Thursday, January 31, 2013

Arsenic compounds in taxidermy collections

Last year we took the Bruker III-V+ on the road to analyze a taxidermy collection for the presence (and hopefully absence) of arsenic. Arsenic compounds are used as pigments, pesticides, and insecticides, so their presence in cultural heritage materials is not uncommon. Due to the high toxicity of arsenic it is often necessary to test collections to verify that they can be safely handled. The use of portable XRF units such as the Bruker II-V+ in the identification of heavy metal compounds in museum collections began in the late 1990s, and is now the standard method for such analyses. Arsenic has been used in the preparation of natural history specimens going back to the early 1800s and was used even as late as the 1980s, so its presence is possible in nearly every collection. One of the most common uses of arsenic in taxidermy preparation was arsenical soap composed of the white powder arsenic trioxide mixed with soap, subcarbonate of potash, camphor, and alcohol. The resulting paste was applied to the inside of the animal and bird skins, and readily comes through the skins to the surface where it can be transferred to human hands or contaminate other objects it contacts.

The analysis can be done literally handheld and once the parameters are established analysis can proceed at a rate of about 1 object every 5 minutes. The XRF spectra shown on the right shows a definite peak for arsenic found on a dusky footed wood rat. The presence of other compounds containing mercury or lead can also be important in some collections and can be detected at the same time.

For further information, see chapter 9 "Handheld XRF use in the identification of heavy metal pesticides in ethnographic collections" in Shugar, Aaron N. and Jennifer L. Mass. 2012. Handheld XRF for art and archaeology.

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