Are mercury pigments and acid hematin deposited in tissue during formalin fixation?

• A. True
• B. False
• C. Not stated
• D. Only mercury pigment is deposited

Answer: (A)

Pigment deposition can occur in tissue as a result of the fixation and processing reagents used, not just from the normal tissue components. Mercury pigments come from fixatives that contain mercuric salts; when tissue is fixed with such fixatives, mercury can become deposited as pigment within the tissue. Acid hematin, on the other hand, forms when tissue (often fixed in formalin) is exposed to acidic conditions used for specific histochemical techniques to visualize hemoglobin-containing cells. The acidic environment converts heme to hematin, which appears as a brown-black pigment in the tissue. Because both scenarios involve reagents or processing steps that occur during or after formalin fixation, both mercury pigments and acid hematin can be deposited in tissue during formalin fixation and subsequent processing.