Chlorsulfuron

Pesticide -> EPA IRIS

Herbicides

Active substance -> EU Pesticides database: Not approved

Pesticides -> Herbicides, Sulfonylurea

Pesticide (Chlorsulfuron) -> USDA PDB

Pesticide

log Kow = 0.74 at pH 5 and -1.34 at pH 7

1.54

White crystalline solid

Crystals from ether

In water, 125 mg/L at 25 °C

Solubility (25 °C) : 4 g/L acetone; 102 g/L dichloromethane, <0.01 g/L hexane, 15 g/L methanol; 3 g/L toluene

Moderately soluble in methylene chloride; less soluble in acetone, acetonitril. Low solubility in hydrocarbon solvents.

Slight solubility in methylene chloride, acetone, methanol, toluene, hexane

>53.7 [ug/mL] (The mean of the results at pH 7.4)

176 °C

MP: 174-178 °C

2.25X10-11 mm Hg at 25 °C

0.81313 [mm Hg] @25 °C

Chlorsulfuron appears as colorless crystals. Non corrosive. Insoluble in water. Used as an herbicide.

Colorless or white odorless solid; [HSDB]

Warning

H400: Very toxic to aquatic life [Warning Hazardous to the aquatic environment, acute hazard]

P273, P391, and P501 (click each P-code to see the statement)

Warning

H400 (100%): Very toxic to aquatic life [Warning Hazardous to the aquatic environment, acute hazard]

P273, P391, and P501 (click each P-code to see the statement)

Commission Regulation (EC) No 1490/2002

Chlorsulfuron is listed in the dataset of EPA Human Health Benchmarks for Pesticides under the Safe Drinking Water Act (40 eCFR 141)

2009/77/EC, Reg. (EU) 2022/801, Reg. (EU) No 540/2011

Chlorsulfuron: Does not have an individual approval but may be used under an appropriate group standard

The New Jersey Worker and Community Right to Know Act requires public and private employers to provide information about hazardous substances at their workplaces. (N.J.S.A. 34:5A-1 et. seq.)

USEPA/Office of Prevention, Pesticides and Toxic Substances; Reregistration Eligibility Decision Document - Chlorsulfuron (May 2005). The RED summarizes the risk assessment conclusions and outlines any risk reduction measures necessary for the pesticide to continue to be registered in the USA.[Available from, as of June 20, 2017 http://www.epa.gov/pesticides/reregistration/status.htm]

Blair AM, Martin TD; Pestic Sci 22 (3): 195-220 (1988). A review of the activity fate and mode of action of sulfonylurea herbicides

Tolerances are established for the combined residues of chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesulfonamide) and its metabolite, 2-chloro-5-hydroxy-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl] benzenesulfonamide in or on the following raw agricultural commodities:[Table#6355]

Tolerances are established for residues of chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2- yl)aminocarbonyl] benzenesulfonamide) in or on the following raw agricultural commodities.[Table#6356]

The Agency has completed its assessment of the residential, occupational, and ecological risks associated with the use of pesticides containing the active ingredient chlorsulfuron as well as a chlorsulfuron-specific dietary risk assessment. Based on a review of these data and public comments on the Agency's assessments for the active ingredient chlorsulfuron, EPA has sufficient information on the human health and ecological effects of chlorsulfuron to make decisions as part of the tolerance reassessment process under Federal Food, Drug and Cosmetic Act (FFDCA) and reregistration under FIFRA, as amended by the Food Quality Protection Act (FQPA). The Agency has determined that currently registered uses of chlorsulfuron will not pose unreasonable risks or adverse effects to humans or the environment if the risk mitigation measures and label changes outlined in the RED are implemented. The Agency has determined that chlorsulfuron is eligible for reregistration.

As the federal pesticide law FIFRA directs, EPA is conducting a comprehensive review of older pesticides to consider their health and environmental effects and make decisions about their continued use. Under this pesticide reregistration program, EPA examines newer health and safety data for pesticide active ingredients initially registered before November 1, 1984, and determines whether the use of the pesticide does not pose unreasonable risk in accordance to newer safety standards, such as those described in the Food Quality Protection Act of 1996. Chlorsulfuron is found on List A, which contains most pesticides that are used on foods and, hence, have a high potential for human exposure. List A consists of the 194 chemical cases (or 350 individual active ingredients) for which EPA issued registration standards prior to FIFRA '88. Case No: 0631; Pesticide type: herbicide; Registration Standard Date: 09/30/82; Case Status: OPP is reviewing data from the pesticide's producers regarding its human health and/or environmental effects, or OPP is determining the pesticide's eligibility for reregistration and developing the Reregistration Eligibility Decision (RED) document.; Active ingredient (AI): Chlorsulfuron; Data Call-in (DCI) Date(s): 08/06/90, 08/16/91, 10/13/95; AI Status: The producers of the pesticide has made commitments to conduct the studies and pay the fees required for reregistration, and are meeting those commitments in a timely manner.

