ToxSci Advance Access originally published online on July 13, 2006
Toxicological Sciences 2006 93(2):390-399; doi:10.1093/toxsci/kfl062
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Acute Pulmonary and Systemic Effects of Inhaled Coal Fly Ash in Rats: Comparison to Ambient Environmental Particles
* Center for Health and the Environment, University of California, Davis, California 95616; Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah 84112; NHEERL, USEPA, Research Triangle Park, North Carolina 27711; and Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300
1 To whom correspondence should be addressed at Center for Health and the Environment, University of California, One Shields Avenue, Davis, CA 95616. Fax: (530) 752-5300. E-mail: kepinkerton{at}ucdavis.edu
Received April 17, 2006; accepted July 6, 2006
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Although primary particle emissions of ash from coal-fired power plants are well controlled, coal fly ash (CFA) can still remain a significant fraction of the overall particle exposure for some plant workers and highly impacted communities. The effect of CFA on pulmonary and systemic inflammation and injury was measured in male Sprague-Dawley rats exposed to filtered air or CFA for 4 h/day for 3 days. The average concentration of CFA particulate matter less than 2.5 µm (PM2.5) was 1400 µg/m3, of which 600 µg/m3 was PM1. Animals were examined 18 and 36 h postexposure. Chemical analysis of CFA detected silicon, calcium, aluminum, and iron as major components. Total number of neutrophils in bronchoalveolar lavage fluid (BALF) following exposure to CFA was significantly increased along with significantly elevated blood neutrophils. Exposure to CFA caused slight increases in macrophage inflammatory protein-2, and marked increases in transferrin in BALF. Interleukin-1ß and total antioxidant potential in lung tissues were also increased in rats exposed to CFA. Histological examination of lung tissue demonstrated focal alveolar septal thickening and increased cellularity in select alveoli immediately beyond terminal bronchioles. These responses are consistent with the ability of CFA to induce mild neutrophilic inflammation in the lung and blood following short-term exposure at levels that could be occupationally relevant. However, when comparing the effects of CFA with those of concentrated ambient particles, CFA does not appear to have greater potency to cause pulmonary alterations. This study furthers our understanding of possible mechanisms by which specific sources of particulate air pollution affect human health.
Key Words: coal fly ash; BALF; IL-1ß; TNF-
; MIP-2; PM2.5; inhalation; pulmonary toxicology; concentrated ambient particles; iron; inflammation.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Coal fly ash (CFA) consists of anthropogenic particles formed by mineral transformation in high-temperature combustion processes. CFA is a primary particle emitted, along with soot as a solid from the power plant stack. Exposure to CFA is a health concern because coal is a major power source used world wide, especially in developing countries such as China and India, and human exposure to particulate matter is associated with increased respiratory and cardiac disease.
Primary emissions from modern power plants are controlled by either an electrostatic precipitator or a fabric filter, but the collection efficiency of both technologies is lowest for particles with an aerodynamic diameter in the range 0.1–1 µm (Helble, 2000
). As a result, CFA emissions are dominated by particles that can travel long distances in the atmosphere and that can be inhaled into the lung. Power plant workers are exposed to CFA, especially during boiler maintenance, and construction workers are exposed to collected CFA that is recycled into cement and construction fill material. In the United States, there is no specific workplace limit for CFA, so occupational exposures to CFA is regulated as a nuisance dust under "Particulates (Insoluble) Not Otherwise Classified" (Meij and te Winkel, 2001). The occupational limit for these types of particles is an 8-h limit of 10 mg/m3 for the inhalable size range and 3 mg/m3 for respirable particles (ACGIH, 2001), which is two to three orders of magnitude higher than for typical ambient particulate matter (PM) concentration.
Besides in the workplace, exposure to CFA may occur by living near clusters of power plants. Time-average ambient concentrations of CFA in the United States are low because pollution controls and tall stacks have eliminated extreme local concentrations of CFA. However, CFA emissions remain a regional-scale source of PM. For example, primary PM from the seven existing coal-fired power plants in Utah represents 30% of the primary PM10 emitted by all regulated stationary sources statewide. In northwest Colorado, the Craig and Hayden coal-fired power plants were found to contribute about 15% of the time-averaged PM2.5 mass close to the Hayden plant but less than 5% at more remote sites (Chow and Watson, 2002). Coal combustion along the Ohio River Valley may be an important contributor to PM2.5 mass in Pittsburgh, PA, when wind is from the southwest (Anderson et al., 2002). Model predictions for China show the maximum annual averaged PM10 and SO2 concentrations caused by existing power plants are 52.6 and 33.6 µg/m3, respectively (Xue et al., 2005).
