Research of diatoms and aquatic bacteria for estimating drowned site of a decomposed cadaver

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We collected 68 fresh, brackish and sea water samples from various sites around the estuaries of two rivers at high and low tides. Sea water flowed about 2.4 (salinity, 2.2% at the site) and 1.2 km (1.8%) upstream of the estuaries, but the surface comprised essentially fresh water up to the mouth. Sites contained 69 - 22,200 diatoms/50 ml of water and the numbers varied by depth and at sites separated by only about 1.2 km. Diatoms ranged from 2.8 to 429 (mean range, 16.1-59.2)μm in size. Large pennate diatoms populated fresh water areas, and most sedimented before reaching the sea. Tides and the nature of the river often altered diatomaceous assemblages at the same estuarial sites. Caution is recommended for forensic interpretation of aqueous media to deduce drowning sites.We also detected numerous bioluminescent bacteria in blood samples from two cadavers that had been immersed in estuarine environments. Homologous analysis based on the 16S rRNA gene identified the bioluminescent colonies as Vibrio fischeri and V. harveyi, which normally inhabit seawater. These findings in the blood from immersed bodies suggested brackish or marine water aspiration because our previous study showed that few other marine bacteria invade and predominate post mortem. This simple and rapid bacteriological test has potential as a marker supporting a conclusion of death by drowning.