An inexpensive method to test for mercury vapor in herbarium cabinets

Abstract

Mercuric chloride has been used for control of insect and fungal infestations in herbarium collections for over two centuries. One of the lasting effects of this use is the long­term evolution of elemental mercury vapor from treated specimens. The vapor can contaminate untreated specimens sharing the same closed environment and can pose a human health hazard. By modifying the technique for use of a commercially available mercury indicating powder (Mallinckrodt Baker, Inc., J. T. Baker Mercury Indicator) it is possible to create an inexpensive and fairly rapid test for mercury vapor in herbarium cabinets. The indicator is mixed with deionized water and applied to glass microscope slides. One or more slides are placed inside a cabinet and any color change in the indicator is compared to unexposed controls. In the authors’ experiments, the indicator results were compared against readings taken using a Jerome 431­X Mercury Vapor Analyzer and a Lumex RA­915+ Multifunctional Mercury Analyzer and were found to be broadly related to the concentration of mercury vapor present in each cabinet. The method can be used to check for mercury contamination in incoming shipments of specimens and to identify cabinets that currently contain or formerly contained contaminated specimens. Practical safety guidelines have been developed for accessing cabinets that give a positive test for the vapor and for handling contaminated specimens.

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

“…A study from 2004 at the National Herbarium developed a novel technique to detect mercury vapor in herbarium cabinets using mercury indicator powder. Their study found concentrations of elemental mercury vapor above 350 mg/m 3 within the herbarium cabinets (Hawks et al 2004). Ongoing efforts led to a proposal and project, starting in 2012, that involved replacing the interleaving of unmounted herbarium specimens.…”

“…It was commonly used as a pesticide to treat natural history collections from the late 1700s to the mid-1980s (Briggs et al 1983, Hawks et al 2004, Purewal et al 2007. Natural history specimens treated with mercuric chloride have been found in countries throughout the world, including the United Kingdom, Spain, South Africa, Canada, and the United States.…”

“…Mercuric chloride exposure results in cell toxicity through direct contact and can cause neurological and kidney damage (WHO 2013, EPA 2014. Mercuric chloride reacts with biologic material in museum specimens to yield elemental mercury and methyl mercuric chloride (Purewal 2001, Hawks et al 2004, Oyarzun et al 2007). Elemental mercury readily vaporizes and can cause respiratory failure at high concentrations.…”

“…This designates that a "significant contribution to the overall exposure" could occur via the cutaneous route (ACGIH 2011). Due to these risks, specimen cabinets should be well ventilated prior to access, and the use of gloves and other protective equipment has been recommended to limit dermal exposure (Hawks et al 2004).…”

“…Application usually required the combination of mercuric chloride with a solvent, often ethanol, methanol, or phenol (Fosberg andSachet 1965, Purewal 2001). Specimens were then sprayed, painted, or fully submerged in the solution and allowed to dry (Briggs et al 1983, Hawks et al 2004. Over time, mercuric chloride decomposes and sublimes, so some institutions retreated their specimens to ensure they remained pest free (Purewal 2001).…”