ABSTRACT Diesel exhaust has been classified a probable human carcinogen, and the National Institute for Occupational Safety and Health (NIOSH) has recommended that employers reduce workers' exposures. Because diesel exhaust is a chemically complex mixture containing thousands of compounds, some measure of exposure must be selected. Previously used methods involving gravimetry or analysis of the soluble organic fraction of diesel soot lack adequate sensitivity and selectivity for low-level determination of particulate diesel exhaust; a new analytical approach was therefore needed. In this paper, results of investigation of a thermal-optical technique for analysis of the carbonaceous fraction of particulate diesel exhaust are reported. With this technique, speciation of organic and elemental carbon is accomplished through temperature and atmosphere control, and by an optical feature that corrects for pyrolytically generated carbon, or "char," which is formed during the analysis of some materials. The thermal-optical method was selected because the instrument has desirable design features not present in other carbon analyzers. Although various carbon types are determined, elemental carbon is the superior marker of diesel particulate matter because elemental carbon constitutes a large fraction of the particulate mass, it can be quantified at low levels, and its only significant source in most workplaces is the diesel engine. Exposure-related issues and results of investigation of various sampling methods for particulate diesel exhaust also are discussed. †Disclaimer: Mention of company name or product does not constitute endorsement by the Centers for Disease Control and Prevention. The views expressed in this paper are those of the authors, and do not necessarily reflect the views or policies of the National Institute for Occupational Safety and Health. Notes †Disclaimer: Mention of company name or product does not constitute endorsement by the Centers for Disease Control and Prevention. The views expressed in this paper are those of the authors, and do not necessarily reflect the views or policies of the National Institute for Occupational Safety and Health.
The increasing prevalence of carbon nanotubes (CNTs) in manufacturing and research environments, together with the potential exposure risks, necessitates development of reliable and accurate monitoring methods for these materials. We examined quantification of CNTs by two distinct methods based on Raman spectroscopy. First, as measured by the Raman peak intensity of aqueous CNT suspensions, and second, by Raman mapping of air filter surfaces onto which CNTs were collected as aerosols or applied as small-area (0.05 cm2) deposits. Correlation (R2 = 0.97) between CNT concentration and Raman scattering intensity for suspensions in cuvettes was found over a concentration range from about 2 to 10 µg/ml, but measurement variance precludes practical determination of a calibration curve. Raman mapping of aerosol sample filter surfaces shows correlation with CNT mass when the surface density is relatively high (R2 = 0.83 and 0.95 above about 5 µg total mass on filter), while heterogeneity of CNT deposition makes obtaining representative maps of lower density samples difficult. This difficulty can be mitigated by increasing the area mapped relative to the total sample area, improving both precision and the limit of detection (LOD). For small-area deposits, detection of low masses relevant to occupational monitoring can be achieved, with an estimated LOD of about 50 ng.
Carbon nanotubes (CNTs) are emerging as important occupational and environmental toxicants owing to their increasing prevalence and potential to be inhaled as airborne particles. CNTs are a concern because of their similarities to asbestos, which include fibrous morphology, high aspect ratio, and biopersistence. Limitations in research models have made it difficult to experimentally ascertain the risk of CNT exposures to humans and whether these may lead to lung diseases classically associated with asbestos, such as mesothelioma and fibrosis. In this study, we sought to comprehensively compare profiles of lung pathology in mice following repeated exposures to multiwall CNTs or crocidolite asbestos (CA). We show that both exposures resulted in granulomatous inflammation and increased interstitial collagen; CA exposures caused predominantly bronchoalveolar hyperplasia, whereas CNT exposures caused alveolar hyperplasia of type II pneumocytes (T2Ps). T2Ps isolated from CNT-exposed lungs were found to have upregulated proinflammatory genes, including interleukin 1ß (IL-1ß), in contrast to those from CA exposed. Immunostaining in tissue showed that while both toxicants increased IL-1ß protein expression in lung cells, T2P-specific IL-1ß increases were greater following CNT exposure. These results suggest related but distinct mechanisms of action by CNTs versus asbestos which may lead to different outcomes in the 2 exposure types.
Miniature helical applicators were designed to operate at 915 MHz, to investigate their potential use in the hyperthermic treatment of Barrett's oesophagus. Heating patterns were studied within a muscle-equivalent phantom using a thermographic camera. The results show that the spacing between the turns of the coil and the insertion depth of the applicator into the phantom significantly influence the microwave heating pattern.