Due to health concerns with CFA exposure, inhalation and instillation studies with CFA have been conducted in a number of laboratory rodents. The following observations have been made from these studies: (1) CFA particles are retained in the lung (Raabe et al., 1982); (2) airway resistance is affected following exposure to CFA (Chen et al., 1990); and (3) CFA causes increased immune cell activity (Dormans et al., 1999) and inflammation in the lung (Gilmour et al., 2004). Reviews and research reports discuss the formation of particles during coal combustion and the implications of these particles for human health (Lighty et al., 2000), the mechanisms and biological effects of iron mobilization from CFA (Ball et al., 2000), CFA particle characteristics responsible for effects on lung epithelial cells (Aust et al., 2002), the effects of nanoparticles from coal combustion (Donaldson et al., 2005), and occupational effects of chronic exposures to CFA (Borm, 1997).
The purpose of this study was to use controlled exposure to a well-characterized particle type to gain insights into the induction of pulmonary inflammation by exposure to particulate air pollution. The approach was to physicochemically characterize CFA and then to examine the acute effects of inhaled resuspended CFA aerosol in rats at concentrations that are relevant to occupational limits. CFA is both an emission of current concern (Fields, 2004), and an excellent prototype particle due to the extensive literature on CFA formation mechanisms (Lighty et al., 2000). In contrast to prior inhalation studies with CFA, this study examined a wide variety of highly sensitive pulmonary and systemic indicators of inflammation and oxidative stress that are relevant to current mechanistic toxicological hypotheses. Although some of the measured biochemical parameters may indicate small changes that are not biologically significant in healthy animals, these changes may be biomarkers that give insights into underlying mechanisms leading to increased susceptibility. Responses induced by a specific pollutant are best placed in context by comparison to studies with real-world ambient particles. Therefore, another objective of this study design was to compare the effect of CFA, a defined-source particle, to responses reported for the mixture of emission sources contributing to the concentrated ambient particles (CAPs) used by recent studies in the United States and Europe.
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MATERIALS AND METHODS |
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Animals.
Forty-eight male Sprague-Dawley rats, 8 weeks of age (260–270 g) and free of respiratory pathogens or disease, were purchased from Harlan (San Diego, CA). Prior to CFA exposure, animals were acclimated to nose-only exposure tubes for 5 days (2, 3, 4, 4, 4 h, on days 1–5, respectively). Animals were handled in accordance with standards established by the U.S. Animal Welfare Acts as set forth in the National Institutes of Health guidelines (Institute of Laboratory Animal Resources (1996) as well as the Animal Care and Use committee of the University of California, Davis. Rats were housed in plastic cages with TEK-Chip pelleted paper bedding (Harlan Teklad, Madison, WI) and maintained on a 12-h light/12-h dark cycle. All animals had access to water and Laboratory Rodent Diet 5001 (LabDiet, Brentwood, MO) ad libitum except during each daily acclimation or exposure period.
Experimental design.
Rats were exposed to filtered air or aerosolized CFA in a nose-only exposure system for 4 h/day for 3 days and examined 18 or 36 h after the last exposure to CFA. These necropsy times were selected to measure acute responses and to approximate the 1- to 3-day lag time between increases in PM concentration and human effects commonly observed in epidemiology studies.
Coal fly ash.
The particulate material used for inhalation was derived from a bulk sample of fly ash collected by air pollution control equipment on a 400-MW power plant burning bituminous coal from multiple mines in the Wasatch Plateau, UT, coal field. Size-fractionated material, enriched in 0.4- to 2-µm-sized particles, was extracted from the bulk fly ash by mechanical resuspension and aerodynamic separation using a previously described method (Veranth et al., 2000). The capture efficiency of typical coal power plant air pollution control equipment is at a minimum for the size range of CFA particles used in the current study, but is still > 90% (Lighty et al., 2000). Size-dependent differences in CFA composition have been reviewed (Lighty et al., 2000). Extracting particles in the minimum efficiency size range from captured power plant fly ash produces an aerosol similar to the emitted particles.
CFA particle generator.
