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imazethapyr Amended Application 9/00

New York State Department of Environmental Conservation
Division of Solid & Hazardous Materials
Bureau of Pesticides Management, Room 498
Pesticide Product Registration Section

50 Wolf Road, Albany, New York 12233-7254
Phone: (518) 457-0300FAX: (518) 485-8836

August 14, 2000


Ms. Rebecca L. Johnston
Global Regulatory Manager
Global Regulatory Affairs
BASF Corporation
P.O. Box 400
Princeton, NJ 08543-0400

Dear Ms. Johnston:

Re: Application to Register a Major Change in Use for Pursuit DG Herbicide, EPA Reg No 241-350, to Allow Use in Clearfield® (IMI) Corn Hybrids.

    This Department has completed review of your application to amend the approved label for the referenced pesticide product in New York State. We have determined that use of the product, as labeled, will not pose unreasonable risks to humans or to the environmental resources of New York State. Therefore, the label amendment for Pursuit DG, EPA Reg No 241-350, allowing use in Clearfield® corn hybrids (originally called IMI Corn®seed hybrids) is accepted with the exclusion of sale and use on Long Island, New York.


    The Department received an application on September 1, 1999 from the then American Cyanamid Company to amend the registration of Pursuit DG, EPA Reg. No. 241-350, containing the active ingredient, imazethapyr, to allow use in field corn (Clearfield® corn hybrids only). This use is a significant new use for imazethapyr and could be a major use if Clearfield® corn hybrids are planted in large acreage in the future. Therefore, the application was determined to be a Major Change in Labeling (MCL) and a complete review was conducted.

    Pursuit DG Herbicide is currently registered in New York State to control weeds in soybeans at 1.0 ounces active ingredient (a.i.) per acre and in alfalfa at 1.5 ounces a.i./acre. Application rate for this use on corn is one application per year at 1.0 ounces a.i./acre/yr. Application may be made as preplant, preplant incorporated, preemergence, or early post emergence and may be made by ground or air equipment.

    The subject application was determined to be incomplete and a letter of incompleteness was sent to American Cyanamid on October 28, 1999. Requested additional information was submitted on December 9, 1999 and the application was deemed complete for purposes of review on February 7, 2000. Pursuant to the time frames specified in ECL§33-0704.2, a registration decision date of July 6, 2000 was established. In response to discussions with the Department that label modifications were needed, you requested a waiver of the registration date until the Department could review those modifications.

    The Department conducted toxicological, ecological effects and environmental fate risk assessments for imazethapyr, and the Pursuit DG formulation, for use on field corn.

Ecological Risk Assessment

Imazethapyr degrades slowly on soil, but rapidly in water. The toxicity is also quite low to birds, mammals, fish, aquatic invertebrate, and green algae.

The Department previously evaluated the potential ecological impacts of the use of imazethapyr prior to registration for use on soybeans and again prior to registration on alfalfa. The proposed label for use on Clearfield® corn hybrids has the same application rate, 0.0625 lbs. a.i./acre, as the application rates previously approved. This review for the proposed use on corn did not reveal an additional anticipated exposure that would prevent registration. Therefore, the additional use of Pursuit DG on Clearfield® corn hybrids is not likely to add any additional risk to fish and wildlife resources.

Toxicological Risk Assessment

    Pursuit products and their active ingredient imazethapyr were evaluated in 1994 and again in 1996 for the registrations on soybeans and alfalfa. The Department did not identify any significant toxicological concerns. A current search of the toxicological literature did not find any significant new information on the toxicity of imazethapyr.

    The United States Environmental Protection Agency (USEPA) established a tolerance of 0.10 parts per million (ppm)for imazethapyr residues in or on corn grain, fodder and forage. The USEPA estimated that chronic dietary exposure to these residues and to other commodities with previously established or pending imazethapyr tolerances would be less than 1 % of the oral reference dose (0.25 milligrams per kilogram body weight per day) for the general population, and also for non-nursing infants and children 1 to 6 years old. This chronic dietary exposure analysis is based on the assumption that all crops are treated and contain tolerance level residues.

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

    Based on our review, use of Pursuit DG (on IMI Corn®) does not appear to pose significant direct risks to public health.

Environmental Fate Risk Assessment

Hydrolysis:    Imazethapyr is stable and persistent.

Solubility:    Imazethapyr has a water solubility of 1 g/1.

Aqueous Photolysis:    Imazethapyr has a half-life of 46 hours under artificial light, but the EPA review has indicated that under actual use conditions, aqueous photolysis will be minimal due to application methods.

Soil Photolysis:    Imazethapyr has a half-life of 33 months.

Aerobic Soil Metabolism:    The half-life ranges from 33 to 37 months.

Anaerobic Soil Metabolism:    The half-life is >2 months.

