A Brief Study On Building Quantitative Diatom Analysis System On The Certain Species Of Cyclotella

?Background and Purpose?Every forensic operator wants to be in good charge of exposing crimes and upholding justice,to solve cases and at the same time consoling the alive.But there are still some dark clouds hanging around their eyes,and the diagnosis of “true drowning” is one among them.Even though nowadays the development of science and technology indeed helps a lot,there are still difficulties in distinguishing true drowning and postmortem immersion,and these two diagnoses indicate two different detective thoughts of converse directions.So,it is of extreme importance to confirm the property of an underwater corpse's death within a short period of time so as to offer accurate investigative direction.Being treated as a routine experimental work which enjoys widespread adoption in assisting the diagnosis of drowning,the diatom test,whose outcome usually gives the final words as the proof of drowning,often plays a significant role in the investigations of cadavers involved in waters.Also,researches on the issue of diatom test coincide the development direction of evidence based science and can build solid foundations to confirming the demand of overall national interest and the judiciary in need of evidence.The diagnosis of drowning still has some unsolved problems in contemporary forensic science,for that drowning itself has no specific signs macroscopically.The corpses underwater are vulnerable to the environment and those non-specific postmortem signs often vanish in a very short period of time,which adds to the trouble in making diagnosis.Labor-intensive as it is,the diatom test remains the golden standard at present.If practiced properly in expelling any possible exogenous contamination,the result of diatom test can be trusted.The quantitative evaluating criteria of diatom test reached no consensus yet.The research on this criterion can no doubt contribute to the diagnosis of drowning and in result making diatom test more reliable.The earlier literatures manifests that the diatom species of Cyclotella is in dominate proportion of all species in local waters in Wuhan city.This research focus on Cyclotella as a sole diatom species under study,trying to make a quantitative evaluating criterion of this species in diatom test,in order to conduct new thesis on the diagnosis of drowning,and at the same time helping the investigations of water involved corpses around Wuhan city.The reported diatom analyzing methods vary a lot,including acid digestion method,enzyme digestion method,Soluene-350 method,microwave digestion method,et.al,but they all keep their own drawbacks.At the same time,the widely-adopted diatom concentration procedure of centrifuging the solution at 4000 rpm after digestion carries diatom loss during experiment.Recently,the invention of microwave digestion-vacuum filtration(MD-VF)conquered the difficulties occurred in the conventional digestion methods.At the same time,the use of digital virtual sliced workstation(OLYMPUS-DotSlide)and the “three districts,four quadrants and two fields” counting method makes it possible for us to do qualitative diatom analysis easily and of more accurate.In this study,we use the kieselguhr that contains only Cyclotella and double distilled water of high purity to create water samples of different diatom densities,and use these water samples to drown rats to death.After noncontaminated autopsy on rats,we extract the internal organs which were then used for diatom test separately.Using the MD-VF method to substantiate digestion and diatom concentration procedure,we conduct a quantitative diatom analysis using digital virtual sliced workstation and the “three districts,four quadrants and two fields” counting method,aiming at building a quantitative diatom analysis system on the Cyclotella as an example for all diatom species.Taking all previous reaches into combination,we want to prove that the diatom test is of great importance and reliable accuracy in drowning diagnosis.?Material and Methods?We set SD rats as objects to be studied and 90 rats were divided into 4 groups,namely the drown group,the postmortem immersion group,and the control group.Each group contains 10 individuals and were drowned in 5 water conditions of different diatom density.The rats in postmortem immersion groups were sacrificed before putting into water.3 groups were all immersed in water for 30 minutes and afterwards autopsy on them was conducted and the inner organs were extracted for further diatom test.After successful digestion and diatom concentration,a quantitative diatom analysis was conducted.Using Microsoft Excel and SPSS 22.0 for Windows,we use the quantitative data for statistical analysis.?Results? 1.The diatom density in all organs from the rats of the drown group revealed a positive correlation relationship with the diatom density in the water sample.2.The positive rate of diatom in all organs raises as the density of diatom in water sample elevates.3.The sensitivity of kidney,spleen,and heart is high in the diatom test.4.The diatom density in inner organs are not isolated separately,they have correlations in one another.The diatom density ratio of Lung to liver,whose positive rates are relatively high,is supportive in diagnosing drowning.5.The control group is found diatom negative.And this ensures that there is no contamination during the experiment.6.The group postmortem immersion is found diatom negative.7.Building this qualitative system in diatom analysis is of great importance in drowning diagnosis.The diatom density data revealed in each organ can beinformative and of investigative value in diagnosing drowning and original scene speculating.?Conclusion?This study uses the newly invented MD-VF method,digital virtual sliced workstation and the “three districts,four quadrants and two fields” counting method substantiating diatom quantitative analysis.Based on experimental data,the relationship between the diatom density value in organs and water sample is confirmed,and at the same time the regression equation in each organ is built.This result makes a further interpretation in that the density of diatom in each organ has relationship with the density in water sample.This indicates the positive result of diatom test must be relied on a comprehensive analysis combining all quantitative analysis results together.This quantitative system can be used to make assessments in the density of water sample and organs,this makes sense in the diagnosis of drowning and the estimation of possible crime scenes.