Metribuzin

Pesticide -> EPA IRIS

Herbicides

Active substance -> EU Pesticides database: Not approved

Pesticides -> Herbicides, Triazine

Herbicides

Environmental transformation -> Pesticides (parent, predecessor)

log Kow= 1.7

1.6

1.7

1.31 (NIOSH, 2024) - Denser than water; will sink

1.28 @ 20 °C/4 °C

1.28 g/cm³

1.31

1.31

Colorless crytals

White crystalline solid

0.1 % (NIOSH, 2024)

Sol in methanol and ethanol; very slightly soluble in water (1200 ppm).

Soluble in ... glycol ether acetate.

In dimethylformamide 1780, cyclohexanone 1000, chloroform 850, acetone 820, methanol 450, dichloromethane 340, benzene 220, n-butanol 150, ethanol 190, toluene 87, xylene 90, n-hexane 1 (all in g/l at 20 °C).

In water, 1.05X10+3 mg/l @ 20 °C

Solubility in water, g/100ml at 0.12 °C:

257 °F (NIOSH, 2024)

126.2 °C

125 °C

257 °F

257 °F

Warning

H302: Harmful if swallowed [Warning Acute toxicity, oral]

P260, P264, P270, P273, P301+P317, P319, P330, P391, and P501 (click each P-code to see the statement)

Danger

H302 (100%): Harmful if swallowed [Warning Acute toxicity, oral]

P260, P261, P264, P270, P271, P273, P301+P317, P304+P340, P316, P319, P321, P330, P391, P403+P233, P405, and P501 (click each P-code to see the statement)

Commission Regulation (EC) No 451/2000

07/25/EC, Reg. (EU) 2018/917, Reg. (EU) 2019/707, Reg. (EU) 2020/869, Reg. (EU) 2021/745, Reg. (EU) 2022/708, Reg. (EU) 2023/918, Reg. (EU) 2024/2806, Reg. (EU) 2024/2806, Reg. (EU) 540/2011

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

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

Combustible.

Classified as slightly toxic with an LD50 in rats of 1090 to 2300 mg/kg; [EXTOXNET] There are no known health effects in humans after occupational exposure. [ACGIH] For the triazine herbicides, systemic toxicity unlikely unless large amounts are ingested; May cause irritation; [EPA Pesticides, p. 121]

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 future use. Under this pesticide reregistration program, EPA examines health and safety data for pesticide active ingredients initially registered before November 1, 1984, and determines whether they are eligible for reregistration. In addition, all pesticides must meet the new safety standard of the Food Quality Protection Act of 1996. Metribuzin is found on List A, which contains most food use pesticides and consists of the 194 chemical cases (or 350 individual active ingredients) for which EPA issued registration standards prior to FIFRA, as amended in 1988. Case No: 0181; Pesticide type: herbicide; Registration Standard Date: 06/30/85; Case Status: RED Approved 04/97; OPP has made a decision that some/all uses of the pesticide are eligible for reregistration, as reflected in a Reregistration Eligibility Decision (RED) document.; Active ingredient (AI): Metribuzin; Data Call-in (DCI) Date(s): 07/31/91, 05/30/95, 10/13/95; AI Status: OPP has completed a Reregistration Eligibility Decision (RED) document for the case/AI.

Tolerances are established for combined residues of the herbicide 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one and its triazinone metabolites in or on the following raw agricultural commodities: Alfalfa, green; Alfalfa, hay; Asparagus; Barley, grain; Barley, milled fractions (except four); Barley, straw; Carrots; Cattle, fat; Cattle, mbyp; Cattle, meat; Corn, fodder; Corn, forage; Corn, fresh (inc. sweet K+CWHR); Corn, grain (inc. popcorn); eggs; Goats, fat; Goats, mbyp; Goats, meat; Grass; Grass, hay; Hogs, fat; Hogs, mbyp; Hogs, meat; Horses, fat; Horses, mbyp; Horses, meat; Lentils (dried); Lentils, vine hay; Milk; Peas; Peas (dried); Peas, forage; Peas, vine hay; Potatoes; Potato waste, processed (dried); Poultry, fat; Poultry, mbyp; Poultry, meat; Sainfoin; Sainfoin, hay; Sheep, fat; Sheep, mbyp; Sheep, meat; Soybeans; Soybeans, forage; Soybeans; Sugarcane; Sugarcane molasses; Tomatoes; Wheat, forage; Wheat, grain; Wheat, milled fractions (except flour); and Wheat, straw.