CFA was aerosolized using a belt feeder and fluidized bed system shown in Figure 1 and previously described by Teague et al. (2005). In brief, PM2.5 size-fractionated particles were premixed with 100- to 200-µm-diameter glass beads and loaded into a dust feed for delivery to a vibrating fluidized bed system for aerosolization of both CFA and glass beads. The aerosol subsequently passed through a cyclone separator to remove the glass beads (Fig. 2), while the CFA remained aerosolized (Fig. 3) passing through a krypton-85 source (to reduce particle agglomeration) to the nose-only inhalation system. Particle concentration during exposure was monitored by a continuous-reading, light-scattering, dust concentration monitor and filter connected to the exposure chamber. A Grimm Series 1.108 Aerosol Spectrometer (GRIMM Aerosol Technik GmbH, Douglasville, GA) extracted a 1.2 Lpm flow, and a proprietary algorithm converted light scattering into particle mass concentration using the default calibration for occupational monitoring (PM10, PM2.5, and PM1). The particle feeder settings of the aerosolization system were adjusted as needed to achieve the target time-averaged concentration for exposure. The aerosol spectrometer was operated in the 16-channel mode to measure particle size distribution. Mass of CFA collected on the filter was used to correct the aerosol spectrometer output to obtain the actual mass concentration during exposures. The filter sample was collected at 3 l/min on a 25-mm Pallflex EMFAB TX40HI20-WW filter using an InTox filter housing connected to a diaphragm pump and a bellows-type dry gas meter. Control animals were exposed to air passed through a high efficiency particulate air (HEPA) filter (Airguard, Louisville, KY).
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Bronchoalveolar lavage and biochemical assay of bronchoalveolar lavage fluid.
Eighteen or 36 h after the last exposure to CFA, rats were anesthetized by ip injection of pentobarbital (100–150 mg/kg body weight). Blood was collected from the caudal vena cava and placed in a collection tube for serum and in a tube containing ethylenediaminetetraacetic acid for determination of hematology parameters including complete blood counts. Animals were exsanguinated via the abdominal aorta. The trachea was cannulated, and the lungs were lavaged with Ca2+/Mg2+-free phosphate-buffered saline (PBS; pH 7.4) at a volume equal to 35 ml/kg body weight. Three in-and-out lavages were performed using the same aliquot to maximize recovery of cells and biochemical markers from the lungs. Bronchoalveolar lavage fluid (BALF) was centrifuged at 2000 rpm for 10 min at 4°C. The supernatant was removed and stored at – 80°C for biochemical analyses. The cell pellet was resuspended in Ca2+/Mg2+-free PBS, and 100 µl of this suspension was used to determine total cell count and viability. Cell viability was measured by exclusion of 0.4% trypan blue (Sigma, St Louis, MO), an indicator of irreversible loss of plasma membrane integrity. A second aliquot of cells was centrifuged using a Shandon Cytospin (Thermo Shandon, Inc., Pittsburgh, PA) to prepare cell differential slides. The slides were dried at room temperature and stained with HEMA 3 (Fisher Scientific International, Inc.) (Biochemical Sciences, Inc., Swedesboro, NJ). Macrophages, neutrophils, and lymphocytes were counted using light microscopy (1000 cells per sample).
BALF supernatant was analyzed for protein content using a Coomassie Plus Protein Assay Kit (Pierce, Rockford, IL) and bovine serum albumin (BSA) standards from Sigma/Aldrich Chemicals. BALF supernatant was analyzed for albumin content using a commercially available kit (Diasorin, Inc., Stillwater, MN). N-acetyl-ß-D-glucosaminidase (NAG) activity was measured in BALF supernatant using a commercially available kit and standards from Roche Diagnostics (Indianapolis, IN). 
-Glutamyltransferase (GGT) activity was measured in the BALF supernatant using a commercially prepared kit from Thermo Trace, Ltd (Melbourne, Australia). Transferrin concentration in BALF supernatant was measured using a Transferrin SPQ II kit from Diasorin, Inc. Total antioxidant status of BALF supernatant was determined using a kit from Randox Laboratories, Inc. (Ardmore, U.K.). These assays were modified and adapted for use on a KONLAB clinical chemistry analyzer (Thermo Clinical Labsystems, Espoo, Finland).
Levels of Interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-), and macrophage inflammatory protein-2 (MIP-2) in the BALF in BALF supernatant were determined using rat enzyme-linked immunosorbent assay (ELISA) kits obtained from Biosource International (Camarillo, CA) and used according to the manufacturer's instructions. Concentrations are reported as pg/ml.
BALF supernatant was analyzed for total glutathione (GSH) and glutathione disulfide (GSSG) content using a Bioxytech reduced to oxidized glutathione-412 (GSH/GSSG-412) kit from Oxis International, Inc. (Portland, OR) according to manufacturer's instructions. Concentrations are reported as µM and as the GSH/GSSG ratio, defined as (GSH-2GSSG)/GSSG.
Hematology parameters.
Whole blood was collected as described above and analyzed using a Mascot Hemavet 850 analyzer (CDC Technologies, Oxford, CT). This system determines a variety of hematologic parameters, including red blood cell count, white blood cell count, and percentages of neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
Lung tissues for biochemistry and histopathology.
