Diatom test with Soluene-350 to diagnose drowning in sea water

Forensic Diatom Analysis: Where Do We Stand and What Are the Latest Diagnostic Advances?

Background: diatoms are unicellular algae that have been used for more than a century for forensic purposes to diagnose drowning, with more or less success depending on the historical era. Although many years have passed, scientific research on diatoms has never ceased, which testifies to their enduring allure in forensics. Of course, diatom research has evolved and expanded over time, changing with the availability of new techniques and technologies. The volume of articles and their production over a period of many years has resulted in old, current, and new knowledge on diatoms being scattered over a large number of books and articles. Objectives: the purpose of this narrative literature review is, therefore, to summarize all this information and bring it together in a single work that can be useful for those who are studying diatoms and their usefulness for forensics for the first time, for those who are looking for proven methods of analysis, and finally for those who are interested in exploring new frontiers of research. Methods: a comprehensive literature search that included all studies dealing with the applications of diatoms in forensic science was performed in the most popular electronic databases. Results: traditional methods have been complemented by molecular and imaging methods and, more recently, by artificial intelligence. In addition, new biological substrates have been found for the analysis of diatoms. Conclusions: all this has led, on the one hand, to the consolidation of a whole body of knowledge on diatoms, on which this forensic analysis is still based, and, on the other hand, has opened up numerous new research directions.

Diatoms in maggots; a potential tool for drowning diagnosis - A preliminary study

Advanced putrefaction causes extensive loss of soft tissue, rendering it difficult to use the diatom test as a reliable diagnostic tool for drowning investigations. A positive diatom test in carrion insect larvae may provide significant assistance in overcoming the challenge of decomposition. The studies determined the utility of diatom test in carrion larvae on severely decomposed bodies. A modified acid digestion method involving nitric acid, K2Cr2O7 and HCl, was used to digest the blowfly larvae feeding on piglet carrion previously drowned in freshwater and sea water, respectively. Extracted diatom frustules were analysed and characterised using light microscopy coupled to a digital camera. Diatoms recovered from maggots on sea-drowned piglets were similar to diatoms from sea water (drowning medium). Centric diatoms recovered in maggots were higher (200 ± 60 diatoms/ mL) than pennate diatoms (80 ± 20 diatoms/mL). Isolated diatoms common to both maggots and water samples included Coscinodiscus sp. and Navicular spp. Albeit, there were no diatoms recovered from maggots on freshwater-drowned piglets. The findings of this study suggest that the diatom test is still a reliable diagnostic tool to determine if drowning was involved in the death of a fully decomposed body. This is the first study that isolated diatoms from maggots feeding on drowned bodies. It serves as the basis for further research into the utility of maggots for drowning investigations.

DiatomNet v1.0: A novel approach for automatic diatom testing for drowning diagnosis in forensically biomedical application

BACKGROUND AND OBJECTIVE

Diatom testing is supportive for drowning diagnosis in forensic medicine. However, it is very time-consuming and labor-intensive for technicians to identify microscopically a handful of diatoms in sample smears, especially under complex observable backgrounds. Recently, we successfully developed a software, named DiatomNet v1.0 intended to automatically identify diatom frustules in a whole slide under a clear background. Here, we introduced this new software and performed a validation study to elucidate how DiatomNet v1.0 improved its performance with the influence of visible impurities.

METHODS

DiatomNet v1.0 has an intuitive, user-friendly and easy-to-learn graphical user interface (GUI) built in the Drupal and its core architecture for slide analysis including a convolutional neural network (CNN) is written in Python language. The build-in CNN model was evaluated for diatom identification under very complex observable backgrounds with mixtures of common impurities, including carbon pigments and sand sediments. Compared to the original model, the enhanced model following optimization with limited new datasets was evaluated systematically by independent testing and random control trials (RCTs).

RESULTS

In independent testing, the original DiatomNet v1.0 was moderately affected, especially when higher densities of impurities existed, and achieved a low recall of 0.817 and F1 score of 0.858 but good precision of 0.905. Following transfer learning with limited new datasets, the enhanced version had better results, with recall and F1 score values of 0.968. A comparative study on real slides showed that the upgraded DiatomNet v1.0 obtained F1 scores of 0.86 and 0.84 for carbon pigment and sand sediment, respectively, slightly worse than manual identification (carbon pigment: 0.91; sand sediment: 0.86), but much less time was needed.

