Electron probe x-ray microanalysis of arsenic inclusions in fish.

Abstract

Adult green sunfish were exposed to aqueous solutions of arsenic as sodium arsenate and sacrificed at regular intervals for morphological and analytical procedures including scanning transmission electron microscopy (STEM), electron probe X-ray microanalysis (XRMA), high voltage electron microscopy (HVEM), and conventional transmission electron microscopy (CTEM). The CTEM and HVEM data indicated that the inclusion is not associated with the nucleous and that it is composed of bead-like subunits arranged linearly to form a structure which twists and coils throughout the nucleus. The use of specimen preparation procedures eliminating osmium tetroxide post-fixation, as well asen bloc and post-stains, allowed visualization of the inclusion despite reduction in contrast compared to specimens prepared by standard methods. Therefore, prior to STEM and XRMA analyses, it was assumed that this unusual morphological entity represented an arsenic deposit which initiated some cytotoxic reaction and subsequent preferential staining in the standard osmium-fixed, stained specimens. The XRMA and STEM data verify the presence of arsenic within the arsenic inclusion; in addition, the ratio of the arsenic K photopeak to the sulfur photopeak was 6 to 1—perhaps indicative of a direct association between arsenic and sulfur-rich protein molecules. The possibility was also considered of arsenate substitution for phosphate on deoxyribonucleic acid.