Aquatic Acute 1 (100%)

Hazardous to the aquatic environment (acute) - category 1

Aquatic Acute 1

Suitable extinguishing media: Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.

Advice for firefighters: Wear self contained breathing apparatus for fire fighting if necessary.

ACCIDENTAL RELEASE MEASURES: Personal precautions, protective equipment and emergency procedures. Use personal protective equipment. Avoid dust formation. Avoid breathing vapors, mist or gas. Ensure adequate ventilation. Evacuate personnel to safe areas. Avoid breathing dust. Environmental precautions: Prevent further leakage or spillage if safe to do so. Do not let product enter drains. Discharge into the environment must be avoided. Methods and materials for containment and cleaning up: Pick up and arrange disposal without creating dust. Sweep up and shovel. Keep in suitable, closed containers for disposal.

SRP: Recycle any unused portion of the material for its approved use or return it to the manufacturer or supplier. Ultimate disposal of the chemical must consider: the material's impact on air quality; potential migration in air, soil or water; effects on animal, aquatic and plant life; and conformance with environmental and public health regulations. If it is possible or reasonable use an alternative chemical product with less inherent propensity for occupational harm/injury/toxicity or environmental contamination.

Product: Offer surplus and non-recyclable solutions to a licensed disposal company; Contaminated packaging: Dispose of as unused product.

ACCIDENTAL RELEASE MEASURES: Personal precautions, protective equipment and emergency procedures. Use personal protective equipment. Avoid dust formation. Avoid breathing vapors, mist or gas. Ensure adequate ventilation. Evacuate personnel to safe areas. Avoid breathing dust. Environmental precautions: Prevent further leakage or spillage if safe to do so. Do not let product enter drains. Discharge into the environment must be avoided.

Precautions for safe handling: Provide appropriate exhaust ventilation at places where dust is formed.

Appropriate engineering controls: Handle in accordance with good industrial hygiene and safety practice. Wash hands before breaks and at the end of workday.

Gloves must be inspected prior to use. Use proper glove removal technique (without touching glove's outer surface) to avoid skin contact with this product. Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. Wash and dry hands.

For more Preventive Measures (Complete) data for Chlorsulfuron (7 total), please visit the HSDB record page.

Tolerances are established for the combined residues of chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesulfonamide) and its metabolite, 2-chloro-5-hydroxy-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl] benzenesulfonamide in or on the following raw agricultural commodities:[Table#6353]

Tolerances are established for residues of chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2- yl)aminocarbonyl] benzenesulfonamide) in or on the following raw agricultural commodities.[Table#6354]

3.9 [mg/m3]

43 [mg/m3]

260 [mg/m3]

Excerpt from ERG Guide 171 [Substances (Low to Moderate Hazard)]:

Eye/face protection: Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).

Skin protection: Handle with gloves.

Body Protection: Choose body protection in relation to its type, to the concentration and amount of dangerous substances, and to the specific work-place.

Respiratory protection: Respiratory protection is not required. Where protection from nuisance levels of dusts are desired, use type N95 (US) or type P1 (EN 143) dust masks. Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).

... Baseline attire (long sleeve shirt, long pants, shoes, and socks).

Pea (Pisum sativum L. cv Alaska) root tips were excised and cultured aseptically in White's medium. Cultures were treated immediately or after a 24 hour equilibration time with 28 nanomolar chlorsulfuron plus isoleucine and valine (each 0.1 millimolar), isoleucine and valine, or untreated. The percentage of mitotic figures in untreated control roots sampled immediately after excision showed a transitory drop and recovery within 24 hours (an excision effect). In chlorsulfuron-treated roots, the percentage of mitotic figures did not recover. In roots treated with chlorsulfuron plus isoleucine and valine, a complete recovery did occur. If roots were treated with chlorsulfuron 24 hours after excision, the percentage of mitotic figures was reduced to near 0 by 8 hours. In roots treated with chlorsulfuron plus isoleucine and valine, no reduction in mitotic figures occurred. The complete reversal of chlorsulfuron-inhibited mitotic entry by isoleucine and valine implicates these amino acids, in some manner, with the control of cell cycles progression.

