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nicosulfuron (Accent) EPA Chemical Fact Sheet 6/90

<ENTR Accepted>
 
                          CHEMICAL FACT SHEET FOR
                                Nicosulfuron                                
FACT SHEET NUMBER: 216             
DATE ISSUED: JUNE 29, 1990                                                  
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1.  Description of the Chemical                                             
                                                                            
    Generic Name:              Nicosulfuron  3-pyridinecarboxamide,         
                                 2-((((4,6-dimethoxypyrimidin-2-yl)         
                                 aminocarbonyl)aminosulfonyl))-N,           
                                 N-dimethyl|                                
    Common Name:               Nicosulfuron                                 
    Code Name:                 DPX-V9360                                    
    Trade Name:                Accent                                       
    EPA (Shaughnessy) Code:    129008                                       
    Chemical Abstracts                                                      
      Service (CAS) Number:    111991-09-4                                  
    Year of Initial                                                         
      Registration:            1990                                         
    Pesticide Type:            Herbicide                                    
    Chemical Family:           Sulfonylurea                                 
    U.S. and Foreign                                                        
      Producers:               E.I. du Pont de Nemours & Co., Inc.          
 
2.  Use Patterns and Formulations                                           
                                                                            
    Application Sites:                                                      
    - Field corn only.  Accent is not to be used on popcorn, sweet corn,    
      or corn grown for seed production.                                    
    Types and Methods of Application:                                       
    - Accent is to be applied by ground equipment to young, actively        
      growing weeds.                                                        
    Application Rates:                                                      
    - Single application - Maximum single application is 1 1/3 ounce (oz)   
      of Accent per acre (A) per any crop year, (1 oz active ingredient     
      (ai)/A) in a minimum of 10 gallons of water.                          
    - Split application - Application not to exceed a total of 1 1/3 oz of  
      Accent/A/crop year  recommended 2/3 oz of Accent each (0.5 oz/ai/A)|. 
    Formulations:                                                           
    - 75% water dispersible granule.                                        
 
3.  Science Findings                                                        
                                                                            
    Chemical Characteristics:                                               
    (NR - Not Required, NA - Not Applicable)                                
                      End-Use Product       Technical                       
                         (Accent)         (Nicosulfuron)                    
     Molecular Weight:   410.4                                              
     Molecular Formula:  C15H18N6O6S                                        
     Color:              Light tan           White                          
     Physical State:     Solid, granular     Solid                          
     Odor:               None                Paste-like                     
     Melting Point:      NR                  141-144 degrees C              
     Boiling Point:      NA                  NA                             
     Density:            0.53 g/ml           0.313 g/ml                     
     Solubility:         NR                  0.04* (pH 5.0 buffer);         
                                             1.2* (pH 7.0 buffer); and      
                                             3.9* (pH 9.0 buffer)           
                         *solubility limit, g/100 g buffer at 25 degrees C  
                                             *18 (acetone),                 
                                             *23 (acetonitrile),            
                                             *1.7 (benzene),                
                                             *64 (chloroform),              
                                             *64 (N,N-dimethylformamide),   
                                             *4.5 (ethanol),                
                                             *3.8 (ethyl acetate),          
                                             *<0.02 (n-hexane),             
                                             *0.44 (methanol),              
                                             *160 (methylene chloride),     
                                             *1.2 (2-propanol),             
                                             *26 (tetrahydrofuran),         
                                             *0.37 (toluene),               
                                             *0.20 (xylenes)                
                         *solubility limit, ppm x 10(3) at 28 plus or minus 
                          1 degree C                                        
     Vapor Pressure:     NR                  1.2 x 10(-16) torr             
     Dissociation                                                           
       Constant:         NR                  pKa value = 4.3 (acid)         
     pH:                 3.9 (1% dispersion  A slurry in HPLC water caused  
                             in water)       the pH of the water to         
                                             decrease from 6.6 to 4.5.      
     Octanol/Water                                                          
       Partition Coefficient (KOW):                                         
                         NR                  0.44 (pH 5)                    
                                             0.017 (pH 7)                   
                                             0.01 (pH 9)                    
     Stability:          NR                  The TGAI is solution stable    
                                             in the presence of iron        
                                             metal and ferrous (Fe +2|).    
                                             The solid TGAI is stable under 
                                             normal storage at 25 degrees C 
                                             and at 45 degrees C for 3      
                                             weeks.                         
     Oxidizing or                                                           
        Reducing Action: Does not contain oxidizing or reducing agents.     
     Flammability:       NA                                                 
     Explodability:      Not explosive.                                     
     Storage Stability:  Ten months result showed product stability at      
                         room temperature.  Aging test continuing for       
                         two additional months.                             
     Viscosity:          NA                                                 
     Miscibility:        NA                                                 
     Corrosion                                                              
       Characteristics:  After being stored in the laboratory at room       
                         temperature for 10 months, no physical change      
                         was observed for either solid granules or          
                         container material of construction (high-density   
                         polyethylene).                                     
     Dielectric                                                             
       Breakdown                                                            
       Voltage:          NA                                                 
 
