Mesotrione

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Tolerances are established for residues of the herbicide mesotrione, including its metabolites and degradates, in or on the commodities in the table below. Compliance with the tolerance levels specified below is to be determined by measuring only mesotrione, 2-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione, in or on the following raw agricultural commodities:[Table#6847]

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... A range of acute, subchronic and reproduction studies in the rat involving administration of different doses of mesotrione, with or without co-administration of dietary L-tyrosine and a developmental study in the rabbit utilising both mesotrione and tyrosine were used to elucidate the role of tyrosine in the pathogenesis of effects. ...The incidence and/or severity of the changes correlated with plasma tyrosine concentrations but not with concentrations of mesotrione.

LC50; Species: Anas platyrhynchos (Mallard Duck) age 10 days; diet (chemical incorporated into food) >5130 ppm for 8 days

LC50; Species: Colinus virginianus (Northern Bobwhite Quail) age 10 days; diet (chemical incorporated into food) >4770 ppm for 8 days

LD50; Species: Colinus virginianus (Bobwhite quail) oral >2000 mg/kg

EC50; Species: Pseudokirchneriella subcapitata (Green Algae); Conditions: freshwater, static; Concentration: 1900 ug/L for 5 days (95% confidence interval: 1500-2400 ug/L); Effect: decreased population abundance /95.1% purity/

For more Ecotoxicity Values (Complete) data for MESOTRIONE (7 total), please visit the HSDB record page.

TERRESTRIAL FATE: Based on a classification scheme(1), Koc values measured in 19 soils from the US and Europe ranging from 15 to 390(2,3), indicate that mesotrione is expected to have very high to moderate mobility in soil(SRC). Mesotrione is a weak acid with a pKa of 3.12(4) which indicates mesotrione will primarily exist in anion form in the environment and anions generally do not adsorb more strongly to organic carbon and clay than their neutral counterparts(5). The anionic form of mesotrione is a resonance enol-tautomer of the undissociated keto-tautomer(2). The Koc is inversely correlated with pH; as the pH increases, the Koc decreases(2,3). Volatilization of mesotrione from moist soil surfaces is not expected to be an important fate process(SRC) given an estimated Henry's Law constant of <1.2X10-10 atm-cu m/mole(SRC) derived from its vapor pressure, <4.27X10-8 mm Hg(6), and water solubility, 160 mg/L(6). Mesotrione is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure. The direct photolysis half-life on soil surfaces has been estimated to be 24 days at a latitude of 37-50 deg north(4). Degradation studies in active versus sterilized soils have demonstrated that biodegradation is the major degradation pathway in soils(3). Aerobic laboratory studies in 17 soils at 20-25 °C have observed dissipation half-lives ranging from 6-27 days(4,6); a half-life of 30 days was approximated for aerobic soil at 10 °C(4). One anaerobic test at 20 °C had a half-life of 4 days(4). Field dissipation studies at 6 sites (1 French, 3 German, 2 Italian) found half-lives of 3-7 days(4,6). Soil degradation was found to be related to soil pH, with half-lives decreasing with increasing soil pH(2,4).

