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

To study the quantitative effect of ethanol on the diatom test for water and lung samples.

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.

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.

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.