CONCLUSIONS

The study verified that forensic diatom testing with aid of DiatomNet v1.0 is much more efficient than traditionally manual identification even under complex observable backgrounds. In terms of forensic diatom testing, we proposed a suggested standard on build-in model optimization and evaluation to strengthen the software's generalization in potentially complex conditions.

Diatoms: A Review on its Forensic Significance

Diatoms also called as the ‘jewels of sea’ are microorganisms which are extensively found in the aquatic system. These unicellular organisms make up nearly half of the biological material in the water body. It is also one of the most significant biological evidence that is obtained in case of drowning. The diatoms that infiltrate inside the body of the deceased may serve as a corroborative or even conclusive evidence to support the diagnosis of death. These diatoms also help in ascertaining whether the drowning is ante-mortem or post-mortem. The review discusses the current extraction procedures and microscopic examination techniques used in forensic science for diagnosis of death by drowning.

Use of cadaveric vitreous humor as an innovative substrate for diatoms research and forensic diagnosis of drowning

The search for diatoms is the test that most of all may contribute to the forensic diagnosis of drowning. Diatoms can be extracted through different methods, which are all complex and long. In this preliminary study, we assessed human vitreous humor as an innovative substrate on which to research diatoms. Sampling and analyses were performed on 3 groups of 10 corpses each. The first one was composed of drowned victims. The second one of victims of traffic accidents with subsequent projection in water; based on the severe traumatic injuries reported at autopsy, we considered such victims as ideally assimilable to bodies immersed in water postmortem. The third group was composed of subjects who died for natural causes and without any relationship with water. The vitreous humor was centrifugated and cytocentrifuged and spotted on two different histological slides: one was left blank and the other one was assessed with hematoxylin and eosin staining. Microscopic observation successfully revealed diatoms in all cases of the first group; in the second group diatoms were not detected in 6 cases; in the third group, no diatoms at all were observed. Diatoms were always qualitatively and quantitatively consistent with those found in the corresponding viscera and waters, which had been investigated through classical acid digestion. Our analyses have demonstrated that the vitreous humor behaves in a completely similar way to the other viscera in cases of drowning. Although further investigations are necessary, vitreous humor has proved to be an innovative, suitable, and reliable substrate for the forensic research of diatoms.

A quantitative comparison between using sodium hypochlorite as a digestion method for the diatom test and the conventional method using fuming nitric acid

OBJECTIVE

To determine the efficacy of using sodium hypochlorite (NaClO, Purelox) as a simple and rapid alternative digestion method for the diatom test through a quantitative comparison with the conventional method that uses fuming nitric acid (HNO₃).

MATERIALS AND METHODS

In experiment 1, using 30 water samples, the NaClO and HNO₃ methods were compared using paired t-test. In experiments 2 and 3, we included blank human lung plus 13 water samples and total of 32 drowned human lung samples, respectively, to compare the NaClO and HNO₃ methods using paired t-test. The relationship between the concentration ratio and background factors was tested in experiment 3. Welch's t-test was used to determine differences in the ratio between the lung side and sex, whereas Pearson's correlation coefficient was used to determine the correlation between the ratio and either age or postmortem interval. The geometric mean of two counts was used for each specimen and all counts were logarithmically transformed to base 2 in the statistical analysis.

RESULTS

The NaClO method was completed within 80 min for any sample. In experiment 1, there was no significant difference between the NaClO and HNO₃ methods using water samples (the mean of the ratios: 0.99, 95% confidence interval (95%CI: 0.89-1.10, P = 0.80). In experiment 2, the count of the NaClO method was lower than that of the HNO₃ method using lung plus water samples (the mean of the ratios: 0.47, 95% CI: 0.35-0.65, P = 0.0002). In experiment 3, the concentration of the NaClO method was lower than that of the HNO₃ method using drowned lung samples (the mean of the ratios: 0.28, 95% CI: 0.20-0.38, P < 0.0001). A weak correlation between the postmortem interval and the ratio of the two methods was observed (r = -0.58, P = 0.012), although no difference between lung sides or sexes were detected (P = 0.87 and P = 0.50, respectively) and no correlation occurred between age and the ratio (r = 0.15, P = 0.43).

