Last data update: Apr 29, 2024. (Total: 46658 publications since 2009)
Records 1-30 (of 33 Records) |
Query Trace: Dahm M [original query] |
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End-stage renal disease incidence in a cohort of US firefighters from San Francisco, Chicago, and Philadelphia
Pinkerton LE , Bertke S , Dahm MM , Kubale TL , Siegel MR , Hales TR , Yiin JH , Purdue MP , Beaumont JJ , Daniels RD . Am J Ind Med 2022 65 (12) 975-984 BACKGROUND: Firefighters perform strenuous work in hot environments, which may increase their risk of chronic kidney disease. The purpose of this study was to evaluate the risk of end-stage renal disease (ESRD) and types of ESRD among a cohort of US firefighters compared to the US general population, and to examine exposure-response relationships. METHODS: ESRD from 1977 through 2014 was identified through linkage with Medicare data. ESRD incidence in the cohort compared to the US population was evaluated using life table analyses. Associations of all ESRD, systemic ESRD, hypertensive ESRD, and diabetic ESRD with exposure surrogates (exposed days, fire runs, and fire hours) were examined in Cox proportional hazards models adjusted for attained age (the time scale), race, birth date, fire department, and employment duration. RESULTS: The incidence of all ESRD was less than expected (standardized incidence ratio (SIR) = 0.79; 95% confidence interval = 0.69-0.89, observed = 247). SIRs for ESRD types were not significantly increased. Positive associations of all ESRD, systemic ESRD, and hypertensive ESRD with exposed days were observed: however, 95% confidence intervals included one. CONCLUSIONS: We found little evidence of increased risk of ESRD among this cohort of firefighters. Limitations included the inability to evaluate exposure-response relationships for some ESRD types due to small observed numbers, the limitations of the surrogates of exposure, and the lack of information on more sensitive outcome measures for potential kidney effects. |
Histopathology of the broad class of carbon nanotubes and nanofibers used or produced in U.S. facilities in a murine model
Fraser K , Hubbs A , Yanamala N , Mercer RR , Stueckle TA , Jensen J , Eye T , Battelli L , Clingerman S , Fluharty K , Dodd T , Casuccio G , Bunker K , Lersch TL , Kashon ML , Orandle M , Dahm M , Schubauer-Berigan MK , Kodali V , Erdely A . Part Fibre Toxicol 2021 18 (1) 47 BACKGROUND: Multi-walled carbon nanotubes and nanofibers (CNT/F) have been previously investigated for their potential toxicities; however, comparative studies of the broad material class are lacking, especially those with a larger diameter. Additionally, computational modeling correlating physicochemical characteristics and toxicity outcomes have been infrequently employed, and it is unclear if all CNT/F confer similar toxicity, including histopathology changes such as pulmonary fibrosis. Male C57BL/6 mice were exposed to 40 µg of one of nine CNT/F (MW #1-7 and CNF #1-2) commonly found in exposure assessment studies of U.S. facilities with diameters ranging from 6 to 150 nm. Human fibroblasts (0-20 µg/ml) were used to assess the predictive value of in vitro to in vivo modeling systems. RESULTS: All materials induced histopathology changes, although the types and magnitude of the changes varied. In general, the larger diameter MWs (MW #5-7, including Mitsui-7) and CNF #1 induced greater histopathology changes compared to MW #1 and #3 while MW #4 and CNF #2 were intermediate in effect. Differences in individual alveolar or bronchiolar outcomes and severity correlated with physical dimensions and how the materials agglomerated. Human fibroblast monocultures were found to be insufficient to fully replicate in vivo fibrosis outcomes suggesting in vitro predictive potential depends upon more advanced cell culture in vitro models. Pleural penetrations were observed more consistently in CNT/F with larger lengths and diameters. CONCLUSION: Physicochemical characteristics, notably nominal CNT/F dimension and agglomerate size, predicted histopathologic changes and enabled grouping of materials by their toxicity profiles. Particles of greater nominal tube length were generally associated with increased severity of histopathology outcomes. Larger particle lengths and agglomerates were associated with more severe bronchi/bronchiolar outcomes. Spherical agglomerated particles of smaller nominal tube dimension were linked to granulomatous inflammation while a mixture of smaller and larger dimensional CNT/F resulted in more severe alveolar injury. |
Serum peptidome: diagnostic window into pathogenic processes following occupational exposure to carbon nanomaterials
Mostovenko E , Dahm MM , Schubauer-Berigan MK , Eye T , Erdely A , Young TL , Campen MJ , Ottens AK . Part Fibre Toxicol 2021 18 (1) 39 BACKGROUND: Growing industrial use of carbon nanotubes and nanofibers (CNT/F) warrants consideration of human health outcomes. CNT/F produces pulmonary, cardiovascular, and other toxic effects in animals along with a significant release of bioactive peptides into the circulation, the augmented serum peptidome. While epidemiology among CNT/F workers reports on few acute symptoms, there remains concern over sub-clinical CNT/F effects that may prime for chronic disease, necessitating sensitive health outcome diagnostic markers for longitudinal follow-up. METHODS: Here, the serum peptidome was assessed for its biomarker potential in detecting sub-symptomatic pathobiology among CNT/F workers using label-free data-independent mass spectrometry. Studies employed a stratified design between High (> 0.5 µg/m(3)) and Low (< 0.1 µg/m(3)) inhalable CNT/F exposures in the industrial setting. Peptide biomarker model building and refinement employed linear regression and partial least squared discriminant analyses. Top-ranked peptides were then sequence identified and evaluated for pathological-relevance. RESULTS: In total, 41 peptides were found to be highly discriminatory after model building with a strong linear correlation to personal CNT/F exposure. The top-five peptide model offered ideal prediction with high accuracy (Q(2) = 0.99916). Unsupervised validation affirmed 43.5% of the serum peptidomic variance was attributable to CNT/F exposure. Peptide sequence identification reveals a predominant association with vascular pathology. ARHGAP21, ADAM15 and PLPP3 peptides suggest heightened cardiovasculature permeability and F13A1, FBN1 and VWDE peptides infer a pro-thrombotic state among High CNT/F workers. CONCLUSIONS: The serum peptidome affords a diagnostic window into sub-symptomatic pathology among CNT/F exposed workers for longitudinal monitoring of systemic health risks. |
An international needs assessment survey of guideline developers demonstrates variability in resources and challenges to collaboration between organizations
