A New Approach Combining Analytical Methods for Workplace Exposure Assessment of Inhalable Multi-Walled Carbon Nanotubes.

To date there is no consensus about the most appropriate analytical method for measuring carbon nanotubes (CNTs), hampering the assessment and limiting the comparison of data. The goal of this study is to develop an approach for the assessment of the level and nature of inhalable multi-wall CNTs (MWCNTs) in an actual workplace setting by optimizing and evaluating existing analytical methods. In a company commercially producing MWCNTs, personal breathing zone samples were collected for the inhalable size fraction with IOM samplers; which were analyzed with carbon analysis, inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX). Analytical methods were optimized for carbon analysis and SEM/EDX. More specifically, methods were applied and evaluated for background correction using carbon analyses and SEM/EDX, CNT structure count with SEM/EDX and subsequent mass conversion based on both carbon analyses and SEM/EDX. A moderate-to-high concordance correlation coefficient (RC) between carbon analyses and SEM/EDX was observed [RC = 0.81, 95% confidence interval (CI): 0.59-0.92] with an absolute mean difference of 59 µg m-3. A low RC between carbon analyses and ICP-MS (RC = 0.41, 95% CI: 0.07-0.67) with an absolute mean difference of 570 µg m-3 was observed. The large absolute difference between EC and metals is due to the presence of non-embedded inhalable catalyst particles, as a result of which MWCNT concentrations were overestimated. Combining carbon analysis and SEM/EDX is the most suitable for quantitative exposure assessment of MWCNTs in an actual workplace situation.

Assessment of Determinants of Emission Potentially Affecting the Concentration of Airborne Nano-Objects and Their Agglomerates and Aggregates.

Background: Nano-specific inhalation exposure models could potentially be effective tools to assess and control worker exposure to nano-objects, and their aggregates and agglomerates (NOAA). However, due to the lack of reliable and consistent collected NOAA exposure data, the scientific basis for validation of the existing NOAA exposure models is missing or limited. The main objective of this study was to gain more insight into the effect of various determinants underlying the potential on the concentration of airborne NOAA close to the source with the purpose of providing a scientific basis for existing and future exposure inhalation models. Method: Four experimental studies were conducted to investigate the effect of 11 determinants of emission on the concentration airborne NOAA close to the source during dumping of ~100% nanopowders. Determinants under study were: nanomaterial, particle size, dump mass, height, rate, ventilation rate, mixing speed, containment, particle surface coating, moisture content of the powder, and receiving surface. The experiments were conducted in an experimental room (19.5 m3) with well-controlled environmental and ventilation conditions. Particle number concentration and size distribution were measured using real-time measurement devices. Results: Dumping of nanopowders resulted in a higher number concentration and larger particles than dumping their reference microsized powder (P < 0.05). Statistically significant more and larger particles were also found during dumping of SiO2 nanopowder compared to TiO2/Al2O3 nanopowders. Particle surface coating did not affect the number concentration but on average larger particles were found during dumping of coated nanopowders. An increase of the powder's moisture content resulted in less and smaller particles in the air. Furthermore, the results indicate that particle number concentration increases with increasing dump height, rate, and mass and decreases when ventilation is turned on. Discussion: These results give an indication of the direction and magnitude of the effect of the studied determinants on concentrations close to the source and provide a scientific basis for (further) development of existing and future NOAA inhalation exposure models.

The Validity and Applicability of Using a Generic Exposure Assessment Model for Occupational Exposure to Nano-Objects and Their Aggregates and Agglomerates.