LC50; Species: Americamysis bahia (Opossum shrimp) juvenile; Conditions: saltwater, static; Concentration: 89000 ug/L for 96 hr (95% confidence limit: 71000-136000 ug/L) /98.2% purity/[USEPA, Office of Pesticide Programs; Pesticide Ecotoxicity Database (2000) on 2-Chloro-N-[

LD50; Species: Anas platyrhynchos (Mallard duck) juvenile; oral via capsule >5000 mg/kg[USEPA, Office of Pesticide Programs; Pesticide Ecotoxicity Database (2000) on 2-Chloro-N-[

LC50; Species: Anas platyrhynchos (Mallard duck) dietary (in food) >5000 ppm for 8 days[USEPA, Office of Pesticide Programs; Pesticide Ecotoxicity Database (2000) on 2-Chloro-N-[

LD50; Species: Apis mellifera (Honey bee) adult; topical >25 ug/bee for 48 hr /98.2% purity/[USEPA, Office of Pesticide Programs; Pesticide Ecotoxicity Database (2000) on 2-Chloro-N-[

For more Ecotoxicity Values (Complete) data for Chlorsulfuron (22 total), please visit the HSDB record page.

TERRESTRIAL FATE: Based on a classification scheme(1), Koc values of 6.3-154(2-3) indicate that chlorsulfuron is expected to have very high to high mobility in soil(SRC). The pKa of chlorsulfuron is 3.4(4), indicating that this compound will exist almost entirely in the anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(5). Volatilization of the anion from moist soil is not expected because anions do not volatilize(SRC). Chlorsulfuron is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 2.25X10-11 mm Hg at 25 °C(4). The degradation half-life of chlorsulfuron incubated at 70% field capacity and 30 °C for 7 weeks was 8 and 6 days in samples from the 0-20 (pH 5.6 and 26.4% organic matter) and 20-40 cm (pH 5.2 and 35.1% organic matter) depths, respectively(6). Degradation of chlorsulfuron in 2 different soils at 25 °C and a moisture content 70% of field capacity followed 1st order kinetics, with rate constants of 0.015 and 0.025/day(7). Chlorsulfuron decomposition was faster in the soil with greater organic matter (3.0 vs 1.9%) and lower pH (6.0 vs 7.6)(7). N-(2-Chlorobenzenesulfonyl)carbamic acid was identified as a breakdown product(7). Chlorsulfuron applied to alkaline soils (pH 7.1-9.4) at 40 ug/kg and maintained at 70% of field capacity and 25 °C, degraded with half-lives of 19 to 42 days in surface soils(8). The rate of degradation decreased with increasing soil depth, as half-lives were nearly four times greater at 30-40 cm, as compared to the surface soils(8). The half-life of chlorsulfuron was 12-28 days in the field in soils with pH values of 4.9-6.5 with temperatures of 2.7-23.2 °C(9).

AQUATIC FATE: Based on a classification scheme(1), Koc values of 6.3-154(2-3) indicate that chlorsulfuron may adsorb to suspended solids and sediment(SRC). A pKa of 3.4(4) indicates chlorsulfuron will exist almost entirely in the anion form at pH values of 5 to 9 and, therefore, volatilization from water surfaces is not expected to be an important fate process(SRC). Chlorsulfuron will undergo hydrolysis with aqueous half-lives of 4 weeks at pH 5.7 and 8 weeks at pH 7.0 at 20 °C(5). According to a classification scheme(6), an estimated BCF of 3(SRC), from its log Kow of -1.34(7) and a regression-derived equation(8), suggests the potential for bioconcentration in aquatic organisms is low. Photolysis in sunlit surface waters may be an important fate process given an aqueous photolysis half-life of 1 month(9). Biodegradation of chlorsulfuron in water is expected to occur slowly given half-lives of 103 to 207 days at 40 °C in alkaline(pH 7.5 to 8.7) river water obtained from the Arno River, Italy(10).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), chlorsulfuron, which has a vapor pressure of 2.25X10-11 mm Hg at 25 °C(2), is expected to exist solely in the particulate phase in the ambient atmosphere. Particulate-phase chlorsulfuron may be removed from the air by wet and dry deposition(SRC). Chlorsulfuron is unlikely to undergo direct photolysis in the atmosphere(3).

