Zinc deposits and elevated levels in prostate and metastases from its tumours may be demonstrated with dithizone (diphenylthiocarbazone).
Zinc salts were recommended as fixing agents many decades ago, but fixatives incorporating them were not popular. Most microscopists preferred the superior mercuric chloride containing mixtures. When concerns about the toxicity of mercury and its potential for pollution became clear, zinc chloride was suggested as a substitute, and those earlier mixtures have been revisited.
Concerns about the dumping of zinc salts instead of mercury salts into our water systems are still valid. As with all laboratory reagents, care should be taken to ensure proper collection and disposal of the waste fixative. It should be noted that zinc is an essential element for human metabolism, unlike mercury, and less harm is done to the environment by its use, but less harm does not equate to no harm.