Sultan S , Siedler MR , Morgan RL , Ogunremi T , Dahm P , Fatheree LA , Getchius TSD , Ginex PK , Jakhmola P , McFarlane E , Murad MH , Temple Smolkin RL , Amer YS , Alam M , Kang BY , Falck-Ytter Y , Mustafa RA . J Gen Intern Med 2021 37 (11) 2669-2677 BACKGROUND: The development of rigorous, high-quality clinical guidelines increases the need for resources and skilled personnel within guideline-producing organizations. While collaboration between organizations provides a unique opportunity to pool resources and save time and effort, the collaboration presents its own unique challenges. OBJECTIVE: To assess the perceived needs and current challenges of guideline producers worldwide related to guideline development and collaboration efforts. DESIGN: Survey questions were developed by the Guidelines International Network and the US GRADE Network, pilot-tested among attendees of a guideline development workshop, and disseminated electronically using convenience and snowball sampling methods. PARTICIPANTS: A total of 171 respondents representing 30 countries and more than 112 unique organizations were included in this analysis. MAIN MEASURES: The survey included free-response, multiple-choice, and seven-point Likert-scale questions. Questions assessed respondents' perceived value of guidelines, resource availability and needs, guideline development processes, and collaboration efforts of their organization. KEY RESULTS: Time required to develop high-quality systematic reviews and guidelines was the most relevant need (median=7; IQR=5.5-7). In-house resources to conduct literature searches (median=4; IQR=3-6) and the resources to develop rigorous guidelines rapidly (median=4; IQR=2-5) were perceived as the least available resources. Difficulties reconciling differences in guideline methodology (median=6; IQR=4-7) and the time required to establish collaborative agreements (median=6; IQR=5-6) were the most relevant barriers to collaboration between organizations. Results also indicated a general need for improvement in conflict of interest (COI) disclosure policies. CONCLUSION: The survey identified organizational challenges in supporting rigorous guideline development, including the time, resources, and personnel required. Connecting guideline developers to existing databases of high-quality systematic reviews and the use of freely available online platforms may facilitate guideline development. Guideline-producing organizations may also consider allocating resources to hiring or training personnel with expertise in systematic review methodologies or utilizing resources more effectively by establishing collaborations with other organizations. |
Occupational Exposures to Engineered Nanomaterials: a Review of Workplace Exposure Assessment Methods
McCormick S , Niang M , Dahm MM . Curr Environ Health Rep 2021 8 (3) 223-234 PURPOSE OF REVIEW: The purpose of this review is to consolidate exposure assessment methods for occupational research on engineered nanomaterials (ENMs) published within the past 5 years (2015-2020). RECENT FINDINGS: The three ENMs that generated the highest volume of new research include titanium dioxide, graphene, and aluminum oxide. A multi-metric approach, using both online and offline instruments and analyses, has been found to be a useful method to characterize ENM workplace exposures and was commonly used in the recently published literature. Particle number concentration was the most common online exposure metric used, followed by the metrics of mass and surface area. There are currently no consensus methods for offline analyses of most ENMs. Researchers generally used gravimetric or elemental analyses for carbonaceous nanomaterials, titanium dioxide, and other nanometals, but there was little overlap between other ENM materials reviewed. Using biological markers of exposure, such as urinary oxidative stress biomarkers, as an indication of chronic exposure may also be useful for some ENMs and should be further researched. Generally, similar online instrumentation and offline electron microscopy methods were used for all ENMs. However, this consistency was not observed for offline mass analysis methods within specific ENMs. Consolidation of the most recent methods and results of exposure assessments within this broad material category can guide researchers toward future areas of study. Establishing consensus methods of exposure assessment for each individual ENM is crucial to characterizing workplace exposures, pooling data to fully understand their associated risks, and developing useful occupational exposure limits. |
Industrial hygiene data standardization: past lessons, present challenges, and future directions
Shockey TM , Dahm MM , Wurzelbacher SJ , Baker J . Synergist 2020 31 (12) 20-25 The collection of industrial hygiene (IH) air, surface, and noise data is a critical task at the center of the IH profession. Industrial hygienists usually collect occupational exposure measurements using sampling methods that have been validated by Occupational Safety and Health Administration (OSHA) or National Institute for Occupational Safety and Health (NIOSH) to protect workers from chemical, biological, and physical hazards. But beyond the information required on a standard chain of custody form (sampler/media type, analysis method, sample time, sample volume, and so on), any additional data elements and variables collected are often left to the discretion of the hygienist. ... American Industrial Hygiene Association (AIHA) has increased efforts to promote data quality and standardization by including an appendix on data quality in the latest edition of "A Strategy for Assessing and Managing Occupational Exposures," which was published in 2015. This appendix introduces literature on how to evaluate historical or current IH data quality and includes a checklist of data elements adapted from the literature, including the 1996 special report in the Applied journal. The checklist serves as a source for comparison, providing a method for evaluating current IH forms to examine which data fields are being captured and how. |
Physicochemical characterization and genotoxicity of the broad class of carbon nanotubes and nanofibers used or produced in U.S. facilities.
Fraser K , Kodali V , Yanamala N , Birch ME , Cena L , Casuccio G , Bunker K , Lersch TL , Evans DE , Stefaniak A , Hammer MA , Kashon ML , Boots T , Eye T , Hubczak J , Friend SA , Dahm M , Schubauer-Berigan MK , Siegrist K , Lowry D , Bauer AK , Sargent LM , Erdely A . Part Fibre Toxicol 2020 17 (1) 62 BACKGROUND: Carbon nanotubes and nanofibers (CNT/F) have known toxicity but simultaneous comparative studies of the broad material class, especially those with a larger diameter, with computational analyses linking toxicity to their fundamental material characteristics was lacking. It was unclear if all CNT/F confer similar toxicity, in particular, genotoxicity. Nine CNT/F (MW #1-7 and CNF #1-2), commonly found in exposure assessment studies of U.S. facilities, were evaluated with reported diameters ranging from 6 to 150 nm. All materials were extensively characterized to include distributions of physical dimensions and prevalence of bundled agglomerates. Human bronchial epithelial cells were exposed to the nine CNT/F (0-24 μg/ml) to determine cell viability, inflammation, cellular oxidative stress, micronuclei formation, and DNA double-strand breakage. Computational modeling was used to understand various permutations of physicochemical characteristics and toxicity outcomes. RESULTS: Analyses of the CNT/F physicochemical characteristics illustrate that using detailed distributions of physical dimensions provided a more consistent grouping of CNT/F compared to using particle dimension means alone. In fact, analysis of binning of nominal tube physical dimensions alone produced a similar grouping as all characterization parameters together. All materials induced epithelial cell toxicity and micronuclei formation within the dose range tested. Cellular oxidative stress, DNA double strand breaks, and micronuclei formation consistently clustered together and with larger physical CNT/F dimensions and agglomerate characteristics but were distinct from inflammatory protein changes. Larger nominal tube diameters, greater lengths, and bundled agglomerate characteristics were associated with greater severity of effect. The portion of tubes with greater nominal length and larger diameters within a sample was not the majority in number, meaning a smaller percentage of tubes with these characteristics was sufficient to increase toxicity. Many of the traditional physicochemical characteristics including surface area, density, impurities, and dustiness did not cluster with the toxicity outcomes. CONCLUSION: Distributions of physical dimensions provided more consistent grouping of CNT/F with respect to toxicity outcomes compared to means only. All CNT/F induced some level of genotoxicity in human epithelial cells. The severity of toxicity was dependent on the sample containing a proportion of tubes with greater nominal lengths and diameters. |