Chlorsulfuron was not detected (detection limit 0.6 ug/kg) in 100 raw milk, 30 full-fat milk, 20 half-skimmed milk and 20 skimmed milk samples(1). Raw milk was provided by a local farm and all other milk samples were obtained from local supermarkets in Shenyang, China(1).

IDENTIFICATION AND USE: Chlorsulfuron is a white crystalline solid. It is a selective preemergence or early postemergence herbicide used at low rates. HUMAN STUDIES: There are no data available. ANIMAL STUDIES: In 2 yr feeding trials, rats receiving 100 mg/kg diet and mice receiving 500 mg/kg diet showed no ill-effects. Developmental studies in rats demonstrated reduced maternal body weights and food consumption at 1500 mg/kg/day and decreased fetal body weights at 1500 mg/kg/day. There were no teratogenic effects. Chlorsulfuron tested negative for mutagenicity in Salmonella typhimurium bacterial strains TA98, TA100, TA1535, TA1537 treated for 48 hours with chlorsulfuron at 0, 0.001, 0.005, 0.01, 0.05, 0.1 or 0.5 ug/plate with or without metabolic activation. ECOTOXICITY STUDIES: Chlorsulfuron is practically non-toxic to birds and mammals on an acute exposure basis and is also practically nontoxic to birds on a subacute dietary exposure basis. Following chronic exposure, bobwhite quail exhibited significant reductions in female body weight, 14-day old survivors/normal hatchlings, viable embryos/eggs set, and 14-day hatchling survival/eggs set. Chlorsulfuron is also practically nontoxic to honeybees on an acute contact basis. Chlorsulfuron is practically nontoxic to both freshwater and estuarine/marine fish on an acute exposure basis and is slightly toxic to estuarine/marine invertebrates. Aquatic plant toxicity ranged from practically nontoxic to very highly toxic. Chlorsulfuron is toxic to nontarget terrestrial plants. Chlorsulfuron is a potent inhibitor of cell division and branched amino acid biosynthesis in plants.

/BIRDS and MAMMALS/ Chlorsulfuron is practically non-toxic to birds and mammals on an acute exposure basis and is also practically nontoxic to birds on a subacute dietary exposure basis. Following chronic exposure, bobwhite quail exhibited significant reductions in female body weight, 14-day old survivors/normal hatchlings, viable embryos/eggs set, and 14-day hatchling survival/eggs set. Chlorsulfuron is also practically nontoxic to honeybees on an acute contact basis.

/AQUATIC SPECIES/ Chlorsulfuron is practically nontoxic to both freshwater and estuarine/marine fish on an acute exposure basis and is slightly toxic to estuarine/marine invertebrates. Chronic exposure of rainbow trout (Oncorhynchus mykiss) to chlorsulfuron resulted in a No Observed Effect Concentration (NOEC) of 32 mg/L while a chronic study of waterfleas (Daphnia magna) resulted in a NOEC of 20 mg/L.

/AQUATIC SPECIES/ Aquatic plant toxicity ranged from practically nontoxic to very highly toxic. Duckweed (Lemna gibba) was the most sensitive vascular aquatic plant ... The most sensitive nonvascular aquatic plant is green algae ...

/AQUATIC SPECIES/ Research has been conducted on the effect of chlorsulfuron on non-target plants but little information is available on its effects on aquatic macrophytes. Potamogeton pectinatus (sago pondweed) is an ecologically important submerged aquatic macrophyte found in freshwater bodies. Many species of wildlife use this plant as a food source. The objective of this study was to measure the phytotoxic effects of chlorsulfuron on sago pondweed. P. pectinatus plants were exposed to chlorsulfuron at 0, 0.25, 0.50, 1.0, or 2.0 ppb, in an environmental growth chamber. Plants exposed to 0.25 ppb chlorsulfuron showed a reduction in length (76%), number of leaves (50%), and number of stems (50%), compared to control plants. A reduction (47%) was also observed in the length of stems produced by plants treated with > or = 0.50 ppb chlorsulfuron. Significant reductions in wet and dry weights, and increased mortality were observed on treatments with > or = 1.0 ppb chlorsulfuron.