    Toxicology Characteristics                                              
    Acute Testing:                                                          
                         Technical                Formulation               
    - Acute Oral:        LD50>5000 mg/kg          LD50>5000 mg/kg           
                         Toxicity Category IV     Toxicity Category IV      
    - Acute Dermal:      LD50>2000 mg/kg          LD50>2000 mg/kg           
                         Toxicity Category III    Toxicity Category III     
    - Acute Inhalation:  LC50>5.9 mg/l            LC50>5600 mg/m(3)         
                         Toxicity Category III    Toxicity Category IV      
    - Primary Dermal                                                        
        Irritation:      Non-irritant             Mild irritant             
                         Toxicity Category IV     Toxicity Category IV      
    - Primary Eye                                                           
        Irritation:      Moderate irritant        Moderate irritant         
                         Toxicity Category III    Toxicity Category III     
    - Dermal                                                                
        Sensitization:   Non-sensitizer           Non-sensitizer            
    Chronic Testing:                                                        
    - Oncogenicity:  In an 18 month oncogenicity study, mice administered   
      dosages of 0, 3.3/4.4, 32.7/44.8, 327/438, and 993/1312 mg/kg/day     
      resulted in a systemic NOEL of 993 and 1312 mg/kg/day (HDT) for       
      male and female mice, respectively.                                   
    - Chronic Toxicity:  In a 1 year feeding study, dogs were treated with  
      Accent at doses of 0, 62.5, 125, and 500 mg/kg/day.  The systemic     
      NOEL of 125 mg/kg/day for both sexes is based upon a decrease in      
      body weight gains and a concomitant increase in relative liver and    
      kidney weights in males.                                              
    - Chronic Toxicity/Oncogenicity:  A 2 year chronic toxicity/            
      oncogenicity study with rats fed dosages of 0, 1.9/2.6, 58.1/77.1,    
      289/382, and 786/1098 mg/kg/day yielded a systemic NOEL of greater    
      than or equal to 786 mg/kg/day in males and 1098 mg/kg/day in         
      females, (HDT).  The systemic Lowest-Observed-Effect-Level (LOEL)     
      is greater than 786 mg/kg/day and 1098 mg/kg/day for male and female  
      rats, respectively.                                                   
    - Teratogenicity:  A rat teratology study using doses of 0, 186, 930,   
      2325, and 5581 mg/kg/day had a developmental and maternal NOEL of     
      greater than or equal to 5581 mg/kg/day (HDT).  The maternal and      
      developmental LOEL is greater than 5581 mg/kg/day.  No treatment-     
      related effects were noted on maternal or developmental toxicity up   
      to and including 5581 mg/kg/day (HDT).                                
      - A rabbit teratology study using doses of 0, 93, 465, 930, and 1860  
        mg/kg/day of Accent yielded a maternal NOEL of 93 mg/kg/day and LOEL
        of 465 mg/kg/day based upon maternal toxicity occurring at 465      
        mg/kg/day; an increase in clinical signs, gross pathological        
        observations, abortions, postimplantation loss and a decrease in bod
