Diatom Analysis in Drowning: A Critical Review of Reliability, Contamination, and Medico-Legal Interpretation

The diagnosis of fatal drowning remains one of the most challenging tasks in forensic pathology, as no single autopsy finding is pathognomonic, and interpretation relies on the integration of scene information, circumstances, and ancillary investigations. Among supportive tests, diatom analysis has been used for decades, yet its medico-legal value continues to be debated due to methodological heterogeneity, contamination risks, and inconsistent interpretive frameworks. This review critically examines diatom evidence in drowning from a comparative and fit-for-purpose perspective, focusing on mechanistic plausibility, alternative non-drowning explanations, and methodological blind spots that undermine evidentiary reliability. Conventional microscopy-based diatom testing and emerging DNA-based and metagenomic approaches are compared with respect to what they detect, how contamination may arise, and how results are currently interpreted in forensic casework. Particular emphasis is placed on low-count diatom findings in closed organs, where recent evidence demonstrates substantial vulnerability to laboratory, consumable, and postmortem contamination. Drawing on recent systematic syntheses, controlled postmortem studies, and newly identified contamination sources, this review argues that mechanistic plausibility does not equate to forensic reliability. Diatom findings are best interpreted as supportive evidence whose weight depends on explicit contamination control, transparent reporting, and alignment with a clearly defined medico-legal proposition. To address persistent comparability and interpretation gaps, a minimum reporting dataset, minimum contamination-control principles, and a decision-oriented interpretive framework are proposed. In conclusion, diatom testing should neither be regarded as definitive proof nor dismissed outright. When applied selectively and interpreted within a contamination-aware, proposition-driven framework, diatom evidence may contribute meaningfully to drowning diagnosis and drowning-site inference, while avoiding overstatement of its probative value.