Page 6: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Chlorpyrifos
Rationale
The ADI for chlorpyrifos has been derived by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO)Footnote 12 as follows:
ADI = 0.1 mg/kg bw per day / 10 = 0.01 mg/kg bw per day
where:
- 0.1 mg/kg bw per day is the NOAEL derived from two-year studies in the dog and ratFootnote 20,Footnote 21 and studies with human volunteersFootnote 19
- 10 is the uncertainty factor.
The maximum acceptable concentration (MAC) for chlorpyrifos in drinking water is derived from the ADI as follows:
MAC = 0.01 mg/kg bw per day × 70 kg × 0.20 / 1.5 L/d ≈ 0.09 mg/L
where:
- 0.01 mg/kg bw per day is the ADI established by the FAO/WHO
- 70 kg is the average body weight of an adult
- 0.20 is the proportion of daily intake of chlorpyrifos allocated to drinking water
- 1.5 L/d is the average daily consumption of drinking water for an adult.
Date reviewed: 2026-06-04