The emerging trend of suicide using nitrite/nitrate in Victoria, Australia

Abstract

Over the last 18 months the ingestion of nitrite/nitrate salts as a method of suicide has drastically increased, with a single case identified in 2017 and eight in 2019. Inorganic salts can be difficult to detect using standard instrumental methods regularly used in a forensic toxicology laboratory. Ingestion of nitrite/nitrate salts can directly oxidise haemoglobin to methaemoglobin (MetHb) and lead to methemoglobinemia (elevated met-haemoglobin). Methaemoglobinemia occurs within 1 h of consumption leading to severe tissue hypoxia. MetHb is subject to significant changes postmortem and testing of a blood sample in suspected cases must be conducted promptly. Detection of raised MetHb is non-specific but can be an indicator of nitrate/nitrite consumption. This study reviewed cases suspected of nitrite/nitrate poisoning in an attempt to identify common characteristics that can assist in identifying the cause of death in other suspected cases. Cases were initially identified from Police reports where either sodium nitrite or sodium nitrate salt was present at the scene of the incident. These cases were referred for testing in a specialised laboratory able to conduct nitrite/nitrate analysis in blood and when available urine and stomach contents. Briefly, samples were diluted with deionised water and analysed using flow injection analysis/ion chromatography on a Metrohm Compact IC comparing nitrate/nitrite levels. Blood methaemoglobin levels were measured using co-oximetry in all cases with a suitable postmortem blood sample. The concentrations of nitrite and nitrate in blood, urine or stomach contents were significantly higher in cases suspected of nitrite/nitrate consumption when compared to endogenous baseline levels. Blood concentrations for nitrite ranged from 135–230 mg/L (normal range < 0.2–10.9 mg/L) and for nitrate, 180 to 750 mg/L (normal range 14–115 mg/L). While nitrate is naturally converted to nitrate endogenously, cases involving sodium nitrate ingestion showed a higher proportion of nitrate in stomach contents. Only 5 of the 14 cases had a blood sample suitable for MetHb analysis, with results ranging from 8 to 14% (baseline level < 1.5%). Timely information provided in case circumstances is critical in enabling the collection and testing of samples in suspected nitrite/nitrate poisonings where these cases may otherwise be overlooked and remain undetected. The presence of nitrite/nitrate at elevated concentrations and in addition to raised MetHb may indicate a likely cause of death in the absence of other possible factors.