Biological Monitoring of Exposure of the General Population to the Organophosphorus Pesticides Chlorpyrifos and Chlorpyrifos-methyl by Determination of Their Specific Metabolite 3,5,6-trichloro-2-pyridinol

In this study we determined the concentrations of 3,5,6-trichloro-2-pyridinol (TCPyr) in urine samples from the general population. TCPyr is a specific metabolite of the organophosphorus pesticides chlorpyrifos and chlorpyrifos-methyl. By the introduction of a new sensitive analytical method a limit of quantification (LOQ) of 0.1 microgram per litre urine could be achieved, a tenfold improvement of recent methods. Extraction of TCPyr from the urine and the clean up process were carried out by automatic steam distillation. Separation and quantitative analysis were performed using capillary gas chromatography and mass selective detection in selected ion monitoring mode. The excretion of TCPyr was studied by analysing spontaneous urine samples from 5 women and 45 men between the ages of 22 and 57 (median: 40 years) living in Mecklenburg-Vorpommern (Germany) who were not occupationally exposed to organophosporus pesticides. TCPyr was detected in all specimens and the concentrations were quantified. The median excretion was 1.4 micrograms/l (range: 0.12 to 124.8 micrograms/l), the 95th percentile 11.3 micrograms/l. Under the worst case assumption that all TCPyr measured in urine originated from the intake of intact pesticides and not (less toxic) breakdown products, a TCPyr concentration of 1.4 micrograms/l urine corresponds to a daily intake of approximately 2.5 micrograms chlorpyrifos/chlorpyrifos-methyl. The intake at the 95th percentile would be about 23 micrograms chlorpyrifos/chlorpyrifos-methyl per day. According to FAO/WHO the acceptable daily intake (ADI) is 10 micrograms per kg bodyweight and day for both chlorpyrifos and chlorpyrifos-methyl.