Species discordance in diatom testing for drowning diagnosis: a biological passive sampling hypothesis with forensic implications.

Diatom testing is a key technique for forensic drowning diagnosis, yet species discordance between diatom taxa in victim tissues and water samples from the recovery site remains a major medico-legal challenge, often misattributed to technical errors or post-mortem contamination. This correspondence proposes an interdisciplinary interpretative hypothesis based on biological passive sampling theory from environmental science, hypothesizing three potential mechanisms driving this discordance: selective sampling by anatomical structures and diatom physical traits, time-integrated accumulation of diatoms during the agonal period of drowning versus snapshot water sampling, and chronic dietary diatom exposure forming a potential background signal. We cautiously distinguish natural biological discordance from artificial post-mortem contamination, and suggest reframing discordance from a methodological flaw to a potential source of actionable forensic information, provided that its interpretative boundaries are clearly defined. Evidence-based forensic interpretation guidelines for different discordance patterns and standardized practice recommendations for diatom testing are provided, including reporting organ-specific diatom profiles, evaluating tissue barrier integrity, and implementing strict blank controls. This framework is presented as a testable hypothesis consistent with recent systematic reviews on diatom test interpretation and provides a theoretical basis for the urgent standardization of forensic diatom testing, enhancing the scientific validity of drowning diagnosis and site inference in medico-legal practice.