Page 6: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Chlorpyrifos

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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 rat^{Footnote 20,Footnote 21} and studies with human volunteers^{Footnote 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.

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