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Metribuzin Quickview (CASRN 21087-64-9)

Health assessment information on a chemical substance is included in IRIS only after a comprehensive review of toxicity data by U.S. EPA health scientists from several Program Offices, Regional Offices, and the Office of Research and Development.

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Status of Data for Metribuzin

File First On-Line: 01/31/1987; Last Significant Revision: 12/01/1993

Category (section)
Last Revised
Oral RfD Assessment Yes 01/31/1987
Inhalation RfC Assessment No
Carcinogenicity Assessment Yes 12/01/1993
  • 21087-64-9
  • 4-Amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4h)-one
  • 4-Amino-6-tert-butyl-3-(methylthio)-1,2,4-triazin-5-on
  • 4-Amino-6-tert-butyl-3-methylthio-as-triazin-5-one
  • Bay 61597
  • Bay dic 1468
  • Bayer 6159h
  • Bayer 6443h
  • Bayer 94337
  • Dic 1468
  • Lexone
  • more...
Metribuzin Source Documents
Revision History
Date Section Description
04/01/1997 III., IV., V. Drinking Water Health Advisories, EPA Regulatory Actions, and Supplementary Data were removed from IRIS on or before April 1997. The IRIS users were directed to the appropriate EPA Program Offices for this information.
Chronic Health Hazard Assessments for Noncarcinogenic Effects

Reference Dose for Chronic Oral Exposure (RfD)

Critical Effect
Point of Departure*
Liver and kidney effects, decreased body weight, mortality NOEL : 2.5 mg/kg-day 100 2.5 x10-2 mg/kg-day

* The Point of Departure listed serves as a basis from which the Oral RfD was derived. See Discussion of Conversion Factors and Assumptions for more details.

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Reference Concentration for Chronic Inhalation Exposure (RfC)

Not Assessed under the IRIS Program.

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Carcinogenicity Assessment for Lifetime Exposure
  • Weight-of-Evidence Characterization
    • D (Not classifiable as to human carcinogenicity)
  • Weight-of-Evidence Narrative:
    • No human data and inadequate evidence ffom animal bioassays. Metribuzin did not increase the incidence of tumors in a lifetime dietary study using CD-1 mice when compared with both concurrent and historic controls. In a 2-year feeding study in Wistar rats, no significant differences in neoplastic findings between the test and control groups were found. Short-term studies in bacteria and mammalian systems suggest that metribuzin is not mutagenic.
    • This may be a synopsis of the full weight-of-evidence narrative. See IRIS Summary.

Quantitative Estimate of Carcinogenic Risk from Oral Exposure

  • Not Assessed under the IRIS Program.

Quantitative Estimate of Carcinogenic Risk from Inhalation Exposure

  • Not Assessed under the IRIS Program.

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