Imazethapyr

SRP: The most favorable course of action is to use an alternative chemical product with less inherent propensity for occupational harm/injury/toxicity 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 and plant life; and conformance with environmental and public health regulations.

SRP: Wastewater from contaminant suppression, cleaning of protective clothing/equipment, or contaminated sites should be contained and evaluated for subject chemical or decomposition product concentrations. Concentrations shall be lower than applicable environmental discharge or disposal criteria. Alternatively, pretreatment and/or discharge to a permitted wastewater treatment facility is acceptable only after review by the governing authority and assurance that "pass through" violations will not occur. Due consideration shall be given to remediation worker exposure (inhalation, dermal and ingestion) as well as fate during treatment, transfer and disposal. If it is not practicable to manage the chemical in this fashion, it must be evaluated in accordance with EPA 40 CFR Part 261, specifically Subpart B, in order to determine the appropriate local, state and federal requirements for disposal.

Container disposal: triple rinse, then offer for recycling or reconditioning or puncture and dispose of in a sanitary landfill or incineration or, if allowed by state and local authorities, by burning. If burned, stay out of smoke.

SRP: Contaminated protective clothing should be segregated in such a manner so that there is no direct personal contact by personnel who handle, dispose, or clean the clothing. The completeness of the cleaning procedures should be considered before the decontaminated protective clothing is returned for reuse by the workers. Contaminated clothing should not be taken home at the end of shift, but should remain at employee's place of work for cleaning.

Avoid skin, eye, clothing contact. Wash contaminated clothing with soap and hot water. Do not breathe spray mist.

For several good reasons, .... herbicides ... should be handled and applied only with full attention to safety measures that minimize personal contact. Many formulations contain adjuvants (stabilizers, penetrants, surfactants) that may have significant irritating and toxic effects. A number of premixed formulations contain two or more active ingredients; the companion pesticides may be more toxic than the principal herbicide. Good hygienic practice should not be disregarded just because a pesticide is reported to have a high LD50 in laboratory rodents. /Herbicides/

Tolerances are established for residues of the herbicide imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo- 1H-imidazol-2-yl]-5-ethyl-3-pyridine carboxylic acid, applied as its acid or ammonium salt, in or on the following raw agricultural commodities: [Table#6170]

Tolerances are established for the sum of the residues of the herbicide imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo- 1H-imidazol-2-yl]-5-ethyl-3-pyridine carboxylic acid; its metabolite CL 288511, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(1-hydroxyethyl)-3-pyridine carboxylic acid; and its metabolite CL 182704, 5-[1-(beta-D-glucopyranosyloxy)ethyl]-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid, applied as its acid or ammonium salt, in or on the following commodities: [Table#6171]

A tolerance is established for the sum of residues of the herbicide imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo- 1H-imidazol-2-yl]-5-ethyl-3-pyridine carboxylic acid, and its metabolite CL 288511, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5- oxo-1H-imidazol-2-yl]-5-(1-hydroxyethyl)-3-pyridine carboxylic acid, applied as its acid or ammonium salt, in or on the following commodities: [Table#6172]

Tolerances with regional registration, as defined in part 180.1(m) of this chapter, are established for the sum of residues of the herbicide imazethapyr, 2- [4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl- 3-pyridine carboxylic acid, as its ammonium salt, and its metabolite, 2- [4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(1- hydroxyethyl)-3-pyridine carboxylic acid, both free and conjugated, applied as its acid or ammonium salt, in or on the following raw agricultural commodities: [Table#6173]

LD50; Species: Colinus virginianus (Bobwhite quail) oral >2150 mg/kg

LD50; Species: Anas platyrhynchos (Mallard) oral >2150 mg/kg

LC50; Species: Lepomis macrochirus (Bluegill); Concentration: 420 mg/L for 96 hr /Conditions of bioassay not specified/

LC50; Species: Onchorhynchus mykiss (Rainbow trout); Concentration: 340 mg/L for 96 hr /Conditions of bioassay not specified/

For more Ecotoxicity Values (Complete) data for IMAZETHAPYR (13 total), please visit the HSDB record page.