Carbonaceous particulate typically represents a large fraction of PM{sub 2.5}. Two primary techniques presently used for the analysis of particulate carbon are Thermal Optical Transmission (TOT - NIOSH Method 5040) and Thermal Optical Reflectance (TOR). These two methods both quantify carbon by heating filters and volatilizing the carbon that is oxidized in a granular bed of MnO{sub 2}, reduced to CH{sub 4} in a Ni methanator, and quantified as CH{sub 4} with a flame ionization detector. However, the methods use different techniques to correct for the formation of pyrolysis products and the temperature programs for defining organic and elemental carbon. The TOT and TOR measurement techniques are being compared using samples from the Chemical Speciation Monitor Evaluation Field Study. All of the samples will be measured with TOR and a subset of samples representing a range of mass concentrations will be measured with TOT. This comparison will provide insight into the effect of the measurement technique parameters on organic and elemental carbon concentrations.
Detailed investigations were conducted at a facility that manufactures and processes carbon nanofibers (CNFs). Presented research summarizes the direct-reading monitoring aspects of the study. A mobile aerosol sampling platform, equipped with an aerosol instrument array, was used to characterize emissions at different locations within the facility. Particle number, respirable mass, active surface area, and photoelectric response were monitored with a condensation particle counter (CPC), a photometer, a diffusion charger, and a photoelectric aerosol sensor, respectively. CO and CO2 were additionally monitored. Combined simultaneous monitoring of these metrics can be utilized to determine source and relative contribution of airborne particles (CNFs and others) within a workplace. Elevated particle number concentrations, up to 1.15 × 106 cm−3, were found within the facility but were not due to CNFs. Ultrafine particle emissions, released during thermal treatment of CNFs, were primarily responsible. In contrast, transient increases in respirable particle mass concentration, with a maximum of 1.1 mg m−3, were due to CNF release through uncontrolled transfer and bagging. Of the applied metrics, our findings suggest that particle mass was probably the most useful and practical metric for monitoring CNF emissions in this facility. Through chemical means, CNFs may be selectively distinguished from other workplace contaminants (Birch et al., in preparation), and for direct-reading monitoring applications, the photometer was found to provide a reasonable estimate of respirable CNF mass concentration. Particle size distribution measurements were conducted with an electrical low-pressure impactor and a fast particle size spectrometer. Results suggest that the dominant CNF mode by particle number lies between 200 and 250 nm for both aerodynamic and mobility equivalent diameters. Significant emissions of CO were also evident in this facility. Exposure control recommendations were described for processes as required.
Diesel exhaust has been classified a probable human carcinogen, and the National Institute for Occupational Safety and Health (NIOSH) has recommended that employers reduce workers' exposures. Because diesel exhaust is a chemically complex mixture containing thousands of compounds, some measure of exposure must be selected. Previously used methods involving gravimetry or analysis of the soluble organic fraction of diesel soot lack adequate sensitivity and selectivity for low-level determination of particulate diesel exhaust; a new analytical approach was therefore needed. In this paper, results of investigation of a thermal–optical technique for the analysis of the carbonaceous fraction of particulate diesel exhaust are discussed. With this technique, speciation of organic and elemental carbon is accomplished through temperature and atmosphere control and by an optical feature that corrects for pyrolytically generated carbon, or 'char,' which is formed during the analysis of some materials. The thermal–optical method was selected because the instrument has desirable design features not present in other carbon analysers. Although various carbon types are determined by the method, elemental carbon is the superior marker of diesel particulate matter because elemental carbon constitutes a large fraction of the particulate mass, it can be quantified at low levels and its only significant source in most workplaces is the diesel engine. Exposure-related issues and sampling methods for particulate diesel exhaust also are discussed.
Total carbon (TC) is sometimes used to measure or characterize diesel particulate matter (DPM) in occupational settings such as underground mines. DPM samples are collected on quartz fiber filters. When using quartz fiber filters, adsorption of gas phase organic carbon (OC) has been reported, causing a positive bias in the particulate TC results (adsorption artifact). Most of the data on the sampling artifacts and corrections applyto environmental air sampling, where samples are collected at a much higher filter face velocity and the OC concentrations are generally much lower relative to occupational sampling. In this study, we investigated the effects of adsorption artifact on samples from occupational settings. Samples were collected with and without denuders to determine the amount of gas phase OC collected and the accuracy of certain corrections. In underground stone mines, the adsorption artifact was found to positively bias the particulate TC by greater than 20% for filter loadings below 25 microg/cm2 TC (8-h time weighted average = 262 microg/m3). The tandem filter correction reduced the effect of the artifact, as high as 60% of the TC value, to less than 11% for laboratory data. It also significantly reduced the effect of the artifact obtained for field samples.
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