CONCLUSION

Using NaClO as a simple and rapid digestion method for diatom testing of water samples would be an excellent alternative to conventional methods. Although the method's diatom detection rate for the lung samples was not optimal, it was still shown to be a feasible method.

Diatom extraction: A new technique with heated H2O2. A technical note

The best method of diatom identification in animal and human tissues is still an important discussion topic, in terms of effectiveness and reliability. In this technical note, authors propose a new method of extraction of diatoms using heated hydrogen peroxide from animal and human tissue samples. This method has been compared with the traditional method of digestion with acids. The results of the comparison show that heated hydrogen peroxide extraction is more efficient in terms of reduction of sediment, extraction of the material and preservation of diatoms proving to be a viable alternative to conventional approaches with acids in terms of costs and operator safety.

An efficient method for building a database of diatom populations for drowning site inference using a deep learning algorithm

Seasonal or monthly databases of the diatom populations in specific bodies of water are needed to infer the drowning site of a drowned body. However, existing diatom testing methods are laborious, time-consuming, and costly and usually require specific expertise. In this study, we developed an artificial intelligence (AI)-based system as a substitute for manual morphological examination capable of identifying and classifying diatoms at the species level. Within two days, the system collected information on diatom profiles in the Huangpu and Suzhou Rivers of Shanghai, China. In an animal experiment, the similarities of diatom profiles between lung tissues and water samples were evaluated through a modified Jensen-Shannon (JS) divergence measure for drowning site inference, reaching a prediction accuracy of 92.31%. Considering its high efficiency and simplicity, our proposed method is believed to be more applicable than existing methods for seasonal or monthly water monitoring of diatom populations from sections of interconnected rivers, which would help police narrow the investigation scope to confirm the identity of an immersed body.

Development of 18S rRNA gene arrays for forensic detection of diatoms

Diatom test is the most commonly used method to diagnose drowning in forensic laboratories. However, microscopic examination and identification of diatom frustules is time-consuming and requires taxonomic expertise. At present, the identification of drowning is still a challenge in forensic casework. In this study, we developed a novel diatom microarray based on the detection of specific 18S rRNA gene fragments of diatom species. The array covers 169 diatom species which were documented as commonly found in a wide range of fresh waters in China. Diatom arrays were prepared from species specific oligonucleotide probes targeting to variable regions of the 18S rRNA gene. We also developed an auxiliary sample preparation method for isolation of diatom DNA from tissues, which enabled detection of diatom species in real forensic samples as well as environmental waters. We applied the diatom arrays to analyze six drowned cases and eight environmental samples. The diatom arrays showed much better sensitivity and more consistent results than those of the conventional SEM methods. We discovered major discrepancies between results generated by the diatom arrays and the routinely used SEM based diatom tests. We verified the results of our diatom arrays by species specific PCR and Sanger sequencing and found that the currently used SEM diatom test method has a serious deficiency in sensitivity due to high loss rate of frustules in the sample preparation procedure. We anticipate that the application of diatom arrays will transform current forensic practice of diagnosing drowning deaths.

Detection of Diatoms by a Combination of Membrane Filtration and Transparentness. J Forensic Sci 2016;61:1643-1646. [PMID: 27507158 DOI: 10.1111/1556-4029.13181] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Diagnosis of drowning remains a difficult issue in current forensic sciences. A large number of diatoms were lost by removing the supernatant after centrifugation in the conventional forensic diatom test. We developed a novel membrane filtration method to enrich diatoms from samples. A new solution using different ratios of acetic acid and eugenol is prepared to make the membrane transparent. These processes allow the diatom-containing membrane to be visualized and identified easily by light microscopy. The tissues contaminated by water rich in diatoms were detected by the new method for the recovery of diatoms. Eleven drowning cases were analyzed by both the new method and the conventional method to compare the sensitivity of both methods. The recovery of the novel diatom test method was 54.2 ± 23.1%. The positive rate of the novel method has been proven to be superior to the conventional method in the diagnosis of drowning.

