Preservation of diatom material

If the sample is to be processed within a few hours, then no preservative is necessary so long as steps are taken to minimize cell division (i.e. by storage in cool, dark place). For short-term storage, the sample can be stored either in refrigerator or Lugol’s iodine may be added. However, Lugol’s iodine sublimates and is unsuitable for long-term storage of samples, for which Ethanol is recommended. Ethanol should be added to reach a final concentration of 20% by volume. Formalin is a preservative commonly used for algal samples, it should be avoided as it is carcinogenic and it damages the fine structure of diatoms (Kolbe, 1948 and Krammer and Lange-Bertalot, 2000). Riemann (1960) demonstrated that formalin — even in extremely low concentrations — causes silicic acid to be released from diatom valves. Appropriate health and safety guidelines must be followed when using these preservatives and the name of the preservative should be marked on the outside of the bottle.