Nanotechnology: New Developments in Exposure Assessment, Sampling Technology, and Respirator Protection

Nanotechnology: New Developments in Exposure Assessment, Sampling Technology, and Respirator Protection

Wednesday, June 3, 2015, 10:00 AM - 12:00 PM

CS-122-01 Refinement of the Nanomaterial Emission Assessment Technique into the​​ Nanomaterial Exposure Assessment Technique (NEAT 2.0)

A. Eastlake, C. Beaucham, K. Martinez, M. Dahm, C. Sparks, L. Hodson, K. Dunn, C. Geraci,K. Dunn, NIOSH, Cincinnati, OH

Situation/Problem: Increasingly, workers in various industries, from cosmetics to transportation, are involved in the research, development, manufacture, production, use, recycling, and disposal of nanomaterials or products containing nanomaterials. The Nanoparticle Emission Assessment Technique (NEAT) was published in 2009 by authors from the National Institute for Occupational Safety and Health (NIOSH) as an initial step to semi-quantitatively evaluate potential occupational emissions that could lead to exposures in workplaces where nanomaterials are used. The method has been applied in numerous workplaces and has demonstrated that release of nanomaterials in an occupational setting does occur. Since the publication of the original NEAT, further studies have broadened our understanding of measurement techniques and interpretation in these environments.

Resolution: Nanomaterial emission and exposure characterization studies have been completed at more than 60 different facilities by the National Institute for Occupational Safety and Health. These experiences have provided NIOSH the opportunity to refine an earlier published technique, the Nanomaterial Emission Assessment Technique, into a more comprehensive method aimed at assessing worker and workplace exposures. This change is reflected in the name Nanomaterial Exposure Assessment Technique and indicated as different from the original method as NEAT 2.0.

Results: This refined version of the original strategy includes a comprehensive assessment of emissions at process and job tasks, and an assessment of worker exposures that includes nanomaterial identification, mass concentration, particle counts and concentrations, and evaluation of the migration of materials throughout a facility. Additionally, evaluation of worker practices, ventilation efficacy, and other engineering exposure control systems serve to allow for a comprehensive exposure assessment.

Lessons Learned: This information is used to develop appropriate risk management strategies for minimizing worker exposure to ENMs. While no individual technique alone can adequately characterize potential exposure to nanomaterials, the combination of all these methods, which constitute NEAT 2.0, allows a more in-depth characterization of the of the potential for occupational exposure within the nanomaterial industry.

SR-122-02 Characterization of Nanoparticles Generated from Synthesizing Advanced Materials

S. Tsai, J. Beltz, A. Dysart, V. Pol, Purdue University, West Lafayette, IN

Objective: This research characterized particle release during an experimental nanomaterial production process, and estimated the risk of human and environmental effects that this process could produce if it were put into industrial production. Prevention through design is a focus of this research.

Methods: The examined process was the laboratory-scale synthesis of advanced materials using solid-state chemical reactions at elevated temperatures. While it appeared that the desired product could be scaled up, the possibility of toxic emissions was of great concern. Direct-reading instruments and samplers were used to take measurements of the exhausted material and analyze the unknown substances which were collected as aerosols and liquid suspensions. Airborne emissions were analyzed using particle counters, i.e. TSI Nanoscan SMPS, OPS, and Dust Trak, for number and mass concentration, and were collected on polycarbonate filters and TEM grids for morphology and elemental composition analysis using SEM, TEM and XEDS. For emissions in liquids, released aerosols were collected in DI water using impinge and analyzed using the Nanosight characterization system for the particle size distribution, concentration and mobility. The production process was studied operando, i.e., heating, reaction and cooling.

Results: An elevated number of nanometer to micrometer diameter particles were generated and released from this synthesis process. Particle number concentration exceeded 106 particles/cm3 for diameters from 10–420 nm; in addition, micrometer-sized particle concentrations were elevated as well. The mass concentration (particle diameter <10µm) exceeded 100 mg/m3. The airborne particle size mode was approximately 200 nm and the mode for particles collected in water using impinger was approximately 100–200 nm. Many nanoparticles were found to contain O, Si, S, Cl, and Sn. Tin, a toxic metal, was present at the highest concentration.