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

Use water spray, powder.

Fresh air, rest.

Rinse and then wash skin with water and soap.

First rinse with plenty of water for several minutes (remove contact lenses if easily possible), then refer for medical attention.

Rinse mouth. Rest.

Excerpt from NIOSH Pocket Guide for Metribuzin:

(General first aid procedures)

Estimated shelf life in excess of 2 yr under normal storage conditions.

Store in a cool, dry place. Do not contaminate water or feed by storage or disposal.

SRP: At the time of review, criteria for land treatment or burial (sanitary landfill) disposal practices are subject to significant revision. Prior to implementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices.

Bury empty container or product that cannot be used in a safe place away from water supplies, or dispose of by alternative procedures recommended by federal, state or local authorities. Open dumping is prohibited.

Avoid contact with skin, eyes, and clothing. Remove contaminated clothing and wash with soap and hot water before reuse.

SRP: Contaminated protective clothing should be segregated in such a manner so that there is no direct personal contact by personnel who handle, dispose, or clean the clothing. Quality assurance to ascertain the completeness of the cleaning procedures should be implemented before the decontaminated protective clothing is returned for reuse by the workers. Contaminated clothing should not be taken home at end of shift, but should remain at employee's place of work for cleaning.

Hepatic

central nervous system, thyroid, liver

TERRESTRIAL FATE: In soil, metribuzin was degraded to carbon dioxide. Autoclaving of soil decreased metribuzin metabolism. Those metabolites observed in plants (metribuzin, 3,5-diketo and deaminated diketo) were also observed in the soil. Deaminated diketo was the primary metabolite in soil. Metribuzin, applied in June to a fine sandy loam soil, degraded during the growing season to the extent that less than 10% of applied herbicide was present by October 25, freeze-up time. Metribuzin, 3,5-diketo and deaminated diketo were observed in soil samples and metabolite residue levels were at their maximum near the middle of July. In a study with Guelp loam, the half-life of metribuzin was about 3 months. Under greenhouse conditions with soils from the lower alluvial floodplain of the Mississippi River, metribuzin half-life varied from 17 to 28 days and followed first-order kinetics. In four Manitoba soils under dry conditions at 15 C, some nonbiological degradation of metribuzin occurred. The rate law was somewhat less than first-order and half-lives varied from 90 to 115 days. Field soil samples awaiting analysis underwent degradation. At -37C, about 50% of the herbicide could be lost in 282 days. 3,5-Diketo and deaminated diketo also degraded under storage conditions. In laboratory studies with a sandy loam soil, metribuzin calculated half-life was about 329, 44 and 16 days at 5, 20 and 35C, respectively. Metribuzin and deaminated diketo were observed.

TERRESTRIAL FATE: Based on a classification scheme(1), an average Koc value of 60(2) suggests that metribuzin is expected to have high mobility(SRC). Little leaching occurs on soils with high organic content, but metribuzin is readily leached in sandy soils(2,4). Adsorption of metribuzin decreases as soil pH increases(2). Loss from soil surfaces via volatilization is not an important fate process(2,3). Volatilization of metribuzin from moist soil surfaces is not expected to be an important fate process given an estimated Henry's Law constant of 1.2X10-10 atm-cu m/mole(SRC), derived from its vapor pressure, 4.4X10-7 mm Hg(5), and water solubility, 1050 mg/l(5). Metribuzin is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(5). Metribuzin had a half-life of 2.5 days on sandy loam soil irradiated outdoors in Kansas City, MO at temperatures up to 31 °C(6). The major photolytic products of metribuzin were pentylidene and hexylidene metribuzin in soil(6). Biodegradation is the primary means of metribuzin dissipation from soils(2). The activity of soil microorganisms, higher temperatures, and aerobic conditions increase the rate of metribuzin biodegradation(2). Half-lives are 172 and 439 days for sandy loam under aerobic and anaerobic conditions, respectively(2). Primary metabolites are the deaminated, diketo, and deamined diketo metabolites(2). The calculated field dissipation half-lives of metribuzin in sandy loam soils in California were 128 and 40 days at Watsonville and Fresno, respectively(6).

