Determination of airborne wood dust in Button samples by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)

Abstract

Emerging concerns regarding the toxicity of inhaled wood dust support the need for techniques to quantitate wood content of mixed industrial dusts. The diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis technique was applied to the determination of wood content of 181 inhalable dust samples (geometric mean concentration: 0.895 mg/m3; geometric standard deviation: 2.73) collected from six wood product industry factories using 25 mm glass fibre filters with the Button aerosol sampler. Prior to direct DRIFTS analysis the filter samples were treated with ethyl acetate and re-deposited uniformly. Standards ranging from 125 µg to 4000 µg were prepared for red oak, southern yellow pine, and red cedar and used for quantitation of samples depending upon the wood materials present at a given factory. The oak standards spectra were quantitated by linear regression of response in Kubelka-Munk units at 1736 cm−1, whereas the pine standards and the cedar standards spectra were quantitated by polynomial regression of response in log 1/R units at 1734 cm−1, with the selected wavenumbers corresponding to stretching vibration of free C=O from cellulose and hemicelluloses. For one factory which used both soft- and hard-woods, a separate polynomial standard curve was created by proportionally combining the oak and pine standards polynomial regression equations based on response (log 1/R) at 1734 cm−1. The analytical limits of detection were approximately 52 µg of oak, 20 µg of pine, 30 µg of cedar, and 16 µg of mixed oak and pine for the factory with mixed woods. Overall, the average of dry wood dust percentage of inhalable dust was approximately 56% and the average dry wood dust weight was 0.572 mg for the Button samples. Across factories, there were statistically significant differences (p < 0.001) for the percentage of dry wood dust in inhalable dust with factory averages ranging from 33.5 to 97.6%.