Final 1,4‑Dioxane Guideline; Malathion Proposed

Summary#

On March 27, 2021, Health Canada published two drinking-water guideline notices under the Canadian Environmental Protection Act, 1999.
One is the final guideline for 1,4-dioxane with a maximum acceptable concentration of 0.050 mg/L (50 μg/L). The other is a proposed guideline for malathion with a proposed value of 0.29 mg/L (290 μg/L) and a public comment period running to May 26, 2021.

What it does#

• Finalizes the guideline for 1,4-dioxane in drinking water at 0.050 mg/L (50 μg/L). It also gives guidance on where 1,4-dioxane can come from, how to test for it, and what kinds of treatment can remove it.
• Releases the technical document for a proposed guideline for malathion and asks for public comments from March 27, 2021 to May 26, 2021 (a 60-day comment period). The proposed maximum is 0.29 mg/L (290 μg/L). The notice explains sources, health evidence, and treatment options that would support that number.

Who's affected#

• Municipal water utilities and operators who manage drinking-water sources and treatment plants — especially those serving groundwater near industrial sites, landfills, or wastewater discharges.
• Owners of private wells in areas near known contamination sources.
• People who work with or near the chemicals:
  • Industries that use or make 1,4-dioxane or that produce ethoxylated surfactants and certain plastics.
  • Farmers and applicators who use malathion (about 25,000 kg sold in Canada in 2018).
• Regulators and public-health officials who set local drinking-water rules and monitoring programs.
• The general public living near sites with known solvent or pesticide contamination may notice testing or treatment changes.

Why it matters#

• The final 1,4-dioxane guideline sets a clear health-protective limit (0.050 mg/L) for a contaminant that moves readily into groundwater and can be hard to remove with standard treatment. Utilities may need advanced treatments (for example, advanced oxidation or reverse osmosis) to reach this level.
• The malathion proposal sets a much higher value (0.29 mg/L) and says malathion is rarely found in Canadian drinking water at levels near that number. It also notes several treatment options (activated carbon, membranes, oxidation) are available if removal is needed.
• For both chemicals, the notices describe monitoring recommendations (for known-impacted sources, monitoring is recommended semi-annually) and encourage utilities to confirm treatment effectiveness if they are treating for these contaminants.
• The malathion guideline is still proposed — it is not final. People and organizations can comment until May 26, 2021; those comments could affect the final value or guidance.