Two drowned cases demonstrating the deduced location of drowning site: hints from the utility of Sr levels in pleural fluids

We have been exploring an auxiliary method using the trace metal element Strontium (Sr), Lithium (Li), and Boron (B) to distinguish seawater drowning (SWD) and freshwater drowning (FWD), as well as to determine the water entry site, in assisting forensic interpretation. In this study, we examined whether the application of Sr-based identification of water bodies could contribute to forensic practice by analyzing two different drowning cases. In case 1, the concentrations of all three elements exceeded the previously established cutoff values, supporting SWD and suggesting a brackish water environment. In Case 2, even the results of surrounding investigations, including the deployment of police dogs by investigative agencies, did not provide any objective evidence to determine the location where the deceased entered the water, and the exact entry site remained unknown. However, based on the predictive regression curve derived from Sr concentration, we suggested that the deceased most likely entered the water where the Sr concentration was 3,881 ppb. Therefore, based on the results such as surrounding geographical conditions, we inferred that the deceased might have entered the water near the exit of a river, located 7.6 km southwest of the discovery site. The Sr concentration detected in the water sample collected from the exit of river was close to the predicted Sr concentration of the water entry site. These cases suggest that Sr-based analysis may serve as a supportive tool not only for differentiating drowning environments but also for reconstructing probable water entry sites.