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Dicamba, Sodium Salt - Registration of Yukon Herbicide 2/03

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

Bureau of Pesticides Management, 9th Floor
625 Broadway, Albany, New York 12233-7254
Phone: (518) 402-8788     FAX: (518) 402-9024

February 28, 2003


Ms. Margaret A. Brown
Monsanto Company
800 N. Lindbergh Blvd. (A2ND)
St. Louis, Missouri 63167

Dear Ms. Brown:

Re: Registration of Yukon Herbicide (EPA Reg. No. 33906-11-524) Containing the Active Ingredients Halosulfuron-methyl and Sodium Salt of Dicamba. Aerial Application was Considered a Major Change in Labeled Use Pattern.

   The New York State Department of Environmental Conservation (Department) has completed its technical review of your application and data packages submitted in support of the registration of YUKON Herbicide (EPA Reg. No. 33906-11-524) containing the active ingredients halosulfuron-methyl and sodium salt of dicamba. The Department has registered this product for labeled use on field corn, seed corn, and grain sorghum with use directions for aerial application.

   The active ingredient halosulfuron-methyl, is a member of the family of compounds known as sulfonyl ureas which inhibit the actions of plant enzymes thus stopping plant growth. These compounds generally have a low mammalian toxicity and are applied at very low rates, generally 1/50 of other common herbicides to achieve the same control. The formulated product is used to control pre- or post-emergent broadleaf weeds and nutsedge in field corn, seed corn, and grain sorghum. The maximum application rate is eight ounces per acre per year on field corn. (0.0625 lb. halosulfuron-methyl and 0.275 lb. dicamba per acre per year)

   There are two products containing the active ingredient halosulfuron-methyl that were previously registered in New York State. Manage Turf Herbicide is registered for turf applications and Permit Herbicide is registered for use on field corn and grain sorghum. These products were registered on April 15, 1997 and May 2, 1997. At that time the Department had concerns that Permit Herbicide could pose a potential risk to aquatic plants via runoff into surface waters adjacent to the application site. However, there were agronomic and environmental benefits associated with the use of Permit Herbicide which led to a positive registration decision of the Permit Herbicide product. The Department has continued to monitor the registration and use of products containing halosulfuron-methyl to limit impacts to aquatic plants.

   The Yukon Herbicide application was received on March 8, 2002 as a routine new product application. The Department notified Monsanto of an incomplete application via letter dated April 15, 2002, which instructed Monsanto to submit technical information to support the Yukon product as a major change in labeling application due to the addition of use directions for aerial application. Monsanto submitted a data package on May 28, 2002, to complete their application for a major change in labeling (MCL) review of Yukon Herbicide. The Yukon Herbicide MCL application package was declared incomplete as per Department letter dated July 18, 2002, in which further data was requested concerning toxicity to aquatic plants. Monsanto submitted a data package on September 16, 2002 in response to the Department's letter of incomplete application. The additional information was sufficient to complete the MCL application as per Department letter dated October 16, 2002. Pursuant to the review time frame specified in ECL §33-0704.2, a registration decision date of March 14, 2003, was established. The Department conducted the following technical reviews with regard to the registration of Yukon Herbicide for impacts to human health, non-target organisms, and the environment. Review summaries are provided below:

Product - Labeled Use:

   The formulated product Yukon Herbicide (EPA Reg. No. 33906-11-524) contains the active ingredients halosulfuron-methyl at 12.5% and Sodium salt of dicamba at 55%. This product controls many annual broadleaf weeds and nutsedge in field corn, field corn grown for seed, and grain sorghum. The product is applied both as pre- and post-emergent weed control as a foliar spray. Ground and aerial applications may use up to four ounces of product per acre of field corn per application with a maximum number of two applications per year. Yukon Herbicide is applied to grain sorghum in one application of four to six ounces. Yukon Herbicide is a water dispersible granule which is mixed with no less than ten gallons of water per acre for ground applications and no less than five to fifteen gallons of water per acre for aerial applications. The Yukon Herbicide label warns the user that the product is known to leach through the soil into the groundwater under certain conditions as a result of agricultural use. The "Environmental Hazards" section of the Yukon label directs the user to not apply the product directly to water and not to contaminate water when disposing of equipment wash waters.

Human Health Summary:

   The New York State Department of Health reviewed the Yukon Herbicide product application which includes aerial use directions, for impacts to human health. On an acute basis, Yukon Herbicide was not very toxic to laboratory animals by the oral, dermal or inhalation routes of exposure. This pesticide product also was neither very irritating to rabbit skin or eyes nor did it cause dermal sensitization (tested on guinea pigs).

   In the past, the active ingredient halosulfuron-methyl has been reviewed as found in the pesticide products Permit Herbicide and Manage Turf Herbicide. Halosulfuron-methyl was not very acutely toxic in laboratory animal studies, did not cause oncogenic effects in rats and mice and was negative in a battery of genotoxicity tests. Developmental toxicity was reported in offspring of rats and rabbits given halosulfuron-methyl, but only at doses that also caused parental toxicity. In addition, no reproductive effects were reported in a rat multi-generation toxicity study.

