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Nicosulfuron

Publication Date: 6/96

TRADE OR OTHER NAMES

Trade names for products containing nicosulfuron include Accent, Challenger, Dasul, Lama, Milagro, Mistral, Motivel, Nisshin and Sanson (3, 4).

REGULATORY STATUS

Nicosulfuron is a general use pesticide with a toxicity classification of IV (relatively non-toxic). Check with specific state regulations for local restrictions which may apply. Products containing nicosulfuron must bear the signal word "Caution" on their label (3).

INTRODUCTION

Nicosulfuron is a member of the sulfonylurea family of herbicides. It controls weeds by inhibiting the plant enzyme acetolactate synthase, or ALS. This enzyme is not found in livestock, fish or man. Inhibiting the ALS enzyme system blocks the production of the amino acids, valine and isoleucine, essential building blocks of proteins and other plant components (1). Nicosulfuron is applied postemergence with a non-ionic surfactant when weeds are 4-12 inches tall and actively growing. Rain within two hours of application will not decrease the effectiveness (4). Nicosulfuron is used for control of weeds such as Johnsongrass, quackgrass, foxtails, shattercane, panicums, barnyardgrass, sandbur, pigweed, morningglory and others. Crops include field corn and popcorn (1, 4, 7, 8).

Nicosulfuron comes in a 75% water dispersible granule formulation. It may be tank mixed with a limited number of other compounds (1, 4, 7, 8).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

The amount of a chemical that is lethal to one-half (50%) of experimental animals fed the material is referred to as its acute oral lethal dose fifty, or LD50. The toxicity of nicosulfuron varies. The acute oral LD50 for technical nicosulfuron was reported to be >5,000 mg/kg body weight (toxicity category IV). The acute dermal LD50 was >2,000 mg/kg body weight (toxicity category IV). The acute inhalation LC50 was >5.9 mg/L (toxicity category III). Primary dermal irritation testing showed nicosulfuron to be a non-irritant and a non-sensitizer (toxicity category IV). The primary eye irritation testing showed nicosulfuron to be a moderate irritant (toxicity category III) (1, 3, 5, 7, 8).

CHRONIC TOXICITY

A ninety-day subchronic toxicity study reported no effects up to 20,000 ppm for rats and dogs and 300 ppm for mice (1). In 28-day feeding trials to mice and rats, no adverse effects were noted up to 30 gm/kg (5, 8).

In a l-year feeding study, dogs were treated with nicosulfuron at doses of 0, 250, 5000, or 20000 ppm. The systemic NOEL of 5000 ppm for males and 20,000 ppm for females (or 147 and 587 mg/kg body weight/day, respectively) is based on a decrease in body weight gains and a concomitant increase in relative liver and kidney weights in males (6, 7, 8).

Reproductive Effects

In a multigeneration reproduction study, rats were fed doses of 0, 12.5, 287, and 1,269 mg/kg body weight/day. The NOEL for systemic toxicity is 287 mg/kg/day with a lowest-observable-effect level (LOEL) of 1,269 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, and in pup weights at postpartum day 14 through 21 in the F2a high dose group. 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 (6, 7, 8).

Teratogenic Effects

A rat teratology study using doses of 0, 186, 930, 2325, and 5581 mg/kg/day showed no a developmental or maternal effects up to 5581 mg/kg/day, the highest dose tested. 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, the highest dose tested (7).

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 body 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 (7).

Mutagenic Effects

No mutagenic activity was observed when tested in four strains of Salmonella typhimurium. In vitro chromosomal aberration test 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 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 5,000 mg/kg. A DNA synthesis study in rat hepatocytes (liver cells) did not cause any DNA damage in the cells at concentrations from 0.04 to 470 ug/ml (1, 6, 7).

Carcinogenic Effects

A 2-year chronic toxicity/oncogenicity study with male and female rats fed dosages of 0, 1.9/2.6, 58.1/77.1, 289/382, and 786/1,098 mg/kg body weight/day showed no effects up to 786 mg/kg/day in males and 1,098 mg/kg/day in females, the highest dose tested. The systemic LOEL is greater than 786 mg/kg/day and 1,098 mg/kg/day for male and female rats, respectively (6, 7).

In an 18-month oncogenicity study, male and female mice administered dosages of 0, 3.3/4.4, 32.7/44.8, 327/438, and 993/1312 mg/kg body weight/day resulted in no effects up to 993 and 1312 mg/kg/day, the highest dose tested for male and female mice, respectively (6, 7).

Organ Toxicity

No information was found.

Fate in Humans and Animals

Five groups of rats, 5 males and 5 females, were dosed in various sequences with either 10 mg/kg or 1,000 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-CO2was 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% total recovered radioactivity (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 (7).

ECOLOGICAL EFFECTS

Effects on Birds

Nicosulfuron is slightly toxic to birds on an acute and dietary basis. The oral LD50 for bobwhite quail was >2,250 mg/kg. The dietary LC50s for mallard ducks and bobwhite quail were >5,620 ppm (1, 3, 7, 8).

Effects on Aquatic Organisms

Nicosulfuron is practically non-toxic to freshwater fish and invertebrates. The 96 hour LC50 for bluegill and rainbow trout is >1,000 mg/L. The 48 hour EC50 for Daphnia magna is >1,000 mg/L (1, 3, 7).

