Assessment of the bioaccessibility of micronized copper wood in synthetic stomach fluid

• Nano to micron-scale particulate copper was observed in thin sections of treated wood.
• Sanding dust from copper-treated wood products was exposed to synthetic stomach fluid.
• Mixtures were fractionated to separate soluble from particulate forms of copper.
• Significantly more Cu was released into low pH-SSF than into water.
• Cu released into SSF was soluble and presumably bioaccessible in this simulated GI system.

The widespread use of copper in treated lumber may result in a potential for human exposure. Due to a lack of information concerning the release of copper from treated wood particles following oral ingestion, the in vitro bioaccessibility of copper from copper-treated wood dust in synthetic stomach fluid (SSF) and DI water was investigated. Copper-containing particles ranging in size from nano-scale to micron-scale were observed by transmission electron microscopy (TEM) in thin sections of these micronized copper-treated wood products. Three copper-treated wood products (liquid alkali copper quaternary and two micronized copper quarternary products) from different manufacturers were incubated in the extraction media. The released copper was then fractionated by centrifugation and filtration through 0.45 μm and 10 kDa filters, respectively. Soluble copper released into isolated fractions was measured using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Total copper from each wood product was also determined using microwave-assisted acid digestion of dried wood samples and ICP-OES. The bioaccessible copper released into SSF was between 83 and 90% for all wood types. However, the percent of copper released in DI water was between 14 and 25% for all wood products. These data suggest that copper is highly bioaccessible at the low pH values present in the stomach and may pose a potential exposure risk upon ingestion.