   The United States Environmental Protection Agency's (USEPA) Office of Pesticide Programs previously established a reference dose (RfD) for halosulfuron-methyl of 0.1 milligrams per kilogram body weight per day (mg/kg/day) based on a no-observed-effect level (NOEL) of 10 mg/kg/day in a one-year dog feeding study and an uncertainty factor of 100 (Federal Register 59: December 27, 2001, pages 66778-66786). More recently, the USEPA's Office of Pesticide Programs revised the RfD to 0.03 mg/kg/day (Federal Register 67: September 20, 2002, pages 59182-59193) based on the same NOEL (10 mg/kg/day) and an uncertainty factor of 300. The uncertainty factor was increased from 100 to 300 because of USEPA's concern for lack of a developmental neurotoxicity study on halosulfuron-methyl. Neither RfD (0.1 mg/kg/day or 0.03 mg/kg/day) has yet been adopted by the USEPA's Integrated Risk Information System (IRIS). A current search of the toxicological literature did not find any significant new information on the toxicity of halosulfuron-methyl.

   The USEPA established tolerances for halosulfuron-methyl of 0.05 parts per million (ppm) in field corn grain and sorghum grain and forage; 0.2 ppm for field corn forage; 0.8 ppm for field corn fodder; and 0.1 ppm for sorghum fodder. These tolerances are revised values from earlier tolerances set for these commodities. The USEPA estimated that chronic dietary exposure to halosulfuron-methyl for the most exposed sub-population group (children one to six years) would be 0.00071 mg/kg/day, which is about 2.4 percent of the RfD. This estimate assumes that 100 percent of a number of crops were treated and that all commodities contain tolerance level residues.

   The USEPA reported the results of a risk assessment for dermal exposure (an inhalation risk assessment was not required) of workers (mixer/loaders) supporting aerial application of halosulfuron-methyl. For these workers, margins of exposure (MOE) of 3,100 and 640 were estimated for short-term and intermediate-term dermal exposures, respectively. These MOEs were based on these workers wearing long sleeves, long pants and gloves and treating 350 acres per day at an application rate of 0.063 pounds of halosulfuron-methyl per acre. The NOEL used to estimate the MOE of 3,100 was 50 mg/kg/day from a rabbit developmental toxicity, whereas the NOEL used to estimate the MOE of 640 was 10 mg/kg/day from the one-year dog toxicity study. Generally, the USEPA considers MOEs of 100-fold or greater to provide adequate worker protection.

   Available environmental fate studies reported that halosulfuron-methyl and some of its degradates have soil adsorption coefficients (Koc's) of less than 400. These relatively low Koc's indicate a high soil mobility and therefore a high capacity to leach through soil and contaminate groundwater. In this regard, the label for Yukon Herbicide states under Environmental Hazards that "This product is known to leach through the soil into the groundwater under certain conditions as a result of agricultural use. The use of this chemical in areas where soils are permeable, particularly where the water table is shallow, may result in groundwater contamination."

   There are no chemical specific federal or State drinking water/groundwater standards for halosulfuron-methyl or its major degradates, 3-chlorosulfonamide acid and 3-chlorosulfonamide ester. Based on their chemical structures, each 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 New York State drinking water standard for the sum of these compounds is 100 micrograms per liter.

   The available information on halosulfuron-methyl and the formulated product Yukon Herbicide indicates that they were not very acutely toxic in laboratory animal studies. Halosulfuron-methyl also was not very toxic in chronic animal feeding studies and did not cause any genotoxic or oncogenic effects. Although this chemical caused some developmental toxicity, these effects occurred at high dose levels that also were associated with maternal toxicity. In addition, the expected exposure to halosulfuron-methyl from the labeled use of Yukon Herbicide should not pose a significant health risk to the general public or to workers involved in the aerial application of this pesticide product.

Non-target Organism Summary:

BACKGROUND OF EARLIER CONCERNS: The first halosulfuron-methyl product reviewed by the Bureau of Habitat (BoH) was received in June, 1996. The review, dated January 14, 1997, showed that halosulfuron-methyl did not present any unacceptable risks to birds, mammals, fish, or aquatic invertebrates. It did show, however, that the risk to aquatic macrophytes as represented by Lemna gibba was extremely high. The EC50 for growth inhibition was 0.042 ug/L. BoH suggested three possible ways to mitigate concerns about the risks to non-target macrophytes to the applicant:    Instead, the applicant submitted the preliminary results of an aquatic dissipation study that showed the concentration of halosulfuron-methyl dissipated to below 0.5 ug/L fairly quickly; within about eight days. This study did not resolve BoH concerns because the Lemna gibba EC50 was more than an order of magnitude lower than the 0.5 ug/L limit of quantification (LOQ) for halosulfuron-methyl for the study.