Conclusions: A follow up study is planned to analyze possible process changes to minimize the metal nanoparticles produced as side products. An in vitro study using human lung cell is planned to investigate the toxicity level corresponding with reduced tin following the process change study. Engineering controls were in use including aerosol filtration and a water bath with air filter. The water bath filter was required to collect the released particles; proper ventilated fume hoods and filtration will have to be used during actual production.

SR-122-03 Exposure Associated with Personal Protective Clothing Contaminated with Nanoparticles

S. Tsai, X. Huangm C. Han, Purdue University, West Lafayette, IN

Objective: This study investigated nanoparticle exposures associated with the contamination of protective clothing during manipulation of clothing fabrics contaminated with nanoparticles. The contaminated clothing could release nanoparticles in the general room while performing other activities and manipulating the clothing after work. Inhalation exposure is the route of exposure of most concern to cause adverse health effects. The objective is to identify the magnitude of particle contamination and release.

Methods: The exposures associated with three different fabric materials (cotton, polyester and Tyvek uses) were investigated in this study by measuring the number concentration increase and the weight change on fabric pieces. This study simulated real life occupational exposure scenarios and was performed in both regular and clean room environments to investigate the effect of background aerosols on the measurements. Concentrations were measured using particle spectrometers for diameters from 10 nm to 10 µm. Collected aerosol particles and contaminated fabric surfaces were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental composition analysis.

Results: The magnitude of particle release from contaminated lab coat fabric was found to vary by the type of fabric material; cotton fabric showed the highest level of contamination and particle release, followed by Tyvek and polyester fabrics. The polyester lab coat material was found to have the lowest particle release to deposition (R/D) ratio. The particle release number concentrations were in a range of 768 to 119 particles/cm3 and 586 to 187 particles/cm3 in regular and clean rooms respectively. Multiple peaks were observed in the number concentration distribution data, with particle diameters peaking at 40 to 50 nm and 100 to 300 nm.

Conclusions: The scanning electron microscope (SEM) analysis of the contaminated fabric surface found test particles and other environmental particles. The elemental composition analysis presented detectable response to the studied alumina oxide particles. The laboratory coat primarily made of cotton woven material is not recommended for worker protection against nanoparticle exposure because of the highest particle contamination and release ability. In addition, the result demonstrated that a cleanroom environment is critical to investigate the factors affecting nanoparticle interaction with protective clothing.

SR-122-04 Evaluation of Self-Supporting, Single-Walled Carbon Nanotube Bucky Paper Sorbents for the Application in Diffusive Sampling and Photothermal Desorption

E. Floyd, OUHSC, Oklahoma City, OK; C. Lungu, J. Oh, M. Saina, UAB, Birmingham, AL

Objective: To describe the fabrication and evaluation process of self-supporting Single-Walled Carbon Nanotube (SWNT) bucky paper sorbents for application in diffusive sampling and analysis by photothermal desorption.

Methods: Approximately 50 mg of SWNT powder was suspended in toluene by ultrasonication for 2 hours in a chilled water bath (~8C). Suspended SWNT was deposited on a 47 mm (5 um pore size, PTFE) membrane using a vacuum apparatus and allowed to fully dry while under vacuum (~ 1 hr.). Deposited SWNT forms a sturdy self-supporting bucky paper that is easily delaminated from the PTFE membrane. Bucky paper sorbents were desorbed in an oven at 130C for at least 48 hrs. prior to obtaining toluene adsorption isotherms at 23C and 732 torr. Toluene adsorption isotherms were collected before and after annealing at 300C in air. Sorbent mass loss due to annealing was measured and adsorption capacity was calculated from adsorption isotherms

Results: Toluene adsorption capacity increased approximately 25% after annealing (pre-annealing = 95 ug toluene / mg sorbent, post-annealing = 120 ug toluene / mg sorbent.) The variability in adsorption capacity was reduced after annealing and sorbents retained their flexibility and durability. Sorbent mass loss after annealing was approximately 9 mg (~18%). Minimal mass loss was observed beyond 4 hours of annealing.