Planning for epidemics and pandemics: assessing the potential impact of extended use and reuse strategies on respirator usage rates to support supply-and-demand planning efforts
Yorio PL , Fisher EM , Kilinc-Balci FS , Rottach D , Harney J , Seaton M , Dahm MM , Niemeier T . J Int Soc Respir Prot 2020 37 (1) 52-60 During epidemics and pandemics healthcare personnel (HCP) are on the front line of disease containment and mitigation. Personal protective equipment (PPE), such as NIOSH-approved N95 filtering facepiece respirators (FFRs), serve an important role in minimizing HCP risks and are in high demand during public health emergencies. Because PPE demand can exceed supply, various public health strategies have been developed to reduce the rate of PPE consumption as supply dwindles. Extended use and limited reuse of N95 FFRs are strategies advocated by many governmental agencies used to increase the number of times a device can be used. Increased use of respirators designed for reuse-such as powered air-purifying respirators (PAPRs) and elastomeric half-mask and full facepiece air-purifying respirators- is another option designed to reduce the continuous need for new devices as the daily need for respirator use increases. Together, these strategies are designed to reduce the number of PPE units that must be discarded daily and, therefore, extend the longevity of available supply. The purpose of this paper is to theoretically estimate the impact of extended use and limited reuse strategies for N95 FFRs and the increased use of reusable respirator options on PPE consumed. The results suggest that a considerable reduction in PPE consumption would result from extended use and limited reuse of N95 FFRs and the increased use of respirators designed for reuse; however, the practical benefits must be balanced with the risks and economic costs. In addition, extended use and reuse strategies must be accompanied by proper procedures to reduce risk. The study is designed to support epidemic and pandemic PPE supply and demand planning efforts. |
Association of occupational exposures with ex vivo functional immune response in workers handling carbon nanotubes and nanofibers
Schubauer-Berigan MK , Dahm MM , Toennis CA , Sammons DL , Eye T , Kodali V , Zeidler-Erdely PC , Erdely A . Nanotoxicology 2020 14 (3) 1-16 The objective of this study was to evaluate the association between carbon nanotube and nanofiber (CNT/F) exposure and ex vivo responses of whole blood challenged with secondary stimulants, adjusting for potential confounders, in a cross-sectional study of 102 workers. Multi-day exposure was measured by CNT/F structure count (SC) and elemental carbon (EC) air concentrations. Demographic, lifestyle and other occupational covariate data were obtained via questionnaire. Whole blood collected from each participant was incubated for 18 hours with and without two microbial stimulants (lipopolysaccharide/LPS and staphylococcal enterotoxin type B/SEB) using TruCulture technology to evaluate immune cell activity. Following incubation, supernatants were preserved and analyzed for protein concentrations. The stimulant:null response ratio for each individual protein was analyzed using multiple linear regression, followed by principal component (PC) analysis to determine whether patterns of protein response were related to CNT/F exposure. Adjusting for confounders, CNT/F metrics (most strongly, the SC-based) were significantly (p < 0.05) inversely associated with stimulant:null ratios of several individual biomarkers: GM-CSF, IFN-gamma, interleukin (IL)-2, IL-4, IL-5, IL-10, IL-17, and IL-23. CNT/F metrics were significantly inversely associated with PC1 (a weighted mean of most biomarkers, explaining 25% of the variance in the protein ratios) and PC2 (a biomarker contrast, explaining 14%). Among other occupational exposures, only solvent exposure was significant (inversely related to PC2). CNT/F exposure metrics were uniquely related to stimulant responses in challenged whole blood, illustrating reduced responsiveness to a secondary stimulus. This approach, if replicated in other exposed populations, may present a relatively sensitive method to evaluate human response to CNT/F or other occupational exposures. |
Mortality in a cohort of US firefighters from San Francisco, Chicago and Philadelphia: an update
Pinkerton L , Bertke SJ , Yiin J , Dahm M , Kubale T , Hales T , Purdue M , Beaumont JJ , Daniels R . Occup Environ Med 2020 77 (2) 84-93 OBJECTIVES: To update the mortality experience of a previously studied cohort of 29 992 US urban career firefighters compared with the US general population and examine exposure-response relationships within the cohort. METHODS: Vital status was updated through 2016 adding 7 years of follow-up. Cohort mortality compared with the US population was evaluated via life table analyses. Full risk-sets, matched on attained age, race, birthdate and fire department were created and analysed using the Cox proportional hazards regression to examine exposure-response associations between select mortality outcomes and exposure surrogates (exposed-days, fire-runs and fire-hours). Models were adjusted for a potential bias from healthy worker survivor effects by including a categorical variable for employment duration. RESULTS: Compared with the US population, mortality from all cancers, mesothelioma, non-Hodgkin's lymphoma (NHL) and cancers of the oesophagus, intestine, rectum, lung and kidney were modestly elevated. Positive exposure-response relationships were observed for deaths from lung cancer, leukaemia and chronic obstructive pulmonary disease (COPD). CONCLUSIONS: This update confirms previous findings of excess mortality from all cancers and several site-specific cancers as well as positive exposure-response relations for lung cancer and leukaemia. New findings include excess NHL mortality compared with the general population and a positive exposure-response relationship for COPD. However, there was no evidence of an association between any quantitative exposure measure and NHL. |
Evaluation of total and inhalable samplers for the collection of carbon nanotube and carbon nanofiber aerosols
Dahm MM , Evans DE , Bertke S , Grinshpun SA . Aerosol Sci Technol 2019 53 (8) 958-970 A growing number of carbon nanotubes and nanofibers (CNT/F) exposure and epidemiologic studies have utilized 25- and 37-mm open-faced cassettes (OFCs) to assess the inhalable aerosol fraction. It has been previously established that the 37-mm OFC undersamples particles >20 µm in diameter, but the size-selective characteristics of the 25-mm OFC have not yet been fully evaluated. This article describes an experimental study conducted to determine if the 25- and 37-mm OFCs performed with relative equivalence to a reference inhalable aerosol sampler when challenged with CNT/F particles. Side-by-side paired samples were collected within a small Venturi chamber using a 25-mm styrene OFC, 37-mm styrene OFC, 25-mm aluminum OFC, and button inhalable aerosol sampler. Three types of CNT/F materials and an Arizona road dust were used as challenge aerosols for the various sampler configurations. Repeated experiments were conducted for each sampler configuration and material. The OFC samplers operated at flow rates of 2 and 5 L/min. Results showed that the 25-mm OFC performed comparably to the button sampler when challenged with CNT/F aerosols, which was demonstrated in five of the six experimental scenarios with an average error of 21%. Overall, the results of this study indicate that the sampling efficiency of the 25- and 37-mm OFCs adequately followed the ISO/ACGIH/CEN inhalable sampling convention when challenged with CNT/F aerosols. Past exposure and epidemiologic studies that used these OFC samplers can directly compare their results to studies that have used other validated inhalable aerosol samplers. ©, This work was authored as part of the Contributor’s official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law. |
Work-related injuries within a large urban public school system in the Mid-Western United States
