Page 5: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Chlorpyrifos

• Previous Page
• Table of Contents
• Next Page

Health Effects

Chlorpyrifos is readily absorbed from the gastrointestinal tract and is rapidly metabolized. Metabolites are excreted principally in the urine and to a lesser extent in the faeces; the main metabolites are 3,5,6-trichloro-2-pyridylphosphate and 3,5,6-trichloro-2-pyridinol.^{Footnote 17} Small amounts of unmetabolized chlorpyrifos have been detected in the blood, brain and liver after accidental human ingestion.^{Footnote 18}

Chlorpyrifos is a cholinesterase inhibitor. Human volunteers (four men per group) were administered oral doses of chlorpyrifos of 0.014 mg/kg bw per day for 27 days, 0.03 mg/kg bw per day for 20 days or 0.10 mg/kg bw per day for nine days.^{Footnote 19} Red blood cell cholinesterase activity was not affected at any level.

Beagle dogs were fed diets containing chlorpyrifos at dose levels of 0, 0.01, 0.03, 0.1, 1.0 or 3.0 mg/kg bw per day for two years.^{Footnote 20} Red blood cell cholinesterase was inhibited in males and females at 1.0 and 3.0 mg/kg bw per day. In a similar study,^{Footnote 21} rats were fed diets containing chlorpyrifos at concentrations of 0, 0.01, 0.03, 0.1, 1.0 and 3.0 mg/kg bw per day for two years. Brain cholinesterase activity was inhibited at 3.0 mg/kg bw per day and slightly depressed at 1.0 mg/kg bw per day. Based on these results, the no-observed-adverse-effect level (NOAEL) for red blood cell and brain cholinesterase inhibition is considered to be 0.1 mg/kg bw per day. The NOAEL in Rhesus monkeys receiving 0.08 mg/kg bw per day of chlorpyrifos by gavage for six months was similar; animals exhibited no depression in red blood cell cholinesterase activity.^{Footnote 22}

In a carcinogenicity study in CD-1 mice, chlorpyrifos was not oncogenic when administered at dose levels up to 15 ppm (1.5 mg/kg bw per day) in food for 105 weeks.^{Footnote 23} Chlorpyrifos was not found to be mutagenic in five microbial assay systems.^{Footnote 24} In a CF-1 mouse teratogenicity study, chlorpyrifos was not teratogenic at doses up to 25 mg/kg bw per day, although significant reductions in plasma and erythrocyte cholinesterase levels were observed in maternal mice at 1 mg/kg bw per day or greater and in foetuses at 10 mg/kg bw per day or more.^{Footnote 25}

• Previous Page
• Table of Contents
• Next Page