Characterizing applications, exposure risks, and hazard communication for engineered nanomaterials in construction.

BACKGROUND: Engineered nanomaterials (ENMs) may pose health risks to workers. Objectives were to characterize ENM applications in construction, identify exposure scenarios, and evaluate the quality of safety data sheets (SDSs) for nano-enabled construction products. METHODS: SDSs and product data were obtained from a public database of nano-enabled construction products. Descriptive statistics were calculated for affected trades, product categories, and types of ENMs. A sample of SDSs (n = 33) was evaluated using modified criteria developed by NIOSH researchers. Bulk analysis via transmission electron microscopy characterized nanoparticles in a subset of products. RESULTS: Companies report using >50 ENMs in construction products. ENM composition could not be determined via SDSs for 38.1% of the 907 products examined. Polymers and metal oxides tied for most frequently reported ENMs (n = 87, 9.6%). Nano silica, graphene, carbon nanotubes, and silver nanoparticles were also frequently reported. Most of the products were paints and coatings (n = 483, 53.3%), followed by pre-market additives, cementitious materials, insulation, and lubricants. Workers in twenty construction trades are likely to handle nano-enabled products, these particularly encompass cement and brick masons, painters, laborers, carpenters, glaziers, and insulators. A wide range of exposure scenarios were identified. SDSs were classified as satisfactory (18%), in need of improvement (12%), or in need of significant improvement (70%). Bulk analyses revealed discrepancies between actual ENM composition and those in SDSs. DISCUSSION AND CONCLUSION: There has been significant progress investigating risks to construction workers posed by ENMs, but SDSs need major improvements. This study provides new insights on the use of ENMs in construction, exposure risks, and hazard communication.

Occupational exposure risk during spraying of biocidal paint containing silver nanoparticles.

The study assessed potential to exceed occupational exposure limits while spraying paint with and without a silver nanoparticle biocidal additive. A tradesperson performed the tasks in a sealed chamber with filtered air supply. Integrated air sampling entailed transmission electron microscopy with energy dispersive X-ray analysis, direct-reading of particle number concentrations, and determination of silver mass concentration by NIOSH Method 7300. Silver nanoparticles were primarily embedded in paint spray droplets but also observed as isolated particles. Using an α-level of 0.05, median nanoparticle number concentrations did not differ significantly when spraying conventional vs. biocidal paint, although statistically significant differences were observed at specific particle size ranges <100 nm. The geometric mean concentration of total silver while spraying biocidal paint (n = 6) was 2.1 µg/m3 (95% CI: 1.5-2.8 µg/m3), and no respirable silver was detected (<0.50 µg/m3). The results address a lack of silver nanoparticle exposure data in construction and demonstrate the feasibility of a practical sampling approach. Given similar conditions, the measurements suggest a low probability of exceeding a proposed silver nanoparticle exposure limit of 0.9 µg/m3 as an airborne 8-hr time-weighted average respirable mass concentration. A full workday of exposure to respirable silver at the highest possible level in this study (<0.50 µg/m3) would not exceed the exposure limit, although limitations in comparing short task-based exposures to an 8-hr exposure limit must be noted. There was airflow in the study chamber, whereas exposure levels could increase over time in work environments lacking adequate ventilation. Potential to exceed the exposure limit hinged upon the respirable fraction of the paint mist, which could vary by material and application method. Additional research would improve understanding of silver nanoparticle exposure risks among construction trades, and biological responses to these exposures. Given the potential for exposure variability on construction jobsites, safety and health professionals should be cognizant of methods to assess and control silver nanoparticle exposures.

Exposure to airborne nano-titanium dioxide during airless spray painting and sanding.

The objectives of the study were to measure and characterize exposure to airborne nanoscale titanium dioxide during airless spraying and sanding of a nano-enabled paint, and to evaluate the effectiveness of dust capture methods in reducing airborne nanoparticle concentrations. A tradesperson performed the work activities in an environmentally controlled chamber. Samples were collected in the tradesperson's breathing zone and in surrounding areas to assess bystander exposure. Filter-based samples were analyzed using gravimetric methods, scanning electron microscopy, and energy dispersive spectroscopy. Differential particle count data were obtained by means of a scanning mobility particle sizer. Local exhaust ventilation provided statistically significant reductions of airborne nanoparticle concentrations during sanding. Sanding the paint after drying with a handheld power sander generated relatively low levels of airborne titanium dioxide. In contrast, task-based exposure measurements collected during the initial airless spray application of the nano-enabled paint suggested a potential for occupational exposures to exceed the time-weighted average exposure limit for ultrafine titanium dioxide recommended by the National Institute for Occupational Safety and Health. Painters applying nano-enabled coatings may have little recourse but to rely, in some instances, on lower tiers of the hierarchy of controls, such as personal protective equipment. In light of these findings, employers and industrial hygienists should characterize exposures and implement the hierarchy of controls to ensure painters are sufficiently protected.

Evaluation of airborne asbestos exposure from routine handling of asbestos-containing wire gauze pads in the research laboratory.

Three independently conducted asbestos exposure evaluations were conducted using wire gauze pads similar to standard practice in the laboratory setting. All testing occurred in a controlled atmosphere inside an enclosed chamber simulating a laboratory setting. Separate teams consisting of a laboratory technician, or technician and assistant simulated common tasks involving wire gauze pads, including heating and direct wire gauze manipulation. Area and personal air samples were collected and evaluated for asbestos consistent with the National Institute of Occupational Safety Health method 7400 and 7402, and the Asbestos Hazard Emergency Response Act (AHERA) method. Bulk gauze pad samples were analyzed by Polarized Light Microscopy and Transmission Electron Microscopy to determine asbestos content. Among air samples, chrysotile asbestos was the only fiber found in the first and third experiments, and tremolite asbestos for the second experiment. None of the air samples contained asbestos in concentrations above the current permissible regulatory levels promulgated by OSHA. These findings indicate that the level of asbestos exposure when working with wire gauze pads in the laboratory setting is much lower than levels associated with asbestosis or asbestos-related lung cancer and mesothelioma.

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

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.