Wu B , Varner K , Dahm MM , Reutman S , Davis KG . Work 2019 62 (3) 373-382 BACKGROUND: More than 13 million employees are working in the public education sector which includes more than just teachers in the United States. This industry sector also employs custodians, maintenance, and administration. To date, there is very limited information about the type and frequency of injuries for these employees. OBJECTIVE: To identify injury trends related to frequency and severity for different occupational injuries in a large urban school district. METHODS: Between 2014-2015, school district employees reported a total of 598 occupational injuries. Initial analysis of the data provided the frequency of injuries overall and for individual occupational categories. The Severity Index provides a score for job category and injury type based on severity and frequency. RESULTS: Overall, the Slip, Trip and Fall category had the highest frequency, followed by Combative Situations, and Over-exertion. Teacher and Para-professional workers experienced the greatest number of injuries with violence being the most frequent cause. Based on the Severity Index, Over-exertion was identified as the primary exposure concern for Custodians, while Slip, Trip and Fall category had the greatest impact on Building Engineers. CONCLUSIONS: With the diversity of negative outcomes, the administration will need targeted interventions for the various professions represented in the school systems. The injury severity profile indicates non-teachers should be a high priority for interventions with over-exertion and slips, trips and falls leading the risk. |
Predicting occupational exposures to carbon nanotubes and nanofibers based on workplace determinants modeling
Dahm MM , Bertke S , Schubauer-Berigan MK . Ann Work Expo Health 2019 63 (2) 158-172 Background: Recent cross-sectional epidemiologic studies have examined the association between human health effects and carbon nanotube and nanofiber (CNT/F) workplace exposures. However, due to the latency of many health effects of interest, cohort studies with sufficient follow-up will likely be needed. The objective of this study was to identify workplace determinants that contribute to exposure and develop predictive models to estimate CNT/F exposures for future use in epidemiologic studies. Methods: Exposure measurements were compiled from 15 unique facilities for the metrics of elemental carbon (EC) mass at both the respirable and inhalable aerosol size fractions as well as a quantitative analysis performed by transmission electron microscopy (TEM). These metrics served as the dependent variables in model development. Repeated personal samples were collected from most of the 127 CNT/F worker participants for 252 total observations. Determinants were categorized as company-level or worker-level and used to describe the exposure relationship within the dependent variables. The influence of determinants on variance components was explored using mixed linear models that utilized a backwards stepwise selection process with a lowering of the AIC for model determinant selection. Additional ridge regression models were created that examined predictive performance with and without all two-way interactions. Cross-validation was performed on each model to evaluate the generalizability of its predictive capabilities while predictive performance was evaluated according to the corresponding R2 value and root mean square error (RMSE). Results: Determinants at the company-level that increased exposure included an inadequate or semi-adequate engineering control rating, increasing average CNT/F diameter/length, daily quantities of material handled from 101 g to >1 kg and >1 kg, the use of CNF materials, the industry type of hybrid producer/user, and the expert assessment of a high exposure potential. Worker-level determinants associated with higher exposure included handling the dry-powdered form of CNT/F, handling daily quantities of material >1 kg, direct/indirect exposure, having the job title of engineer, using a respirator, using a ventilated or unventilated enclosure, and the job task of powder handling. The mixed linear models explained >60% of the total variance when using all company- and worker-level determinants to create the three exposure models. The cross-validated RMSE values for each of the three mixed models ranged from 2.50 to 4.23. Meanwhile, the ridge regression models, without all two-way interactions, estimated cross-validated RMSE values of 2.85, 2.23, and 2.76 for the predictive models of inhalable EC, respirable EC, and TEM, respectively. Conclusions: The ridge regression models demonstrated the best performance for predicting exposures to CNT/F for each exposure metric, although they only provided a modest predictive capability. Therefore, it was concluded that the models alone would not be adequate in predicting workplace exposures and would need to be integrated with other methods. |
Association of pulmonary, cardiovascular, and hematologic metrics with carbon nanotube and nanofiber exposure among U.S. workers: a cross-sectional study
Schubauer-Berigan MK , Dahm MM , Erdely A , Beard JD , Eileen Birch M , Evans DE , Fernback JE , Mercer RR , Bertke SJ , Eye T , de Perio MA . Part Fibre Toxicol 2018 15 (1) 22 BACKGROUND: Commercial use of carbon nanotubes and nanofibers (CNT/F) in composites and electronics is increasing; however, little is known about health effects among workers. We conducted a cross-sectional study among 108 workers at 12 U.S. CNT/F facilities. We evaluated chest symptoms or respiratory allergies since starting work with CNT/F, lung function, resting blood pressure (BP), resting heart rate (RHR), and complete blood count (CBC) components. METHODS: We conducted multi-day, full-shift sampling to measure background-corrected elemental carbon (EC) and CNT/F structure count concentrations, and collected induced sputum to measure CNT/F in the respiratory tract. We measured (nonspecific) fine and ultrafine particulate matter mass and count concentrations. Concurrently, we conducted physical examinations, BP measurement, and spirometry, and collected whole blood. We evaluated associations between exposures and health measures, adjusting for confounders related to lifestyle and other occupational exposures. RESULTS: CNT/F air concentrations were generally low, while 18% of participants had evidence of CNT/F in sputum. Respiratory allergy development was positively associated with inhalable EC (p=0.040) and number of years worked with CNT/F (p=0.008). No exposures were associated with spirometry-based metrics or pulmonary symptoms, nor were CNT/F-specific metrics related to BP or most CBC components. Systolic BP was positively associated with fine particulate matter (p-values: 0.015-0.054). RHR was positively associated with EC, at both the respirable (p=0.0074) and inhalable (p=0.0026) size fractions. Hematocrit was positively associated with the log of CNT/F structure counts (p=0.043). CONCLUSIONS: Most health measures were not associated with CNT/F. The positive associations between CNT/F exposure and respiratory allergies, RHR, and hematocrit counts may not be causal and require examination in other studies. |
Carbon nanotube and nanofiber exposure and sputum and blood biomarkers of early effect among U.S. workers
