Modern targeted nerve agent incidents: toxicokinetic complexity, biomarker interpretation and forensic uncertainty

Nerve agent poisoning is often linked with mass-casualty events. Typical examples are battlefield use or large terrorist attacks. However, documented incidents from the last decades show a broader and more complex picture. The perspective follows a line of documented cases. It starts with the 1978 ricin "umbrella" murder of Georgi Markov in London (non-nerve agent attack, but historically important). It then moves to the sarin attacks in Matsumoto (1994) and the Tokyo subway (1995), the VX assassinations by the Aum Shinrikyo cult (1994-1995), the 2013 sarin attack in Ghouta and the recent targeted poisonings of Kim Jong-nam (2017), Sergei and Yulia Skripal (2018), Dawn Sturgess and Charlie Rowley (2018) and Alexei Navalny (2020). We use these cases to show how route of exposure, dose, formulation and environmental persistence shape toxicokinetics, clinical presentation, biomarker formation and forensic interpretation. For each case we give the circumstances, the agent, the route, the clinical course, the treatment and the forensic confirmation in detail. We focus on acetylcholinesterase and butyrylcholinesterase inhibition, aging, protein adduct formation, dermal absorption and environmental persistence. We describe a recurring "toxicological paradox": greater control over exposure can reduce immediate lethality, but at the same time it increases diagnostic uncertainty and forensic complexity. The cases also show that mass and targeted use are not two separate historical stages. They coexist within the same period, sometimes even within one perpetrator organisation. This perspective has direct implications for emergency preparedness, biomarker development, antidotal treatment windows and international chemical incident response.