Abstract
A comparison between various methods for real-time measurements of lung deposited surface area (LDSA) using spherical particles and powder dust with specific surface area ranging from 0.03 to 112 m 2 g –1 was conducted. LDSA concentrations measured directly using Nanoparticle Surface Area Monitor (NSAM) and Aerotrak and were compared to LDSA concentrations recalculated from size distribution measurements using Electrical Low Pressure Impactor (ELPI) and Fast Mobility Particle Sizer (FMPS). FMPS and ELPI measurements were also compared to dust surface area concentrations estimated from gravimetrical filter measurements and specific surface areas. Measurement of LDSA showed very good correlation in measurements of spherical particles (R 2 > 0.97, Ratio 1.0 to 1.04). High surface area nanomaterial powders showed a fairly reliable correlation between NSAM and Aerotrak (R 2 0.73– 0.93) and a material-dependent offset in the ratios (1.04–2.8). However, the correlation and ratio were inconsistent for lower LDSA concentrations. Similar levels of correlation were observed for the NSAM and the FMPS for high surface area materials, but with the FMPS overestimating the LDSA concentration. The ELPI showed good correlation with NSAM data for high LDSA materials (R 2 0.87–0.93), but not for lower LDSA concentrations (R 2 0.50–0.72). Comparisons of respirable dust surface area from ELPI data correlated well (R 2 > 0.98) with that calculated from filter samples, but materials-specific exceptions were present. We conclude that there is currently insufficient reliability and comparability between methods in the measurement of LDSA concentrations. Further development is required to enable use of LDSA for reliable dose metric and regulatory enforcement of exposure.
Highlights
There is increasing evidence that the pulmonary toxicological response of ambient air-pollution and manufactured nanomaterials may, at least partially, be driven by the specific surface area dose of the test materials (Oberdorster, 2000; Maynard and Kuempel, 2005; Duffin et al, 2007; Jacobsen et al, 2009; Giechaskiel et al, 2009; Donaldson et al, 2013; Saber et al, 2014)
It should be remembered that the Fast Mobility Particle Sizer (FMPS) classifies particles according to their electrical mobility equivalent diameter while the Electrical Low Pressure Impactor (ELPI) measures aerodynamic equivalent diameter, which are equal if particles are spherical and have unit density (1 g cm–3)
The deviating FMPS measurement is explained by Levin et al (2015) where it is shown that FMPS is unable to measure distributions of spherical particles with a Geometric Mean Diameter (GMD) higher than 200 nm
Summary
There is increasing evidence that the pulmonary toxicological response of ambient air-pollution and manufactured nanomaterials may, at least partially, be driven by the specific surface area dose of the test materials (Oberdorster, 2000; Maynard and Kuempel, 2005; Duffin et al, 2007; Jacobsen et al, 2009; Giechaskiel et al, 2009; Donaldson et al, 2013; Saber et al, 2014). It is of high interest to include airborne particle surface area measurements to offer a potentially more biologically relevant metric in exposure and risk assessment. The surface area of airborne dust particles may be determined by either direct or indirect methods. Even-though this method has been demonstrated (LeBouf et al, 2011a; Lebouf et al, 2011b), the method is in reality not yet straight-forward and changes could potentially occur in the aerosol during filter-sampling and storage that might change the surface area. This method may not be generally applicable
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