Beard JD , Erdely A , Dahm MM , de Perio MA , Birch ME , Evans DE , Fernback JE , Eye T , Kodali V , Mercer RR , Bertke SJ , Schubauer-Berigan MK . Environ Int 2018 116 214-228 BACKGROUND: Carbon nanotubes and nanofibers (CNT/F) are increasingly used for diverse applications. Although animal studies suggest CNT/F exposure may cause deleterious health effects, human epidemiological studies have typically been small, confined to single workplaces, and limited in exposure assessment. OBJECTIVES: We conducted an industrywide cross-sectional epidemiological study of 108 workers from 12 U.S. sites to evaluate associations between occupational CNT/F exposure and sputum and blood biomarkers of early effect. METHODS: We assessed CNT/F exposure via personal breathing zone, filter-based air sampling to measure background-corrected elemental carbon (EC) (a CNT/F marker) mass and microscopy-based CNT/F structure count concentrations. We measured 36 sputum and 37 blood biomarkers. We used factor analyses with varimax rotation to derive factors among sputum and blood biomarkers separately. We used linear, Tobit, and unconditional logistic regression models to adjust for potential confounders and evaluate associations between CNT/F exposure and individual biomarkers and derived factors. RESULTS: We derived three sputum and nine blood biomarker factors that explained 78% and 67%, respectively, of the variation. After adjusting for potential confounders, inhalable EC and total inhalable CNT/F structures were associated with the most sputum and blood biomarkers, respectively. Biomarkers associated with at least three CNT/F metrics were 72kDa type IV collagenase/matrix metalloproteinase-2 (MMP-2), interleukin-18, glutathione peroxidase (GPx), myeloperoxidase, and superoxide dismutase (SOD) in sputum and MMP-2, matrix metalloproteinase-9, metalloproteinase inhibitor 1/tissue inhibitor of metalloproteinases 1, 8-hydroxy-2'-deoxyguanosine, GPx, SOD, endothelin-1, fibrinogen, intercellular adhesion molecule 1, vascular cell adhesion protein 1, and von Willebrand factor in blood, although directions of associations were not always as expected. CONCLUSIONS: Inhalable rather than respirable CNT/F was more consistently associated with fibrosis, inflammation, oxidative stress, and cardiovascular biomarkers. |
Demographic and operational factors predicting study completion in a multisite case-control study of preschool children
Bradley CB , Browne EN , Alexander AA , Collins J , Dahm JL , DiGuiseppi CG , Levy SE , Moody EJ , Schieve LA , Windham GC , Young L , Daniels JL . Am J Epidemiol 2018 187 (3) 592-603 Participant attrition can limit inferences drawn from study results and inflate research costs. We examined factors associated with completion of the Study to Explore Early Development (2007-2011), a multiple-component, case-control study of risk factors for autism spectrum disorder in preschoolers, conducted in California, Colorado, Georgia, Maryland, North Carolina, and Pennsylvania. Participants (n = 3,769) were asked to complete phone interviews, questionnaires, an in-person evaluation, and biologic sampling. We examined whether participant demographic and administrative factors predicted completion using mixed-effects logistic regression models. Completion of individual key study components was generally 70% or higher. However, 58% of families completed all per-protocol data elements (defined a priori as key study components). Per-protocol completion differed according to mother's age, race, educational level, driving distance to clinic, number of contact attempts to enroll, and number of telephone numbers provided (all P < 0.05). Case status was not associated with completion, despite additional data collection for case-confirmation. Analysis of a subset that completed an early interview revealed no differences in completion by household factors of income, primary language spoken, number of adults, or number of children with chronic conditions. Differences in completion by race and education were notable and need to be carefully considered in developing future recruitment and completion strategies. |
Exposure assessments for a cross-sectional epidemiologic study of US carbon nanotube and nanofiber workers
Dahm MM , Schubauer-Berigan MK , Evans DE , Birch ME , Bertke S , Beard JD , Erdely A , Fernback JE , Mercer RR , Grinshpun SA . Int J Hyg Environ Health 2018 221 (3) 429-440 BACKGROUND: Recent animal studies have suggested the potential for wide-ranging health effects resulting from exposure to carbon nanotubes and nanofibers (CNT/F). To date, no studies in the US have directly examined the relationship between occupational exposure and potential human health effects. OBJECTIVES: Our goal was to measure CNT/F exposures among US workers with representative job types, from non-exposed to highly exposed, for an epidemiologic study relating exposure to early biologic effects. METHODS: 108 participants were enrolled from 12 facilities across the US. Personal, full-shift exposures were assessed based on the mass of elemental carbon (EC) at the respirable and inhalable aerosol particle size fractions, along with quantitatively characterizing CNT/F and estimating particle size via transmission electron microscopy (TEM). Additionally, sputum and dermal samples were collected and analyzed to determine internal exposures and exposures to the hands/wrists. RESULTS: The mean exposure to EC was 1.00mug/m(3) at the respirable size fraction and 6.22mug/m(3) at the inhalable fraction. Analysis by TEM found a mean exposure of 0.1275 CNT/F structures/cm(3), generally to agglomerated materials between 2 and 10mum. Internal exposures to CNT/F via sputum analysis were confirmed in 18% of participants while approximately 70% had positive dermal exposures. CONCLUSIONS: We demonstrated the occurrence of a broad range of exposures to CNT/F within 12 facilities across the US. Analysis of collected sputum indicated internal exposures are currently occurring within the workplace. This is an important first step in determining if exposures in the workforce have any acute or lasting health effects. |
Characterizing workforces exposed to current and emerging non-carbonaceous nanomaterials in the U.S
Babik KR , Dahm MM , Dunn KH , Dunn KL , Schubauer-Berigan MK . J Occup Environ Hyg 2017 15 (1) 0 OBJECTIVE: Toxicology studies suggest that exposure to certain types of engineered nanomaterials (ENMs) may cause adverse health effects, but little is known about the workforce in the United States that produces or uses these materials. In addition, occupational exposure control strategies in this industry are not well characterized. This study identified US ENM manufacturers and users (other than carbon nanotubes and nanofibers, which have been characterized elsewhere), determined workforce size, characterized types and quantities of materials used, occupational exposure control strategies, and the feasibility of occupational ENM exposure studies. METHODS: Eligible companies were identified and information was collected through phone surveys on nanomaterials produced or used, workforce size, location, work practices, and exposure control strategies. The companies were classified into groups for additional examinations. RESULTS: Forty-nine companies producing or using ENMs in the US were identified. These companies employed at least 1500 workers. Most companies produced or used some form of nanoscale metal. More than half of the eligible companies were suppliers for the coatings, composite materials, or general industries. Each company provided information about worker exposure reduction strategies through engineering controls, administrative controls, or personal protective equipment. Production-scale companies reported greater use of specific exposure control strategies for ENMs than laboratory-scale companies. CONCLUSIONS: Workplaces producing or using ENMs report using engineering and administrative controls as well as personal protective equipment to control worker exposure. Industrywide exposure assessment studies appear feasible due to workforce size. However, more effort must be taken to target industries using specific ENMs based on known toxicological effects and health risks. |
In Vivo Toxicity Assessment of Occupational Components of the Carbon Nanotube Life Cycle To Provide Context to Potential Health Effects