Six animals per group (separate from those used for collection of BALF) were anesthetized by ip injection of pentobarbital (100–150 mg/kg body weight). Blood was collected from the caudal vena cava and placed in a tube containing citrate for collection of plasma. Animals were exsanguinated via the abdominal aorta. The trachea was cannulated, the chest cavity was opened by a midline incision, and the right main-stem bronchus was ligated. Right lung lobes were snap frozen individually in liquid nitrogen and stored at – 80°C until analysis of cytokines, chemokines, glutathione, and total antioxidant potential. The left lung was inflation fixed by intratracheal instillation of 4% paraformaldehyde at 30 cm of water pressure for 1 h. The lung was sliced into pieces, dehydrated in a series of graded ethanol and embedded in paraffin for use in histochemical studies. Sections of paraffin-embedded lung tissue were cut at a thickness of 5 µm and stained with hematoxylin and eosin (H&E) or Prussian blue iron stain. Airways and the lung parenchyma were examined for the presence of cellular changes and inflammation in H&E-stained sections, while the presence of CFA particles in tissues was detected using Prussian blue iron stain.
Cytokines and chemokines in lung tissue.
The right-middle lung lobe was homogenized in T-PER Reagent (Pierce, Rockford, IL) at a ratio of 0.1 g tissue to 1 ml T-PER Reagent. The homogenate was centrifuged, and the supernatant was collected according to the manufacturer's instructions. Protein concentration in the supernatant was determined using the BCA Protein Assay from Pierce with BSA as the standard. Levels of IL-1ß, TNF-, and MIP-2 in the supernatant were determined using rat ELISA kits obtained from Biosource International and used according to the manufacturer's instructions. Concentrations are reported as pg/µg protein.
Glutathione in lung tissue.
The right caudal lung lobe was divided in half. One half of the lobe used to measure total glutathione was homogenized in ice-cold 5% metaphosphoric acid at a ratio of 0.1 g tissue to 0.5 ml 5% metaphosphoric acid. The homogenate was placed on ice for 15 min and then centrifuged at 12,000 x g for 15 min at 4°C. The supernatant was aliquoted and stored at – 80°C. The other half of the lobe used to measure oxidized glutathione was homogenized as described, but with the addition of 1-methyl-2-vinylpyridinium trifluoromethanesulfonate. Lung tissue supernatant was analyzed for total glutathione (GSH) and glutathione disulfide (GSSG) content using a Bioxytech GSH/GSSG-412 kit from Oxis International, Inc. according to manufacturer's instructions. Concentrations are reported as nmol/mg tissue and as the GSH/GSSG ratio, defined as (GSH-2GSSG)/GSSG.
Total antioxidant potential in lung tissue.
The accessory lobe of the lung was homogenized in ice-cold PBS at a ratio of 0.1 g tissue to 1 ml PBS. The homogenate was centrifuged at 3000 x g for 15 min at 4°C. The supernatant was removed and stored at – 80°C. A colorimetric, quantitative assay from OxisResearch (Portland, OR) was used according to the manufacturer's instructions to determine total antioxidant potential. Results are presented as nmol uric acid equivalents/µg protein.
Statistics.
All numerical data were calculated as the mean and standard deviation. Comparisons between animals exposed to CFA and filtered air were made by Student's t-test or, where appropriate, by analysis of variance followed by Fisher's protected least significant difference posttest. Comparisons were considered significant if a value of p < 0.05 was observed. Statistical analysis was performed with StatView 5.0.1 (SAS Institute, Inc., Cary, NC).
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RESULTS |
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CFA Aerosol Characteristics
The chemical composition of the aerodynamically size-fractionated CFA powder is shown in Table 1. Average concentration of CFA in the PM2.5 range was 1400 ± 150 µg/m3, of which 600 ± 70 µg/m3 was in the PM1 range. The composition was analyzed by ion chromatography for soluble ions, by x-ray fluorescence (XRF) for elements, and by thermal/optical reflectance for carbon fractions. These methods are the same as used by ambient air monitoring networks; therefore, the data are useful for comparing to ambient PM samples. The cumulative chemical composition data percentages do not equal 100% because oxygen and hydrogen from mineral oxides, chemically bound water, and organic molecules are not measured. XRF analysis is also subject to artifacts from x-ray adsorption within the sample.
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Particle Deposition
The particle size distribution of the resuspended CFA is shown in Figure 4. A lognormal size distribution equation (Hinds, 1982
) was fit to the measured aerosolized particle number distribution. The actual aerosol particle size generated can be approximated by a count median diameter of 0.3 µm and a geometric standard deviation of 1.4, which corresponds to a mass mode near 1 µm. Using this information, deposition of the CFA aerosol generated was modeled using MPPD V1.0 software developed by Chemical Industry Institute of Toxicology (CIIT Center for Health Research) and Rijksinstituut voor volksgezondheid en milieu (RIVM National Institute for Public Health and the Environment) (Asgharian et al., 2002). The model inputs include measured particle size distribution, time-averaged aerosol concentration during exposure, and observed breathing rate. Based on the MPPD model, the total CFA mass deposited over the 3-day exposure was 32 µg per rat, and the regional deposition was head, 25%; tracheobronchial, 20%; and pulmonary, 55%.
