Proposed Drinking Water Guideline for Dicamba

Summary#

Health Canada has published a proposed drinking-water guideline for the herbicide dicamba under the Canadian Environmental Protection Act, 1999. It would set a proposed maximum acceptable concentration (MAC) of 0.11 mg/L (110 μg/L) in drinking water. Comments were invited between October 23, 2020 and December 21, 2020.

What it does#

• Proposes a guideline (a protective limit) for dicamba in drinking water: a MAC of 0.11 mg/L (110 μg/L).
• Explains the health basis for the MAC: it is based on changes in clinical chemistry and inflammation of the prostate seen in a one‑year dog study.
• Summarizes how dicamba gets into water: surface run‑off, spray drift and soil leaching; it can reach both surface water and groundwater.
• Reports monitoring findings: dicamba is not commonly found in Canadian source or drinking water, but low levels have been detected in some agricultural areas.
• Notes how dicamba can be measured and removed:
  • Analytical methods can detect dicamba well below the proposed MAC.
  • Municipal treatments such as advanced oxidation are most effective; oxidation and other options show lower removals.
  • Activated carbon adsorption and membrane processes (including reverse osmosis) may also work, but fewer studies exist; pilot testing is recommended before full implementation.
  • For private wells or household treatment, activated carbon and reverse osmosis are possible options; users should test water before and after treatment.
• Advises on what to do if the guideline is exceeded: confirm with further monitoring, investigate the source, consider alternate water supplies or install appropriate treatment, and adjust existing treatment if needed.
• Places the proposal in context: the document was prepared with the Federal-Provincial-Territorial Committee on Drinking Water and draws on an assessment by the Pest Management Regulatory Agency.

Who's affected#

• People living in agricultural areas where dicamba is applied — they are most likely to see traces in local source or treated water.
• Municipal water utilities and treatment operators in those areas — may need to monitor and, if necessary, adjust treatment.
• Owners of private wells — may need testing and possibly residential treatment if contamination is found.
• Farmers and pesticide applicators — their use patterns affect whether dicamba reaches nearby water.
• Provincial, territorial and federal drinking‑water authorities — they would use the guideline when planning monitoring and responses.

Why it matters#

• The proposed MAC is meant to protect health over a lifetime of drinking the water. Even though dicamba is not commonly detected, low levels have appeared near some agricultural areas, so the guideline helps set a clear threshold for action.
• Municipal systems generally have ways to reduce dicamba, but small systems and private wells may face higher costs or need point‑of‑use solutions and testing.
• International comparisons show different approaches (for example, Australia has 0.1 mg/L, while the EU uses 0.1 µg/L for any single pesticide and 0.5 µg/L for total pesticides), so jurisdictions may weigh health science and policy choices differently.
• If you live near farms using dicamba, or manage a small water system or private well, this is a guideline you might want to watch for monitoring results and any local follow-up actions.