SPECTRUM

Chemical Fact Sheet

Chemical Abstract Number (CAS #) 21087649
CASRN 21087-64-9
SynonymsMetribuzin
4-Amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one
Analytical Method EPA Method 633
Molecular FormulaC8H14N4OS

Link to the National Library of Medicine's Hazardous Substances
Database for more details on this compound.

Use Controls a large number of grass and broadleaf weeds infesting agricultural crops. Control of many annual broad leaved and grass weeds in asparagus, potatoes, tomatoes, lucerne, sainfoin, peas, lentils, soya beans, sugar cane, pineapples, and cereals. Pre- and post-emergence triazone herbicide.
Apparent Color Colorless crytals; White crystalline solid
Odor Mild chemical odor
Melting Point 125-126.5 deg C
Molecular Weight 214.3
Density 1.28 at 20 deg C/4 deg C
Environmental Impact Metribuzin will be released to the environment primarily during agricultural spraying operations. If released to the atmosphere, degradation of vapor phase metribuzin by reaction with photochemically produced hydroxyl radicals (estimated half-life of 11 hrs) will be important. Metribuzin can be removed from air via rainfall and particulate phase metribuzin may be removed from air via dry deposition. If released to soil, biodegradation will be the primary fate process. Metribuzin is moderately adsorbed (Koc of 95) on soils with high clay and(or) organic content by a H-bonding mechanism and adsorption decreases with an increase in soil pH. Little leaching occurs on soils with high organic content, but metribuzin is readily leached in sandy soils. The soil half-life is in the range of 14-60 days. In water, biodegradation may be important based on studies in soil. Slow hydrolysis may aid in metribuzin degradation. Volatilization from water and bioconcentration in fish will not be important. Exposure of the general population to metribuzin may occur through ingestion of contaminated foods and drinking water as well as inhalation of dust and dermal contact resulting from its use. Workers may be exposed via dermal contact and inhalation of dust.
Environmental Fate TERRESTRIAL FATE: In soil, metribuzin was degraded to CO2. 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. TERRESTRIAL FATE: 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. TERRESTRIAL FATE: 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. TERRESTRIAL FATE: 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: Microbial degradation is the primary fate process of metribuzin in soil . Activity of soil microorganisms, higher temperatures and aerobic conditions increase the rate of metribuzin biodegradation . Metribuzin is moderately adsorbed (Koc of 95 ) on soils with high clay and(or) organic content by a H-bonding mechanism and adsorption decreases with an increase in soil pH . Little leaching occurs on soils with high organic content, but metribuzin is readily leached in sandy soils(1,4). The half-life of metribuzin in soil at normal use rates is about 30 to 60 days during the growing season . Under optimum conditions for degradation, most studies have determined the half-life of metribuzin to be 14-28 days . For example, half-lives of 3.08 and 2.04 weeks were determined in Plainfield sand after rainfall and supplementary water treatments . Loss from soil surfaces via photodecomposition and volatilization will not be important(1,3). Mineralization of 1 ppm (14)C metribuzin occured in the surface (0- to 10-cm depth) of a silty clay loam soil with 15-20% (14)CO2 evolution after 91 days; 5% (14)CO2 observed in the subsurface(6). AQUATIC FATE: Based on an estimated Henry's Law constant of less than 2.31X10-9 atm-cu m/mole at 20 deg C and a BCF of 10 in the Golden ide fish (Leuciscus idus melanotus) , volatilization from water and bioconcentration in fish, respectively, are not expected to be important fate processes of metribuzin in aquatic systems. Metribuzin is moderately adsorbed (Koc of 95 ) on sediments with high clay and(or) organic content by a H-bonding mechanism and adsorption decreases with a increase in soil pH . No data were located on the biodegradation of metribuzin water; however, microbial degradation is the primary fate process of metribuzin in