Bishop L , Cena L , Orandle M , Yanamala N , Dahm MM , Birch ME , Evans DE , Kodali VK , Eye T , Battelli L , Zeidler-Erdely PC , Casuccio G , Bunker K , Lupoi JS , Lersch TL , Stefaniak AB , Sager T , Afshari A , Schwegler-Berry D , Friend S , Kang J , Siegrist KJ , Mitchell CA , Lowry DT , Kashon ML , Mercer RR , Geraci CL , Schubauer-Berigan MK , Sargent LM , Erdely A . ACS Nano 2017 11 (9) 8849-8863 Pulmonary toxicity studies on carbon nanotubes focus primarily on as-produced materials and rarely are guided by a life cycle perspective or integration with exposure assessment. Understanding toxicity beyond the as-produced, or pure native material, is critical, due to modifications needed to overcome barriers to commercialization of applications. In the first series of studies, the toxicity of as-produced carbon nanotubes and their polymer-coated counterparts was evaluated in reference to exposure assessment, material characterization, and stability of the polymer coating in biological fluids. The second series of studies examined the toxicity of aerosols generated from sanding polymer-coated carbon-nanotube-embedded or neat composites. Postproduction modification by polymer coating did not enhance pulmonary injury, inflammation, and pathology or in vitro genotoxicity of as-produced carbon nanotubes, and for a particular coating, toxicity was significantly attenuated. The aerosols generated from sanding composites embedded with polymer-coated carbon nanotubes contained no evidence of free nanotubes. The percent weight incorporation of polymer-coated carbon nanotubes, 0.15% or 3% by mass, and composite matrix utilized altered the particle size distribution and, in certain circumstances, influenced acute in vivo toxicity. Our study provides perspective that, while the number of workers and consumers increases along the life cycle, toxicity and/or potential for exposure to the as-produced material may greatly diminish. |
Generation and characterization of aerosols released from sanding composite nanomaterials containing carbon nanotubes
Kang J , Erdely A , Afshari A , Casuccio G , Bunker K , Lersch T , Dahm MM , Farcas D , Cena L . NanoImpact 2017 5 41-50 An adaptable system was developed to generate and characterize particles released from composite materials containing carbon nanotubes (CNTs). The system was tested with a belt sander by sanding 1) glass fiber/epoxy resin, 2) acrylonitrile butadiene styrene (ABS), and 3) ABS with carbon black. Each material was tested with fine and coarse sandpaper in its neat form and with CNT additives. Total number concentrations, respirable mass concentrations, and particle number/mass distributions of the released particles were measured with a combination of direct-read instruments. Airborne particle samples for electron microscopy analysis were collected on polycarbonate filters, and onto a transmission electron microscopy grid supported carbon film using a thermophoretic sampler. Using automated microscopy analysis and a newly developed method, over 200 particles from each filter sample were analyzed for chemical composition, size, and the presence of CNT protrusions. Direct-read instruments revealed that the highest number and mass concentrations were generated with Material 1 (6 × 104 particles/cm3 and 0.5 mg/m3 with coarse sandpaper) and that the addition of C'NTs decreased number concentrations (4.5 × 104 particles/cm3 with coarse sandpaper). Respirable concentrations of the materials containing CNTs were higher than the respective base materials without additives with the exception of Material 1 with coarse sandpaper. Microscopy analysis results indicated that particles were primarily micrometer-sized and some particles had protruding features. From the chemical analysis, the percentages of particles generated during sanding that were attributable to the deterioration of sandpaper were 59–83% for Material 1 and 6–27% for Materials 2 and 3. The highest number of protrusions were found in Material 3 with CNT additive and fine sandpaper (3.71 average protrusions per particle) while the lowest number or protrusions were found in Material 2 with short CNTs and fine sandpaper (0.66 average protrusions per particle). No free-standing CNTs were observed in the samples. The combination of direct-read instruments and automated electron microscopy provides greater insights in particle chemistry, size measurements and CNT associations. |
Bridging the gap between exposure assessment and inhalation toxicology: Some insights from the carbon nanotube experience
Erdely A , Dahm MM , Schubauer-Berigan MK , Chen BT , Antonini JM , Hoover MD . J Aerosol Sci 2016 99 157-162 The early incorporation of exposure assessment can be invaluable to help design, prioritize, and interpret toxicological studies or outcomes. The sum total of the exposure assessment findings combined with preliminary toxicology results allows for exposure-informed toxicological study design and the findings can then be integrated, together with available epidemiologic data, to provide health effect relevance. With regard to engineered nanomaterial inhalation toxicology in particular, a single type of material (e.g. carbon nanotube, graphene) can have a vast array of physicochemical characteristics resulting in the potential for varying toxicities. To compound the matter, the methodologies necessary to establish a material adequate for in vivo exposure testing raises questions on the applicability of the outcomes. From insights gained from evaluating carbon nanotubes, we recommend the following integrated approach involving exposure-informed hazard assessment and hazard-informed exposure assessment especially for materials as diverse as engineered nanomaterials: 1) market-informed identification of potential hazards and potentially exposed populations, 2) initial toxicity screening to drive prioritized assessments of exposure, 3) development of exposure assessment-informed chronic and sub-chronic in vivo studies, and 4) conduct of exposure- and hazard-informed epidemiological studies. |
Refinement of the nanoparticle emission assessment technique into the Nanomaterial Exposure Assessment Technique (NEAT 2.0)
Eastlake AC , Beaucham C , Martinez KF , Dahm MM , Sparks C , Hodson LL , Geraci CL . J Occup Environ Hyg 2016 13 (9) 0 Engineered nanomaterial emission and exposure characterization studies have been completed at more than 60 different facilities by the National Institute for Occupational Safety and Health (NIOSH). These experiences have provided NIOSH the opportunity to refine an earlier published technique, the Nanoparticle Emission Assessment Technique (NEAT 1.0), into a more comprehensive technique for assessing worker and workplace exposures to engineered nanomaterials. This change is reflected in the new name Nanomaterial Exposure Assessment Technique (NEAT 2.0) which distinguishes it from NEAT 1.0. NEAT 2.0 places a stronger emphasis on time-integrated, filter-based sampling (i.e., elemental mass analysis and particle morphology) in the worker's breathing zone (full shift and task specific) and area samples to develop job exposure matrices. NEAT 2.0 includes a comprehensive assessment of emissions at processes and job tasks, using direct-reading instruments (i.e., particle counters) in data-logging mode to better understand peak emission periods. Evaluation of worker practices, ventilation efficacy, and other engineering exposure control systems and risk management strategies serve to allow for a comprehensive exposure assessment. |
Creation of a retrospective job-exposure matrix using surrogate measures of exposure for a cohort of US career firefighters from San Francisco, Chicago and Philadelphia