BACKGROUND: Control banding can be used as a first-tier assessment to control worker exposure to nano-objects and their aggregates and agglomerates (NOAA). In a second tier, more advanced modelling approaches are needed to produce quantitative exposure estimates. As currently no general quantitative nano-specific exposure models are available, this study evaluated the validity and applicability of using a generic exposure assessment model (the Advanced REACH Tool-ART) for occupational exposure to NOAA. METHOD: The predictive capability of ART for occupational exposure to NOAA was tested by calculating the relative bias and correlations (Pearson) between the model estimates and measured concentrations using a dataset of 102 NOAA exposure measurements collected during experimental and workplace exposure studies. RESULTS: Moderate to (very) strong correlations between the ART estimates and measured concentrations were found. Estimates correlated better to measured concentration levels of dust (r = 0.76, P < 0.01) than liquid aerosols (r = 0.51, P = 0.19). However, ART overestimated the measured NOAA concentrations for both the experimental and field measurements (factor 2-127). Overestimation was highest at low concentrations and decreased with increasing concentration. Correlations seemed to be better when looking at the nanomaterials individually compared to combined scenarios, indicating that nanomaterial-specific characteristics are not well captured within the mechanistic model of the ART. DISCUSSION: Although ART in its current state is not capable to estimate occupational exposure to NOAA, the strong correlations for the individual nanomaterials indicate that the ART (and potentially other generic exposure models) have the potential to be extended or adapted for exposure to NOAA. In the future, studies investigating the potential to estimate exposure to NOAA should incorporate more explicitly nanomaterial-specific characteristics in their models.

Evaluation of Decision Rules in a Tiered Assessment of Inhalation Exposure to Nanomaterials.

Tiered or stepwise approaches to assess occupational exposure to nano-objects, and their agglomerates and aggregates have been proposed, which require decision rules (DRs) to move to a next tier, or terminate the assessment. In a desk study the performance of a number of DRs based on the evaluation of results from direct reading instruments was investigated by both statistical simulations and the application of the DRs to real workplace data sets. A statistical model that accounts for autocorrelation patterns in time-series, i.e. autoregressive integrated moving average (ARIMA), was used as 'gold' standard. The simulations showed that none of the proposed DRs covered the entire range of simulated scenarios with respect to the ARIMA model parameters, however, a combined DR showed a slightly better agreement. Application of the DRs to real workplace datasets (n = 117) revealed sensitivity up to 0.72, whereas the lowest observed specificity was 0.95. The selection of the most appropriate DR is very much dependent on the consequences of the decision, i.e. ruling in or ruling out of scenarios for further evaluation. Since a basic assessment may also comprise of other type of measurements and information, an evaluation logic was proposed which embeds the DRs, but furthermore supports decision making in view of a tiered-approach exposure assessment.

Potential Release of Manufactured Nano Objects During Sanding of Nano-Coated Wood Surfaces.

Increasing production and applications of manufactured nano objects (MNOs) have become a source for human exposure and therefore raise concerns and questions about the possible health effects. In this study, the potential release of nano objects, their agglomerates, and aggregates (NOAA) as a result of sanding of hardwood treated with MNOs-containing coating was examined. Two types of MNO-containing coating were compared with untreated hardwood that allowed the evaluation of the influence of the chemical composition on the release of particles. Furthermore, the rotation speed of the sander and the grit size of the sanding paper were varied in order to assess their influence on the release of particles.Measurements were conducted in a gas-tight chamber with a volume of 19.5 m(3) in which ventilation was minimized during experiments. Particle size distributions were assessed by scanning mobility particle sizer , aerodynamic particle sizer, and electrical low pressure impactor. Furthermore, aerosol number concentrations (Nanotracer), active surface area (LQ1), and fractionated mass (Cascade Impactor) were measured before, during, and after sanding. Scanning electron microscope/energy dispersive X-ray (SEM/EDX) analysis was performed to adequately characterize the morphology, size, and chemical composition of released particles.SEM/EDX analysis indicated that sanding surfaces treated with MNO-containing coating did not release the designated MNO as free primary particles. In both coatings, clusters of MNO were perceived embedded in and attached to micro-sized wood and/or coating particles created by sanding the coated surface. Real-time measurements indicated a lower release of micro-sized particles from sanding of surfaces treated with Coating I than from sanding untreated surfaces or surfaces treated with Coating II. A substantial increase in nanosized and a slight increase in micro-sized particles was perceived as the rotation speed of the sander increased. However, most nanosized particles were most likely emitted by the sanding machine. No effect of the grit size on the release of particles was detected.