        weight gain during the dosing period.  The developmental NOEL       
        of 465 mg/kg/day and LOEL of 930 mg/kg/day is based upon            
        developmental toxicity occurring at 930 mg/kg/day; reduced mean     
        fetal body weight and the apparent increase in postimplantation     
        loss at 465 mg/kg/day and above.                                    
    - Reproduction:  In a multigeneration reproduction study, rats were fed 
      doses of 0, 12.5, 287, and 1269 mg/kg/day.  The NOEL for systemic     
      toxicity is 287 mg/kg/day with a LOEL of 1269 mg/kg/day, based on     
      F1 (first mating) females with a lower body weight gain during the    
      final week of gestation and a similar pattern in the F0 females       
      during the same gestational period.  The reproductive NOEL is         
      287 mg/kg/day with a LOEL of 1269 mg/kg/day based on minimal          
      reduction in litter size at birth and in pup weights at postpartum    
      day 14 through 21 in the F2a high dose group.                         
    Special Testing:                                                        
    - Metabolism:  The requirement for a metabolism study in rats has       
      been satisfied.  Five groups of rats, 5 males and 5 females, were     
      dosed in various sequences with either 10 mg/kg or 1000 mg/kg         
      of  pyridinyl-14C|-DPX-V9360 or  pyrimidinyl-14C|DPX-V9360            
      either orally or intravenously.  Both males and females excreted      
      essentially all of the radionuclide in the feces and urine.           
      Elimination of 14C-CO2 was not observed.  No organ or tissue          
      showed total 14C-radioactivity >0.01 of the administered dose.        
      The major radioactivity was recovered as the parent which ranged from 
      85 to 97%.  Two metabolites, pyridine sulfonamide and 5-hydroxy       
      pyrimidine amine, were identified.  The presence of pyridine acid     
      sulfonamide was also suggested, but not positively identified.        
      Several undefined metabolites makeup <10% TRR. Based on the           
      metabolites identified, the major pathway in the rat is cleavage      
      of the parent DPX-V9360, to yield pyridine sulfonamide and            
      pyrimidine amine; 5-OH pyrimidine amine could be formed either        
      before or after the cleavage.                                         
    Mutagenicity Testing:                                                   
    - No mutagenic activity was observed when tested in four strains        
      (TA97A, TA98, TA100, and TA1535) of Salmonella typhimurium.           
      In vitro chromosomal aberration tests in cultured human lymphocytes   
      indicated negative responses at the concentrations from 40 to 470     
      ug/ml.  Nicosulfuron assayed with or without metabolic activation     
      in vitro in Chinese Hamster Ovary (CHO) cells was nonmutagenic at     
      the concentrations from 4 to 465 ug/ml and a micronucleus assay       
      in mouse bone marrow cells was negative at dose levels from 500       
      to 5000 mg/kg.  An unscheduled DNA synthesis study in rat             
      hepatocytes did not cause any DNA damage in rat hepatocytes at the    
      concentrations from 0.04 to 470 ug/ml.                                
 