Diatoms in forensic analysis: A practical approach in rats

A diagnosis of drowning is a challenge in legal medicine, as there is generally a lack of pathognomonic findings indicative of drowning. Diatom analysis has been considered very supportive for a diagnosis of drowning, although the test is still controversial for some investigators. We assessed diatoms association with drowning in the peripheral tissues of drowned rats and the effects of the drowning medium on the diatom yield. A modified acid digestion method was optimised for diatom recovery in water and rat tissues. Eighteen adult Wistar rats were employed for the study, subdivided into six groups of three rats. Groups 1, 3 and 5 were drowned in seawater, lake water, or river water respectively, while groups 2, 4 and 6 were controls (immersed after death in seawater, lake water or river water respectively). Water samples were taken from the sea, lake and river in Málaga and Córdoba (Spain) for the purposes of diatomological mapping and drowning of the rats. Diatoms were successfully recovered from all water samples and matched with tissues of the drowned rats. There were significant differences in diatom numbers between control and test samples for all the tissues studied, as well as within test samples. Histological investigations conducted on lung samples obtained from drowned rats provided complementary and valuable information. This study demonstrates the feasibility of the diatom test as a reliable method for the diagnosis of drowning, especially if adequate precautions are taken to avoid contamination, and if interpretation of the analysis is performed in light of other complementary investigations.

Application of the microwave digestion-vacuum filtration-automated scanning electron microscopy method for diatom detection in the diagnosis of drowning

The cause of death for the decomposed corpses recovered from water is still a difficult issue in current forensic practice. In this article, we present two cases of bodies recovered from water with no positive findings to indicate the cause of their death. We apply both conventional acid digestion method as well as the microwave digestion-vacuum filtration-automated scanning electron microscopy method (MD-VF-Auto SEM) for diatom detection in different organs of both bodies. Our results indicate that MD-VF-Auto SEM method provide more accurate information and match further police investigation. This novel method would be a useful technique in assessing cause of death for body found in water.

A simple digestion method with a Lefort aqua regia solution for diatom extraction

Presence of diatoms in tissues has been considered as a significant sign of drowning. However, there are limitations in the present extraction methods. We developed a new digestion method using the Lefort aqua regia solution (3:1 nitric acid to hydrochloric acid) for diatom extraction and evaluated the digestive capability, diatom destruction, and diatoms' recovery of this new method. The kidney tissues from rabbit mixed with water rich in diatoms were treated by the Lefort aqua regia digestion method (n = 10) and the conventional acid digestion method (n = 10). The results showed that the digestive capability of Lefort aqua regia digestion method was superior to conventional acid digestion method (p < 0.01); the structure of diatom remained almost intact; and the recovery of diatom was comparable to the conventional acid digestion method (p > 0.05). The Lefort aqua regia reagent is an improvement over the conventional acid digestion for recovery of diatoms from tissue samples.

Testing the specificity of the diatom test: search for false-positives

The diatom test is widely used by forensic pathologists as proof of drowning, notwithstanding some criticisms mainly concerning the occurrence of false-positive results (presence of diatoms in the tissues of subjects who died from causes other than drowning). The aim of the present study was to verify the claimed inaccuracy of the method caused by an excessive rate of false-positives related to inadvertent exposure to diatoms of the general population. The study was carried out to investigate the presence of diatoms in the tissues (lungs and sternum) of subjects who died from causes other than drowning. Two groups of cadavers that underwent an autopsy at the Institute of Forensic Medicine of the University of Verona were included in the study. Group A comprised 45 individuals who died from causes other than drowning, whereas Group B comprised 20 bodies which had been recovered from water. The extraction of the diatoms was performed by incubation of samples in nitric acid for 48 hours at 60°C. The analysis of the samples from Group A showed the absence of diatoms in both lung and sternum samples. In Group B all lung samples showed the presence of diatoms, whereas only six sternum samples were shown to contain diatoms. The difference between Groups A and B was statistically highly significant. The absence of diatoms in the samples collected from Group A falsified the hypothesis that false-positive results from the diatom test may occur due to diatoms entering living bodies through the respiratory and/or digestive tracts via air, water or food, supporting the validity of the diatom test as proof of drowning.