Dahm MM , Bertke S , Allee S , Daniels RD . Occup Environ Med 2015 72 (9) 670-7 OBJECTIVES: To construct a cohort-specific job-exposure matrix (JEM) using surrogate metrics of exposure for a cancer study on career firefighters from the Chicago, Philadelphia and San Francisco Fire Departments. METHODS: Departmental work history records, along with data on historical annual fire-runs and hours, were collected from 1950 to 2009 and coded into separate databases. These data were used to create a JEM based on standardised job titles and fire apparatus assignments using several surrogate exposure metrics to estimate firefighters' exposure to the combustion byproducts of fire. The metrics included duration of exposure (cumulative time with a standardised exposed job title and assignment), fire-runs (cumulative events of potential fire exposure) and time at fire (cumulative hours of potential fire exposure). RESULTS: The JEM consisted of 2298 unique job titles alongside 16 174 fire apparatus assignments from the three departments, which were collapsed into 15 standardised job titles and 15 standardised job assignments. Correlations were found between fire-runs and time at fires (Pearson coefficient=0.92), duration of exposure and time at fires (Pearson coefficient=0.85), and duration of exposure and fire-runs (Pearson coefficient=0.82). Total misclassification rates were found to be between 16-30% when using duration of employment as an exposure surrogate, which has been traditionally used in most epidemiological studies, compared with using the duration of exposure surrogate metric. CONCLUSIONS: The constructed JEM successfully differentiated firefighters based on gradient levels of potential exposure to the combustion byproducts of fire using multiple surrogate exposure metrics. |
Carbon nanotube and nanofiber exposure assessments: an analysis of 14 site visits
Dahm MM , Schubauer-Berigan MK , Evans DE , Birch ME , Fernback JE , Deddens JA . Ann Occup Hyg 2015 59 (6) 705-23 Recent evidence has suggested the potential for wide-ranging health effects that could result from exposure to carbon nanotubes (CNT) and carbon nanofibers (CNF). In response, the National Institute for Occupational Safety and Health (NIOSH) set a recommended exposure limit (REL) for CNT and CNF: 1 microg m-3 as an 8-h time weighted average (TWA) of elemental carbon (EC) for the respirable size fraction. The purpose of this study was to conduct an industrywide exposure assessment among US CNT and CNF manufacturers and users. Fourteen total sites were visited to assess exposures to CNT (13 sites) and CNF (1 site). Personal breathing zone (PBZ) and area samples were collected for both the inhalable and respirable mass concentration of EC, using NIOSH Method 5040. Inhalable PBZ samples were collected at nine sites while at the remaining five sites both respirable and inhalable PBZ samples were collected side-by-side. Transmission electron microscopy (TEM) PBZ and area samples were also collected at the inhalable size fraction and analyzed to quantify and size CNT and CNF agglomerate and fibrous exposures. Respirable EC PBZ concentrations ranged from 0.02 to 2.94 microg m-3 with a geometric mean (GM) of 0.34 microg m-3 and an 8-h TWA of 0.16 microg m-3. PBZ samples at the inhalable size fraction for EC ranged from 0.01 to 79.57 microg m-3 with a GM of 1.21 microg m-3. PBZ samples analyzed by TEM showed concentrations ranging from 0.0001 to 1.613 CNT or CNF-structures per cm3 with a GM of 0.008 and an 8-h TWA concentration of 0.003. The most common CNT structure sizes were found to be larger agglomerates in the 2-5 microm range as well as agglomerates >5 microm. A statistically significant correlation was observed between the inhalable samples for the mass of EC and structure counts by TEM (Spearman rho = 0.39, P < 0.0001). Overall, EC PBZ and area TWA samples were below the NIOSH REL (96% were <1 mug m-3 at the respirable size fraction), while 30% of the inhalable PBZ EC samples were found to be >1 mug m-3. Until more information is known about health effects associated with larger agglomerates, it seems prudent to assess worker exposure to airborne CNT and CNF materials by monitoring EC at both the respirable and inhalable size fractions. Concurrent TEM samples should be collected to confirm the presence of CNT and CNF. |
Exposure-response relationships for select cancer and non-cancer health outcomes in a cohort of US firefighters from San Francisco, Chicago and Philadelphia (1950-2009)
Daniels RD , Bertke S , Dahm MM , Yiin JH , Kubale TL , Hales TR , Baris D , Zahm SH , Beaumont JJ , Waters KM , Pinkerton LE . Occup Environ Med 2015 72 (10) 699-706 OBJECTIVES: To examine exposure-response relationships between surrogates of firefighting exposure and select outcomes among previously studied US career firefighters. METHODS: Eight cancer and four non-cancer outcomes were examined using conditional logistic regression. Incidence density sampling was used to match each case to 200 controls on attained age. Days accrued in firefighting assignments (exposed-days), run totals (fire-runs) and run times (fire-hours) were used as exposure surrogates. HRs comparing 75th and 25th centiles of lagged cumulative exposures were calculated using loglinear, linear, log-quadratic, power and restricted cubic spline general relative risk models. Piecewise constant models were used to examine risk differences by time since exposure, age at exposure and calendar period. RESULTS: Among 19 309 male firefighters eligible for the study, there were 1333 cancer deaths and 2609 cancer incidence cases. Significant positive associations between fire-hours and lung cancer mortality and incidence were evident. A similar relation between leukaemia mortality and fire-runs was also found. The lung cancer associations were nearly linear in cumulative exposure, while the association with leukaemia mortality was attenuated at higher exposure levels and greater for recent exposures. Significant negative associations were evident for the exposure surrogates and colorectal and prostate cancers, suggesting a healthy worker survivor effect possibly enhanced by medical screening. CONCLUSIONS: Lung cancer and leukaemia mortality risks were modestly increasing with firefighter exposures. These findings add to evidence of a causal association between firefighting and cancer. Nevertheless, small effects merit cautious interpretation. We plan to continue to follow the occurrence of disease and injury in this cohort. |
Characterizing adoption of precautionary risk management guidance for nanomaterials, an emerging occupational hazard
Schubauer-Berigan MK , Dahm MM , Schulte PA , Hodson L , Geraci CL . J Occup Environ Hyg 2014 12 (1) 0 Exposure to engineered nanomaterials (substances with at least one dimension of 1-100 nm) has been of increased interest, with the recent growth in production and use of nanomaterials worldwide. Various organizations have recommended methods to minimize exposure to engineered nanomaterials. The purpose of this study was to evaluate available data to examine the extent to which studied U.S. companies (which represent a small fraction of all companies using certain forms of engineered nanomaterials) follow the guidelines for reducing occupational exposures to engineered nanomaterials that have been issued by the National Institute for Occupational Safety and Health (NIOSH) and other organizations. Survey data, field reports, and field notes for all NIOSH nanomaterial exposure assessments conducted between 2006 and 2011 were collected and reviewed to: (1) determine the level of adoption of precautionary guidance on engineering controls and personal protective equipment, and (2) evaluate the reliability of companies' self-reported use of engineering controls and personal protective equipment. Use of personal protective equipment was observed among 89% [95% confidence interval (CI): 76%-96%] of 46 visited companies, and use of containment-based engineering controls for at least some processes was observed among 83% (95% CI: 76%-96%). In on-site evaluations, more than 90% of the 16 engineered carbonaceous nanomaterial companies that responded to an industrywide survey were observed to be using engineering controls and personal protective equipment as reported or more stringently than reported. Since personal protective equipment use was slightly more prevalent than engineering controls, better communication may be necessary to reinforce the importance of the hierarchy of controls. These findings may also be useful in conducting exposure assessment and epidemiologic research among U.S. workers handling nanomaterials. |
Carbon nanotube dosimetry: from workplace exposure assessment to inhalation toxicology