soil . Activity of soil microorganisms, higher temperatures and aerobic conditions increase the rate of metribuzin biodegradation . Slow hydrolysis (half-life of 90 days ) may be an important removal mechanism in conjunction with biodegradation. ATMOSPHERIC FATE: Based on a reported vapor pressure of less than 1X10-5 mm Hg at 20 deg C , metribuzin should exist in the vapor and particulate phases in the ambient atmosphere . Vapor phase metribuzin is readily degraded in the ambient atmosphere by reaction with photochemically formed hydroxyl radicals; the half-life for this reaction in air can be estimated to be about 11 hrs(3,SRC). Particulate phase metribuzin is removed from air via dry deposition. Metribuzin has been detected in rainwater(4-5); therefore, it can be removed from air via wet depostion. Photolysis is not expected to be important . TERRESTRIAL FATE: Metribuzin is moderately adsorbed on soils with high clay and/or organic matter content, presumably by a H-bonding mechanism. Adsorption decreases as soil pH increases. Metribuzin is readily leached in sandy soils low in organic matter content but intermediate in leaching potential on heavier soils. Little leaching occurs on soils very high in organic matter. Half life in various soil types varies . Minimum under field conditions is 7 to 28 days and in most studies has been determined to be 14 to 28 days under optimum conditions for degradation.
Drinking Water Impact SURFACE WATER: Metribuzin was detected at a concn of 0.33 ug/l in 1 of 7 surface water samples taken in April-October of 1985 from Tuttle Creek Lake, Kansas . In 1975-1977, metribuzin was detected at an average concn of 0.02 ug/l in 11 agricultural watersheds in Ontario, Canada . During 1983 to 1991, metribuzin time-weighted average concns in Lake Erie tributaries, which drain agricultural watersheds, were: 0.29 ug/l in the Maumee River, 0.28 ug/l in the Sandusky River, 0.24 ug/l in Honey Creek, 0.23 ug/l in Rock Creek, 0.20 ug/l in Lost Creek, 0.07 ug/l in the Cuyahoga River, and 0.11 ug/l in the Raisin River . Metribuzin was detected in Shell Creek, a tributary to the Platte River in Nebraska, at a concn range of 0.5-1.7 ug/l in 11 samples taken about 72 hr after a spring rainstorm; no metribuzin was detected in the creek prior to the storm . Metribuzin was detected in 1984-85 in subbasins within the Cedar River, Iowa . In 1977, metribuzin was qualitatively identified in water from Lake Huron, Lake Erie, the St. Clair River, Lake St. Clair and the Detroit River(6). SURFACE WATER: In 6 of 55 samples drawn at the mouth of the Thames River, Ontario, Canada, the average metribuzin concn was 1.1 ug/l during the months May-August, 1981-85 . Metribuzin average concns in samples drawn during 1982-86 from the Sydenham River, Ontario, Canada, were: 1.2, 1.5, 7.7, 0.8 and 1.7 ug/l in 3, 1, 3, 1 and 1 samples, respectively . On September 24, 1990, metribuzin was detected at a concn of 1550 ng/l in the Grand River, Ontario, Canada . GROUNDWATER: Metribuzin was qualitatively detected in 2 groundwater wells in Wisconsin during the early 1980s . According to the USEPA's Groundwater Data Base, metribuzin has been quantified in groundwater from Iowa, Illinois, Kansas, Maine, Minnesota and Wisconsin at an average concn range of 0.05-2.10 ppb . RAINWATER: In 1990-1991, metribuzin was detected at average concns of 0.067 ug/l in 5 rain samples taken in Schauinsland, 0.031 ug/l in 4 rain samples taken in Deuselbach, and 0.057 ug/l in 2 rain samples taken in Bensheim, Germany . Metribuzin was detected in 1985 at concns less than 0.1 ug/l in 2 of 24 rain samples taken in Tiffin, OH and 1 of 21 samples taken in Potsdam, NY . DRINKING WATER: Metribuzin was detected in treated drinking water samples at a concn range of 0.14-0.45 ug/l during a study of 33 Iowa public water supplies that receive water from surface water sources; it was detected in 1 untreated drinking water sample at a concn of 0.89 ug/l . Metribuzin average concns in samples drawn from Dresden municipal drinking water, Ontario, Canada, were: 0.1 ug/l in 1 sample during June of 1982 and 3.7 in 2 samples during May-July of 1986 .

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