AQUATIC FATE: Based on a classification scheme(1), Koc values measured in 19 soils from the US and Europe ranging from 15 to 390(2,3), indicate that mesotrione is not expected to adsorb to suspended solids and sediment(SRC). In water-sediment distribution tests, mesotrione was predominantly found in the water phase (>82%) with a maximum of 3.8% partitioning to sediment(4). Mesotrione is a weak acid with a pKa of 3.12(4) which indicates mesotrione will primarily exist in anion form in the environment and the anionic form of mesotrione is a resonance enol-tautomer of the undissociated keto-tautomer(2). Volatilization from water surfaces is not expected(5) based upon an estimated Henry's Law constant of <1.2X10-10 atm-cu m/mole(SRC), derived from its vapor pressure, <4.27X10-8 mm Hg(6), and water solubility, 160 mg/L(6). According to a classification scheme(7), an estimated BCF of 3(SRC), from its log Kow of 0.90 at pH 5(4) and a regression-derived equation(8), suggests the potential for bioconcentration in aquatic organisms is low. Mesotrione is stable to hydrolysis at pH 4-9(4). Mesotrione is susceptible to direct photolysis in water with estimated half-lives of 81-97 days under summer conditions at 40-50 deg N latitude(4). The presence of organic matter in natural waters may increase the photodegradation rate by an order of magnitude due to sensitized photo-oxidation(9). Degradation studies in active versus sterilized soil-water systems have demonstrated that biodegradation is the major degradation pathway(3). Laboratory dissipation studies in water and water-sediment systems have observed mesotrione half-lives of 3.9-6.6 days(4).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), mesotrione, which has a vapor pressure of <4.27X10-8 mm Hg at 20 °C(2), is expected to exist solely in the particulate phase in the ambient atmosphere. Particulate-phase mesotrione may be removed from the air by wet and dry deposition(SRC). Mesotrione absorbs at wavelengths >290 nm(3) and, therefore, may be susceptible to direct photolysis by sunlight(SRC).

IDENTIFICATION AND USE: Mesotrione is a pale yellow solid with a faint pleasant odor. Mesotrione is an herbicide used on field corn, seed corn, sweet corn, yellow popcorn, and grain sorghum. 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. HUMAN EXPOSURE AND TOXICITY: Limited information is available on the effects of exposure to mesotrione on humans. Administration of mesotrione to volunteers resulted in an increase in plasma tyrosine concentrations, which reached a maximum of approximately 300 nmol/mL following a dose of 4 mg/kg body weight. Concentrations returned to background levels within 2 days of dosing. Urinary excretion of tyrosine metabolites was increased during the 24 hr immediately following a dose of 4 mg/kg, but returned to background levels during the following 24 hr period. Thus, the minimal and transient effects of mesotrione minimize the likelihood of a clinical effect in the event of systemic exposure occurring during occupational use. Mesotrione is not likely to be carcinogenic to humans. ANIMAL STUDIES: In animals, mesotrione is a mild eye irritant, but is not a dermal irritant or a dermal sensitizer. In subchronic and chronic oral studies, ocular lesions, liver and kidney effects, and/or body weight decrements were the major adverse effects seen in rat, mouse, and dog. Plasma tyrosine levels were increased in rat, mouse and dog in the chronic and reproduction studies. The ocular, liver and kidney effects are believed to be mediated by high tyrosine levels in the blood caused by inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase. No evidence of neuropathology was found in acute and sub-chronic neurotoxicity studies in rat. However, sciatic nerve demyelination in the chronic rat study was associated with increased plasma tyrosine concentration. Increased incidence of thyroid adenomas in female rats only at the highest dose level in the 2 year rat study was also associated with increased plasma tyrosine concentration. Reduced/delayed ossification in rat, rabbit and mouse developmental studies were noted in the absence of overt maternal toxicity. ECOTOXICITY STUDIES: Antioxidative stress systems, saturation changes of lipid membranes, and the capacity of bacteria to degrade mesotrione were examined. The results showed that Escherichia coli DH5-alpha was able to tolerate high doses of the herbicide (10 times field rate), and completely degraded mesotrione after 3 hr of exposure. Growth rates in the presence of mesotrione were lower than in the control, prior to the period of degradation, showing toxic effects of this herbicide on bacterial cells. Changes in the saturation of the membrane lipids reduced the damage caused by reactive oxygen species and possibly hindered the entry of xenobiotics in the cell, while activating glutathione-S-transferase enzyme.

