C. Wang, A.K. Dozier, P. Kulkarni
National Institute for Occupational Safety and Health,
Keywords: nanoparticles, aerosol, copper
Summary:In many wood preservative formulations, copper-based components are usually used as primary biocides to protect wood structures against microbial, fungal, and insect decay. The wood preservation industry has recently introduced a particulate copper (i.e., micronized copper or MC) system as a replacement for ionized copper preservative in pressure-treated lumber (PTL). The use of MC treated wood in workplaces has raised concerns over the potential exposure of workers to the wood dust that contains micronized/nanoscale copper particles. However, there is a lack of information on release, identification and characterization of copper particles in wood dust generated by mechanical processing. A laboratory testing system was used to generate wood dust to simulate the cutting and sanding of wood (treated with MC) at construction sites. Airborne wood dust were collected on carbon-coated nickel grids for Transmission Electron Microscopy (TEM) analysis. Three major elements in the dust samples (carbon, copper and oxygen) were identified by their characteristic K lines with an Energy Dispersive x-ray Spectroscopy (EDS). The oxidation states of copper species were determined by the electron energy-loss near-edge structures (ELNES) of their characteristic L2,3 edges. Large particles (mostly basic copper carbonate precipitates) were found accumulated in wood cell secondary layers and on membranes within the bordered pits that connect wood fibers. Nanoscale copper particles were mostly embedded in the wood matrices with sizes in the range from 5 to 1000 nm. Released copper particles were identified in pristine or oxidized forms, which indicated the potential chemical transformation of copper particles. The microstructures of particles generated from different sample processing methods and testing conditions were also evaluated.