The Comparative Study Of Four Diatom-Test Methods

Objective To compare the advantages and disadvantages of four methods (nitric acid added ethanol, enzymatic digestion, disorganization can and Soluene-350) for extracting diatom in order to provide theoretic basis for selection in medico-legal practice.Methods 56 rabbits of either sex weighed 2.5-3.5 kg, were randomly distributed into group A, B, C, D and E. There are 16 rabbits in group A,B and 8 rabbits in group C, D and E. The rabbits were killed , 2g tissue(Liver, kidney and bone marrow) were minced and then digested by nitric acid added ethanol, enzymatic digestion, disorganization can and Soluene-350 for group A. Time for complete digestion of above three different tissues were analyzed. After killing the rabbits, 2g tissue (Liven kidney and bone marrow) were minced and then digested by these four methods for group B. The digestive degree of different tissues in the limited time (2 hours) were compared and so the digestive capability of each method can be analyzed. In group C, the rabbits were killed and 2g minced tissue (kidney) added some Cyclotella(fresh water) were digested by these four methods, reclaiming ratio of diatom (Cyclotella) of each method was analyzed. In group D, the experimental methods underwent the same process as the group C except the diatom (Cybella, fresh water), reclaiming ratio of diatom (Cybella) of each method was also analyzed. In group E, the experimental methods underwent the same process as the group C except the diatom (Navicula, sea water), reclaiming ratio of diatom (Navicula) of each method was analyzed. For group C, D and E, their destruction to diatom were analyzed using Scanning Electronic Microscopy (SEM).Results The longest time was spent for digesting 2g different tissues with Soluene-350, the second longest time by enzymatic method, the third by nitric acid added ethanol method and disorganization can required the shortest time. Disorganization can had the strongest digestive capability, nitric acid added ethanol method took the second place, enzymatic digestion method the third, and Soluene-350method the weakest. For Cyclotella and Cybella, reclaiming ratio of diatom by enzymatic digestion method was the highest, then nitric acid added ethanol method, disorganization can method and Soluene-350 method the lowest. For Navicula, a majority of diatoms could be extracted by enzymatic digestion method, while only a few diatoms could be detected by other three methods. Under scanning electronic microscopy (SEM), the structure of diatoms remained almost intact by enzymatic digestion method but destroyed by the other three methods.Conclusion when selecting the diatom-test method in medico-legal practice, Nitric acid added ethanol method and disorganization can method should been selected firstly because these were better than others in terms of saving money and time in practice. Enzymatic digestion method should been selected if safety and environmental protection were considered, or the drowning fluid was sea water and less diatoms were found in it. Soluene-350 method had the disadvantages of being time-consuming and expensive, in addition, reclaiming ratio of diatom was low and Soluene-350 was not easy to be bought in china, so it was inapplicable in our country.