Concentrations of parent pesticide and corresponding diethylphosphorus
metabolites in blood serum and urine were investigated in persons who
had ingested a concentrated solution of organophosphorus pesticide ch
lorpyrifos. The organophosphate poisoning was indicated by a significa
nt depression of blood cholinesterase (EC 3.1.1.7 and EC 3.1.1.8) acti
vities. Blood and spot urine samples were collected daily after admiss
ion of the persons to hospital. Chlorpyrifos was detected only in seru
m samples in a period up to 15 days after posioning. In the same sampl
es chlorpyrifos oxygen analogue, chlorpyrifos oxon, was not detected.
The presence of diethylphosphorothioate in all serum and urine samples
confirmed that part of chlorpyrifos was hydrolysed before its oxidati
on. The maximum concentrations of chlorpyrifos in serum and of metabol
ites in serum and urine were measured on the day of admission. The dec
rease in concentrations followed the first-order kinetics with the ini
tial rate constant faster and the later one slower. In the faster elim
ination phase chlorpyrifos was eliminated from serum twice as fast (t1
/2 = 1.1 - 3.3 h) as the total diethylphosphorus metabolites (t1/2 = 2
.2 - 5.5 h). The total urinary diethylphosphorus metabolites in six ch
lorpyrifos posioned persons were excreted with an average elimination
half-time of 6.10 +/- 2.25 h (mean +/- S.D.) in the faster and of 80.3
5 +/- 25.8 h in the slower elimination phase.