TERRESTRIAL FATE: Based on a classification scheme(1), Koc values of 1.4 to 173(2-5), indicate that imazethapyr is expected to have very high to moderate mobility in soil(SRC). The pKa2 of imazethapyr is 3.9(6), indicating that this compound exists almost entirely in anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(7). Volatilization of imazethapyr from moist soil surfaces is not expected to be an important fate process(SRC) given an estimated Henry's Law constant of 1.0X10-16 atm-cu m/mole(SRC), using a fragment constant estimation method(8). Although low amounts of imazethapyr have evaporated from dry soil(9), volatilization is not expected based upon its very low estimated vapor pressure of 2.1X10-11 mm Hg at 25 °C(SRC), determined from a fragment constant method(10). Imazethapyr has been shown to biodegrade under aerobic conditions with biodegradation half-lives of 23.5 days(11) to 10.6 months(12). Photo decomposition of 14C-imazethapyr from Taloka silt loam, irradiated with sunlight between 8:00 am and 5:00 pm from June 26 thru July 5th was 8% for 43 hours, chain labeled degraded more than ring labeled imazethapyr(9).

TERRESTRIAL FATE: In a two year (1987-1988) field study, imazethapyr was applied to two soil types at pre-plant and pre-emergence times and plots were tilled with conventional and reduced conditions(1). Dissipation half-lives were 49 to 122 days, this included all environmental factors (volatilization, leaching, surface runoff, plant uptake and degradation)(1). Two test fields established in 1991 were treated with imazethapyr both pre-emergence and post-emergence(2). Pre-emergence and post-emergence half-lives were 47 and 19 days for Prince Edward Island site (60% sand, 29% silt, 11% clay, 2.9% organic matter, pH 5.8), and 63 and 34 days for Nova Scotia site (57% sand, 34% silt, 9% clay, 3.3% organic matter, pH 5.8), respectively(2).

AQUATIC FATE: Based on a classification scheme(1), Koc values of 1.4 to 173(2-5), indicate that imazethapyr is expected to adsorb to suspended solids and sediment(SRC). A pKa2 of 3.9(6) indicates imazethapyr will exist almost entirely in the anion form at pH values of 5 to 9 and therefore volatilization from water surfaces is not expected to be an important fate process(SRC). According to a classification scheme(7), an estimated BCF of 3(SRC), from an estimated log Kow of 1.49(6) and a regression-derived equation(8), suggests the potential for bioconcentration in aquatic organisms is low(SRC). Imazethapyr has been reported to biodegrade in soil under aerobic conditions with half-lives of 23.5 days(9) to 10.6 months(10). Imazethapyr had measured aqueous photodegradation half-lives of 4.0 to 5.1 hours in 3 rice paddy waters collected from Beaumont and Eagle Lake, TX and Clarksdale, MS(11).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), imazethapyr, which has an estimated vapor pressure of 2.3X10-11 mm Hg at 25 °C(SRC), determined from a fragment constant method(2), is expected to exist solely in the particulate phase in the ambient atmosphere. Particulate-phase imazethapyr may be removed from the air by wet or dry deposition(SRC).

/AQUATIC SPECIES/ Cyprinus carpio was exposed to imazethapyr and imazapic at laboratory and at field conditions. The laboratory experiment was carried out for 7 days and at rice field for 7, 30 and 90 days. Oxidative stress parameters and antioxidant profile were studied as well as metabolic parameters. After 7 days, brain AChE activity increases in laboratory and field, but in muscle, reduction was observed only in laboratory. At the same period, brain and muscle TBARS and liver CAT increase in the laboratory. Metabolic parameters showed changes in both conditions and exposure periods. After 30 days in rice field, brain AChE activity decreases and in muscle it was enhanced. After 90 days in field, only muscle AChE activity was reduced. The disorders in oxidative stress parameters and metabolism remained, indicating mainly a protein catabolism.

/OTHER TERRESTRIAL SPECIES/ Imazethapyr is a member of the imidazolinone class of herbicides. These chemicals are active through inhibition of acetohydroxyacid synthase (AHAS) which is involved in amino acid synthesis (leucine, isoleucine, and valine). The inhibition causes a disruption in protein synthesis that leads to an interference in cell growth.

