Cleaning protocol for mercuric chloride–contaminated herbarium cabinets at the Smithsonian Museum Support Center

Mercuric chloride has been used to control insect and fungal infestations in natural history collections for the past two centuries. Due to health concerns, its use was discontinued in the mid-1980s, but specimens treated with mercuric chloride are commonly found in modern collections and present a hazard to collection staff and researchers. Cabinets used to store mercuric chloride–treated specimens also become contaminated with the substance and represent a source of exposure even after specimens are removed. A team at the US National Herbarium, in coordination with the Smithsonian’s Office of Safety, Health and Environmental Management, developed a protocol to clean herbarium cabinets that were contaminated with mercuric chloride. Cabinets were cleaned with 70% ethanol and laboratory wipes, and effectiveness was measured using a portable mercury vapor analyzer and surface wipe sampling. Cleaning with ethanol was found to be more effective than just removing treated specimens, but the differences in reduction of airborne and surface mercury concentrations were not statistically significant. This study provides important insight and guidance for museums seeking to eliminate legacy mercuric chloride contamination from their herbarium cabinets.