Development and standardization of a microalgae test for determining deaths by drowning

The diatom test for the diagnosis of drowning is widely used in countries of the Northern Hemisphere such as France and Japan. In Latin America, however, it has not been adopted as a routine procedure in forensic autopsies. In aquatic ecosystems, dinoflagellates and some chlorophytes are microalgae that, like diatoms, have cell walls and other resistant structures. As a result, they can be found in tissues from drowning victims, which is important because diatoms may be rare under particular environmental conditions. On this basis, we propose to extend the "diatom test" to include other microalgae for the determination of death by drowning. In this work, we developed a standardized procedure for detecting microalgae in tissues from drowning victims, with techniques described in the international literature and designed by us. The corpses were recovered from coastal areas in Antofagasta Region, Chile, during summer 2005. The most effective procedure for the treatment of water and tissue samples involved the combination of enzymatic digestion (proteinase K) and chemical digestion. The technique allowed the recovery of dinoflagellate evidence belonging to genera Prorocentrum, Ceratium, Dinophysis and Protoperidinium; silicoflagellates of the genus Dictyocha; an undetermined, filamentous chlorophyte; entire valves of centric diatoms and fragments of pennate and centric diatoms. This is the first protocol using microalgae other than diatoms for forensic cases in Latin America, and particularly in Chile.

Evaluation of four digestive methods for extracting diatoms

OBJECTIVE

To compare the merit of four digestive methods (nitric acid plus hydrogen peroxide, proteinase K, nitric acid in Disorganization Can and Soluene-350) for extracting diatoms in order to choose the best digestive method for the diagnosis of drowning.

METHODS

Liver, kidney and bone marrow of rabbits were minced and then digested by four digestive methods separately with the following indices compared: (1) time demanded for complete digestion; (2) degree of digestion for different tissues; (3) the reclaiming ratio of diatoms; (4) the degree of digestive destruction to diatoms.

RESULTS

For sufficiently digesting the same tissue, the demanded times for the different methods ranked from the longest to the shortest were as follows: Soluene-350, proteinase K, nitric acid plus hydrogen peroxide, nitric acid in Disorganization Can. Nitric acid in Disorganization Can method and nitric acid plus hydrogen peroxide method digested the tissues more thoroughly than proteinase K, than Soluene-350 methods. For Cyclotella and Cybella, proteinase K method reclaimed most diatoms and nitric acid plus hydrogen peroxide method reclaimed less, while nitric acid in Disorganization Can and Soluene-350 methods reclaimed the least. For Navicula, the majority of diatoms could be extracted using proteinase K method, but only a few diatoms with other three methods. Under scanning electron microscopy (SEM), the structure of diatoms remained almost perfect after digestion with proteinase K, but destroyed to some extent with other three methods.

CONCLUSION

This study demonstrated that different diatoms (in fresh or sea water) have different resistance to different digestive reagents. As far as the reliability and applicability of the diatom test is concerned, proteinase K method is of the best choice, nitric acid plus hydrogen peroxide can be its substitute. Soluene-350 cannot be used for extracting sea water diatoms.

The Development and Application of a Diatom-Based Quantitative Reconstruction Technique in Forensic Science

Diatoms are a group of unicellular algae that have been recorded and classified for over 200 years and have been used in a range of applications in forensic science. We have developed a quantitative diatom-based reconstruction technique to confirm drowning as a cause of death and localize the site of drowning in two recent, high-profile, case studies. In both case studies we collected diatom samples from the local and/or regional area to act as a control in the examination of diatom assemblages associated with lungs and clothing. In Case Study 1 the modern analog technique suggested that all lung and clothing samples have statistically significant similarities to control samples from shallow water habitats. In Case Study 2, the analog matching suggested that the majority of lung samples show a statistically significant relationship to samples from a pond, indicating that this was the drowning medium.

Drowning: still a difficult autopsy diagnosis

Investigation of bodies recovered out of water comprises an important proportion of the medico-legal requests. However, the key question whether the victim died due to "true" drowning can frequently not easily be solved. In addition, the diagnosis of hydrocution is even more difficult. In this manuscript, a review of reported diagnostic methods is discussed in order to provide guidelines, which can be used in current forensic practice. In particular, the (dis)advantages of various biological and thanato-chemical methods, described in literature during the last 20 years, will be confronted with the classical techniques such as the detection of diatoms and algae. Indeed, the diatom test is still considered as the "golden standard". In conclusion, the ideal diagnostic test as definite proof for drowning still needs to be established. At present, the combination of the autopsy findings and the diatom test is a good compromise in arriving at a conclusion. Additional biochemical and technical methods could be useful. Unfortunately, the cost-benefit analysis in current practice could be hard to defend. However, the importance of this subject asks for further scientific approaches and research.