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NYS DEC Letter - Registration of the New Active Ingredient Contained in the Pesticide Product Imazapic Herbicide Technical 12/04

New York State Department of Environmental Conservation
Division of Solid & Hazardous Materials

Bureau of Pesticides Management
Pesticide Product Registration Section
625 Broadway, Albany, New York 12233-7257
Phone 518-402-8768     FAX 518-402-9024

December 2, 2004


Ms. Judy Fersch
State Registration Specialist
BASF Corporation
P.O. Box 13528
Research Triangle Park, North Carolina 27709-3528

Dear Ms. Fersch:

Re: Registration of the New Active Ingredient Imazapic Contained in the Pesticide Product Imazapic Herbicide Technical (EPA Reg. No. 241-363)

    The New York State Department of Environmental Conservation (Department) has completed a technical review of the data package and application (received May 13, 2004) submitted in support of registration of the referenced product. Imazapic Herbicide Technical (EPA Reg. No. 241-363) contains the new active ingredient imazapic: (+/-)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid.

    Imazapic Herbicide Technical (96.4% imazapic) is an alternate trade name for Cadre® Herbicide Technical (EPA Reg. No. 241-363). Product is labeled for formulating purposes only.

    The registration package was deemed complete for purposes of technical review on July 9, 2004. Pursuant to the review time frame specified in Environmental Conservation Law (ECL) §33-0704.2, a registration decision date of December 6, 2004 was established.

    Toxicological and environmental fate risk assessments were conducted for Imazapic Herbicide Technical. An ecotoxicity risk assessment was not conducted for this manufacturing use product.

TOXICOLOGICAL RISK ASSESSMENT: On an acute basis, Imazapic Herbicide Technical was not very toxic by the oral, dermal or inhalation routes of exposure. This chemical was not very irritating to the eyes or skin (tested on rabbits), nor was it a skin sensitizer (tested on guinea pigs).

    Imazapic caused some effects in a chronic feeding study in dogs. At the lowest doses tested, 137 milligrams per kilogram body weight per day (mg/kg/day) in males and 180 mg/kg/day in females, an increased incidence of minimal degeneration and/or necrosis and white blood cell infiltration in skeletal muscle was observed. By contrast, no effects were observed in chronic feeding studies either in rats or mice, even at the highest doses tested which were 1,237 mg/kg/day and 1,442 mg/kg/day, respectively. The United States Environmental Protection Agency (USEPA) Office of Pesticide Programs calculated an oral reference dose (RfD) for imazapic of 0.5 mg/kg/day based on the lowest dose tested of 137 mg/kg/day in the chronic feeding study in dogs and using an uncertainty factor of 300. This RfD value has not yet been placed in the USEPA's Integrated Risk Information System (IRIS).

    The USEPA assigned imazapic to a Group E cancer classification, based on no evidence of carcinogenicity in rats and mice, as well as a lack of effects in a number of genotoxicity studies.

    Imazapic did not cause any developmental toxicity either in rabbits or rats at the highest doses tested, which were 500 mg/kg/day and 1,000 mg/kg/day, respectively. Also, imazapic did not cause any maternal toxicity at the highest dose tested (1,000 mg/kg/day) in the rat developmental toxicity study. In the rabbit study, maternal toxicity characterized by a decrease in body weight and food consumption was reported at a dose of 500 mg/kg/day; the no-observed-effect level was 350 mg/kg/day. In a rat multigeneration reproduction study, imazapic caused neither reproductive nor parental toxicity effects at the highest dose tested, which was 1,484 mg/kg/day.

    The New York State Department of Health briefly reviewed the environmental fate data on imazapic. These data indicate that this chemical may have the ability to leach through certain soil types and contaminate groundwater; the adsorption coefficients (Koc) in several of these soil types ranged from seven to 267. These values suggest that imazapic may have a high mobility through some soils.

    There are no chemical specific federal or State drinking water/groundwater standards for imazapic. Based on its chemical structure, this compound falls under the 50 microgram per liter New York State drinking water standard for "unspecified organic contaminants" (10 NYCRR Part 5, Public Water Systems).

    The available information on Imazapic Herbicide Technical indicates that it is not very acutely toxic in laboratory animal studies. In addition, imazapic caused only limited toxicity in chronic testing, and did not demonstrate developmental/reproductive toxicity, genotoxicity or carcinogenicity. This chemical, however, appears to have the potential to leach through soil and contaminate groundwater/drinking water. Mitigative measures may be required prior to registration of any formulated products containing imazapic in New York State.

