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Marrocco A, Frawley K, Pearce LL, Peterson J, O'Brien JP, Mullett SJ, Wendell SG, St Croix CM, Mischler SE, Ortiz LA. Metabolic Adaptation of Macrophages as Mechanism of Defense against Crystalline Silica. THE JOURNAL OF IMMUNOLOGY 2021; 207:1627-1640. [PMID: 34433619 DOI: 10.4049/jimmunol.2000628] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 07/08/2021] [Indexed: 11/19/2022]
Abstract
Silicosis is a lethal pneumoconiosis for which no therapy is available. Silicosis is a global threat, and more than 2.2 million people per year are exposed to silica in the United States. The initial response to silica is mediated by innate immunity. Phagocytosis of silica particles by macrophages is followed by recruitment of mitochondria to phagosomes, generation of mitochondrial reactive oxygen species, and cytokine (IL-1β, TNF-α, IFN-β) release. In contrast with LPS, the metabolic remodeling of silica-exposed macrophages is unclear. This study contrasts mitochondrial and metabolic alterations induced by LPS and silica on macrophages and correlates them with macrophage viability and cytokine production, which are central to the pathogenesis of silicosis. Using high-resolution respirometer and liquid chromatography-high-resolution mass spectrometry, we determined the effects of silica and LPS on mitochondrial respiration and determined changes in central carbon metabolism of murine macrophage cell lines RAW 264.7 and IC-21. We show that silica induces metabolic reprogramming of macrophages. Silica, as well as LPS, enhances glucose uptake and increases aerobic glycolysis in macrophages. In contrast with LPS, silica affects mitochondria respiration, reducing complex I and enhancing complex II activity, to sustain cell viability. These mitochondrial alterations are associated in silica, but not in LPS-exposed macrophages, with reductions of tricarboxylic acid cycle intermediates, including succinate, itaconate, glutamate, and glutamine. Furthermore, in contrast with LPS, these silica-induced metabolic adaptations do not correlate with IL-1β or TNF-α production, but with the suppressed release of IFN-β. Our data highlight the importance of complex II activity and tricarboxylic acid cycle remodeling to macrophage survival and cytokine-mediated inflammation in silicosis.
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Affiliation(s)
- Antonella Marrocco
- Department of Environmental and Occupational Health, Graduate School of Public Health at the University of Pittsburgh, Pittsburgh, PA
| | - Krystin Frawley
- Department of Environmental and Occupational Health, Graduate School of Public Health at the University of Pittsburgh, Pittsburgh, PA
| | - Linda L Pearce
- Department of Environmental and Occupational Health, Graduate School of Public Health at the University of Pittsburgh, Pittsburgh, PA
| | - James Peterson
- Department of Environmental and Occupational Health, Graduate School of Public Health at the University of Pittsburgh, Pittsburgh, PA
| | - James P O'Brien
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA
| | - Steven J Mullett
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA.,Health Sciences Metabolomics and Lipidomics Core, University of Pittsburgh, Pittsburgh, PA
| | - Stacy G Wendell
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA.,Health Sciences Metabolomics and Lipidomics Core, University of Pittsburgh, Pittsburgh, PA.,Clinical Translational Science Institute, University of Pittsburgh, Pittsburgh, PA; and
| | | | - Steven E Mischler
- Department of Environmental and Occupational Health, Graduate School of Public Health at the University of Pittsburgh, Pittsburgh, PA
| | - Luis A Ortiz
- Department of Environmental and Occupational Health, Graduate School of Public Health at the University of Pittsburgh, Pittsburgh, PA;
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Russ KA, Thompson JA, Reynolds JS, Mercer RR, Porter DW, McKinney W, Dey RD, Barger M, Cumpston J, Batchelor TP, Kashon ML, Kodali V, Jackson MC, Sriram K, Fedan JS. Biological effects of inhaled hydraulic fracturing sand dust. IV. Pulmonary effects. Toxicol Appl Pharmacol 2020; 409:115284. [PMID: 33068619 PMCID: PMC7736927 DOI: 10.1016/j.taap.2020.115284] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 10/07/2020] [Accepted: 10/10/2020] [Indexed: 01/12/2023]
Abstract
Hydraulic fracturing creates fissures in subterranean rock to increase the flow and retrieval of natural gas. Sand ("proppant") in fracking fluid injected into the well bore maintains fissure patency. Fracking sand dust (FSD) is generated during manipulation of sand to prepare the fracking fluid. Containing respirable crystalline silica, FSD could pose hazards similar to those found in work sites where silica inhalation induces lung disease such as silicosis. This study was performed to evaluate the possible toxic effects following inhalation of a FSD (FSD 8) in the lung and airways. Rats were exposed (6 h/d × 4 d) to 10 or 30 mg/m3 of a FSD collected at a gas well, and measurements were performed 1, 7, 27 and, in one series of experiments, 90 d post-exposure. The following ventilatory and non-ventilatory parameters were measured in vivo and/or in vitro: 1) lung mechanics (respiratory system resistance and elastance, tissue damping, tissue elastance, Newtonian resistance and hysteresivity); 2) airway reactivity to inhaled methacholine (MCh); airway epithelium integrity (isolated, perfused trachea); airway efferent motor nerve activity (electric field stimulation in vitro); airway smooth muscle contractility; ion transport in intact and cultured epithelium; airway effector and sensory nerves; tracheal particle deposition; and neurogenic inflammation/vascular permeability. FSD 8 was without large effect on most parameters, and was not pro-inflammatory, as judged histologically and in cultured epithelial cells, but increased reactivity to inhaled MCh at some post-exposure time points and affected Na+ transport in airway epithelial cells.