For more Ecotoxicity Excerpts (Complete) data for Chlorsulfuron (10 total), please visit the HSDB record page.

EPA has released the Interactive Chemical Safety for Sustainability (iCSS) Dashboard. The iCSS Dashboard provides an interactive tool to explore rapid, automated (or in vitro high-throughput) chemical screening data generated by the Toxicity Forecaster (ToxCast) project and the federal Toxicity Testing in the 21st century (Tox21) collaboration. /The title compound was tested by ToxCast and/or Tox21 assays/[USEPA; ICSS Dashboard Application; Available from, as of July 27, 2017: http://actor.epa.gov/dashboard/]

Chlorsulfuron

5 x 10 ^-2 mg/kg-day

Experimental Koc values of 6.3 to 154 have been reported in many different soil types(1-8). Decreases in the amount of organic carbon, an increase in soil pH and an increase in soil temperature have been observed to result in an increase in the mobility of chlorsulfuron(1-6). At a pH of approximately 4, chlorsulfuron was moderately adsorbed to soil, but was weakly adsorbed and very mobile at higher pH(3). According to a classification scheme(9), these Koc values suggest that chlorsulfuron is expected to have very high to high mobility in soil.

Experimental soil adsorption coefficient's of chlorsulfuron were reported in soils at different temperatures as follows(1):[Table#6357]

The soil distribution coefficients (Kd and Koc) of chlorsulfuron in three tilled surface soils collected in Spain were as follows(1):[Table#6358]

Leaching of the herbicides chlorsulfuron and metsulfuron methyl was studied using field lysimeters containing either undisturbed soil monoliths or packed soil. Three soil types were represented, two sandy soils and one clay soil. Each herbicide was applied at two rates, 4 and 8 g ai/ha, representing normal and double doses of the compound for spring cereals. All lysimeters received supplementary watering in addition to natural rainfall. With the exception of a single sample that had a chlorsulfuron concentration (14 ng/L) just above the detection limit, neither compound was detectable in leachate from lysimeters receiving the normal dose of the herbicides. For both herbicides at double dose, levels above the minimum detectable were found in selected lysimeters, reaching 43 and 21 ng/L drainage water for chlorsulfuron and metsulfuron methyl, respectively. Converted to fluxes over the 7 mo period, considerably less than 1% of the applied chlorsulfuron and metsulfuron methyl appeared in leachate.

For more Soil Adsorption/Mobility (Complete) data for Chlorsulfuron (7 total), please visit the HSDB record page.

AEROBIC: The half-life of chlorsulfuron in non-sterile soils was 5 and 15 days at 30 °C compared to the half-life of 21 and 28 days in the sterile soils(1). Microbial breakdown accounted for 79% of the total initial degradation in a silt loam soil (pH 5.9, organic matter 5%), 50% in a sandy loam soil (pH 6.5, organic matter 1%) and 91% in a silt loam soil (pH 8.0, organic matter 5%)(1). Microbial breakdown accounted for only 25% of total loss in a silty clay loam soil (pH 5.6, organic matter 2.4%)(2).

Tolerances are established for the combined residues of chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesulfonamide) and its metabolite, 2-chloro-5-hydroxy-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl] benzenesulfonamide in or on the following raw agricultural commodities:[Table#6355]

Tolerances are established for residues of chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2- yl)aminocarbonyl] benzenesulfonamide) in or on the following raw agricultural commodities.[Table#6356]

The Agency has completed its assessment of the residential, occupational, and ecological risks associated with the use of pesticides containing the active ingredient chlorsulfuron as well as a chlorsulfuron-specific dietary risk assessment. Based on a review of these data and public comments on the Agency's assessments for the active ingredient chlorsulfuron, EPA has sufficient information on the human health and ecological effects of chlorsulfuron to make decisions as part of the tolerance reassessment process under Federal Food, Drug and Cosmetic Act (FFDCA) and reregistration under FIFRA, as amended by the Food Quality Protection Act (FQPA). The Agency has determined that currently registered uses of chlorsulfuron will not pose unreasonable risks or adverse effects to humans or the environment if the risk mitigation measures and label changes outlined in the RED are implemented. The Agency has determined that chlorsulfuron is eligible for reregistration.

