Handheld XRF for Art and Archaeology

9. Handheld XRF use in the identification of heavy metal pesticides in ethnographic collections

Aaron N. Shugar and P. Jane Sirois 314 the density and thickness of the treated material, the overall composition of the material(s), the X-ray source used, the analytical parameters used to collect data, any additional adornments to the artifact (e.g. beads, paint layers), the surface geometry (i.e. non-flat or flat surfaces) and the availability of reference materials for calibrating instrumentation. This chapter outlines some of the key issues that need to be considered when developing a sound methodology for the reproducible analysis of ethnographic collections by handheld XRF. Two of the key issues are understanding the construction and materials of the objects and choosing appropriate reference materials. The difficulties in obtaining reproducible quantitative results and their proper reporting will also be discussed. Historical overview of inorganic pesticide use Today’s pesticide products, available as consumer products for home use, are properly labeled and designate the pesticide(s) being used, for example, pyrethrins and carbaryl (1- naphthyl methylcarbamate). Pesticides are also used by museums in certain situations such as to combat insect infestations when integrated pest management is not successful. The composition of currently used pesticides in museum contexts is known because of proper labeling, MSDS availability, and rigorous record keeping by conservation staff. This is not the case, however, with historic pesticides. Typically we do not know what pesticide was applied, how it was applied, when it was applied, and how many times it was applied to a collection artifact. There can be several reasons for this but two overriding issues prevail. First, record keeping was not as rigorous in the past as it is today, so complete documentation of potential pesticide treatments were not kept for each artifact. Second, the products that museums used for treatment may not have been labeled with their component ingredients. In fact, labels were not required on pesticides until the 1910 Insecticide Act in Canada, and in the USA until 1927 when the Caustic Poisons Act was enacted requiring that labels include warnings about dangerous chemicals present in the products as well as provide antidote information. From extended research projects focusing on the history of pesticide treatments in museum collections it appears that the pesticides used were many and varied and were applied to ethnographic collections over long periods of time dating from as early as the early 1800s when arsenic was being used for natural history specimens (Pequinot et al. 2006) to the mid 1900s (Goldberg 1996, Conserve-O-Gram 2001, Hawks 2001, Odegaard, Sadongei and Boyer Handheld XRF use in the identification of heavy metal pesticides in ethnographic 315 2005, Sirois et al. 2008). It was even recommended for use in natural history specimens as recently as 1985 (Hangay and Dingley 1985). Although the range of pesticides used in museums is extensive they can typically be broken down into two overriding groups; inorganic and organic chemicals. Inorganic pesticides are the most persistent followed by organochlorines, carbamates, organophosphates (diazinon {O,O-Diethyl O-[2-isopropyl-6methylpyrimidin4 -yl] phosphorothioate} for example) and botanical compounds, which have a life span of up to several weeks. Organic compounds themselves can be broken down into two sub-groups; natural, which includes spices, alcohols, tobaccos and cedar, and synthetic which includes halogenated organics (aromatics including DDT {1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (International Chemical Safety Card, Sept 9/11)} and paradichlorobenzene{1,4-dichlorobenzene}; and non-aromatics including carbon tetrachloride {tetrachloromethane}and methyl bromide {bromomethane}), organophophorous pesticides such as dichlorvos (2,2-dichlorovinyl dimethyl phosphate) and diazinon (O,O-diethyl O-2-isopropyl6 -methylpyrimidin-4-yl phosphorothioate), phenols such as pentachlorophenol (2,3,4,5,6-pentachlorophenol) and cresol (methylphenol) and carbamates such as bendiocarb (2,2-dimethyl-1,3-benzodioxol-4-yl methylcarbamate) and aldicarb (2-methyl-2-(methylthio)propionaldehyde O-methylcarbamoyloxime). The most frequently encountered inorganic compounds used by museums include arsenical compounds (i.e. arsenic oxides), mercury compounds (i.e. mercuric chloride), and lead compounds (i.e. lead oxide(s) such as litharge and minium, the common white pigment lead carbonate hydroxide, and the pesticide lead arsenate). These inorganic compounds are persistent, having very long life spans, are highly toxic, and are difficult to dispose of or mitigate. Not only were many types of poisons used, but the application methods varied greatly. Objects may have been sprinkled with a powder, slathered with a paste, dipped or soaked in a solution, or sprayed with an...