/FIELD STUDIES/ Population /of Pardosa spp /SRP: wolf spiders/ (all life stages)/ in test plots mirrored that in control plots. Application rate 0.150 kg as/ha. No long term adverse effects seen. /From table/

/OTHER TOXICITY INFORMATION/ Antioxidative stress systems, saturation changes of lipid membranes, and the capacity of bacteria to degrade mesotrione were examined. Escherichia coli DH5-alpha was chosen as a non-environmental strain, which is already a model bacterium for studying metabolism and adaptation. The results showed that this bacterium was able to tolerate high doses of the herbicide (10x field rate), and completely degraded mesotrione after 3 hr of exposure, as determined by a High Performance Liquid Chromatography. Growth rates in the presence of mesotrione were lower than in the control, prior to the period of degradation, showing toxic effects of this herbicide on bacterial cells. Changes in the saturation of the membrane lipids reduced the damage caused by reactive oxygen species and possibly hindered the entry of xenobiotics in the cell, while activating glutathione-S-transferase enzyme in the antioxidant system and in the metabolizing process of the herbicide. Considering that E. coli DH5-alpha is a non-environmental strain and it had no previous contact with mesotrione, the defense system found in this strain could be considered non-specific. This bacterium system response may be a general adaptation mechanism by which bacterial strains resist to damage from the presence of herbicides in agricultural soils.

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Koc values for mesotrione were measured in 15 soils from the US and Europe and ranged from 15 to 390(1). Koc values of 22.4 to 183.9 were measured in four different loam soils(2). According to a classification scheme(3), these Koc values suggest that mesotrione is expected to have very high to moderate mobility in soil. Mesotrione is a weak acid with a pKa of 3.12 at 20 °C(4) which indicates mesotrione will primarily exist in anion form in the environment and anions generally do not adsorb more strongly to organic carbon and clay than their neutral counterparts(5). The anionic form of mesotrione is a resonance enol-tautomer of the undissociated keto-tautomer(1). The measured Koc values were determined in soils with pH values ranging from 4.6 to 7.7 with the Koc inversely correlated with pH(1,2); as the pH increases, the Koc decreases(1,2).

/HUMAN EXPOSURE STUDIES/ ... Mesotrione (2-(4-methylsulphonyl-2-nitrobenzoyl)-1,3-cyclohexanedione) inhibits 4-hydroxyphenyl pyruvate dioxygenase (HPPD). ... The mesotrione study was performed to determine the magnitude and duration of the effect on tyrosine catabolism. Additionally, the urinary excretion of unchanged mesotrione was measured to assess the importance of this route of clearance and to help develop a strategy for monitoring occupational exposure. /Three groups, each consisting of six male volunteers between 19 and 53 years, were given a single oral dose of either 0.1, 0.5 or 4 mg mesotrione/kg./ ... Plasma tyrosine concentrations were monitored and the urinary excretion of mesotrione and tyrosine metabolites was measured. ... Administration of mesotrione resulted in an increase in tyrosine concentrations, which reached a maximum of approximately 300 nmol/mL following a dose of 4 mg/kg body weight. Concentrations returned to those of background within 2 days of dosing. Urinary excretion of tyrosine metabolites was increased during the 24 hr immediately following a dose of 4 mg mesotrione/kg, but returned to background levels during the following 24 hr period. ... /The/ minimal and transient effects of mesotrione minimize the likelihood of a clinical effect in the event of systemic exposure occurring during occupational use.

/OTHER TOXICITY INFORMATION/ Mechanistic studies show that the toxic effects of /mesotrione/ are largely attributable to increased plasma tyrosine levels following 4-hydroxyphenyl pyruvate dioxygenase (HPPD) inhibition. Tyrosine levels are increased to a greater extent in rats (particularly males) due to differences in the activity of enzymes in the tyrosine catabolic pathway. Studies show that the mouse is more predictive of the response in humans. Human volunteer study (single oral dose) shows a NOAEL of 0.5 mg/kg bw.

AEROBIC: Half-lives determined in 15 soils from the US and Europe ranged from 4.5 to 32 days(1). The degradation half-life of mesotrione was tested in four different soils using microbially active soil and soil sterilized by irradiation(2); in plant-available water systems, the half-life ranged from 0.87-2.8 days in active soil and 4.62-9.90 days in sterilized soils indicating degradation was occurring primarily via microbial degradation(2); in total soil-water systems, the half-life ranged from 3.1-25.5 days in active soil and generally >28 days (the observation period) in sterilized soils(2). Degradation was found to be related to soil pH, with half-lives decreasing with increasing soil pH(1).

