Diatoms and homicide

doi:10.1016/S0379-0738(97)00162-X

Forensic Science International

Volume 91, Issue 1, 9 January 1998, Pages 29-34

https://doi.org/10.1016/S0379-0738(97)00162-X Get rights and content

Abstract

Six illustrative cases of homicidal drowning are reported in which the diatom test for drowning was a useful adjunct to the medicolegal investigation of death. In all six cases, diatom frustules were recovered from the femoral bone marrow. In five cases, diatoms extracted from the bone marrow were compared with diatoms obtained from samples of putative drowning medium. In all of these case, the same types of diatoms were observed in both the water samples and the marrow. In an additional case, watery fluid from the maxillary sinus contained the same diatom types as were present in the femoral bone marrow. Four of the six cases were found submerged in water and had autopsy findings consistent with drowning. In the remaining two cases, the bodies were found on land; one case was grossly decomposed and one body was extensively burned since the body was set afire on dry land after death. In some of the cases drowning was associated with blunt force head injury (one case), sharp force injuries of the chest (one case), or strangulation (three cases). These results indicate that the diatom test for drowning is an important adjunct to the medicolegal investigation of homicidal drowning, particularly in those cases were autopsy and scene findings do not imply drowning as a cause of death.

Introduction

We have recently assessed the validity and utility of the diatom test for drowning by analysing the outcome of the test in 771 cases of drowning [1]. We found that the presence of diatom frustules in bone marrow can be used to diagnose drowning in approximately one-third of freshwater drownings. There was a high incidence of positive test outcomes in months of peak freshwater concentration of diatoms. In an analysis of cases of drowning in which a sample of drowning medium was available for examination, we found that the same types of diatoms could be found in 90% of cases indicating that the diatoms originated from the drowning medium [2]. Taken together these data support the utility and validity of the diatom test for determining cause of death when drowning is suspected on the basis of autopsy findings or circumstances surrounding death.

In this report, we describe six illustrative cases of homicidal drowning (Table 1) in which the application of the diatom test implicated drowning as a cause of death. In many of these cases, the circumstances and postmortem findings did not initially suggest drowning as a cause of death. These cases underscore the utility of the diatom test in suspicious deaths or homicides in which conventional investigations do not led to determination of a definitive cause of death. In addition, the cases show that the correlation of the type of diatoms recovered from tissues and putative sites of drowning may help to localize a site of drowning.

Section snippets

Material and methods

In all cases, bone marrow from one or both femurs were used for the extraction of diatoms utilizing a method described previously 1, 3. Briefly, femurs were sawed along the long axis, the bone marrow (∼50 g) removed using a clean spatula and placed into a boiling flask. Approximately 50 ml of concentrated analytical grade nitric acid was added and the marrow-acid suspension was simmered on a hot plate for approximately 48 h in a fume hood. The suspension was then cooled to room temperature and

Case 1

The body of a 56 year old woman was found face down floating in a river. At autopsy, there was recent haemorrhage into the right sternomastoid muscle with fracture of the right greater cornu of the hyoid bone with local haemorrhage and recent bruising involving the tip of the tongue. There was bilateral pulmonary oedema (right lung 450 g, left lung 400 g) and 300 ml of watery fluid in the stomach. Death was attributed to the combined asphyxial effects of strangulation and drowning.

A nitric acid

Discussion

The reported cases illustrate the utility of the diatom test in the medicolegal investigation of homicidal drowning Table 1. The main points illustrated by the case reports are that: (i) the diatom test for drowning can implicate drowning as a cause of death even when the autopsy and circumstances do not suggest drowning; and (ii) drowning is further substantiated when the type of diatom in the bone marrow matches diatoms present in the putative drowning medium.

In most of the reported cases,

Acknowledgements

Some of the cases were processed under the direction of the late Dr. John Hillsdon-Smith, former Director of Forensic Pathology for the Province of Ontario. The investigating officer who collected the water sample for case three was Supt. William C. Bowles. The author thanks Vera Mont and Jurek Ladziak for preparation of acid digests.

References (3)

M.S. Pollanen et al.
The diagnostic value of the diatom test for drowning. I. Utility: a retrospective analysis of 771 cases of drowning in Ontario, Canada
J. Forensic Sci.
(1997)

There are more references available in the full text version of this article.