Effects on Other Animals (Nontarget species)

Nicosulfuron has an acute contact toxicity LD50 >20 ug/bee and an acute dietary LC50 >1000 ppm. It is considered practically non-toxic to honey bees (7, *).

ENVIRONMENTAL FATE

Breakdown of Chemical in Soil and Groundwater

Biodegradation is an important degradation mechanism for nicosulfuron. The half-life of nicosulfuron in a silt clay soil is 26 days. 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 (2, 4, 7).

Nicosulfuron is very mobile in sandy loam and silt loam soils. The pyridine sulfonamide degradate is more mobile than the parent compound. The pyrimidine amine degradate is the least mobile (7).

The formulated product Accent has a photolysis half-life at 25 degrees C of 60-67 days in soil with a pH of 6.2. Field dissipation half-life of the same material was 3 weeks at pH 6.5, 7 weeks at pH 7.4, and 2 weeks at pH 8 (2). Accent poses minimal risk of leaching to groundwater according to calculations using EPA's Pesticide Root Zone model (PRZM). The soil-binding characteristics and values place the herbicide in EPA's classification of low to intermediate soil mobility (1).

Breakdown of Chemical in Surface Water

The formulated product Accent has a photolysis half-life at 25 degrees C of 14-19 days in water with a pH of 5, 200-250 days at a pH of 7, and 180-200 days at a pH of 9. The hydrolysis half-life of the same material is 15 days at a pH of 5 (2).

Breakdown of Chemical in Vegetation

Foliar absorption is the primary means of nicosulfuron uptake by plants (7).

PHYSICAL PROPERTIES AND GUIDELINES

Technical nicosulfuron can be recognized as white powder or colorless crystals (3). It may form flammable or explosive dust-air mixtures. It is stable under normal temperatures and pressures. Thermal decomposition products may include toxic oxides of carbon, nitrogen, and sulfur (5). No corrosion or physical change was observed for the end use product after being stored at room temperature for 10 months for either solid granules or container material of construction (high-density polyethylene) (7).

Exposure Guidelines:

NOEL: 125 mg/kg/body weight/day (6)
ADI: 1.25 mg/kg/body weight/day (6)

Physical Properties:

CAS #: 111991-09-4 (3)
Chemical name: 2-[[(4,6-dimethoxypyrimidin-2-yl)aminocarbonyl]aminosulfonyl]-N,N-dimethyl-3-pyridinecarboxamide (1)
Chemical Class/Use: Nicosulfuron is a sulfonylurea compound used as a selective postemergence herbicide (4).
Specific gravity: 0.313 g/ml (technical); 0.53 g/ml (end use product) (7)
Solubility in water: @ 25 degrees C: 0.04 g/100g pH=5.0; 1.2 g/100g pH=7.0; 3.9 g/100g pH=9.0 (8)
Solubility in other solvents: Soluble in acetone, acetonitrile, chloroform, hexane, dimethylformamide, dichloromethane, ethanol, and toluene (5).
Melting point: 141-144 degrees C (1, 7)
Vapor pressure: 1.2 x 10 to the minus 16 torr at 25 degrees C (1, 7)
Kd: at 25 degrees C: 0.61 (pH 4.3), Keyport Silt Loam; 1.73 (pH 5.4), Flanagan Silt Loam; 0.28 (pH 6.5), Cecil Sandy Loam; 0.16 (pH 6.6), Woodstown Sandy Loam (2)
Koc: at 25 degrees C: 15.4 (pH 4.3), Keyport Silt Loam; 78.8 (pH 5.4), Flanagan Silt Loam; 28.8 (pH 6.5), Cecil Sandy Loam; 38.4 (pH 6.6), Woodstown Sandy Loam (2)
Kow: at 25 degrees C: 0.44 (pH 5); 0.017 (pH 7); 0.01 (pH 9) (2, 7)

BASIC MANUFACTURER

DuPont Agricultural Products
Walker's Mill, Barley Mill Plaza
P. O. Box 80038
Wilmington, DE 19880-0038
Fax: 302-992-6470
Telephone: 800-441-7515
Emergency: 800-441-3637

Review by Basic Manufacturer:

Comments solicited: April, 1995
Comments received: May, 1995

REFERENCES

  1. Technical Bulletin: Accent Herbicide. 1990. DuPont Agricultural Products, Wilmington, DE 19880.
  2. DuPont Data Sheet. 1990. E.I. du pont de Nemours and Co., Wilmington, DE.
  3. Farm Chemicals Handbook. 1995. Meister Pub. Co., Willoughby, OH.
  4. Thomson, W. T. 1993. Agricultural Chemicals. Book II: Herbicides. Thomson Publications, Fresno, CA.
  5. OHS Database. 1994. MDL Information Systems, Inc. 1994 (June) MSDS for Nicosulfuron. MDL Infor-mation Systems, Inc., San Leandro, CA.
  6. U.S. Environmental Protection Agency. 1990. Pesticide Tolerances for Nicosulfuron. Federal Register. Vol. 55, No. 134. Rules and Regulations. Thursday, July 12, 1990.
  7. U.S. Environmental Protection Agency. June 29, 1990. Pesticide Fact Sheet Number: 216. US EPA, Office of Pesticides and Toxic Substances, Washington, DC.
  8. Review by E.I. DuPont Co., Inc. May 30, 1995.