Drinking Water Limit for Metribuzin

Summary#

The Government published final guidelines for drinking water quality for metribuzin under the Canadian Environmental Protection Act, 1999. The guideline sets a maximum acceptable concentration of 0.08 mg/L (80 μg/L) in drinking water and was finalized after a 60 days public consultation in 2020; the notice is dated June 4, 2021.

What it does#

• Sets the maximum acceptable concentration (MAC) for metribuzin in drinking water at 0.08 mg/L (80 μg/L).
• Summarizes how people and the environment can be exposed to metribuzin, noting it is used as an agricultural herbicide and that about more than 100 000 kg (active ingredient) was sold in Canada in 2018.
• Describes the health evidence: repeated-dose animal studies showed effects mainly on the liver (the MAC is based on a two-year dog study); available human studies did not show links to cancer or Parkinson’s disease.
• Lists how metribuzin can be measured and reduced in drinking water, including municipal options like oxidation, activated carbon adsorption, and membrane filtration, and household options such as activated carbon or reverse osmosis units.
• Advises that any exceedance of the MAC should be investigated and that steps could include extra monitoring, switching water source, or installing treatment.

Who's affected#

• Farmers and agricultural operations that use metribuzin where runoff or drainage can reach water sources.
• Municipal and regional drinking water systems in agricultural regions, which may need to monitor or adjust treatment.
• Owners of private wells near areas where metribuzin is applied.
• Provincial and territorial drinking water authorities and operators who handle monitoring and responses to exceedances.

Why it matters#

• The guideline gives a clear health-based limit for metribuzin in drinking water to protect people over a lifetime.
• Communities near agricultural areas may see more testing or treatment work to make sure drinking water is below the 0.08 mg/L (80 μg/L) limit.
• Private well owners in farming areas may need to test their water and consider treatment if levels are high.
• Municipalities that already treat water should check that treatment keeps metribuzin below the MAC and watch for any disinfection by-products if they change processes.