As the federal pesticide law FIFRA directs, EPA is conducting a comprehensive review of older pesticides to consider their health and environmental effects and make decisions about their continued use. Under this pesticide reregistration program, EPA examines newer health and safety data for pesticide active ingredients initially registered before November 1, 1984, and determines whether the use of the pesticide does not pose unreasonable risk in accordance to newer safety standards, such as those described in the Food Quality Protection Act of 1996. Chlorsulfuron is found on List A, which contains most pesticides that are used on foods and, hence, have a high potential for human exposure. List A consists of the 194 chemical cases (or 350 individual active ingredients) for which EPA issued registration standards prior to FIFRA '88. Case No: 0631; Pesticide type: herbicide; Registration Standard Date: 09/30/82; Case Status: OPP is reviewing data from the pesticide's producers regarding its human health and/or environmental effects, or OPP is determining the pesticide's eligibility for reregistration and developing the Reregistration Eligibility Decision (RED) document.; Active ingredient (AI): Chlorsulfuron; Data Call-in (DCI) Date(s): 08/06/90, 08/16/91, 10/13/95; AI Status: The producers of the pesticide has made commitments to conduct the studies and pay the fees required for reregistration, and are meeting those commitments in a timely manner.

The sulfonylurea herbicide chlorsulfuron blocks the biosynthesis of the amino acids valine and isoleucine in plants. Addition of these two amino acids to excised pea root (Pisum sativum L. var Alaska) cultures incubated in the presence of chlorsulfuron completely alleviates herbicide-induced growth inhibition. The site of action of chlorsulfuron is the enzyme acetolactate synthase which catalyzes the first step in the biosynthesis of valine and isoleucine. This enzyme is extremely sensitive to inhibition by chlorsulfuron having I(50) values ranging from 18 to 36 nanomolar. In addition, acetolactate synthase from a wide variety of tolerant and sensitive plants species is highly sensitive to inhibition by chlorsulfuron.

Chlorsulfuron, an inhibitor of acetolactate synthase markedly inhibited the growth of Lemna minor at concentrations of 10(-8) molar and above, but had no inhibitory effects on growth at 10(-9) molar. At growth inhibitory concentrations, chlorsulfuron caused a pronounced increase in total free amino acid levels within 24 hours. Valine, leucine, and isoleucine, however, became smaller percentages of the total free amino acid pool as the concentration of chlorsulfuron was increased. At concentrations of chlorsulfuron of 10(-8) molar and above, a new amino acid was accumulated in the free pool. This amino acid was identified as alpha-amino-n-butyrate by chemical ionization and electron impact gas chromatography-mass spectrometry. The amount of alpha-amino-n-butyrate increased from undetectable levels in untreated plants, to as high as 840 nanomoles per gram fresh weight (2.44% of the total free pool) in plants treated with 10(-4) molar chlorsulfuron for 24 hours. The accumulation of this amino acid was completely inhibited by methionine sulfoximine. Chlorsulfuron did not inhibit the methionine sulfoximine induced accumulations of valine, leucine, and isoleucine, supporting the idea that the accumulation of the branched-chain amino acids in methionine sulfoximine treated plants is the result of protein turnover rather than enhanced synthesis. Protein turnover may be primarily responsible for the failure to achieve complete depletion of valine, leucine, and isoleucine even at concentrations of chlorsulfuron some 10(4) times greater than that required to inhibit growth. Tracer studies with (15)N demonstrate that chlorsulfuron inhibits the incorporation of (15)N into valine, leucine, and isoleucine. The alpha-amino-n-butyrate accumulated in the presence of chlorsulfuron and [(15)N]H(4) (+) was heavily labeled with (15)N at early time points and appeared to be derived by transamination from a rapidly labeled amino acid such as glutamate or alanine. We propose that chlorsulfuron inhibition of acetolactate synthase may lead to accumulation of 2-oxobutyrate in the isoleucine branch of the pathway, and transamination of 2-oxobutyrate to alpha-amino-n-butyrate by a constitutive transaminase utilizing either glutamate or alanine as alpha-amino-N donors.