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Affiliation(s)
- Kristen A Russ
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Janet A Thompson
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Jeffrey S Reynolds
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Robert R Mercer
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Dale W Porter
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Walter McKinney
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Richard D Dey
- Department of Physiology and Pharmacology, Anatomy and Laboratory Medicine, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, United States of America; Department of Pathology, Anatomy and Laboratory Medicine, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, United States of America
| | - Mark Barger
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Jared Cumpston
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Thomas P Batchelor
- Department of Physiology and Pharmacology, Anatomy and Laboratory Medicine, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, United States of America; Department of Pathology, Anatomy and Laboratory Medicine, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, United States of America
| | - Michael L Kashon
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Vamsi Kodali
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Mark C Jackson
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Krishnan Sriram
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Jeffrey S Fedan
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America.
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3
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Fedan JS. Biological effects of inhaled hydraulic fracturing sand dust. I. Scope of the investigation. Toxicol Appl Pharmacol 2020; 409:115329. [PMID: 33181145 PMCID: PMC7745082 DOI: 10.1016/j.taap.2020.115329] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Hydraulic fracturing ("fracking") is a process in which subterranean natural gas-laden rock is fractured under pressure to enhance retrieval of gas. Sand (a "proppant") is present in the fracking fluid pumped down the well bore to stabilize the fissures and facilitate gas flow. The manipulation of sand at the well site creates respirable dust (fracking sand dust, FSD) to which workers are exposed. Because workplace exposures to FSD have exceeded exposure limits set by OSHA, a physico-chemical characterization of FSD along with comprehensive investigations of the potential early adverse effects of FSDs on organ function and biomarkers has been conducted using a rat model and related in vivo and in vitro experiments involving the respiratory, cardiovascular, immune systems, kidney and brain. An undercurrent theme of the overall hazard identification study was, to what degree do the health effects of inhaled FSD resemble those previously observed after crystalline silica dust inhalation? In short-term studies, FSD was found to be less bioactive than MIN-U-SIL® 5 in the lungs. A second theme was, are the biological effects of FSD restricted to the lungs? Bioactivity of FSD was observed in all examined organ systems. Our findings indicate that, in many respects, the physical and chemical properties, and the short-term biological effects, of the FSDs share many similarities as a group but have little in common with crystalline silica dust.
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Affiliation(s)
- Jeffrey S Fedan
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America.
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Olgun NS, Morris AM, Stefaniak AB, Bowers LN, Knepp AK, Duling MG, Mercer RR, Kashon ML, Fedan JS, Leonard SS. Biological effects of inhaled hydraulic fracturing sand dust. III. Cytotoxicity and pro-inflammatory responses in cultured murine macrophage cells. Toxicol Appl Pharmacol 2020; 408:115281. [PMID: 33065155 PMCID: PMC7952011 DOI: 10.1016/j.taap.2020.115281] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 10/07/2020] [Accepted: 10/10/2020] [Indexed: 12/16/2022]
Abstract
Cultured murine macrophages (RAW 264.7) were used to investigate the effects of fracking sand dust (FSD) for its pro-inflammatory activity, in order to gain insight into the potential toxicity to workers associated with inhalation of FSD during hydraulic fracturing. While the role of respirable crystalline silica in the development of silicosis is well documented, nothing is known about the toxicity of inhaled FSD. The FSD (FSD 8) used in these studies was from an unconventional gas well drilling site. FSD 8was prepared as a 10 mg/ml stock solution in sterile PBS, vortexed for 15 s, and allowed to sit at room temperature for 30 min before applying the suspension to RAW 264.7cells. Compared to PBS controls, cellular viability was significantly decreased after a 24 h exposure to FSD. Intracellular reactive oxygen species (ROS) production and the production of IL-6, TNFα, and endothelin-1 (ET-1) were up-regulated as a result of the exposure, whereas the hydroxyl radical (.OH) was only detected in an acellular system. Immunofluorescent staining of cells against TNFα revealed that FSD 8 caused cellular blebbing, and engulfment of FSD 8 by macrophages was observed with enhanced dark-field microscopy. The observed changes in cellular viability, cellular morphology, free radical generation and cytokine production all confirm that FSD 8 is cytotoxic to RAW 264.7 cells and warrants future studies into the specific pathways and mechanisms by which these toxicities occur.
