Bioavailability of Arsenic in Dislodgeable Residue from Pressure-Treated Wood
EMSL Project ID
3602a
Abstract
Arsenic compounds are used in wood preservation largely because of the excellent results achieved by chromated copper arsenate (CCA). The concentration of CCA in wood products typically are between 2 and 6%, when calculated on an oxide basis. Studies of the microdistribution of CCA in wood have shown that most of the preservative forms a dense deposit on the cell lumen, sometimes completely filling the cell. Recently, concern has arisen over the toxicity of fine particulate released from treated wood by weathering and abrasion. As a result, the EPA, concerned scientists, and manufacturers of treated wood products have begun assessing the potential for releases of arsenic from residue that can easily become dislodged from wood surfaces and possibly ingested into the human body. Small quantities of this dislodgeable residue from residential structures have been procured by an industry-sponsored study group. The residue was collected with the prospect that the bioavailability of arsenic could be determined by advanced methods for chemical analysis.
Few analytical techniques have sufficient sensitivity and specificity to identify inorganic solids when they are diluted within heterogeneous wood matrices. XAFS is the only proven method for elucidating the chemistry of heavy metals in treated wood. However, this technique is generally unsuitable for routine analysis, because of the costs associated with this method and the difficulty of interpreting the spectra. There are fundamental limitations with XAFS as well, including each element of interest usually has to be in a nearly identical chemical environment.
A number of surface analytical techniques have advantages over bulk methods, due to the heterogeneous nature of wood. In particular, three very useful techniques for determining the chemical state of arsenic include X-ray photoelectron spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF SIMS), and Scanning Auger Microprobe (SAM). XPS provides surface elemental analysis with information on chemical bonding and oxidation state, so it can differentiate between As(III)/As(V), as well as Cr(III)/Cr(VI), which also is of much interest. ToF SIMS offers high-definition imaging and quantitative chemical analysis with spatial resolution in the neighbourhood of 0.12 ?m. In addition, ToF SIMS is capable of elemental mapping and depth-profiling, which could be beneficial for probing the wood cellular structure for arsenic compounds. It is advantageous to perform XPS and ToF SIMS at EMSL, because of the complementary analytical data they produce and because of the ease of switching samples between these instruments. In addition, the high resolution imaging and mapping capabilities of the SAM would be an extremely useful complement to the ToF SIMS analysis.
We intend to submit one sample of dislodgeable residue from CCA-treated wood and one sample of bulk wood. Because of the difficulty in obtaining the former, less than one gram is available for the analyses, but this is expected to be sufficient. The bulk sample can be cut to any convenient size.
Project Details
Project type
Exploratory Research
Start Date
2004-09-29
End Date
2006-04-13
Status
Closed
Released Data Link
Team
Principal Investigator