Pursuit

Hematologic

2.5 x 10 ^-1 mg/kg-day

Imazethapyr had a reported mean Koc of 13.2 (range of 2 to 55) in 101 allophanic and non-allophanic surface soil samples collected throughout New Zealand(1). Imazethapyr had a reported Koc of 19 at pH 7.7 and an increased Koc of 163 as the pH was reduced to 5.4(2). Imazethapyr has a reported Koc range of 75 to 173(3). Koc values for Trani (55.1% sand, 22.0% silt, 22.9% clay, pH 7.5, organic carbon 1.46%) and Andria (69.1% sand, 18% silt, 12.9% clay, pH 7.8, organic carbon 0.62%) soils were 1.4 and 12.9, respectively(4). According to a classification scheme(5), these reported Koc values suggest that imazethapyr is expected to have very high to moderate mobility in soil. In an adsorption study using 2 humic acids, no measurable adsorption of imazethapyr occurred at pH 4.7, while at pH 3.6 and 3.7, the compound did adsorb(6). The pKa2, 3.9, indicates that at the lower pH values, about half of the amount of herbicide would exist in the molecular form and most of the carboxyl groups of humic acids are combined(6); at pH 4.7, the herbicide is mainly in the ionic form and most of the carboxyl groups of humic acids are also ionized(6). Using 10 soils, Kd values ranging from no detectable adsorption (pH 7.5, % organic carbon 0.86-1.39) to 14.74 (pH 4.5, % organic carbon 11.66) were obtained(6).

Little anaerobic biodegradation was reported in soil and sediment(1). Aerobic field soil half-lives of 53 to 122 days were reported(1).

AEROBIC: 14C Radio-labeled imazethapyr was incubated for 12 weeks at 28 °C in the dark in two soil types; Drummer silty loam (9% sand, 57% silt, 34% clay, pH 5.7, 5.8% organic carbon) and Cisne silt (14% sand, 74% silt, 12% clay, pH 7.0, 1.3% organic carbon)(1). Imazethapyr was biodegraded 18.2 and 26.8% in Drummer loam when 14C labeled on the carboxyl group and ring structure, respectively(1). Imazethapyr was biodegraded 46.9 and 53.5% in Cisne silt when 14C labeled on the carboxyl group and ring structure, respectively(1). Maury silt loam (8% sand, 67% silt, 25% clay, 2.6% organic matter, pH 6.3) was used in an 8 week study with radio-labeled 14C imazethapyr to determine effects of temperature and moisture on biodegradation(2). 14CO2 evolution from soil incubated at 15 and 30 °C was 1.5 and 4.4% for ring labeled imazethapyr and 2.0 and 5.4% for carboxyl labeled imazethapyr, respectively(2). 14CO2 evolution from ring labeled imazethapyr was 1.1, 3.4, 4.3, 5.4 and 4.6% at 15, 25, 50, 75 and 100% field capacity water content, respectively(2). Biodegradation half-lives of 14C-labeled imazethapyr were 2.6 to 9.0 months for Taloka silt loam (23% sand, 62% silt, 15% clay, 1.7% organic matter, pH 6.3) and 6.4 to 10.6 months for Sharkey silty clay (9% sand, 40% silt, 51% clay, 2.4% organic matter, pH 6.7)(3). Aerobic biodegradation rates were measured in six soils with a range of physico-chemical properties, incubation time was 60 days in the dark at 25 °C and 50% moisture(4). Half-lives were 23.5 to 62.2 days(4). Biodegradation half-lives for imazethapyr in soil are reported as 72.94 to 257.28 days under 33 to 75% field capacity moisture, 10 to 20 °C incubation temperature and 0.1 to 10 ppm initial concentration(5).

An estimated BCF of 3 was calculated in fish for imazethapyr(SRC), using a log Kow of 1.49(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is low(SRC).

A pKa2 of 3.9(1) indicates imazethapyr will exist almost entirely in the anion form at pH values of 5 to 9 and therefore volatilization from water surfaces is not expected to be an important fate process(SRC). Volatilization of imazethapyr from moist soil surfaces is not expected to be an important fate process(SRC) given an estimated Henry's Law constant of 1.0X10-16 atm-cu m/mole(SRC), calculated using a fragment constant estimation method(2). Volatilization of 14C radio-labeled imazethapyr (ring and chain labeled) from dry soil was 1.5% from Taloka silt loam (23% sand, 62% silt, 15% clay, 1.7% organic matter, pH 6.3) and 1.0% from Sharkey silty clay (9% sand, 40% silt, 51% clay, 2.4% organic matter, pH 6.7), soil was incubated at 49 °C for a maximum of 168 hours(3); these values are very low(SRC). Volatilization is not expected based upon its very low estimated vapor pressure of 2.1X10-11 mm Hg at 25 °C(SRC), determined from a fragment constant method(4).

