Laboratory of Forensic Toxicology of the Institute of Legal Medicine of Coimbra, University of Coimbra, 3000 Coimbra, Portugal

In this paper we describe metabolism and toxicokinetic studies following oral administration of a standard and a commercial formulation of parathion to the rabbit. Parathion and its metabolites aminoparathion ( C₁₀H₁₆NO₃PS) and paraoxon (C₁₀H₁₄NO₆P) were analysed in biological products (blood, heart, vitreous humour, kidney, liver, lung, small intestine) after 30 min., 1, 2, 4, 8, and 24 hours. Gas chromatography with a nitrogen phosphorus detector and a mass spectrometry detector were used in the determination of the analytes.

The absorption process of parathion was very fast and this compound had a high elimination rate. The three compounds were detected in the different specimens. A low bioavailability and an interindividual variability in parathion metabolism were found for all analytes. Paraoxon presented the lowest concentrations in all samples. Aminoparathion was found in higher concentrations in the liver and kidneys. In the vitreous humour, the concentration levels were lower than in the other substracts. Generally speaking, the concentration levels of parathion and its metabolites increased up to 2 hours and decreased after 4 hours.

Although the determinations of the different specimens/blood partition coefficients (PCs) are not a reliable biomarker to evaluate the elapsed time between ingestion and death, the PCs can help the diagnostic interpretation of the poisoning cases by this insecticide.