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Affiliation(s)
- Nicole S Olgun
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America.
| | - Anna M Morris
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Aleksandr B Stefaniak
- Respiratory Health Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Lauren N Bowers
- Respiratory Health Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Alycia K Knepp
- Respiratory Health Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Matthew G Duling
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Robert R Mercer
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Michael L Kashon
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Jeffrey S Fedan
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Stephen S Leonard
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
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Sager TM, Roberts JR, Umbright CM, Barger M, Kashon ML, Fedan JS, Joseph P. Biological effects of inhaled hydraulic fracturing sand dust. V. Pulmonary inflammatory, cytotoxic and oxidant effects. Toxicol Appl Pharmacol 2020; 408:115280. [PMID: 33065154 PMCID: PMC7748298 DOI: 10.1016/j.taap.2020.115280] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 10/07/2020] [Accepted: 10/10/2020] [Indexed: 11/24/2022]
Abstract
The pulmonary inflammatory response to inhalation exposure to a fracking sand dust (FSD 8) was investigated in a rat model. Adult male Sprague-Dawley rats were exposed by whole-body inhalation to air or an aerosol of a FSD, i.e., FSD 8, at concentrations of 10 or 30 mg/m3, 6 h/d for 4 d. The control and FSD 8-exposed rats were euthanized at post-exposure time intervals of 1, 7 or 27 d and pulmonary inflammatory, cytotoxic and oxidant responses were determined. Deposition of FSD 8 particles was detected in the lungs of all the FSD 8-exposed rats. Analysis of bronchoalveolar lavage parameters of toxicity, oxidant generation, and inflammation did not reveal any significant persistent pulmonary toxicity in the FSD 8-exposed rats. Similarly, the lung histology of the FSD 8-exposed rats showed only minimal changes in influx of macrophages following the exposure. Determination of global gene expression profiles detected statistically significant differential expressions of only six and five genes in the 10 mg/m3, 1-d post-exposure, and the 30 mg/m3, 7-d post-exposure FSD 8 groups, respectively. Taken together, data obtained from the present study demonstrated that FSD 8 inhalation exposure resulted in no statistically significant toxicity or gene expression changes in the lungs of the rats. In the absence of any information about its potential toxicity, a comprehensive rat animal model study (see Fedan, J.S., Toxicol Appl Pharmacol. 000, 000-000, 2020) has been designed to investigate the bioactivities of several FSDs in comparison to MIN-U-SIL® 5, a respirable α-quartz reference dust used in previous animal models of silicosis, in several organ systems.
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Affiliation(s)
- Tina M Sager
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, United States of America.
| | - Jenny R Roberts
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, United States of America
| | - Christina M Umbright
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, United States of America
| | - Mark Barger
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, United States of America
| | - Michael L Kashon
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, United States of America
| | - Jeffrey S Fedan
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, United States of America
| | - Pius Joseph
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, United States of America
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Krajnak K, Kan H, Russ KA, McKinney W, Waugh S, Zheng W, Kashon ML, Johnson C, Cumpston J, Fedan JS. Biological effects of inhaled hydraulic fracturing sand dust. VI. Cardiovascular effects. Toxicol Appl Pharmacol 2020; 406:115242. [PMID: 32931794 DOI: 10.1016/j.taap.2020.115242] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Revised: 08/27/2020] [Accepted: 09/09/2020] [Indexed: 12/24/2022]
Abstract
Hydraulic fracturing is used to access oil and natural gas reserves. This process involves the high-pressure injection of fluid to fracture shale. Fracking fluid contains approximately 95% water, chemicals and 4.5% fracking sand. Workers may be exposed to fracking sand dust (FSD) during the manipulation of the sand, and negative health consequences could occur if FSD is inhaled. In the absence of any information about its potential toxicity, a comprehensive rat animal model study (see Fedan et al., 2020) was designed to investigate the bioactivities of several FSDs in comparison to MIN-U-SIL® 5, a respirable α-quartz reference dust used in previous animal models of silicosis, in several organ systems. The goal of this study was to assess the effects of inhalation of one FSD, i.e., FSD 8, on factors and tissues that affect cardiovascular function. Male rats were exposed to 10 or 30 mg/m3 FSD (6 h/d for 4 d) by whole body inhalation, with measurements made 1, 7 or 27 d post-exposure. One day following exposure to 10 mg/m3 FSD the sensitivity to phenylephrine-induced vasoconstriction in tail arteries in vitro was increased. FSD exposure at both doses resulted in decreases in heart rate (HR), HR variability, and blood pressure in vivo. FSD induced changes in hydrogen peroxide concentrations and transcript levels for pro-inflammatory factors in heart tissues. In kidney, expression of proteins indicative of injury and remodeling was reduced after FSD exposure. When analyzed using regression analysis, changes in proteins involved in repair and remodeling were correlated. Thus, it appears that inhalation of FSD does have some prolonged effects on cardiovascular, and, possibly, renal function. The findings also provide information regarding potential mechanisms that may lead to these changes, and biomarkers that could be examined to monitor physiological changes that could be indicative of impending cardiovascular dysfunction.
