AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Correlation of Method 5040 with Other Methods for Carbon Nanotube Exposure Assessment
PATRICK O'SHAUGHNESSY, Adrianne Horne, Ralph Altmaier, University of Iowa
Abstract Number: 570 Working Group: Engineered Nanoparticles: Emissions, Transformation and Exposure
Abstract The study objective was to compare the use of NIOSH Method 5040 (Elemental Carbon) with other methods for the assessment of carbon nanotubes (CNTs) that may occur in workplace settings. Method 5040 has a limit of quantification of the same magnitude, 7 ug/m3 of elemental carbon (EC), as the proposed recommended exposure limit (REL) for CNTs. We therefore compared results obtained using Method 5040 with other metrics including those obtained with a portable aethelometer (model AE51, AethLabs, San Francisco, CA) and a scanning mobility particle counter. CNT aerosols of varying purity, type, and concentration were dispersed via a nebulized suspension of bulk powder into a small (3 L) chamber from which a gravimetric sample was taken, in addition to readings made by the aethelometer and SMPS. SMPS readings were converted to a volumetric concentration. Filter samples were weighed to determine a mass concentration and then sent to a laboratory for EC, organic carbon (OC), and total carbon (TC) analysis. Surprisingly, the laboratory reported EC content ranging from 6 to 19% with the remainder OC. The highest percentage was found in 99% pure single-walled CNTs. This finding resulted in relatively poor associations between EC and the other measurement methods. Correlations were therefore made between those measurements and TC. Aethelometer readings correlated well with TC concentrations (r2 = 0.94) but were 2.5x lower in magnitude. This correlation was not affected by CNT type or purity. Volumetric concentration resulting from SMPS measurements was less well correlated to TC (r2 = 0.65). Interestingly, TC measurements had a positive bias relative to mass-based concentration with reported results near 80 ug/m3 when filter measurements were at the limit of detection of the filter balance. Based on these results, a portable aethelometer can be used as an accurate surrogate for Method 5040 for TC measurement.