| [Backgound]Drowning is defined as death from asphyxia within24hours of submersion in water, and always a problem in judicial practice and scientific research in forensic pathology. It has not been accepted and unified that some biological and chemical indexes were sufficiently specific or sensitive for diagnosis of drowning. At present, the detection of foreign plant elements such as diatoms is assessed and the value of diatom test as the "golden standard" is evaluated. In addition, it enables an estimate of position falled in water by testing the diatom species and proportions in bodies and comparing to which are observed among the different waters, because of various shapes, structures, taxonomic characters of each diatom and different features, species compositions of distribution of diatoms in different regions. So the research on diatom test has important value for the key evidence in case of drowning. Nitric acid added ethanol method is the most well rounded and widely used method at present, despite its limitations, among the many diatom laboratory examination methods. Disorganization can method is a new technology for testing diatom developed in recent years, with specific mensurable criteria of time consuming, amout of samples and volume of reagents. It was modified on nitric acid added ethanol method, and had been providing new opportunities in forensic expertise.[Objectives]1. Study the quantity and distribution of diatoms in Xicheng, Dongcheng, Chaoyang, Haidian, Fengtai, Shijingshan District of Beijing City, and draw the map of distribution of diatoms species in central city of Beijing;2. Contrast the dominant population of diatoms about Beijing, Guiyang Municipality, Binzhou, the Changjiang River estuary, Hanjiang catchment, Ulungur River Valley in Xinjiang, Niangziguan Karst spring.3. Present a review on species composition, shapes, structures, taxonomic characters for each taxon, and describes the distribution of diatoms on central city of Beijing;4. To study the optimal experimental conditions (nitric acid consumption, temperature and time for complete digestion) to detect ratio of diatom of rabbit heart, lungs, liver and kidneys by using disorganization can;5. To compare the difference between disorganization can and nitric acid added ethanol method.[Methods]1.80water samples collected from16waters of central city of Beijing were examined by the method of disorganization can, which digested by nitric acid at100℃for0.5h, then centrifuging, washing and conventional smear. To identify the diatom species and proportions of water samples, collect image data under the DotSlide microscope, and draw the map of distribution of diatoms species in central city of Beijing. Moreover, to contrast the dominant population of diatoms about Beijing, Guiyang Municipality, Binzhou, the Changjiang River estuary, Hanjiang catchment, Ulungur River Valley in Xinjiang, Niangziguan Karst spring.2. Rabbits were put to death by air embolism. Four kinds of rabbit tissue of heart, lung, liver and kidney were sampled, and each kind of tissue was divided into180parts, which put in disorganization cans with diatoms for subsequent test. All the cans were detected in groups randomly according to3indexes of experimental condition, including nitric acid consumption (5mL,10mL,15mL,20mL), temperature (100℃,105℃,110℃) and time (60min,75min,90min,105min,120min) for complete digestion.3. Four kinds of rabbit tissue of heart, lung, liver and kidney were digested by disorganization can with different experimental conditions, respectively. All the groups weighted the surplus of organs, selected the groups digested completely (the surplus was less than50mg), and recorded the clarity of background. For the groups digested completely, the statistical quantity of unbroken diatoms, diatom debris, and demolition rate were counted.4. Rabbits were put to death by drowning in a large, glass container with distilled water, mixed diatoms. Four kinds of rabbit tissue of heart, lung, liver and kidney were sampled, and tissues of every rabbit were divided into two groups randomly.5. Four kinds of rabbit tissue of heart, lung, liver and kidney were completely digested by disorganization can with optimal experimental conditions for group A and nitric acid added ethanol method for group B, respectively. Both groups weighted the surplus of organs, and counted the statistical quantity of unbroken diatoms, diatom debris, and demolition rate.6. The data obtained were statistical analyzed by SPSS17.0software.[Results]1. Having analyzed80water samples collected from16waters of Xicheng, Dongcheng, Chaoyang, Haidian, Fengtai, Shijingshan District of Beijing in September and October2011, and mapped the distribution of diatoms species in central city of Beijing, a total of10taxa belonging to10genera,5orders,2classes were identified. Significant differences of diatom species and proportions were observed among the different waters. After contrasting the dominant population of diatoms about Beijing, Guiyang Municipality, Binzhou, the Changjiang River estuary, Hanjiang catchment, Ulungur River Valley in Xinjiang, Niangziguan Karst spring, it is confirmed the distribution of diatoms species was affected by the differences of climate, terrain, water.2. The most appropriate conditions for diatom test in heart tissue were digested at110℃, lasted90min, and the tissues (g) and nitric acid (mL) was at the ratio of2:3. The most appropriate conditions for diatom test in lung tissue were digested at100℃, lasted105min, and the tissues (g) and nitric acid (mL) was at the ratio of2:3. The most appropriate conditions for diatom test in liver tissue were digested at105℃, lasted105min, and the tissues (g) and nitric acid (mL) was at the ratio of2:3. The most appropriate conditions for diatom test in renal tissue were digested at110℃, lasted120min, and the tissues (g) and nitric acid (mL) was at the ratio of2:3. 3. The surplus of organs came up to the standard of complete digestion, and degree of digestion had greater stability by using disorganization can, but nitric acid added ethanol method was not. Moreover, disorganization can had preferable detection rate and lower demolition rate compare to nitric acid added ethanol method.[Conclusion]1. This study confirmed the feasibility of using DotSlide microscope.2. The features of distribution of diatoms in central city of Beijing were summarized, and the map of distribution of diatoms species in central city of Beijing was drew for the first time. We also discussed its meaning in criminal detection. Furthermore, these theoretical and experimental investigations have laid a solid foundation for establishing the diatom database in central city of Beijing.3. This strdy first contrasted the dominant population of diatoms about Beijing, Guiyang Municipality, Binzhou, the Changjiang River estuary, Hanjiang catchment, Ulungur River Valley in Xinjiang, Niangziguan Karst spring, it is confirmed the value of examination of diatom in forensic science.4. This paper presents a review on species composition, shapes, structures, taxonomic characters for each taxon, and describes the distribution of diatoms on central city of Beijing. And the study has laid a solid foundation for determining the position of drowning based on the structures of diatoms.5. The optimal experimental conditions (nitric acid consumption, temperature and time for complete digestion) varied in different tissues because of the quality of heart, lungs, liver and kidneys, which ensured preferable detection rate.6. In contrast with nitric acid added ethanol method, the features of disorganization can are shown as follows:①Less amount of nitric acid;②Little environmental pollution;③Digestion is complete and stabilized;④Diatom damage small;⑤High detection rate;⑥High accuracy of diatom qualitative/quantitative analysis.
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