The Native American Graves Protection and Repatriation Act (NAGPRA) has generated increased interest in the mitigation of metal toxicity associated with metal-treated museum collections, which pose health risks to museum personnel and tribal members.  Historically, mercury- and arsenic-based pesticides were used by collectors to preserve sensitive cultural materials.  The long term persistence and toxicity of these metal-based chemicals is problematic, and their removal needs to be addressed.  With funding from the NCPTT program, we were able to investigate an innovative biological approach to the removal and detoxification of mercury from culturally sensitive materials.  The goal of our work was to assess the ability of surface applied bacteria to convert mercuric salts into a gaseous form of mercury that will diffuse out of the material.  This diffusion will reduce the amount of mercury associated with the material itself, while allowing the gaseous mercury to be properly collected and disposed of.

In order to find the bacteria capable of converting the mercury, we turned to the contaminated materials themselves.  Bacteria are ubiquitous in the environment and can be found on any surface.  Ideally adapted to the particular environment they are inhabiting, the bacteria on the surface of a mercury-treated item will have inherent resistance to the mercury toxicity.  Our job was to find these naturally mercury-resistant bacteria and determine if they are converting the mercury into a gas.  In collaboration with the Arizona State Museum, upon sampling nine mercury-contaminated museum materials, including leather pouches and feathered headdresses, 16 mercury-resistant bacteria were identified.  Of the 16 bacterial isolates, one in particular was highly resistant capable of growing in the presence of up to 50 ppm mercury.  This isolate, genetically identified as Arthrobacter sp. 2604, a commonly found environmental bacterium, had the ability to convert the mercury in its immediate environment into a gaseous form.  When Arthrobacter sp. 2604 was grown on the surface of mercury-contaminated materials, including paper, the bacterium was able to remove up to 20% of the mercury within a 10 day incubation period.  The other isolates, also identified as commonly occurring bacteria such as Bacillus and Pseudomonas spp., showed varying abilities to grow in the presence of mercury.  Future experiments will focus on enhancing the mercury removal by the bacteria on other material types, e.g., hair and leather.  The novel approach of using microorganisms for mercury removal has widespread applications for contaminated environments and is an exciting new application for microorganisms in museums.

This research was made possible through Grant MT-2210-04-NC-08 from the National Center for Preservation Technology and Training (NCPTT).

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