Where does most tissue contamination from floaters occur?

• A. Deparaffination steps.
• B. Embedding steps.
• C. Section mounting steps.
• D. Staining steps.

Answer: (A)

Floaters cause contamination most often when tissues are in liquid baths, because fragments can freely move and spread. During deparaffinization, slides with tissue sections are immersed in large volumes of solvent that completely cover the tissue. If a fragment detaches, it can float around, potentially attaching to other slides, racks, or instruments and spreading to multiple samples. Other steps involve more solid handling or milder contact with liquids, so there’s less opportunity for loose fragments to disperse widely. Keeping sections well-adhered and handling baths carefully helps reduce this risk, but the solvent-based deparaffinization step is the stage where floating tissue pieces are most likely to cause cross-contamination.