AQUATIC FATE: Based on a classification scheme(1), an average experimental Koc value of 60(2), indicates that metribuzin is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is not expected based upon an estimated Henry's Law constant of 1.2X10-10 atm-cu m/mole(SRC), derived from its vapor pressure, 4.35X10-7 mm Hg(3), and water solubility, 1100 mg/l(3). Photodecomposition is an important process for the degradation of metribuzin in aqueous solution(3). Metribuzin was found to have a half-life of 4.3 hours in surface water from Kansas City, MO (pH 6.6) irradiated with natural sunlight at 25 °C(4). The identified degradate was deaminated metribuzin(4). A BCF of 10 was measured for Golden ide fish (Leuciscus idus melanotus)(5). According to a classification scheme(6), this whole body BCF suggests the potential for bioconcentration of metribuzin in aquatic organisms is low(SRC). No data were located on the biodegradation of metribuzin in water; however, microbial degradation is the primary fate process of metribuzin in soil(2,3), which suggests that biodegradation may be an important fate process in water(SRC).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), metribuzin, which has a vapor pressure of 4.35X10-7 mm Hg at 20 °C(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase metribuzin is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 21 hrs(SRC), calculated from its rate constant of 1.8X10-11 cu cm/molecule-sec at 25 °C(SRC) determined using a structure estimation method(3). Particulate-phase metribuzin may be removed from the air by wet and dry deposition(SRC).

Metribuzin was qualitatively identified in 1 root vegetable composite from Total Diet samples taken in 1975(1). Metribuzin was found in 1 of 1219 samples of domestic and imported tomatoes at trace quantities (Trace, present but below the level of detection)(2).

The substance can be absorbed into the body by inhalation of its aerosol and by ingestion.

inhalation, ingestion, skin and/or eye contact

Beef and dairy cattle fed a diet of 10 ppm metribuzin had total metribuzin residues (metribuzin and metabolites) in the muscle, liver, kidney, and fat tissues ranging from non-detectable, 0.55-1.01 ppm, 0.08-0.17 ppm, and 0.06-1.13 ppm respectively(1). Poultry feed a diet of 15 ppm metribuzin had total metribuzin residues (metribuzin and metabolites) in eggs, giblet, muscle, fat, and skin ranging from 0.032-0.053 ppm, 0.23-0.27 ppm, 0.06-0.07 ppm, 0.04-0.08 ppm, and 0.03-0.08 ppm respectively(1).

Metribuzin

Hepatic

2.5 x 10 ^-2 mg/kg-day

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 future use. Under this pesticide reregistration program, EPA examines health and safety data for pesticide active ingredients initially registered before November 1, 1984, and determines whether they are eligible for reregistration. In addition, all pesticides must meet the new safety standard of the Food Quality Protection Act of 1996. Metribuzin is found on List A, which contains most food use pesticides and consists of the 194 chemical cases (or 350 individual active ingredients) for which EPA issued registration standards prior to FIFRA, as amended in 1988. Case No: 0181; Pesticide type: herbicide; Registration Standard Date: 06/30/85; Case Status: RED Approved 04/97; OPP has made a decision that some/all uses of the pesticide are eligible for reregistration, as reflected in a Reregistration Eligibility Decision (RED) document.; Active ingredient (AI): Metribuzin; Data Call-in (DCI) Date(s): 07/31/91, 05/30/95, 10/13/95; AI Status: OPP has completed a Reregistration Eligibility Decision (RED) document for the case/AI.

