Potential for occupational exposure to engineered carbon-based nanomaterials in environmental laboratory studies

Abstract

Background: The potential exists for laboratory personnel to be exposed to engineered carbon-based nanomaterials (CNMs) in studies aimed at producing conditions similar to those found in natural surface waters [e.g., presence of natural organic matter (NOM)].

Objective: The goal of this preliminary investigation was to assess the release of CNMs into the laboratory atmosphere during handling and sonication into environmentally relevant matrices.

Methods: We measured fullerenes (C60), underivatized multiwalled carbon nanotubes (raw MWCNT), hydroxylated MWCNT (MWCNT-OH), and carbon black (CB) in air as the nanomaterials were weighed, transferred to beakers filled with reconstituted freshwater, and sonicated in deionized water and reconstituted freshwater with and without NOM. Airborne nanomaterials emitted during processing were quantified using two hand-held particle counters that measure total particle number concentration per volume of air within the nanometer range (10-1,000 nm) and six specific size ranges (300-10,000 nm). Particle size and morphology were determined by transmission electron microscopy of air sample filters.

Discussion: After correcting for background particle number concentrations, it was evident that increases in airborne particle number concentrations occurred for each nanomaterial except CB during weighing, with airborne particle number concentrations inversely related to particle size. Sonicating nanomaterial-spiked water resulted in increased airborne nanomaterials, most notably for MWCNT-OH in water with NOM and for CB.

Conclusion: Engineered nanomaterials can become airborne when mixed in solution by sonication, especially when nanomaterials are functionalized or in water containing NOM. This finding indicates that laboratory workers may be at increased risk of exposure to engineered nanomaterials.

Figure 1

Experimental setup for evaluating engineered carbon-based nanomaterial in the laboratory using air filters to collect airborne CNM for TEM analysis. (A) Weighing CNMs in an electronic balance and transferring CNMs to a beaker of water being stirred; this process occurred inside a hood with no ventilation. (B) Sonication process inside an unventilated enclosure. In both A and B, note the proximity of the air filter (arrows) to the laboratory processes.

Figure 2

Aerosolization of water containing 100 mg/L NOM. Water droplets are visualized in a plume after sonication pulses (area between white lines). Inset: broader view of water droplet plume (indicated by white outline) after sonication pulse.

Figure 3

TEM images of engineered CNMs during laboratory processes. (A) Background air sample; bar = 0.3 μm. (B) Weighing/transferring C60 inside hood with no ventilation; bar = 0.3 μm. (C) Sonicating C60 in DI water inside unventilated enclosure; bar = 0.3 μm. (D) Weighing/transferring raw MWCNT inside hood with no ventilation; bar = 0.3 μm. Note that no tubular structures are present. (E) Sonicating raw MWCNT in DI water inside unventilated enclosure; bar = 0.5 μm. (F) Sonicating raw MWCNT in reconstituted water containing 100 mg/L (parts per million) NOM inside unventilated enclosure; bar = 0.5 μm. (G) Weighing/transferring MWCNT-OH inside hood with no ventilation; bar = 1 μm. (H) Weighing/transferring CB inside hood with no ventilation; bar = 0.3 μm. (I) Sonicating CB in DI water inside unventilated enclosure; bar = 0.3 μm.

Figure 4

Graphical representation of potential exposure to engineered CNMs in the laboratory through inhalation and dermal contact.