Effect of ethanol on the diatom test using nitric acid or sodium hypochlorite.

OBJECTIVE: To study the quantitative effect of ethanol on the diatom test for water and lung samples. MATERIALS AND METHODS: In experiment 1, we tested 20 water samples taken from natural water areas. In experiments 1-1 and 1-2, each sample was digested with sodium hypochlorite (NaClO) solution (Purelox) and fuming nitric acid (HNO3), respectively. In Experiments 1-3 and 1-4, each sample was added to a lung sample containing few diatoms and digested with NaClO and HNO3, respectively. In Experiment 2, eight lung samples containing diatoms were digested with NaClO. Then, each digested sample was divided into two portions; one portion was washed with ethanol before being washed with water, and the other was washed only with water. After base-2 logarithmic transformation, the counts from the methods with and without ethanol wash were compared with a paired t-test. RESULTS: In experiments 1-1, 1-2, 1-3, 1-4, and 2, the geometric means of the ratios derived from the two methods (with/without ethanol) were 0.70 (95 % confidence interval [CI]: 0.65-0.77, P < 0.001), 0.83 (95 % CI: 0.73-0.93, P = 0.005), 3.00 (95 % CI: 2.31-3.91, P < 0.001), 0.91 (95 % CI: 0.79-1.04, P = 0.164), and 3.06 (95 % CI: 2.28-4.41, P < 0.001), respectively. CONCLUSION: Our experiments suggest that ethanol would be useless in diatom tests of water samples or in the conventional (HNO3) digestion of lung samples. However, ethanol is essential for the NaClO digestion of lung samples and could also be useful for other alternative methods of lung samples.

The effect of ethanol or long-time reaction on the diatom test in water samples using sodium hypochlorite.

BACKGROUND: The diatom test method using sodium hypochlorite (NaClO) was equivalent to the conventional method in water samples. However, the method using NaClO was inferior to the conventional method in lung samples, in which ethanol was used and the reaction with NaClO was longer compared with the method in water samples. Using water samples, we aimed to clarify whether these differences affect the diatom test result. MATERIALS AND METHODS: Thirteen water samples from natural water sources were each divided into four parts corresponding to four (2 × 2) digestion methods: 3 "digestion" vs. 1 "digestion" and with ethanol vs. without ethanol. After the base-2 logarithmic transformation, the diatom counts were analyzed using three-way analysis of variance (ANOVA); factor 1 was "digestion times," factor 2 was "ethanol," and factor 3 was "sample number," and the interaction between factors 1 and 2 was also analyzed. RESULTS: The geometric means of the diatoms from the 3 "digestion" with ethanol method, the 3 "digestion" without ethanol method, the 1 "digestion" with ethanol method, and the 1 "digestion" without ethanol method were 373.5, 551.8, 436.6, and 522.0, respectively. ANOVA showed a significant difference in factor 2 (P = 1.7 × 10-4). There was no significant difference in factor 1 (P = 0.46), and no significant interaction between factors 1 and 2 (P = 0.13). CONCLUSION: Ethanol may decrease the diatom count in the diatom test using NaClO. In contrast, the diatom frustules do not dissolve through three-times digestion using NaClO.

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.