Mobility(Adsorption/Desorption):     Kocs range from 97 to 283 in various soil types, Freundlich Kds range from 0.45 to 0.82 for four soils.

Degradates:     Only one major degradate was found, 5-ethyl-3-pryidine carboxylic acid, at 19.8%, during aqueous photolysis. However, aqueous photolysis is not considered to be a significant factor in the breakdown of the parent material.

Field Dissipation:     Field dissipation studies consistently show persistence regardless of soil type, agriculture practice and climatic effects. Studies done with an application rate of 2 oz/ai/acre (twice the labeled rate) in a permeable sandy loam indicated that the half-life is in the two to four month range at sites that approximate conditions in New York State. The compound was detected in the 6-12 inch sampling interval, and 14 ppb was detected in the 12-18 inch sampling interval. The USEPA reviewer indicated in his March 9, 1994 memorandum that residues may have leached deeper than 18 inches, but were not detected. It was also stated that given the low application rate and relatively high limit of analytical sensitivity, analyzing the soil in six inch increments may have diluted residues.

Ground Water Monitoring:    Two small-scale prospective ground water studies were started in 1997, one in the mid-west, one in the southeast. Monitoring wells and lysimeters were installed, and soil samples were collected. Application rate was 1.0 oz ai/a/yr, or 0.063 lb ai/a/yr, the labeled application rate for field corn. The second progress report was submitted in November of 1999. Analytical results for DAT 0 through 180 of imazethapyr in soil and analytical results for DAT 7 through 300 for imazethapyr in soil-water samples were presented. No ground water sample results from sampling after application were available in the southeast site due to low water levels.

    In the southeast site (loamy sand), the soil-water sample concentrations were all less than 0.05 ppb at 3-foot, 6-foot, 9-foot, and 15-foot lysimeters. Soil samples from 0-6 inches reached 5.8 ppb at DAT 8, and declined to less than 1 ppb by DAT 90. Concentrations from the 6-24 inch depth were less than 1 ppb.

    In the mid-west site (loamy sand), the soil-water sample concentrations ranged from 0.11 to 0.69 ppb in the 3-foot lysimeter. In lysimeter L3, the 15-foot lysimeter had from 0.77 to 0.85 ppb up to DAT 175. For some reason, they did not analyze for imazethapyr after day 175 in any lysimeters. Soil samples from 0-6 inches reached 39 ppb at DAT 3, and declined to less than 7.5 ppb by DAT 232. Concentrations from the 6-9 inch depth were 3.7 to less than 1 ppb, from 9-12 inches were 1.9 and 1.2 ppb, and less than 1 ppb from 12 to 23 inches. Ground water sample results were not available.

EPA Comments (1/14/94 EPA One Line Summary):     Imazethapyr is persistent and mobile according to laboratory environmental fate studies. Calculations using data from two aerobic metabolism studies gave the half-life as 33-37 months; absorption/desorption studies with aged parent showed the compound to be very mobile with Kds of 0.46 to 0.82 for four soils, two sandy loams and two silt loams. Percentages for sand, silt, clay and organic matter did not appear to have an effect on sorption. Field dissipation studies with Imazethapyr consistently show persistence regardless of soil type, agriculture practice and climate effects.

Computer Modeling:     Running the LEACHM model on Riverhead soil (typical for Long Island) using a Koc of 97, a half-life of 3 years and an application rate of 1.0 oz. ai/acre/year, the model projected breakthrough in year 1, and consistent peaks of 10-11 ppb. However, on Howard soil (which is more representative of upstate soils) using a Koc of 283 with all other parameters the same as the Riverhead soil, the model projected peaks of 0.5 ppb after about 9 years.

    While model projections for the worst case (Long Island) at 10 ppb do not approach the trigger value of _ of the 50 microgram per liter NEW YORK STATE drinking water standards for an "unspecified organic contaminant", or 25 ppb, there is still concern for use of imazethapyr on Long Island because of its mobility and persistence. The label prohibition preventing sale and use of Pursuit DG on Long Island, NY on any crop resolves this concern.


    When used as directed, Pursuit DG should not cause any unreasonable risks to humans or environmental resources of New York State. The Department hereby accepts the label amendment for Pursuit DG, EPA Reg No 241-350, allowing use in field corn (Clearfield® corn hybrids only).

    Enclosed for your files is the New York State stamped "ACCEPTED" labeling.

    Please note that any future proposal to register a product containing imazethapyr, whose labeled uses are likely to increase the potential for significant impact to humans, property, or the environment would constitute a major change in labeled (MCL) use pattern. Such an application must be accompanied by a new application and fee, and must meet the requirements listed in Appendix 1.B. of "New York State Pesticide Product Registration Procedures" (August 1996).

    Please contact Frank Hegener, Chief of our Pesticide Product Registration Section, at (518) 457-7446, if you have any questions.


Maureen P. Serafini
Bureau of Pesticides Management


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