Characterization and workplace exposure assessment of nanomaterial released from a carbon nanotube-enabled anti-corrosive coating

Abstract

Improvement of methods to quantify the release and characterization of engineered nanomaterials (ENMs) from nano-enabled products is essential to enhance the accuracy and usability of environmental health and safety evaluations. An anticorrosive coating containing multi-wall carbon nanotubes (MWCNTs) was analyzed for nano-scale material and workplace exposure potential. Worker breathing zone measurements for elemental carbon (EC) and electron-microscopy-based structure counts showed negligible MWCNT exposure to workers during laboratory and spray-painting operations over the course of two 8-hour shifts (arithmetic mean inhalable EC and electron microscopy structure count concentrations were 6.47 μg/m3 and 0.084 structures/cm3 respectively). UV weathering prior to abrasion testing increased the nano-size fraction of released material as measured by a fast mobility particle sizer (FMPS) and visual inspection by SEM indicated increased presence of exposed MWCNTs embedded in the polymer matrix. However, no free MWCNTs were identified, despite evidence of MWCNTs embedded in airborne particles. TiO2, used as a pigment in the coating and not anticipated as a candidate for nano-specific scrutiny, contained a small fraction (3.5% in number) of nano-sized constituents (<100 nm). This work emphasizes need for rigorous characterization of additive materials to properly assess potential health hazards and to better our understanding of what qualifies as “nano”.