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Animal Responses (BALF, Blood, Lung Tissue)
All BALF, blood, and lung tissue parameters showing statistically significant changes at either postexposure time are summarized in Table 2. These changes included a significant increase in neutrophils, both in the lung BALF and in the blood (Fig. 5), and increases in cytokines such as MIP-2 in BALF and IL-1ß in lung tissue (Fig. 6). Other significant changes included increased levels of transferrin, lung tissue total antioxidant potential, plasma protein, and blood complement 4. Biological endpoints showing no statistically significant changes at either time point are shown in Table 3.
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Lung Histopathology
Following CFA exposure, a moderate elevation in the number of alveolar macrophages was noted within the bronchiole-alveolar duct regions of the lungs both 18- and 36-h postexposure (Fig. 7). This region of the lungs was associated with a subtle, but obvious increase in the cellularity of alveolar septal tips immediately beyond terminal bronchioles (Fig. 7B). Although not every bronchiole-alveolar duct region was involved, there was a clear distinction between the sham control animals and those exposed to CFA both 18- and 36-h postexposure. Staining with Prussian blue iron stain demonstrated in a small fraction of alveolar macrophages the presence of iron-positive cytoplasmic inclusions (inset, Fig. 7B), suggestive of phagocytosized CFA particles.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The purpose of this study was to examine pulmonary and systemic effects of CFA at occupationally relevant exposure concentrations on a variety of biological indicators/markers. Sprague-Dawley rats exposed to resuspended CFA rich in silica, aluminum, iron, and calcium demonstrated a mild pulmonary inflammatory response and associated cytokine increase. CFA caused subtle thickening and increased cellularity of the centriacinar (bronchiole-alveolar duct) region. Positive staining of alveolar macrophages for iron and increased transferrin, an iron-binding protein, in BALF was likely to be due to the iron associated with CFA. These pulmonary effects (maximum at 18-h postexposure) of CFA were associated with moderate, but significant systemic neutrophilic inflammation, decreased lymphocytes, increased complement 4, and increased hematocrit at 36 h. These later systemic changes could be critical in potential cardiovascular effects of CFA. Some of these statistically significant changes may be too small to indicate biologically significant tissue damage, but the results are valuable both as biomarkers of exposure and as indicators of underlying mechanisms.
Few systemic effects have been reported in animals exposed to CFA. No changes in hematological parameters were observed in rabbits intratracheally instilled with a Nigeria bituminous CFA with a size range of 4–5 µm mean particle diameter (Ogugbuaja et al., 2001). Pulmonary toxicology studies using CFA particles have generally shown few effects following instillation of 2–10 mg/kg in rats (Borm, 1997). In contrast, our study demonstrates small, but significant systemic effects. These differences may be a reflection of the importance of particle size, composition, and the exposure methods used in this study.
Although the increase in neutrophils due to inhaled CFA was significant compared with that observed in studies using CAPs at similar mass concentrations (Cassee et al., 2005; Kodavanti et al., 2005), the proportion of polymorphonuclear leukocytes (PMNs) measured in BALF was only 1.5% of the total cell number, which can represent baseline neutrophil levels in some rat strains. Therefore, it is possible that the detection power of increased neutrophilic inflammation was much greater in our study using Sprague-Dawley rats compared with Wistar Kyoto and spontaneously hypertensive rats.
Two time points were used in our study in an attempt to more efficiently capture possible pulmonary and systemic biological responses of CFA following a 3-day exposure. Most pulmonary biomarkers such as neutrophilic inflammation and proinflammatory cytokines were found to be increased at 18-h postexposure. However, systemic neutrophilic inflammation was most evident at 36 h associated with a decrease in circulating lymphocytes and a concomitant increase in complement 4 and hematocrit. Our results indicate by 36-h postexposure that there is a general trend of recovery in many of the pulmonary parameters, including cytokine levels, while systemic changes become most prominent at this postexposure time. The data imply that systemic inflammation peaked after pulmonary inflammation had already subsided, but confirming this observation and developing a plausible mechanistic explanation would require data at additional time points.
Time-related changes in inflammation and injury markers are likely to be affected by specific PM components, which might act via different mechanisms and temporal patterns. The time course of effect and recovery are also likely to be influenced by the extent of lung injury caused by particles. Pulmonary messenger RNA expression for IL-1ß and MIP-2 increased 1 day following intratracheal instillation of diesel in rats and returned to control levels 7 days postexposure, with a second increase again at 30 days postexposure (Rao et al., 2005).