Erdely A , Dahm M , Chen BT , Zeidler-Erdely PC , Fernback JE , Birch ME , Evans DE , Kashon ML , Deddens JA , Hulderman T , Bilgesu SA , Battelli L , Schwegler-Berry D , Leonard HD , McKinney W , Frazer DG , Antonini JM , Porter DW , Castranova V , Schubauer-Berigan MK . Part Fibre Toxicol 2013 10 (1) 53 BACKGROUND: Dosimetry for toxicology studies involving carbon nanotubes (CNT) is challenging because of a lack of detailed occupational exposure assessments. Therefore, exposure assessment findings, measuring the mass concentration of elemental carbon from personal breathing zone (PBZ) samples, from 8 U.S.-based multi-walled CNT (MWCNT) manufacturers and users were extrapolated to results of an inhalation study in mice. RESULTS: Upon analysis, an inhalable elemental carbon mass concentration arithmetic mean of 10.6 mug/m3 (geometric mean 4.21 mug/m3) was found among workers exposed to MWCNT. The concentration equates to a deposited dose of approximately 4.07 mug/d in a human, equivalent to 2 ng/d in the mouse. For MWCNT inhalation, mice were exposed for 19 d with daily depositions of 1970 ng (equivalent to 1000 d of a human exposure; cumulative 76 yr), 197 ng (100 d; 7.6 yr), and 19.7 ng (10 d; 0.76 yr) and harvested at 0, 3, 28, and 84 d post-exposure to assess pulmonary toxicity. The high dose showed cytotoxicity and inflammation that persisted through 84 d after exposure. The middle dose had no polymorphonuclear cell influx with transient cytotoxicity. The low dose was associated with a low grade inflammatory response measured by changes in mRNA expression. Increased inflammatory proteins were present in the lavage fluid at the high and middle dose through 28 d post-exposure. Pathology, including epithelial hyperplasia and peribronchiolar inflammation, was only noted at the high dose. CONCLUSION: These findings showed a limited pulmonary inflammatory potential of MWCNT at levels corresponding to the average inhalable elemental carbon concentrations observed in U.S.-based CNT facilities and estimates suggest considerable years of exposure are necessary for significant pathology to occur at that level. |
Mortality and cancer incidence in a pooled cohort of US firefighters from San Francisco, Chicago and Philadelphia (1950-2009)
Daniels RD , Kubale TL , Yiin JH , Dahm MM , Hales TR , Baris D , Zahm SH , Beaumont JJ , Waters KM , Pinkerton LE . Occup Environ Med 2013 71 (6) 388-97 OBJECTIVES: To examine mortality patterns and cancer incidence in a pooled cohort of 29 993 US career firefighters employed since 1950 and followed through 2009. METHODS: Mortality and cancer incidence were evaluated by life table methods with the US population referent. Standardised mortality (SMR) and incidence (SIR) ratios were determined for 92 causes of death and 41 cancer incidence groupings. Analyses focused on 15 outcomes of a priori interest. Sensitivity analyses were conducted to examine the potential for significant bias. RESULTS: Person-years at risk totalled 858 938 and 403 152 for mortality and incidence analyses, respectively. All-cause mortality was at expectation (SMR=0.99, 95% CI 0.97 to 1.01, n=12 028). There was excess cancer mortality (SMR=1.14, 95% CI 1.10 to 1.18, n=3285) and incidence (SIR=1.09, 95% CI 1.06 to 1.12, n=4461) comprised mainly of digestive (SMR=1.26, 95% CI 1.18 to 1.34, n=928; SIR=1.17, 95% CI 1.10 to 1.25, n=930) and respiratory (SMR=1.10, 95% CI 1.04 to 1.17, n=1096; SIR=1.16, 95% CI 1.08 to 1.24, n=813) cancers. Consistent with previous reports, modest elevations were observed in several solid cancers; however, evidence of excess lymphatic or haematopoietic cancers was lacking. This study is the first to report excess malignant mesothelioma (SMR=2.00, 95% CI 1.03 to 3.49, n=12; SIR=2.29, 95% CI 1.60 to 3.19, n=35) among US firefighters. Results appeared robust under differing assumptions and analytic techniques. CONCLUSIONS: Our results provide evidence of a relation between firefighting and cancer. The new finding of excess malignant mesothelioma is noteworthy, given that asbestos exposure is a known hazard of firefighting. |
Occupational exposure assessment in carbon nanotube and nanofiber primary and secondary manufacturers: mobile direct-reading sampling
Dahm MM , Evans DE , Schubauer-Berigan MK , Birch ME , Deddens JA . Ann Occup Hyg 2012 57 (3) 328-44 RESEARCH SIGNIFICANCE: Toxicological evidence suggests the potential for a wide range of health effects from exposure to carbon nanotubes (CNTs) and carbon nanofibers (CNFs). To date, there has been much focus on the use of direct-reading instruments (DRIs) to assess multiple airborne exposure metrics for potential exposures to CNTs and CNFs due to their ease of use and ability to provide instantaneous results. Still, uncertainty exists in the usefulness and interpretation of the data. To address this gap, air-monitoring was conducted at six sites identified as CNT and CNF manufacturers or users and results were compared with filter-based metrics. METHODS: Particle number, respirable mass, and active surface area concentrations were monitored with a condensation particle counter, a photometer, and a diffusion charger, respectively. The instruments were placed on a mobile cart and used as area monitors in parallel with filter-based elemental carbon (EC) and electron microscopy samples. Repeat samples were collected on consecutive days, when possible, during the same processes. All instruments in this study are portable and routinely used for industrial hygiene sampling. RESULTS: Differences were not observed among the various sampled processes compared with concurrent indoor or outdoor background samples while examining the different DRI exposure metrics. Such data were also inconsistent with results for filter-based samples collected concurrently at the same sites [Dahm MM, Evans DE, Schubauer-Berigan MK et al. (2012) Occupational exposure assessment in CNT and nanofiber primary and secondary manufacturers. Ann Occup Hyg; 56: 542-56]. Significant variability was seen between these processes as well as the indoor and outdoor backgrounds. However, no clear pattern emerged linking the DRI results to the EC or the microscopy data (CNT and CNF structure counts). CONCLUSIONS: Overall, no consistent trends were seen among similar processes at the various sites. The DRI instruments employed were limited in their usefulness in assessing and quantifying potential exposures at the sampled sites but were helpful for hypothesis generation, control technology evaluations, and other air quality issues. The DRIs employed are nonspecific, aerosol monitors, and, therefore, subject to interferences. As such, it is necessary to collect samples for analysis by more selective, time-integrated, laboratory-based methods to confirm and quantify exposures. |
Focused actions to protect carbon nanotube workers
Schulte PA , Kuempel ED , Zumwalde RD , Geraci CL , Schubauer-Berigan MK , Castranova V , Hodson L , Murashov V , Dahm MM , Ellenbecker M . Am J Ind Med 2012 55 (5) 395-411 There is still uncertainty about the potential health hazards of carbon nanotubes (CNTs) particularly involving carcinogenicity. However, the evidence is growing that some types of CNTs and nanofibers may have carcinogenic properties. The critical question is that while the carcinogenic potential of CNTs is being further investigated, what steps should be taken to protect workers who face exposure to CNTs, current and future, if CNTs are ultimately found to be carcinogenic? This paper addresses five areas to help focus action to protect workers: (i) review of the current evidence on the carcinogenic potential of CNTs; (ii) role of physical and chemical properties related to cancer development; (iii) CNT doses associated with genotoxicity in vitro and in vivo; (iv) workplace exposures to CNT; and (v) specific risk management actions needed to protect workers. (Am. J. Ind. Med. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.) |
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