A Simple, Inexpensive Method for Cleaning Diatoms

Abstract

Diatom frustules are rapidly and inexpensively cleared of protoplasts using commercially available bleach (5.25% sodium hypochlorite). A comparison of periphyton subsamples cleaned by the bleach method described, and the standard nitric acid/potassium dichromate method, showed little difference in the extent to which frustules are disjoined (hypotheca from epitheca). A community analysis of subsamples showed no differences in taxa or disappearance of small forms when comparing the two methods. No sample heating, subsequent treatment, or fume hoods are required for this procedure. Traditionally, diatom cleaning techniques have involved the use of strong acids, alone or in combination with chemical agents, to dissolve protoplast material. Van Heurck (1896) reviewed methods used by nineteenth century diatomists; his own procedures involved use of either boiling nitric acid, or boiling sulfuric acid with added potassium chlorate. He cautioned that the nitric acid emits harmful fumes, but with the latter method there is risk of explosion. In the more recent literature, hot sulfuric acid with added potassium dichromate (Patrick & Reimer, 1966) and boiling nitric acid with potassium dichromate (American Public Health Association, 1981) are recommended to clear diatom frustules. Heating of either acid requires use of a fume hood or other ventilating device. The technique using hydrogen peroxide and potassium dichromate or potassium permanganate (Werff, 1955) was proposed as an alternative to the acid cleaning methods. This method, however, involves a sometimes violent reaction. In addition, hydrogen peroxide is relatively expensive to use when numerous samples are involved. A more thorough review of modern diatom cleaning techniques is given by Ma & Jeffery (1978). Commercially available bleach (5.25% sodium hypochlorite) has been used by others to clear aquatic plant leaves to enable direct microscopic viewing of periphytic assemblages (Carter, 1982) and to clear zooplankton for identification of their gut contents (Infante, 1978). In this paper, we describe a onestep cleaning method to clear diatom frustules using bleach, followed by a succession of rinsings and decantations, which produces material equivalent to This method was developed for use in a study of Missouri River periphyton supported by U.S. Army Corps of Engineers Contract DACW45-83-C-0206 to G. L. Hergenrader. Verification of diatom taxa at the Diatom Herbarium of the Academy of Natural Sciences of Philadelphia was made possible through McHenry Funds awarded to J. Carr by the Academy. Assistance and encouragement by Dr. Charles W. Reimer of the Academy of Natural Sciences and G. A. Cunningham is gratefully acknowledged. 2 Present address: Department of Forest Resources, 110 Green Hall, 1530 North Cleveland Ave., St. Paul, Minnesota 55108, U.S.A. TRANS. AM. MICROSC. SOC., 105(2): 152-157. 1986. ? Copyright, 1986, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.110 on Wed, 14 Dec 2016 05:02:35 UTC All use subject to http://about.jstor.org/terms VOL. 105, NO. 2, APRIL 1986