Mercury pigment in tissue sections is:

• A. Preventable and can be removed with iodine followed by Sodium Thiosulfate.
• B. Not preventable, and can be removed with iodine followed by Sodium Thiosulfate.
• C. Preventable and can be removed with alcoholic picric acid.
• D. Removable with distilled water.

Answer: (B)

Mercury pigment is an artifact that comes from tissues fixed with mercurial fixatives (such as Zenker’s or Helly’s). The mercury in the fixative can deposit as a dark pigment in the tissue, and this pigment tends to persist despite routine processing, making it not practically preventable in standard workflows.

The way to address it is a two-step decolorization/removal method: first treat the section with iodine to convert the mercury deposits into a form (like mercuric iodide) that is more soluble, then treat with sodium thiosulfate to complex and dissolve those mercury compounds so the pigment is removed during washing. This combination reliably clears the pigment from the section, enabling proper subsequent staining.

Distilled water won’t remove the pigment, and alcoholic picric acid isn’t an established method for removing mercury pigment.