    Physiological and Biochemical Characteristics                           
    - Mechanism of Pesticidal Actio:  Biodegradation is an important        
      degradation mechanism of nicosulfuron.                                
    - Foliar Absorption:  Foliar absorption is the primary means of         
      nicosulfuron uptake by plants.                                        
 
    Environmental Characteristics                                           
    - Hydrolysis:  Nicosulfuron is stable in aqueous solutions at neutral   
      and alkaline pHs.  Solubility increases with increasing pH.  The      
      main hydrolytic mechanism involves cleavage of the sulfonylurea       
      bridge, but a minor mechanism involving -SO2- elimination followed    
      by rebridging also occurs at acidic pHs.  The mail hydrolytic         
      degradates are pyrimidine amine and pyridine sulfonamide.             
    - Photodegradation in Water and on Soil:  Photodegradation is not a     
      significant degradation mechanism for nicosulfuron.                   
    - Aerobic Soil Metabolism:  Biodegradation is an important degradation  
      mechanism for nicosulfuron.  The half-life of nicosulfuron in a silt  
      clay soil is 26 days.  The main degradates are pyridine sulfonamide   
      and pyrimidine amine.                                                 
    - Anaerobic Soil/Aquatic Metabolism:  Biodegradation is an important    
      degradation mechanism for nicosulfuron.  However, anaerobic           
      conditions slow down the degradation process.  The half-life of       
      nicosulfuron in silt clay soil/water is 63 days.  The main degradates 
      are pyridine sulfonamide and pyrimidine amine.                        
    - Mobility in Soil:  Nicusulfuron is very mobile in sandy loam and      
      silt loam soils.  The pyridine sulfonamide degradate is more          
      mobile than the parent.  The pyrimidine amine degradate is the        
      least mobile.                                                         
    - Volatility from Soil:  Nicosulfuron is not likely to volatilize       
      from soil.                                                            
    - Terrestrial Field Dissipation:  This study was determined to be       
      supplemental and cannot be used to define a depth of leaching or      
      to use the reported half-lives to estimate the persistence of         
      nicosulfuron under field conditions.                                  
    - Accumulation in Confined Rotational Crops and in Fish:  Degradates    
      containing the pyridine ring are more readily uptaken by the plants.  
      The minimum rotational crop interval is 10 months.  Nicosulfuron      
      has a low tendency to accumulate in fish.                             
      The Environmental Fate and Ground Water Branch (EFGWB) has            
      determined that the following data requirements have been             
      satisfied:  hydrolysis, photodegradation on soil and in water,        
      aerobic and anaerobic soil metabolism, anaerboic aquatic              
      metabolism, mobility in soil, and accumulation in confined            
      rotational crops.  The volatility from soil studies and the           
      bioaccumulation in fish study have been waived.  The terrestrial      
      field dissipation study was considered supplemental and a new         
      study must be submitted as a condition for registration.              
      - Spray drift studies are being requested as a part of the            
        conditional registration.  Submission of these data will address    
        concerns about the potential to harm nontarget plants during        
        application and ways to prevent adverse effects.                    
 
    Ecological Characteristics                                              
                                                  Classification            
      - Avian Acute Toxicity:                                               
        - Bobwhite quail      LD50>2000 mg/kg     Practically non-toxic     
      - Avian Dietary Toxicity:                                             
        - Mallard duck        LC50>5000 mg/kg     Slightly toxic            
        - Bobwhite quail      LC50>5000 mg/kg     Slightly toxic            
      -Freshwater Fish Acute                                                
         Toxicity:                                                          
        - Rainbow trout       LC50>1000 ppm       Practically non-toxic     
        - Bluegill sunfish    LC50>1000 ppm       Practically non-toxic     
      - Freshwater Invertebrate                                             
         Toxicity:                                                          
        - Daphnia magna       LC50>1000 ppm       Practically non-toxic     
      - Acute Contact                                                       
         Toxicity:                                                          
        - Honey bee           LD50>20 ug/bee      Practically non-toxic     
                                                                            
    - Available data indicates that the hazard to avian, aquatic, and       
      mammalian species will be minimal.  The terrestrial nontarget plant   
      data does not fulfill data requirements.  Nicosulfuron is practically 
      non-toxic to freshwater fish and invertebrates.  This chemical is     
      slightly toxic to birds on an acute and dietary basis.  In addition,  
      nicosulfuron is practically non-toxic to honey bees.                  
    - The Agency does not believe that conditional registration of this     
      chemical will cause substantially greater adverse effects to the      
      environment than other sulfonylurea products.                         
    - Potential Problems Related to Endangered Species:  It is not          
      expected that nicosulfuron will pose any hazards to endangered        
      species.                                                              
 
    Tolerance Assessment                                                    
    - Tolerances have been established for residues of the herbicide in or  
      on the raw agricultural commodity corn, in the form of grain, forage, 
      silage, and fodder (40 CFR 180.).                                     
          corn, grain         0.1 ppm                                       
          corn, fodder        0.1 ppm                                       
          corn, silage        0.1 ppm                                       
          corn, forage        0.1 ppm                                       
      There are no tolerances established for residues of nicosulfuron      
      in/on corn in Canada, Mexico, or by Codex.                            
    - Summary of Other Permanent Tolerances for Nicosulfuron - The only     
      permanent tolerances established for nicosulfuron at this time are    
      the above corn raw agricultural commodities (RACs).  No other         
      permanent tolerances have been established for nicosulfuron.          
 