PURE CULTURE: The biodegradation pathway of mesotrione was examined using bacterial strains of Bacillus sp.; 4-methylsulfonyl-2-nitrobenzoic acid and 2-amino-4-methylsulfonyl benzoic acid were identified as degradation products(1,2).

An estimated BCF of 3 was calculated for mesotrione(SRC), using a measured log Kow range of 0.90 at pH 5 to <-1.0 at pH 9(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is low(SRC).

Tolerances are established for residues of the herbicide mesotrione, including its metabolites and degradates, in or on the commodities in the table below. Compliance with the tolerance levels specified below is to be determined by measuring only mesotrione, 2-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione, in or on the following raw agricultural commodities:[Table#6848]

Reregistration Eligibility Decision (RED): Because it was registered after November 1984, mesotrione was not subject to reregistration.

Tolerance Reassessment Eligibility Decision (TRED): Because it was registered after November 1984, mesotrione was not subject to tolerance reassessment.

Synthetic form of leptospermone (natural herbicide from the bottlebrush plant); Used as herbicide for maize; [Merck Index]

Farming (Pesticides) [Category: Industry]

For mesotrione (USEPA/OPP Pesticide Code: 122990) 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./

Mesotrione is a selective herbicide registered for use to control broadleaf weeds in many agricultural and non-agricultural use sites.

Herbicide; For use on field corn, seed corn, sweet corn, yellow popcorn, and grain sorghum.

For pre-emergence and post-emergence control of broad-leaved weeds, such as Xanthium strumarium, Ambrosia trifida, Abutilon theophrasti, and Chenopodium, Amaranthus and Polygonum spp., and some grass weeds, in maize.

A review of total mesotrione usage data for the last 5 years indicates that the primary use site is corn, accounting for approximately 98% of both total pounds applied and total acres treated. Field corn represents the highest percent crop treated in terms of acres grown and acres treated at 20.2%. Usage data is not available for mesotrione use in non-agricultural sites.

Mesotrione is prepared by reaction of 3-methylmercaptonitrobenzene with acetyl chloride in the presence of aluminum trichloride yielding the corresponding ketone, which is oxidized with sodium oxychloride giving the corresponding 4-methylsulfonyl compound, which in turn is condensed with cyclohexane-1,3-dione to give the corresponding enol ester. The latter is rearranged to the desired product with potassium cyanide in the presence of triethylamine.

Preparation: C. G. Carter, European Patent Office 186118 (1986 to Stauffer); idem, United States of America 5006158 (1991 to ICI).

Formulation Type(s): Granular, water dispersible granules, emulsifiable concentrate, soluble concentrate, solution-ready to use, pressurized liquid, and soluble concentrate/solid.

Suspension concentrate.

Premix Partners: Atrazine; Glyphosate; S-Metolachlor; Nicosulfuron; Rimsulfuron; Terbuthylazine.

Callisto Herbicide (Syngenta Crop Protection, LLC): Active ingredient: mesotrione 40.0%.

For more Formulations/Preparations (Complete) data for MESOTRIONE (28 total), please visit the HSDB record page.

Environmental transformation -> Pesticides (parent, predecessor)

Herbicides

Callisto Herbicide is effective in controlling broadleaf weeds in field corn. It will replace atrazine and isoxaflutole herbicides. Mesotrione is a new class of herbicide and if used in Resistance Management Programs it can mitigate the increase in resistant biotypes.

The manufacturing impurity 1-cyano-6-(methylsulfonyl)-7-nitro-9H-xanthen-9-one is considered to be of toxicological concern and must remain below 0.0002% (w/w) in the technical product.

Triketone herbicide for use in maize; inhibits p-hydroxyphenylpyruvate dioxygenase (HPPD). Synthetic mimic of leptospermone, a natural herbicide produced by the bottlebrush plant, Callistemon citrinus Stapf.