CURRENT MCL APPLICATION: In June 2002, the Bureau of Habitat received the MCL application for Yukon Herbicide for review. In July, 2002, the application was found to be incomplete on the basis that the data submitted still did not address previously identified concerns about halosulfuron-methyl's potential non-target toxicity to aquatic macrophytes. In September 2002 the applicant submitted a supplemental data support package that contained significant new data. The supplemental data package included the results of a second Lemna gibba toxicity test conducted at a higher pH. The original Lemna gibba test was conducted at a pH range of 4.9 - 6.5). Halosulfuron-methyl has a much slower half life in water at lower pH. The reason for conducting the original test at such a low pH was not explained in either the original study or USEPA DER. It can be surmised, though, that the reason was to slow the degradation of halosulfuron-methyl for the duration of the test so the test concentration would remain constant without having to resort to a flow-through test protocol.

   For the subsequent Lemna gibba test, the pH of the test water ranged from 7.3 to 8.9. The applicant documented that this range was more consistent with the ambient surface water pH levels expected to occur within major corn producing areas of New York State. The applicant documented this pH range with USGS surface water pH data from across New York.

   In the second test, the concentration of halosulfuron-methyl dropped off quickly. As a result, it was not possible to accurately determine an EC50. The results of the test suggest that the 14-day EC50 for Lemna gibba growth inhibition would lie between 0.55 - 3.5 ug/L based on the 14-day time-weighted average concentration. The study authors suggested that Lemna gibba was less sensitive to halosulfuron-methyl at higher pH values. It is more likely the higher EC50 was due simply to the rapidly diminishing concentration of the active ingredient.

   In the second study, the authors also held the test specimens in fresh media after the conclusion of the test to examine for recovery. They were able to document fairly rapid recovery once the plants had been removed from exposure to halosulfuron-methyl.

CONCLUSION: The second Lemna gibba growth inhibition study shows that at pH levels expected to occur in most of the ambient waters of New York, halosulfuron-methyl degrades/dissipates rapidly. Growth inhibition occurs at a concentration (EC50) one to two orders of magnitude higher than the concentrations that caused growth inhibition in low pH water. Furthermore, rapid recovery was demonstrated once the exposure was terminated. This study satisfies the BoH recommendation that the applicant needed to demonstrate that halosulfuron-methyl would not be as toxic in the field as the results the first laboratory Lemna gibba growth inhibition study suggested. Furthermore, the aquatic dissipation study that was originally rejected because it could not document the disappearance of halosulfuron-methyl below the original EC50 concentration (0.042 ug/L) is now considered to be useful. It documents the rapid dissipation/degradation of halosulfuron-methyl to the LOQ of 0.5 ppb, which is the lower end of the range wherein the alkaline EC50 might lie (0.55 - 3.5 ug/L).

   This study suggests that any halosulfuron-methyl transported to water would dissipate/degrade before significant growth inhibition could occur in exposed non-target macrophytes. Any macrophyte affected would recover rapidly as the halosulfuron-methyl concentration disappeared. Because halosulfuron-methyl can only be used once or twice per season and must be applied early in the season (it must be applied to weeds that are rapidly growing), it is unlikely that it would have any adverse ecological impact.

   Dicamba has also been evaluated several times by BoH. Dicamba exhibits low toxicity to birds, mammals, fish, and aquatic invertebrates. Unlike halosulfuron-methyl, dicamba is more toxic to algae than it is to aquatic macrophytes. However, review of other products that include dicamba show that the labeled use of Yukon Herbicide does not present any unacceptable risks.

Environmental Fate Summary:

   The environmental fate data for halosulfuron-methyl suggest a concern for groundwater/drinking water contamination. However, the application rate of halosulfuron-methyl in Yukon Herbicide is quite low (0.0625 lb. or 28.4 grams per acre per year) and previous evaluation by the Department have determined that a prohibition from Long Island was not necessary. The addition of aerial use application to the Yukon Herbicide label will not significantly change the impact to groundwater from the labeled use of this product.

Registration Summary:

   The Department will register Yukon Herbicide for use as labeled in New York State. However, the Department will require Monsanto to clarify the maximum application rate to field corn at your next label printing. If the correction is not made by the next renewal (12/31/2003) the product may be suspended. The current statement in the Yukon label directions under the Field Corn and Field Corn Grown For Seed section is: "Yukon Herbicide may be applied up to two applications with a total not to exceed 8 ounces of product by weight." It is unclear whether this means a total of 8 ounces for two applications (i.e., 4 ounces per application) or an upper limit of 8 ounces per application for a total of 16 ounces. The statement should clarify the maximum application rate not to exceed 8 ounces of product per acre per year.

   Enclosed for your records are a copy of the stamped accepted label and the Certificate of Registration for Yukon Herbicide (EPA Reg. No. 33906-11-524). Please note that a proposal by Monsanto or any other registrant, to register a product that contains halosulfuron-methyl, and whose labeled uses are likely to increase the potential for significant impact to humans, non-target organisms, or 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 listed in Appendix 1.B. of "New York State Pesticide Product Registration Procedures" (August, 1996). Such information as well as forms can be accessed at our website as listed in our letterhead.

   Please be aware that any unregistered product may not be sold, offered for sale, distributed, or used in New York State.

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


Maureen 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
G. Good/W. Smith - Cornell University, PMEP