Guidelines for Canadian Drinking Water Quality - Dimethoate and Omethoate

This guideline technical document was prepared in collaboration with the Federal-Provincial-Territorial Committee on Drinking Water and is based on assessments of dimethoate (which included an assessment of omethoate) completed by Health Canada’s Pest Management Regulatory Agency and supporting documents.

The toxicological effects of dimethoate are the result of omethoate, its oxygen analogue metabolite (oxon). Since omethoate can be formed through the environmental degradation of dimethoate or during treatment of water containing dimethoate, an additive approach should be taken in which the sum of the detected concentrations of dimethoate and omethoate (expressed as a dimethoate equivalent value) does not exceed the MAC for dimethoate.

The maximum acceptable concentration (MAC) for dimethoate and omethoate in drinking water is 0.02 mg/L (20 μg/L).

Link to the Canada Gazette, Part I, Volume 156, Number 38: Index