Occupational Exposure to Multi-Walled Carbon Nanotubes During Commercial Production Synthesis and Handling.

The world-wide production of carbon nanotubes (CNTs) has increased substantially in the last decade, leading to occupational exposures. There is a paucity of exposure data of workers involved in the commercial production of CNTs. The goals of this study were to assess personal exposure to multi-walled carbon nanotubes (MWCNTs) during the synthesis and handling of MWCNTs in a commercial production facility and to link these exposure levels to specific activities. Personal full-shift filter-based samples were collected, during commercial production and handling of MWCNTs, R&D activities, and office work. The concentrations of MWCNT were evaluated on the basis of EC concentrations. Associations were studied between observed MWCNT exposure levels and location and activities. SEM analyses showed MWCNTs, present as agglomerates ranging between 200 nm and 100 µm. Exposure levels of MWCNTs observed in the production area during the full scale synthesis of MWCNTs (N = 23) were comparable to levels observed during further handling of MWCNTs (N = 19): (GM (95% lower confidence limit-95% upper confidence limit)) 41 µg m(-3) (20-88) versus 43 µg m(-3) (22-86), respectively. In the R&D area (N = 11) and the office (N = 5), exposure levels of MWCNTs were significantly (P < 0.05) lower: 5 µg m(-3) (2-11) and 7 µg m(-3) (2-28), respectively. Bagging, maintenance of the reactor, and powder conditioning were associated with higher exposure levels in the production area, whereas increased exposure levels in the R&D area were related to handling of MWCNTs powder.

Occupational Exposure to Nano-Objects and Their Agglomerates and Aggregates Across Various Life Cycle Stages; A Broad-Scale Exposure Study.

BACKGROUND: Occupational exposure to manufactured nano-objects and their agglomerates, and aggregates (NOAA) has been described in several workplace air monitoring studies. However, data pooling for general conclusions and exposure estimates are hampered by limited exposure data across the occupational life cycle of NOAA and a lack in comparability between the methods of collecting and analysing the data. By applying a consistent method of collecting and analysing the workplace exposure data, this study aimed to provide information about the occupational NOAA exposure levels across various life cycle stages of NOAA in the Netherlands which can also be used for multi-purpose use. METHODS: Personal/near field task-based exposure data was collected using a multi-source exposure assessment method collecting real time particle number concentration, particle size distribution (PSD), filter-based samples for morphological, and elemental analysis and detailed contextual information. A decision logic was followed allowing a consistent and objective way of analysing the exposure data. RESULTS: In total, 46 measurement surveys were conducted at 15 companies covering 18 different exposure situations across various occupational life cycle stages of NOAA. Highest activity-effect levels were found during replacement of big bags (<1000-76000 # cm(-3)), mixing/dumping of powders manually (<1000-52000 # cm(-3)) and mechanically (<1000-100000 # cm(-3)), and spraying of liquid (2000-800000 # cm(-3)) showing a high variability between and within the various exposure situations. In general, a limited change in PSD was found during the activity compared to the background. CONCLUSIONS: This broad-scale exposure study gives a comprehensive overview of the NOAA exposure situations in the Netherlands and an indication of the levels of occupational exposure to NOAA across various life cycle of NOAA. The collected workplace exposure data and contextual information will serve as basis for future pooling of data and modelling of worker exposure.

Human exposure to conventional and nanoparticle--containing sprays-a critical review.