Few systemic responses have been reported in animals following exposure to combustion source or ambient particles. A small, but significant increase in circulating neutrophils may suggest a release of these cells in the circulation from the bone marrow. Such changes in bone marrow stimulation and the appearance of band cells in the circulation have been reported in animals exposed to particles (Mukae et al., 2001). The significance of increased circulating levels of complement 4 is not clear and will require further study to elucidate its source and biological significance.
The observation of positive iron staining in alveolar macrophages and the elevation of transferrin, an iron-binding protein, in BALF following exposure to CFA may indicate increased availability of iron from inhaled CFA particles. Similar results have been reported in the lungs of rats exposed to iron-containing particles (Ghio et al., 1998), where transferrin levels were elevated 24 h after instillation, but were decreased to control levels by 96-h postinstillation. These data suggest that iron may modulate some of the responses caused by particles. Ball et al. (2000) reviewed generation of reactive oxygen species by CFA-associated iron via the Fenton reaction.
A unique feature of this study was the ability to aerosolize over a cumulative period of 12 h a limited amount (1 g) of size-fractionated CFA sample from a specific power plant burning a specific coal. The composition of CFA depends on the mineralogy of the coal, combustion conditions, and types of equipment used to control NOx and SO2 (Lighty et al., 2000). In vitro results have shown that both the bioavailability of transition metals and the cytokine signaling responses vary with the size of particles and the coal source (Smith et al., 1998, 2000). The aerosol generation methods used in this study provide data on biological responses to a controlled exposure with particles of known and consistent chemical composition.
The same aerodynamically separated CFA sample that was used in this study was also used in an in vitro toxicology study in which IL-6 and IL-8 were measured in BEAS-2B cells. CFA was less potent for cytokine induction in vitro than the soil-derived PM2.5 particles (Veranth et al., 2006). The degree of neutrophilic inflammation induced in vivo by CFA in our study was mild, which is similar to what has been reported with other CFA studies. It is also possible that the different chemical components in the CFA interact to modify the inflammatory response. For example, neutrophilic inflammation has been negatively correlated with the level of soluble iron in oil combustion particles (Kodavanti et al., 1998).
The effects of a more widely studied, but less well-characterized pollutant, CAPs, can be compared to the effects of CFA. Table 4 lists the fold increases over control for the rat responses measured in this study and CAPs studies conducted by Cassee et al. (2005) and Kodavanti et al. (2005). Although rat strains and procedures differed between studies, the particle concentrations and exposure durations were similar: 1400 µg/m3, 4 h x 3 days (this CFA study); 144–2758 µg/m3 CAPs, 4 h x 2 days (Kodavanti et al., 2005); and 270–3720 µg/m3 CAPs, 6 h x 1 day (Cassee et al., 2005). Both CAPs studies used PM2.5 aerosol, but detailed particle size distribution data were not reported for the CAPs. Sulfate was present at 3.97% and nitrate was not detected in the CFA, while average composition was 26.3% sulfate and 1.6% nitrate for the eastern U.S. CAPs (Kodavanti et al., 2005) and 17.8% sulfate and 18.3% nitrate for the Netherlands CAPs (Cassee et al., 2005).
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Small changes in parameters associated with inflammation and oxidative stress were observed in all three studies, suggesting some commonalities in the effect of ambient particles and CFA. Although the reported CAPs studies represent a mean of multiple repeat studies done with chemically heterogeneous particles relative to CFA used in this study, these similarities in inflammatory response may indicate common mechanistic pathways that are likely to be induced regardless of varied composition and quantities of different PM samples.
In conclusion, this study shows that primary mineral ash particles in the PM2.5 size range from coal-fired power plants can induce mild, but statistically significant time-dependent alterations in pulmonary and systemic parameters that are associated with inflammation. Acute inhalation exposure of healthy adult rats to CFA resulted in responses at particle concentrations relevant to current occupational exposure limits for nuisance dusts. CFA particles are not biologically inert; however, for the BALF, lung tissue, and blood endpoints measured CFA particles are also not highly potent compared to an equal mass of PM2.5 CAPs. Air quality management will benefit if toxicology research can identify the specific emissions that are most important for causing the morbidity and mortality associated with increased air pollution. Since CFA is typically less than 1–5% of the ambient PM mass, the comparison of CFA and CAPs study results suggests that CFA alone is a minor, but incremental, contributor to the potency of the ambient air PM mixture.
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NOTES |
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The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and the policies of the Agency and mention of trade names or commercial products does not constitute endorsement or recommendation for use.
