Toxicological and analytical investigations in organophosphate pesticides fatal poisoning. A case report on fatal terbufos poisoning

Abstract

The identification of pesticides in postmortem samples can be challenging, especially when organophosphates compounds (OPs) are involved. OPs are unstable and share several common metabolites, namely dialkylphosphates (DAP). Through a fatal poisoning case caused by the ingestion of terbufos, we demonstrate the importance of using specific analytical methods and the necessity to detect DAP for the identification of the culprit compound. The corpse of a 29-year-old male farmer was discovered 2 km away from his farm. A letter was found nearby with instructions to be respected for his funeral. He was last seen alive 24 h before his body was discovered and it was noted that this was not his first suicide attempt. Three months before his death, he had been admitted to ICU after ingesting OPs pesticides but the molecule was not identified at the time. The autopsy was performed 1 week after death and no external lesions were found. Only, a moderate non-specific asphyxia syndrome with left ventricular hypertrophy was reported. Gastric content, cardiac and peripheral blood and urine were sampled. Exhaustive analytical researches including general unknown screening (GUS) Methods were performed [GC-MS (QP2010, Shimadzu), HS-GC-MS (TurboMix S40-QP2010, Shimadzu) and UHPLC-MS/MS (API 3200 QTRAP, Sciex)] plus a UHPLC-MS/MS screening method (API 5500 QTRAP, Sciex) including about 350 pesticides. Then, OPs and DAP were determined using specific quantitative methods: GC-MS/MS (7010, Agilent) and HPLC-MS/MS (API 5500 TQ, Sciex), respectively. The first analysis only reported opioids in urine: codeine, morphine, hydrocodone and dihydrocodone at insignificant concentrations (< 10 μg/L). The screening of pesticides showed the presence of Ethion (an OP) and 3 DAP [Diethylphosphate (DEP), Diethylthiophosphate (DETP) and Diethyldithiophosphate (DEDTP)] in cardiac blood and in urine. Table 1 resumes these results. The presence of DEP, DETP and DEDTP suggests the ingestion of Ethion, Disulfoton, Phorate, Phosalone or Terbufos. The OPs specific method only found traces of Ethion (< LDQ) but detected terbufos at a blood concentration of 22 μg/L and at a concentration greater than 1000 μg/L in gastric content. To the best of our knowledge, we report the first case of intentional terbufos poisoning. Only one case of fatal occupational transdermal exposure was recently published where blood concentration was similar (14 μg/L) [1] . The concentration of terbufos after poisoning could be very low. GUS methods fail to identify OPs and DAP which need very sensitive and specific methods to be detected. The knowledge of metabolic pathways of OPs is mandatory to facilitate the identification of the involved pesticide.