SOFT - TIAFT 1998 Poster Session 4 Friday October 9, 1998

Estela G. Pinho Marques, D. Nuno Vieira, Paula C. V. Monsanto, Beatriz P. Simões da Silva, Maria Margarida F. Oliveira, M. Teresa Ávila

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

Parathion ( C10H14NO5PS) is an insecticide which is highly toxic for mammals (the lethal dosis for man is from 20 to 100 mg). It has a high toxicity because it is a powerful colinesterase inhibitor. In Portugal's Central Region, this insecticide is responsible for the majority of fatal intoxications. Practically all fatalities are the result of suicides through ingestion of commercial formulations with parathion (> 90%).

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.

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