ENVIRONMENTAL FATE RISK ASSESSMENT: Imazapic is in the imidazolinone class of herbicides. Other active ingredients in this family which are registered in New York include imazapyr (Arsenal, Stalker, Chopper ) and imazethapyr (Extreme, Lightning, Pursuit, Stronghold). Imazethapyr is not registered for use on Long Island. Other active ingredients in this family, imazamethabenz and imazaquin, are not registered for use in New York State.

Solubility: The solubility of imazapic at 25OC is 2150, 36000, 479000, and 518000 ppm in deionized water, pH 5, 7, and 9 buffers, respectively.

Hydrolysis: Imazapic is stable to hydrolysis at pHs 5, 7 and 9.

Aqueous Photolysis: Imazapic photolyzes rapidly with half-lives of 7.2, 6.0 and 6.24 hours in pH 5, 7 and 9 solutions, respectively. Six major degradates were found: carbon dioxide; 5-methyl-3-pyridine carboxylic acid at 29.9% at pH 5; 2-[(1-carbamoyl-1,2-dimethylpropyl) carbamoyl]-5-methyl-nicotinic acid at 41.3% at pH 9; 5-methyl-2,3-pyridine dicarboxylic acid at 13% at pH 5; 2-carbamoyl-5-methyl-nicotinic acid at 12.9% at pH 7; and 2-carbamoyl-5-methyl-3-nicotinic acid at 44.3% at pH 9.

Soil Photolysis: Imazapic degrades slowly with a calculated half-life of 106 days with one major degradate, the diacid (AC 312 622) at 11%.

Anaerobic Aquatic Metabolism: Imazapic is stable to degradation under anaerobic aquatic conditions with a calculated half-life of > six years.

Aerobic Soil Metabolism: In a study that the USEPA found acceptable, imazapic had a calculated half-life of 2,010 days in a sandy loam soil with a pH of 5.2 and 1.3% OM. USEPA questions the validity of the study because there is a marked discrepancy between the lab half-life (2,010 days) and the field (15-410 days). No DER was submitted for a second lab study that indicated the half-life was 133 days. None of the studies had degradates at > ten percent.

Terrestrial Field Dissipation: In a loam soil, loam soil, loam soil, silt loam soil, loamy sand soil, and loamy sand soil, the calculated half-lives were 93, 223, 184, 93, 104, 99 days, respectively. None of the studies fulfilled the USEPA requirement for field dissipation. Samples were not analyzed for degradates. In a study that USEPA found to be supplemental on a silt loam soil (pH 5.8, 2.9% OM), imazapic had a half-life value of 410 days in a bareground plot and 256 days in a prariegrass plot.

Soil Type
Adsorption Koc
% Organic Carbon
Loamy sand
Clay loam
Sandy loam
Silty clay loam
Silt loam

Groundwater Monitoring: In 1995 reviews of an application for use of Cadre Herbicide on peanuts, the USEPA's Environmental Fate and Ground Water Branch and Ground Water Technology Section determined that a small-scale prospective ground water monitoring study was required because Cadre was both extremely mobile and extremely persistent in many soils. A Prospective Ground Water Monitoring (PGW) study was conducted in Georgia with an application rate of 0.063 lb ai/acre on peanuts. The soil was a loamy sand with 1.2% OM and a pH of 6.3. The concentrations found in the monitoring well samples were all below the LOD of 0.02 ppb during the first 43 months of study.

DISCUSSION: Laboratory and field data indicate that imazapic can be very persistent and very mobile under certain use conditions. While labeled use of the subject manufacturing use product should not expose the environment to this active ingredient, end-use products containing imazapic will need to be evaluated for their potential to impact groundwater/drinking water.

REGISTRATION ACTION: When used as labeled, the subject product should not cause unreasonable adverse effects to humans or the environment. The Department hereby accepts Imazapic Herbicide Technical (EPA Reg. No. 241-363) for registration in New York State. Enclosed for your files are the Certificate of Pesticide Registration and New York State stamped "ACCEPTED" label.

    Please note that a proposal by BASF Corporation or any other registrant to register a product containing imazapic, whose labeled uses are likely to increase the potential for significant exposure to humans or impact to the environment, would constitute a major change in labeled (MCL) use pattern. Such an application must be accompanied by a new application fee and meet the requirements specified in 6 NYCRR Part 326.17.

    Please contact Samuel Jackling, Chief of our Pesticide Product Registration Section, at (518) 402-8768, if you have any questions.


Maureen P. Serafini
Bureau of Pesticides Management

cc: w/enc. - N. Kim/D. Luttinger, NYS Dept. of Health
R. Zimmerman/R. Mungari, NYS Dept. of Ag. & Markets
W. Smith, Cornell University, PSUR