Carbon nanotube exposure assessment: an evaluation of workplace exposures in the US.
Dahm-M; Schubauer-Berigan-M; Erdely-A
Toxicologist 2014 Mar; 138(1):4-5
Just as there has been much advancement in the field of toxicology over the past decade relative to health outcomes from carbon nanotube (CNT) exposures, similar strides are being made in the field of exposure assessment. Recent developments in sampling methodologies have led to more accurate estimates for worker exposure levels as compared to preliminary studies, which may have overestimated exposures. As part of an ongoing NIOSH exposure assessment and epidemiologic study, worker exposure to CNT has been examined by sampling 14 different worksites across the US over a three year period. Personal breathing zone exposure levels were measured using a chemical specific marker for the mass concentration of elemental carbon (EC) at both the inhalable and respirable size fractions. The sampling methodologies are in accordance with the NIOSH Current Intelligence Bulletin on CNTs and carbon nanofibers which set a mass based Recommended Exposure Limit at 1 mg/m^3 of EC at the respirable size fraction. Overall, personal workplace exposures at the respirable size fraction to EC ranged from 0.02 - 1.47 mg/m^3 with an 8 hr time weighted geometric mean of 0.16 mg/m3. Inhalable personal breathing zone exposures ranged from 0.003 - 22.40 mg/m^3 with a geometric mean of 0.38 mg/m^3. Concurrent personal breathing zone samples were also collected and analyzed by electron microscopy using methods similar to the asbestos counting convention. CNT structure agglomerate sizes averaged > 4 mm while few single CNT fibers were found. This study also focused on how exposure level and type change within the various industries in which CNTs are being applied (composites, electronics, production), between types of materials (multi-walled vs. single-walled), and under varying work conditions. The detailed information from these exposure assessment findings bring awareness to industries with higher exposure potentials and provide valuable data on job specific tasks where exposures are likely to occur. In addition, the findings from this study can provide valuable insight for designing and interpreting in vivo exposures.
Toxicology; Nanotechnology; Pulmonary-disorders; Airborne-dusts; Airborne-particles; Exposure-levels; Epidemiology; Sampling; Workers; Work-environment; Analytical-processes
The Toxicologist. Society of Toxicology 53rd Annual Meeting and ToxExpo, March 23-27, 2014, Phoenix, Arizona