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imazethapyr NYS DEC Letter - Application to Register a Major Change in Label 8/00

New York State Department of Environmental Conservation 
Division of Solid and Hazardous Materials
Bureau of Pesticides Management, Room 498 
50 Wolf Road, Albany, New York 12233-7254 
Phone: (518) 457-0300 o FAX: (518) 485-88366 

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, 
0.06251bs. 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 

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 

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 %2 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

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