Inhalation exposure during spray application and subsequent sanding of a wood sealant containing zinc oxide nanoparticles

ABSTRACT

Nano-enabled construction products have entered into commerce. There are concerns about the safety of manufactured nanomaterials, and exposure assessments are needed for a more complete understanding of risk. This study assessed potential inhalation exposure to ZnO nanoparticles during spray application and power sanding of a commercially available wood sealant and evaluated the effectiveness of local exhaust ventilation in reducing exposure. A tradesperson performed the spraying and sanding inside an environmentally-controlled chamber. Dust control methods during sanding were compared. Filter-based sampling, electron microscopy, and real-time particle counters provided measures of exposure. Airborne nanoparticles above background levels were detected by particle counters for all exposure scenarios. Nanoparticle number concentrations and particle size distributions were similar for sanding of treated versus untreated wood. Very few unbound nanoparticles were detected in aerosol samples via electron microscopy, rather nano-sized ZnO was contained within, or on the surface of larger airborne particles. Whether the presence of nanoscale ZnO in these aerosols affects toxicity merits further investigation. Mass-based exposure measurements were below the NIOSH Recommended Exposure Limit for Zn, although there are no established exposure limits for nanoscale ZnO. Local exhaust ventilation was effective, reducing airborne nanoparticle number concentrations by up to 92% and reducing personal exposure to total dust by at least 80% in terms of mass. Given the discrepancies between the particle count data and electron microscopy observations, the chemical identity of the airborne nanoparticles detected by the particle counters remains uncertain. Prior studies attributed the main source of nanoparticle emissions during sanding to copper nanoparticles generated from electric sander motors. Potentially contrary results are presented suggesting the sander motor may not have been the primary source of nanoparticle emissions in this study. Further research is needed to understand potential risks faced by construction workers exposed to mixed aerosols containing manufactured nanomaterials. Until these risks are better understood, this study demonstrates that engineering controls can reduce exposure to manufactured nanomaterials; doing so may be prudent for protecting worker health.

KEYWORDS:

• Coating
• construction
• local exhaust ventilation
• nano-enabled
• nanomaterial
• nano-objects and their agglomerates and aggregates

Acknowledgments

The authors would like to express our appreciation to TSI Inc. for technical support and use of real-time instrumentation, to Spencer Schwegler and the International Union of Painters and Allied Trades for guidance on tool and material selection and work practices, and to Daniel Marsick of Marsick Consulting, LLC and Jenny Roberts, Walter McKinney and Charles Geraci at NIOSH for their advice and input.

Disclaimer

Any mention of specific companies or products does not imply that they are endorsed or recommended by CPWR or NIOSH. Opinions expressed are those of the authors and do not necessarily represent the official views of CPWR or NIOSH.

Funding

The National Institute for Occupational Safety and Health (NIOSH) supported and funded this study through a cooperative agreement (Number U60-OH009762) with The Center for Construction Research and Training (CPWR).