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ACKNOWLEDGMENTS |
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This research was funded by the Health Effects Institute contracts 97-8 and 02-3, U.S. Environmental Protection Agency (USEPA) STAR grants 829215 and 831714, USEPA Center grant R832414, National Institute for Occupational Safety and Health (NIOSH) grant OH07550 and National Institute of Environmental Health Sciences (NIEHS) grants K25011281, and ES05707. We would like to thank Imelda Espiritu, Julian J. Recendez, Judy H. Richards, Mette C. Schladweiler, and Stephen V. Teague for their technical assistance and Dr Judith Chow at the Desert Research Institute, who provided the elemental composition data. We would also like to thank Dr Suzette Smiley-Jewell for editorial assistance in the preparation of this manuscript.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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ACGIH (2001). TLVs Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. American Conference of Governmental Industrial Hygienists, Cincinnati, OH.
Anderson, R. R., Martello, D. V., Rohar, P. C., Strazisar, B. R., Tamilia, J. P., Waldner, K., White, C. M., Modey, W. K., Mangelson, N. F., and Eatough, D. J. (2002). Sources and composition of PM2.5 at the National Energy Technology Laboratory in Pittsburgh during July and August 2000. Energy Fuels 16, 261–269.[CrossRef]
Asgharian, B., Miller, F. J., Price, O. T., Cassee, F. R., Freijer, J., and van Bree, L. (2002). Multiple Path Particle Dosimetry Model MPPD. V1.0. CIIT Center for Health Research and RIVM National Institute for Public Health and the Environment.
Aust, A. E., Ball, J. C., Hu, A., Lighty, J. S., Smith, K. R., Straccia, A. M., Veranth, J. M., and Young, W. C. (2002). Particle Characteristics Responsible for Effects on Human Lung Epithelial Cells. Health Effects Institute, Boston, MA.
Ball, B. R., Smith, K. R., Veranth, J. M., and Aust, A. E. (2000). Bioavailability of iron from coal fly ash: Mechanisms of mobilization and of biological effects. Inhal. Toxicol. 12, S209–S225.
Borm, P. J. A. (1997). Toxicity and occupational health hazards of coal fly ash (CFA). A review of data and comparison to coal mine dust. Ann. Occup. Hyg. 41, 659–676.
Cassee, F. R., Boere, A. J., Fokkens, P. H., Leseman, D. L., Sioutas, C., Kooter, I. M., and Dormans, J. A. (2005). Inhalation of concentrated particulate matter produces pulmonary inflammation and systemic biological effects in compromised rats. J. Toxicol. Environ. Health A 68, 773–796.[ISI][Medline]
Chen, L. C., Lam, H. F., Kim, E. J., Guty, J., and Amdur, M. O. (1990). Pulmonary effects of ultrafine coal fly ash inhaled by guinea pigs. J. Toxicol. Environ. Health 29, 169–184.[ISI][Medline]
Chow, J. C., and Watson, J. G. (2002). Review of PM2.5 and PM10 apportionment for fossil fuel combustion and other sources by the chemical mass balance receptor model. Energy Fuels 16, 222–260.[CrossRef]
Donaldson, K., Tran, L., Jimenez, L. A., Duffin, R., Newby, D. E., Mills, N., Macnee, W., and Stone, V. (2005). Combustion-derived nanoparticles: A review of their toxicology following inhalation exposure. Part. Fibre Toxicol. 2, 10.[CrossRef][Medline]
Dormans, J. A., Steerenberg, P. A., Arts, J. H., van Bree, L., de Klerk, A., Verlaan, A. P., Bruijntjes, J. P., Beekhof, P., van Soolingen, D., and van Loveren, H. (1999). Pathological and immunological effects of respirable coal fly ash in male Wistar rats. Inhal. Toxicol. 11, 51–69.[CrossRef][ISI][Medline]
Fields, S. (2004). Coal: Poised for a comeback? Environ. Health Perspect. 112, A888–A891.[ISI][Medline]
Ghio, A. J., Richards, J. H., Dittrich, K. L., and Samet, J. M. (1998). Metal storage and transport proteins increase after exposure of the rat lung to an air pollution particle. Toxicol. Pathol. 26, 388–394.[ISI][Medline]
Gilmour, M. I., O'Connor, S., Dick, C. A., Miller, C. A., and Linak, W. P. (2004). Differential pulmonary inflammation and in vitro cytotoxicity of size-fractionated fly ash particles from pulverized coal combustion. J. Air Waste Manag. Assoc. 54, 286–295.[ISI][Medline]
Helble, J. J. (2000). A model for the air emissions of trace metallic elements from coal combustors equipped with electrostatic precipitators. Fuel Process. Technol. 63, 125–147.[CrossRef]
Hinds, W. C. (1982). Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles. John Wiley & Sons, New York.
