; these were considered to be an adaptive response and not adverse. Significant treatment-related clinical, ophthalmoscopic, gross pathological and histopathological findings were observed in the eye in males at 10 mg/kg bw/day and in both sexes at 100 mg/kg bw/day. Clinical and ophthalmoscopic observations included increased incidences of bilateral and unilateral opaque eyes and focal corneal opacity, respectively. Focal corneal opacity was first apparent during week 3 and persisted throughout the study. Significant gross pathological observation included an increased incidence of corneal opacity (unilateral and bilateral) in both sexes at 100 mg/kg bw/day. The overall incidence of corneal lesions was similar in both sexes, although the severity of the lesions was more significant in the males. The most notable histopathological findings included vacuolation (males and females) and superficial exfoliation of the epithelial cells (males and females), epithelial thickening (males), necrosis and inflammation (males and females), subepithelial fibroblastic reaction (males and females) and vascularization of the stroma (males and females). The changes were considered by the study author to be reversible after a short recovery period following cessation of treatment in the previous study..., with the exception of residual evidence of tissue repair detectable only by histopathological examination. There were no treatment-related effects at 1.0 or 3.0 mg/kg bw/day; therefore, the NOEL for isoxaflutole was 3.0 mg/kg bw/day.

/LABORATORY ANIMALS: Subchronic or Prechronic Exposure/ In a 28-day preliminary dietary study, groups of 10 male or female CD-1 mice received isoxaflutole (99.9% purity) via dietary administration at concentrations of 0, 175, 700, 2800 or 7000 ppm daily for 28 days. The dose levels were equal to 0, 29.4, 120.7, 474.6 and 1140.1 mg/kg bw/day in males and 0, 34.7, 142.9, 534.4 and 1347.4 mg/kg bw/day in females. There were no treatment-related mortalities, clinical or ophthalmoscopic observations or treatment-related effects on body weight, body-weight gain or food consumption. The liver appeared to be the target organ. Significant treatment-related clinical chemistry findings included increased alanine aminotransferase (ALAT) (males at 2800 and 7000 ppm and females at 700, 2800 and 7000 ppm) and aspartate aminotransferase (ASAT) (males at 2800 and 7000 ppm and females at 7000 ppm) activity. Increased liver weights were observed at all dose levels in both sexes. Significant treatment-related gross pathological observations were noted in the liver and included enlarged liver (males at 700, 2800 and 7000 ppm and females at 2800 and 7000 ppm) and white striations (both sexes at 7000 ppm). Treatment-related histopathological findings in the liver included centrilobular hepatocellular hypertrophy (both sexes at 700 ppm and above) and hepatocellular necrosis (males at 2800 and 7000 ppm and females at 7000 ppm). Other histopathological findings included increased extramedullary hematopoiesis in spleen(both sexes at 7000 ppm) and X-zone cell vacuolation in the adrenal glands (females at 7000 ppm). In the absence of any other significant findings at 175 ppm, the increased liver weights were considered a minor adaptive change; therefore, the no observed adverse effect level (NOAEL) was 175 ppm, equal to 29 mg/kg bw/day in males and 35 mg/kg bw/day in females.

Tolerances are established for combined residues of the herbicide isoxaflutole [5-cyclopropyl-4-(2-methylsulfonyl-4-trifluoromethyl benzoyl) isoxazole] and its metabolites 1-(2-methylsulfonyl-4-trifluoromethylphenyl)-2-cyano-3-cyclopropyl propan-1,3-dione (RPA 202248) and 2-methylsulphonyl-4-trifluoromethyl benzoic acid (RPA 203328), calculated as the parent compound, in or on the following raw agricultural commodities: corn, field, forage; corn, field, grain; and corn, field, stover.

Tolerances are established for combined residues of the herbicide isoxaflutole [5-cyclopropyl-4-(2-methylsulfonyl-4-trifluoromethyl benzoyl) isoxazole] and its metabolite 1-(2-methylsulfonyl-4-trifluoromethylphenyl)-2-cyano-3-cyclopropyl propan-1,3-dione (RPA 202248), calculated as the parent compound, in or on the following raw agricultural commodities: cattle, fat; cattle, liver; cattle, meat; cattle, meat byproducts, except liver; egg; goat, fat; goat, liver; goat, meat; goat, meat byproducts, except liver; hog, fat; hog, liver; hog, meat; hog, meat byproducts, except liver; horse, fat; horse, liver; horse, meat; horse, meat byproducts, except liver; milk; poultry, fat; poultry, liver; poultry, meat; sheep, fat; sheep, liver; sheep, meat; and sheep, meat byproducts, except liver.

Used as pre-emergence herbicide for maize; [Merck Index]

Farming (Pesticides) [Category: Industry]

For isoxaflutole (USEPA/OPP Pesticide Code: 123000) ACTIVE products with label matches. /SRP: Registered for use in the U.S. but approved pesticide uses may change periodically and so federal, state and local authorities must be consulted for currently approved uses./

Herbicide; for use on corn fields

This is a man-made compound that is used as a pesticide.

Trade names: Balance, BalancePro

Water dispersible granules

Technical is about 98% pure.

Tradenames: Merlin; Alliance; Converge; Provence. Mixtures: Acajou (+aclonifen); Atoll (+atrazine); Lagon (+aclonifen); Cadou Star (+flufenacet); Epic (+flufenacet).

Formulation type: Water dispersible granule; Guarantee: 75% /isoxaflutole/. /Converge 75 WDG Herbicide/ /from table/

Herbicides

Environmental transformation -> Pesticides (parent, predecessor)