Tolerances are established for combined residues of the herbicide 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one and its triazinone metabolites in or on the following raw agricultural commodities: Alfalfa, green; Alfalfa, hay; Asparagus; Barley, grain; Barley, milled fractions (except four); Barley, straw; Carrots; Cattle, fat; Cattle, mbyp; Cattle, meat; Corn, fodder; Corn, forage; Corn, fresh (inc. sweet K+CWHR); Corn, grain (inc. popcorn); eggs; Goats, fat; Goats, mbyp; Goats, meat; Grass; Grass, hay; Hogs, fat; Hogs, mbyp; Hogs, meat; Horses, fat; Horses, mbyp; Horses, meat; Lentils (dried); Lentils, vine hay; Milk; Peas; Peas (dried); Peas, forage; Peas, vine hay; Potatoes; Potato waste, processed (dried); Poultry, fat; Poultry, mbyp; Poultry, meat; Sainfoin; Sainfoin, hay; Sheep, fat; Sheep, mbyp; Sheep, meat; Soybeans; Soybeans, forage; Soybeans; Sugarcane; Sugarcane molasses; Tomatoes; Wheat, forage; Wheat, grain; Wheat, milled fractions (except flour); and Wheat, straw.

(FL) FLORIDA 180 ug/L

(ME) MAINE 175 ug/l

(MN) MINNESOTA 200 ug/l

(WI) WISCONSIN 250 ug/l

When (14)C metribuzin was applied to tomatoes, preliminary evidence indicated that the first (14)C metabolite may be a complex with deaminated diketometribuzin or metribuzin.

Metribuzin applied to roots of soybean (Glycine max (Leguminatae) Merr. 'Cutler') seedlings was rapidly absorbed and translocated to the shoots. The major product observed was deaminated metribuzin. The 3,5-diketo and deaminated diketo derivatives were also observed. Identity of these metabolites was determined by cochromatography and MS. Roots and shoots both produced these compounds. The aglycones of four acid labile carbohydrate conjugates formed were identified as 3,5-diketo derivative and deaminated derivative.

Potatoes were planted in soil treated with metribuzin. Analyses of plant material showed the presence of metribuzin, 3,5-diketo and deaminated derivative as well as conjugated material. Analyses indicated that deaminated diketo was the aglycone of one conjugate. When these studies were repeated in the same soil, another metabolite was found in the top part of the plants and identified as trimethylpyruvic acid semicarbazone. Similar results were observed with carrots and the soil in which these plants had been grown.

Absorbed through the leaves from surface treatment, but the major significant route for uptake is via root system. ... Uptake through the roots is best described as osmotic diffusion. Metribuzin is translocated upward in the xylem and moves distally when applied at the base of leaves.

After absorption, it is rapidly distributed and rapidly excreted unchangd or metabolized (oxidized) and excreted via the urine.

Metribuzin is a herbicide used to control weeds in alfalfa, asparagus, barley, carrots, corn, peas, potatoes, soybeans, sugarcane, tomatoes, turf grass, and wheat. [ACGIH]

Farming (Pesticides) [Category: Industry]

For Metribuzin (USEPA/OPP Pesticide Code: 101101) 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./

Controls a large number of grass and broadleaf weeds in agricultural crops.

Herbicide

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

USEPA/OPP Pesticide Code 101101; Trade Names: Sencor; Bay 94337; Lexone; Canopy.

Wettable powder; water dispersible granules; suspension concentrate

Combinations: saline (with trifluralin); Turbo (with metolachlor).

Liquid suspension, water dispersible granules, dry flowable

Herbicides

Environmental transformation -> Pesticides (parent, predecessor)

Pesticides -> Herbicides -> Triazinone herbicides

HERBICIDES