/LABORATORY ANIMALS: Subchronic or Prechronic Exposure/ In 28 days feeding trials, no effect level for rats was 10,000 mg/kg (highest dose tested).

/LABORATORY ANIMALS: Chronic Exposure or Carcinogenicity/ A 1-year feeding study in dogs fed diets containing 0, 1,000, 5,000, or 10,000 ppm with a NOEL of 1,000 ppm (25 mg/kg/day and a LOEL of 5,000 ppm (125 mg/kg/day), based on decreased packed cell volume, hemoglobin, and erythrocytes in females.

/LABORATORY ANIMALS: Chronic Exposure or Carcinogenicity/ A 2-year chronic toxicity/ carcinogenicity study in rats fed diets containing 0, 1,000, 5,000, or 10,000 ppm with no carcinogenic effects observed under the conditions of the study at levels up to and including 10,000 ppm (500 mg/kg/day [HDT]) and a systemic NOEL of 10,000 ppm (500 mg/kg/day (HDT)).

/LABORATORY ANIMALS: Chronic Exposure or Carcinogenicity/ An 18-month carcinogenicity study with mice fed diets containing 0, 1,000, 5,000, or 10,000 ppm with no carcinogenic effects observed under the conditions of the study at levels up to and including 10,000 ppm (1,500 mg/ kg/day) (highest dose tested [HDT]), a systemic no-observed-effect level (NOEL) of 5,000 ppm (750 mg/kg/day), and a systemic LOEL of 10,000 ppm (1,500 mg/kg/day), based on decreased body weight gain in both sexes.

For more Non-Human Toxicity Excerpts (Complete) data for IMAZETHAPYR (9 total), please visit the HSDB record page.

Tolerances are established for residues of the herbicide imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo- 1H-imidazol-2-yl]-5-ethyl-3-pyridine carboxylic acid, applied as its acid or ammonium salt, in or on the following raw agricultural commodities: [Table#6174]

Tolerances are established for the sum of the residues of the herbicide imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo- 1H-imidazol-2-yl]-5-ethyl-3-pyridine carboxylic acid; its metabolite CL 288511, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(1-hydroxyethyl)-3-pyridine carboxylic acid; and its metabolite CL 182704, 5-[1-(beta-D-glucopyranosyloxy)ethyl]-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid, applied as its acid or ammonium salt, in or on the following commodities: [Table#6175]

A tolerance is established for the sum of residues of the herbicide imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo- 1H-imidazol-2-yl]-5-ethyl-3-pyridine carboxylic acid, and its metabolite CL 288511, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5- oxo-1H-imidazol-2-yl]-5-(1-hydroxyethyl)-3-pyridine carboxylic acid, applied as its acid or ammonium salt, in or on the following commodities: [Table#6176]

Tolerances with regional registration, as defined in part 180.1(m) of this chapter, are established for the sum of residues of the herbicide imazethapyr, 2- [4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl- 3-pyridine carboxylic acid, as its ammonium salt, and its metabolite, 2- [4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(1- hydroxyethyl)-3-pyridine carboxylic acid, both free and conjugated, applied as its acid or ammonium salt, in or on the following raw agricultural commodities: [Table#6177]

New Active Ingredients ... includes chemicals not previously registered as pesticides, as well as pesticide active ingredients initially registered after November 1, 1984 and that currently have active product registrations. By law, these pesticides must meet new safety standards, such as those described in the Food Quality Protection Act of 1996 and, if new safety standards are met, will be reviewed again on a 15-year cycle. Imazethapyr is designated by EPA as a New Pesticide Active Ingredient. Active Ingredient Number: 128922; Type of Pesticide: conventional - herbicide; Use Site: food use turf, rights of way; Year: 1989.