Conclusions: Self-supporting, low mass bucky paper sorbents can be fabricated using a simple, scalable process; low energy sonication, vacuum filtration, thermal treatment. Self-supporting bucky paper sorbents are well suited for application as a sorbent in a diffusive sampler with analysis using photothermal desorption.

SR-122-05 Comparison of Simulated Workplace Protection Factors Offered by N95 and P100 Air-Purifying Respirators against Particles of 10 to 400 nm

X. He, West Virginia University, Morgantown, WV; Z. Zhuang, E. Vo, M. Bergman, M. Horvatin, NIOSH/NPPTL, Pittsburgh, PA

Objective: To compare the simulated workplace protection factors (SWPFs) provided by NIOSH-approved N95 and P100 class filtering facepiece respirators (FFR) and elastomeric half-mask respirators (EHR) against sodium chloride particles (NaCl) in a range of 10 to 400 nm.

Methods: Twenty-five human test subjects performed modified OSHA fit test exercises in a test chamber filled with generated NaCl particles while wearing respirators (two FFR models and two EHR models) containing N95 class filters and respirators (two FFRs and two EHRs) containing P100 class filters. Two Scanning Mobility Particle Sampling Systems (SMPS) (Model: 3080 EC with Model 3772 CPC, TSI, Inc.) were used to measure aerosol concentrations (in the 10-400 nm size range) inside (Cin) and outside (Cout) of the respirator, simultaneously. SWPF was calculated as the ratio of Cout to Cin. The SWPF values obtained from the models with N95 filters were then compared to those measured with respirators containing P100 filters.

Results: SWPFs were found to be significantly different (P < 0.05) between respirators containing N95 and P100 class filters. The 10th, 25th, 50th, 75th and 90th percentiles of the SWPFs for the respirators with N95 filters were much lower than those for the respirators with P100 filters. Respirators with N95 filters had 5th percentiles of SWPFs > 10. In contrast, respirators with P100 class filters were able to generate 5th percentile SWPFs > 100. No significant difference was found in the SWPFs when evaluated for nano-size (10 to 100 nm) and large-size (100 to 400 nm) particles.

Conclusions: Overall, the findings suggest that, for subjects that pass a quantitative fit test, respirators containing P100 class filters provide better protection against 10 to 400 nm particles than the respirators containing N95 class filters. This trend is also true for nanoparticles (10 to 100 nm).

SR-122-06 Simulated Workplace Protection Factors Offered by N95 and P100 Air-Purifying Respirators against Submicron Particles

Z. Zhuang, E. Vo, M. Bergman, NIOSH, Pittsburgh, PA; X. He, West Virginia University, Morgantown, WV; M. Horvatin, URS, Inc., Pittsburgh, PA

Objective: This study investigated simulated workplace protection factors (SWPFs) measured utilizing N95 and P100 class filtering facepiece respirators (FFR) and elastomeric half-mask respirators (EHR) against submicron particles (20 nm to 1,000 nm).

Methods: Twenty-five human test subjects performed a modified version of a U.S. Occupational Safety and Health Administration (OSHA) quantitative fit test (6 exercises, 3 minutes each) in a chamber of sodium chloride aerosols primarily in the submicron range. The six exercises were: 1) normal breathing, 2) deep breathing, 3) moving head side-to-side, 4) moving head up and down, 5) bending over, and 6) a simulated laboratory vessel cleaning motion. Eight respirator models were evaluated (two N95 FFRs, two N95 EHRs, two P100 FFRs, and two P100 EHRs). The SWPFs for each model were measured using a PortaCount Pro+ (regular mode for measuring both face seal leakage and filter penetration). Before a SWPF test for a given respirator model, each subject had to pass a quantitative fit test.

Results: The effect of the respirator model on SWPFs was significant (p < 0.05). Geometric mean (GM) SWPFs were statistically different for P100 EHRs and P100 FFRs. GM SWPFs were not statistically different for N95 EHRs and N95 FFRs. GM SWPFs of P100 EHRs and FFRs combined were > 1,000, which was 10-fold higher than the GM SWPF of the N95 class EHRs and FFRs. 

Conclusions: The 5th percentiles of the SWPFs for the P100 EHRs and FFRs combined were > 20, whereas those for the N95 models were all < 10.​