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Affiliation(s)
- Kristine Krajnak
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America.
| | - Hong Kan
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Kristen A Russ
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Walter McKinney
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Stacey Waugh
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Wen Zheng
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Michael L Kashon
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Claud Johnson
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Jared Cumpston
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
| | - Jeffrey S Fedan
- Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, United States of America
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Biological effects of inhaled hydraulic fracturing sand dust VII. Neuroinflammation and altered synaptic protein expression. Toxicol Appl Pharmacol 2020; 409:115300. [PMID: 33141058 DOI: 10.1016/j.taap.2020.115300] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 10/16/2020] [Accepted: 10/18/2020] [Indexed: 12/26/2022]
Abstract
Hydraulic fracturing (fracking) is a process used to recover oil and gas from shale rock formation during unconventional drilling. Pressurized liquids containing water and sand (proppant) are used to fracture the oil- and natural gas-laden rock. The transportation and handling of proppant at well sites generate dust aerosols; thus, there is concern of worker exposure to such fracking sand dusts (FSD) by inhalation. FSD are generally composed of respirable crystalline silica and other minerals native to the geological source of the proppant material. Field investigations by NIOSH suggest that the levels of respirable crystalline silica at well sites can exceed the permissible exposure limits. Thus, from an occupational safety perspective, it is important to evaluate the potential toxicological effects of FSD, including any neurological risks. Here, we report that acute inhalation exposure of rats to one FSD, i.e., FSD 8, elicited neuroinflammation, altered the expression of blood brain barrier-related markers, and caused glial changes in the olfactory bulb, hippocampus and cerebellum. An intriguing observation was the persistent reduction of synaptophysin 1 and synaptotagmin 1 proteins in the cerebellum, indicative of synaptic disruption and/or injury. While our initial hazard identification studies suggest a likely neural risk, more research is necessary to determine if such molecular aberrations will progressively culminate in neuropathology/neurodegeneration leading to behavioral and/or functional deficits.
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Biological effects of inhaled hydraulic fracturing sand dust. II. Particle characterization and pulmonary effects 30 d following intratracheal instillation. Toxicol Appl Pharmacol 2020; 409:115282. [PMID: 33068622 DOI: 10.1016/j.taap.2020.115282] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 10/07/2020] [Accepted: 10/10/2020] [Indexed: 01/29/2023]
Abstract
Hydraulic fracturing ("fracking") is used in unconventional gas drilling to allow for the free flow of natural gas from rock. Sand in fracking fluid is pumped into the well bore under high pressure to enter and stabilize fissures in the rock. In the process of manipulating the sand on site, respirable dust (fracking sand dust, FSD) is generated. Inhalation of FSD is a potential hazard to workers inasmuch as respirable crystalline silica causes silicosis, and levels of FSD at drilling work sites have exceeded occupational exposure limits set by OSHA. In the absence of any information about its potential toxicity, a comprehensive rat animal model was designed to investigate the bioactivities of several FSDs in comparison to MIN-U-SIL® 5, a respirable α-quartz reference dust used in previous animal models of silicosis, in several organ systems (Fedan, J.S., Toxicol Appl Pharmacol. 00, 000-000, 2020). The present report, part of the larger investigation, describes: 1) a comparison of the physico-chemical properties of nine FSDs, collected at drilling sites, and MIN-U-SIL® 5, a reference silica dust, and 2) a comparison of the pulmonary inflammatory responses to intratracheal instillation of the nine FSDs and MIN-U-SIL® 5. Our findings indicate that, in many respects, the physico-chemical characteristics, and the biological effects of the FSDs and MIN-U-SIL® 5 after intratracheal instillation, have distinct differences.
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