Institute of Laboratory Animal Resources (1996). Guide for the Care and Use of Laboratory Animals. National Academy Press, Washington, DC.
Kodavanti, U. P., Meng, Z. H., Hauser, R., Christiani, D. C., Ledbetter, A., Mcgee, J., Richards, J., and Costa, D. L. (1998). In vivo and in vitro correlates of particle-induced lung injury: Specific roles of bioavailable metals. In Relationships between Respiratory Disease and Exposure to Air Pollution. ILSI Monographs (U. Mohr, D. L. Dungworth, J. D. Brain, K. E. Driscoll, R. C. Grafstrom, and C. C. Harris, Eds.), pp. 261–266. ILSI Press, Washington.
Kodavanti, U. P., Schladweiler, M. C., Ledbetter, A. D., McGee, J. K., Walsh, L., Gilmour, P. S., Highfill, J. W., Davies, D., Pinkerton, K. E., Richards, J. H., et al. (2005). Consistent pulmonary and systemic responses from inhalation of fine concentrated ambient particles: Roles of rat strains used and physicochemical properties. Environ. Health Perspect. 113, 1561–1568.[ISI][Medline]
Lighty, J. S., Veranth, J. M., and Sarofim, A. F. (2000). Combustion aerosols: Factors governing their size and composition and implications to human health. J. Air Waste Manag. Assoc. 50, 1565–1618; discussion 1619–1622.[ISI][Medline]
Meij, R., and te Winkel, H. (2001). Health aspects of coal fly ash. International Ash Utilization Symposium. Center for Applied Energy Research, University of Kentucky. Available at: http://www.flyash.info. Accessed January 2005.
Mukae, H., Vincent, R., Quinlan, K., English, D., Hards, J., Hogg, J. C., and van Eeden, S. F. (2001). The effect of repeated exposure to particulate air pollution (PM10) on the bone marrow. Am. J. Respir. Crit. Care Med. 163, 201–209.
Ogugbuaja, V. O., Onyeyili, P. A., and Moses, E. A. (2001). Study of effects on haematological parameters of rabbits intratracheally exposed to coal fly ash. J. Environ. Sci. Health A Tox. Hazard. Subst. Environ. Eng. 36, 1411–1418.[CrossRef][ISI][Medline]
Raabe, O. G., Tyler, W. S., Last, J. A., Schwartz, L. W., Lollini, L. O., Fisher, G. L., Wilson, F. D., and Dungworth, D. L. (1982). Studies of the chronic inhalation of coal fly ash by rats. Ann. Occup. Hyg. 26, 189–211.
Rao, K. M., Ma, J. Y., Meighan, T., Barger, M. W., Pack, D., and Vallyathan, V. (2005). Time course of gene expression of inflammatory mediators in rat lung after diesel exhaust particle exposure. Environ. Health Perspect. 113, 612–617.[ISI][Medline]
Smith, K. R., Veranth, J. M., Hu, A. A., Lighty, J. S., and Aust, A. E. (2000). Interleukin-8 levels in human lung epithelial cells are increased in response to coal fly ash and vary with the bioavailability of iron, as a function of particle size and source of coal. Chem. Res. Toxicol. 13, 118–125.[CrossRef][ISI][Medline]
Smith, K. R., Veranth, J. M., Lighty, J. S., and Aust, A. E. (1998). Mobilization of iron from coal fly ash was dependent upon the particle size and the source of coal. Chem. Res. Toxicol. 11, 1494–1500.[CrossRef][ISI][Medline]
Teague, S. V., Veranth, J. M., Aust, A. E., and Pinkerton, K. E. (2005). Dust generator for inhalation studies with limited amounts of archived particulate matter. Aerosol Sci. Technol. 39, 85–91.[CrossRef]
Veranth, J. M., Moss, T. A., Chow, J. C., Labban, R., Nichols, W. K., Walton, J. C., Watson, J. G., and Yost, G. S. (2006). Correlation of in vitro cytokine responses with the chemical composition of soil-derived particulate matter. Environ. Health Perspect. 114, 341–349.[ISI][Medline]
Veranth, J. M., Smith, K. R., Aust, A. E., Dansie, S. L., Griffin, J. B., Hu, A. A., Huggins, M. L., and Lighty, J. S. (2000). Coal fly ash and mineral dust for toxicology and particle characterization studies: Equipment and methods for PM2.5- and PM1-enriched samples. Aerosol Sci. Technol. 32, 127–141.
Xue, Z., Hao, J., Chai, F., Duan, N., Chen, Y., Li, J., Chen, F., Liu, S., and Pu, W. (2005). Air quality impact of the coal-fired power plants in the northern passageway of the China West-East Power Transmission Project. J. Air Waste Manag. Assoc. 55, 1816–1826.[ISI][Medline]
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