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Pitfalls when determining tissue distributions of organophosphorus chemicals: sodium fluoride accelerates chemical
F Moriya1, Y Hashimoto, T L Kuo
1Department of Legal Medicine, Kochi Medical School, Japan.
Abstract:
This paper describes the tissue distributions of dichlorvos, an organophosphate, and chlorpyrifos-methyl, an organophosphorothioate, in a male individual who died after ingesting an insecticidal preparation containing these chemicals and the results of an in vitro stability study on dichlorvos and chlorpyrifos-methyl in blood and buffers. Tiny amounts of dichlorvos, 0.067 and 0.027 mg/L, were detected in the vitreous humor and cerebrospinal fluid, respectively. Although dichlorvos (0.082-8.99 mg/L or mg/kg) was detected in the thoracic aortic blood, thoracic inferior vena caval blood, pericardial fluid, bile, and spleen, it was strongly suggested that it had diffused postmortem from the stomach, which contained 879 mg, because no dichlorvos was detected in the other blood samples and tissues tested. Substantial amounts (0.615-4.15 mg/L) of chlorpyrifos-methyl were detected in all blood samples, and the order of its concentrations was as follows: pulmonary vessel blood > thoracic inferior vena caval blood > blood in the right cardiac chambers > blood in the left cardiac chambers approximately thoracic aortic blood > right femoral venous blood. The total amount of chlorpyrifos-methyl in the stomach was 612 mg. However, it was strongly suggested that virtually no chlorpyrifos-methyl diffused from the stomach into surrounding fluids and tissues postmortem because no chlorpyrifos-methyl was detected in the bile and little was found in the pericardial fluids. Neither compound was detected in the urine. In vitro experiments showed that dichlorvos (10 mg/L) almost disappeared from fresh (pH 7.4) and acidified (pH 6.2) blood samples within 24 and 72 h, respectively. However, 53 and 77% of the original amount of dichlorvos in 0.05M phosphate buffers at pH 7.4 and 6.2 were detected 72 h later. Chlorpyrifos-methyl (1 mg/L) was very stable in blood samples, regardless of the pH, during the 72-h study period, but in the pH 7.4 and 6.2 phosphate buffers, approximately 80% of the original amount had degraded after 72 h. These results indicate that organophosphates are degraded more rapidly by esterase activities than by chemical mechanisms and that organophosphorothioates are hydrolyzed chemically in aqueous solutions but are very stable in biological specimens and not metabolized by esterases. When sodium fluoride was added to blood samples, dichlorvos degraded completely within 15 min, and chlorpyrifos-methyl became very unstable. Thus, when analyzing samples to detect organophosphorus chemicals, this common preservative should not be added to fluid specimens.
Insights
Dichlorvos rapidly degrades in blood due to esterase activity, while chlorpyrifos-methyl is stable in blood but degrades in buffers. Sodium fluoride accelerates degradation of both organophosphates.
Area of Science:
- Forensic Toxicology
- Environmental Chemistry
- Biochemistry
Background:
- Organophosphate pesticides, including dichlorvos and chlorpyrifos-methyl, are widely used but pose risks upon ingestion.
- Understanding their distribution and stability in biological samples is crucial for postmortem investigations and environmental monitoring.
Observation:
- Dichlorvos showed limited distribution in postmortem fluids, suggesting postmortem diffusion from the stomach.
- Chlorpyrifos-methyl was found in substantial amounts in blood, with minimal postmortem diffusion into other tissues or fluids.
- In vitro studies revealed dichlorvos rapidly degrades in blood via esterase activity, while chlorpyrifos-methyl is stable in blood but degrades chemically in aqueous buffers.
Findings:
- Dichlorvos degradation in blood is primarily enzymatic, occurring rapidly at physiological pH.
- Chlorpyrifos-methyl exhibits stability in blood, indicating resistance to biological metabolism, but undergoes chemical hydrolysis in aqueous solutions.
- Sodium fluoride, a common preservative, significantly accelerates the degradation of both dichlorvos and chlorpyrifos-methyl in blood samples.
Implications:
- The differential stability and distribution patterns of dichlorvos and chlorpyrifos-methyl have significant implications for interpreting toxicological findings in postmortem cases.
- Accurate quantification of these pesticides requires careful consideration of sample matrices and potential degradation pathways.
- The use of sodium fluoride as a preservative in biological fluid samples should be avoided when analyzing for organophosphates due to its interference with compound stability.