The sulfonylurea herbicide chlorsulfuron and the imidazolinone herbicide imazaquin were shown to be noncompetitive and uncompetitive inhibitors, respectively, of purified acetolactate synthase from barley (Hordeum vulgare L.) with respect to pyruvate. From double-reciprocal plots of the time-dependent biphasic inhibition by chlorsulfuron, an initial apparent inhibition constant of 68 nanomolar was calculated (a 0 to 4 minute assay was used for the initial inhibition), and a final steady-state dissociation constant of 3 nanomolar was estimated. The corresponding constants for imazaquin were 10 and 0.55 micromolar. Specific binding of [(14)C]chlorsulfuron and [(14)C]imazaquin to purified acetolactate synthase from barley and partially purified enzyme from corn (Zea mays L.) could be demonstrated by gel filtration and equilibrium dialysis. Evidence is presented that the binding of the inhibitors to the enzyme follows the previously described mechanism of slow reversibility once excess inhibitor has been removed. However, after formation of the slowly reversible complex and subsequent dissociation, both chlorsulfuron and imazaquin seem to permanently inactivate acetolactate synthase. These results add a new feature to the mode of action of these herbicides with respect to their high herbicidal potency.

The DNA sequence of a 196 base pair region of the acetolactate synthase genes of three weed species, kochia, prickly lettuce, and Russian thistle, was determined. This region encompasses the coding sequence for Domain A, a region of the amino acid sequence previously demonstrated to play a pivotal role in conferring resistance to herbicides that inhibit acetolactate synthase. The Domain A DNA sequence from a chlorsulfuron resistant prickly lettuce biotype differed from that of a chlorsulfuron susceptible biotype by a single point mutation, which substituted a histidine for a proline. The Domain A DNA sequence from a chlorsulfuron resistant kochia biotype also differed from that of an chlorsulfuron susceptible biotype by a single point mutation in the same proline codon. This point mutation, however, conferred substitution of threonine for proline. Two different acetolactate synthase homologous sequences were isolated from an chlorsulfuron resistant biotype of Russian thistle. Neither sequence encoded amino acid substitutions in Domain A that differed from the consensus chlorsulfuron susceptible sequence. Most collections showed excellent correspondence between the chlorsulfuron susceptibility and restriction digest pattern and the phenotypic response to chlorsulfuron application. However, one entirely chlorsulfuron resistant collection had the chlorsulfuron susceptibility and restriction digest pattern of the chlorsulfuron susceptible biotype, suggesting that resistance was not due to mutation in the proline codon.

For more Mechanism of Action (Complete) data for Chlorsulfuron (7 total), please visit the HSDB record page.

Used as pre- and post-emergence herbicide to control weeds on cereal grains, pasture, rangeland, industrial sites, and turf grass; [Reference #1]

Farming (Pesticides) [Category: Industry]

For chlorsulfuron (USEPA/OPP Pesticide Code: 118601) ACTIVE products with label matches. /SRP: Registered for use in the U.S. but approved pesticide uses may change periodically and so federal, state and local authorities must be consulted for currently approved uses./

A selective preemergence or early postemergence herbicide used at low rates.

This is a man-made compound that is used as a pesticide.

Chlorsulfuron is produced by reaction of 2-sulfonylisocyanate chlorobenzene with 2-amino-4,6-dimethoxy-1,3,5-triazine.

Prepn: G. Levitt, German patent 2715786; idem, United States of America patent 4127405 (1977, 1978 both to du Pont).

NUP 08136 (Nufarm Americas, Inc): Active ingredient: chlorsulfuron 15% and metsulfuron 48%.

Nufarm Chlorsulf SPC 75 WDG Herbicide (Nufarm Americas, Inc): Active ingredient: chlorsulfuron 75%.

ETI 123 01 H-D2 (Nufarm Americas, Inc): Active ingredient: chlorsulfuron 75%.

ETI 122 01 H-D (Nufarm Americas, Inc): Active ingredient: chlorsulfuron 62.5% and metsulfuron 12.5%.

For more Formulations/Preparations (Complete) data for Chlorsulfuron (33 total), please visit the HSDB record page.

The WHO Recommended Classification of Pesticides by Hazard identifies Chlorsulfuron (technical grade) as unlikely to present an acute hazard in normal use; Main Use: herbicide.

Application methods: Preemergence or early postemergence treatments show the most activity on annual grass weeds and broadleaf weeds. Later postemergence treatments are effective on most broadleaf weeds but less effective on grasses. Treatments may be made with aerial or ground equipment. Rates: 0.2-0.5 oz/acre preemergence or postemergence on wheat and only postemergence on barley, oats, rye and flax. 0.5-1.5 oz/acre for fallow weed control. Usual carrier: water 1.5-40 gallons/acre plus a surfactant @ 0.1% by volume for control of emerged weeds.