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This idea stems from the forensic dogma “every contact leaves a trace” – known as Locard's exchange principle [11] – and in the field of forensic geoscience [12]. In this context, forensic geoscience refers to the possibility of using trace evidence such as soil, sediment and microscopic algae (diatoms especially), to support the diagnosis of death by drowning [13,14] and to verify that contact occurred between a suspect and a specific water body [8,15]. Diatoms are photosynthesizing unicellular microalgae that have a siliceous skeleton (frustule made of two overlapping valves) with specie-specific morphological features.
Crime scene investigation protocols and procedures are well established when concerning terrestrial environments, but are limited when associated with aquatic environments.
In aquatic contexts, the soil, sediments and microscopic algae (e.g. diatoms) may all be used as sources of trace evidence for criminal investigations. Diatoms are one such source that can be used to support the diagnosis of death by drowning and can be used to verify contact between a suspect and a specific water body. For the latter, diatoms can be collected from clothing and shoes for forensic comparisons. Over the years, there have been several methods proposed for the extraction of diatoms from clothing, however, a best practice method is yet to be established and is still open to debate.
The present research represents the first investigation that evaluates four different methods for the extraction of native and common Australian diatom species from four different types of fabrics. Diatoms of two different species and shape (pennate and centric) were cultivated in stimulated experimental waters – prepared using either monocultures or mixed cultures of the selected diatoms. Diatom concentrations were set to mimic the natural population (low to bloom events) as commonly found in the Swan River Estuary of Western Australia. Cotton, denim, blend, and acrylic fabric types were placed in experimental waters. Diatom extraction was attempted using methods already proposed in the literature, these include: rinsing with ethanol (RE); rinsing with ethanol together with the application of centrifugal force (RECF); digestion with hydrogen peroxide (H); and a new method of ashing that has never been tested before (dry ash, DA).
Results of this research showed that a) the type and the concentration of the mono and mix diatom mixtures significantly affects the transfer and extraction from different types of fabric; b) a noticeable extraction difference is observed between the fabrics, establishing denim, acrylic and blend fabrics as possessing the better extraction rates; c) H treatment had the highest extraction rate of diatoms; d) the application of centrifugal force on the RE method significantly improved the extraction of diatoms; e) DA is a potential method for the extraction of pennate-shaped diatoms from all of the tested fabrics, however, does have a tendency to induce modifications of the morphological structure of the diatoms. Overall, the application of different extraction methods is suggested to maximise the extraction of diatoms that would closely reflect their natural assemblage in the water body under investigation.
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Diatoms are a reliable diagnostic tool for drowning. Yet, they are at the origin of controversies due to limits linked to the discovery site, discrepancies in the results induced by the methods used or non-conformities affecting the expression of the results. A survey of 26 forensic institutes (metropolitan France and DROM/COM) and 10 French laboratories was undertaken to get state of the art about drowning diagnostic techniques used from a sample of freshwater human corpses discovered in 2010 and 2011. The analysis highlights biases and limitations mainly related to methodological sampling rules, rate of decomposition of the corpse likely to cause hypothetic post mortem contamination of organs. Comparison of medico-legal data and laboratories results focus on representativeness of autopsy samples. In 2014, a “diatom” sampling kit was developed in the department 3F of the IRCGN. Single-use materials allow standardization of a sampling method at the discovery field and during autopsy. Between 2014 and 2016, the balance of diatoms activity at the IRCGN highlights an increase of analyses and a significant reduction of expertise delays. If the problem of water sampling is being resolved with the use of the kit, the main source of nonconformity always concerns the autopsy sample mass. A lower mass than normally required by the protocol is able to induce the rejection of analysis results. Standardization of a sampling method seems to be an effective solution to the problem of samples non-conformity. Furthermore, study of the “statistical weight” of an organ and blood diffusion phenomena will allow diatoms to give new light in case of suspicion of underlying pathology or sampling problem.
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Simultaneously, recent years have also seen a growing interest in environmental forms of trace evidence; the use of mineral grains [16–18], palynomorphs [19–21], bryophyte shoots [22,23], and algae [24,25] to exclude (or fail to exclude) contact between suspects, victims, objects, and crime scenes within forensic scenarios. One form of evidence that has proved particularly useful within aquatic environments is diatoms; unicellular algae that have traditionally found forensic application within the field of pathology [25–28]. Composed of two silica valves linked by a girdle element, the diatom frustule can be well-preserved within sediments and forensic contexts [25].
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Valves could be extracted from all five footwear materials after 3 min of immersion, and more valves were extracted from the rougher, woven upper materials than the smoother sole materials. Canvas yielded the most valves (a mean of 2511/cm²) and polyurethane the fewest (a mean of 15/cm²). The persistence of diatoms on the three upper materials was addressed with a preliminary pilot investigation, with ten intervals sampled between 0 and 168 h. Valves were seen to persist in detectable quantities after 168 h on all three upper materials. However, some samples produced slides with no valves, and the earliest time after which no diatom valves were found was 4 h after the transfer. Analysis of the particle size distributions over time, by image analysis, suggests that the retention of diatoms may be size-selective; after 168 h, no particles larger than 200 μm² could be found on the samples of canvas, and > 95% of the particles on the samples of suede were less than or equal to 200 μm². A pilot investigation into the effects of immersion interval was carried out upon samples of canvas. Greater numbers of valves were extracted from the samples with longer immersion intervals, but even after 30 s, > 500 valves could be recovered per cm², suggesting that footwear may be sampled for diatoms even if the contact with a water body may have been brief. These findings indicate that, if the variability within and between experimental runs can be addressed, there is significant potential for diatoms to be incorporated into the trace analysis of footwear and assist forensic reconstructions.

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