    Summary Science Statement                                               
                                                                            
    - Review of the product chemistry, environmental fate, toxicology,      
      and ecological effects data have been completed.  The available       
      data supports the conditional registration of Accent for the          
      proposed food use.  Data deficiencies exist in the ecological         
      effects and environmental fate and ground water areas.                
    - In the area of Environmental Fate and Ground Water, new field         
      dissipation and spray drift studies are required.  However, the       
      available environmental fate data supports the conditional            
      registration of Accent.                                               
    - With respect to ecological effects data, the Agency is requiring      
      the company to submit a new seedling emergence study and              
      additional information to upgrade the vegetative vigor study.         
      However, the available ecological effects data supports the           
      conditional registration of this chemical.                            
    - Available ecological effects data indicates that the hazard to        
      avian, aquatic, and mammalian species will be minimal.                
    - The Agency does not believe that registration of this chemical        
      will cause substantially greater adverse effects the environment      
      than other sulfonylurea products.                                     
 
4.  Summary of Regulatory Position and Rationale                            
                                                                            
    - As a condition of registration, the registrant must submit a new      
      terrestrial field dissipation study, additional information on the    
      photodegradation in water study, spray drift studies, a new           
      seedling emergence study, and additional information to upgrade       
      the vegetative vigor study.                                           
    - Required Unique Labeling                                              
      - Precautionary Statements:                                           
                                                                            
        "Do not apply where/when condition could favor runoff."             
                                                                            
        "Do not apply if rainfall or storm is expected within 24 hours."    
                                                                            
      - Use Directions:                                                     
                                                                            
        "The minimum rotational crop interval is 10 months, except          
         for alfalfa which is 12 months."                                   
                                                                            
      - Restriction:                                                        
                                                                            
        "The minimum time interval for sorghum, cotton, and all other       
        rotational crops is 10 months on soils with pH less than or         
        equal to 6.5 or 18 months for all soils with pH greater than 6.5."  
                                                                            
        "Do not apply to popcorn, sweet corn, or corn grown for seed        
        production."                                                        
                                                                            
        "Single or split applications of Accent must not exceed a total     
        of 1 1/3 oz/A in any crop year."                                    
                                                                            
        "Do not graze or feed forage or grain from the treated areas to     
        livestock within 30 days after application of Accent."              
 
5.  Summary of Major Data Gaps                                              
                                                                            
    Environmental Fate                       Ecological Effects             
    164-1 Terrestrial Field Dissipation      122-1 Seedling Emergence       
    201-1 Droplet Size Spectrum              122-1 Vegetative Vigor         
    202-1 Drift Field Evaluation                                            
 
6.  Contact Person at EPA                                                   
                                                                            
    - Robert J. Taylor                                                      
      Product Manager (25)                                                  
      Fungicide-Herbicide Branch                                            
      Registration Division (H7505C)                                        
      Office of Pesticide Programs                                          
      Environmental Protection Agency                                       
      401 M Street, S.W.                                                    
      Washington, DC  20460                                                 
      - Office Location and Telephone Number:                               
        Room 245, Crystal Mall #2                                           
        1921 Jefferson Davis Highway                                        
        Arlington, VA  22202                                                
        (703) 557-1800                                                      
DISCLAIMER:
THE INFORMATION PRESENTED IN THIS CHEMICAL INFORMATION FACT SHEET
IS FOR INFORMATIONAL PURPOSES ONLY AND NOT TO BE USED TO FULFILL
DATA REQUIREMENTS FOR PESTICIDE REGISTRATION AND REREGISTRATION.
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