The release of pesticides from conventional spray products has been investigated in depth, and suitable analytical techniques detecting the mass of the released substances are available. In contrast, nanoparticle-containing sprays are less studied, although they are perceived as critical for consumers because inhalation exposure can occur to potentially toxic nanoparticles. A few recent studies presented analytical concepts for exposure experiments and generated data for exposure assessment. This study attempts to review and compare the current approaches to characterize nanosprays and to identify challenges for future research. Furthermore, experimental setups used for exposure assessment from conventional sprays are reviewed and compared to setups used for nanoparticle-containing sprays. National and international norms dealing with nanoparticle characterization, spray characterization and exposure are inspected with regard to their usefulness for standardizing exposure assessment. Different approaches in the field of exposure modeling are reviewed and compared. The conclusion is that due to largely varying experimental setups to date exposure values for nanosprays are difficult to compare. All studies are only conducted with a limited set of sprays, and no systematic evaluation of the study conditions is available. A suitable set of experimental setups as well as minimum reporting requirements should be agreed upon to enable the systematic evaluation of consumer sprays in the future. Indispensable features of such experimental setups are developed in this review.

Airborne manufactured nano-objects released from commercially available spray products: temporal and spatial influences.

This paper reports a study of the dispersion of manufactured nano-objects (MNOs) through the air, both in time and space, during the use of two commercially available nano-spray products and comparable products without MNOs. The main objective was to identify whether personal exposure can occur at a greater distance than the immediate proximity of the source (>1 m from the source), that is, in the "far field" (bystanders), or at a period after the emission occurred (re-entry). The spray experiments were conducted in an experimental room with well-controlled environmental and ventilation conditions (19.5 m(3)). The concentration of MNOs was investigated by measuring real-time size distribution, number, and active surface area concentration. For off-line analysis of the particles in the air, samples for scanning/transmission electron microscopy and elemental analysis were collected. The release of MNOs was measured at ∼30 and 290 cm from the source ("near field" and "far field", respectively). For all four spray products, the maximum number and surface area concentrations in the "near field" exceeded the maximum concentrations reached in the "far field". At 2 min after the emission occurred, the concentration in both the "near field" and "far field" reached a comparable steady-state level above background level. These steady-state concentrations remained elevated above background concentration throughout the entire measurement period (12 min). The results of the real-time measurement devices mainly reflect the liquid aerosols emitted by the spray process itself rather than only the MNO, which hampers the interpretation of the results. However, the combination of the off-line analysis and the results of the real-time devices indicates that after the use of nano-spray products, personal exposure to MNOs can occur not only in the near field, but also at a greater distance than the immediate proximity of the source and at a period after emission occurred.

Industrial production and professional application of manufactured nanomaterials-enabled end products in Dutch industries: potential for exposure.

BACKGROUND: In order to make full use of the opportunities while responsibly managing the risks of working with manufactured nanomaterials (MNM), we need to gain insight into the potential level of exposure to MNM in the industry. Therefore, the goal of this study was to obtain an overview of the potential MNM exposure scenarios within relevant industrial sectors, applied exposure controls, and number of workers potentially exposed to MNM in Dutch industrial sectors producing and applying MNM-enabled end products in the Netherlands. METHODS: A survey was conducted in three phases: (i) identification of MNM-enabled end products; (ii) identification of relevant industrial sectors; and (iii) a tiered telephone survey to estimate actual use of the products among 40 sector organizations/knowledge centres (Tier 1), 350 randomly selected companies (Tier 2), and 110 actively searched companies (Tier 3). RESULTS: The most dominant industrial sectors producing or applying MNM-enabled end products (market penetration >5%) are shoe repair shops, automotive, construction, paint, metal, and textile cleaning industry. In the majority of the companies (76%), potential risks related to working with MNM are not a specific point of interest. The total number of workers potentially exposed to MNM during the production or application of MNM-enabled end products was estimated at approximately 3000 workers in the Netherlands. The results of this study will serve as a basis for in-depth exposure and health surveys that are currently planned in the Netherlands. In addition, the results can be used to identify the most relevant sectors for policy makers and future studies focussing on evaluating the risks of occupational exposure to MNM.