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Does Low Exposure to Chrysotile Pose a Health Risk?

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Does Low Exposure to Chrysotile Pose a Health Risk? Does Low Exposure to Chrysotile Pose a Health Risk? Dr. Tom Hesterberg Principal Toxicologist Center for Toxicology and Environmental Health American Conference Institute’s Asbestos Claims and Litigation January 30-31, 2014 San Francisco, California 5120 North Shore Drive | North Little Rock, AR 72118 | Main Line: 501.801.8500 Overview of Fiber Toxicology Studies • Basics of Fiber Toxicology • Chromosomal Effects • Fiber Biopersistence • Rodent Inhalation Studies • Thresholds for Fiber Toxicity 2 Basics of Fiber Toxicology 3 Dose The Cornerstone of Toxicology “All substances are poisons; there is none which is not a poison. The right dose differentiates a poison from a remedy.” Paracelsus (1493-1541). 4 Definition of Threshold The dose below which a given effect is not observed A threshold is a result of our bodies’ protective mechanisms 5 Doses of Common Substances Substance Normal Lethal Water 1.5 qts 15 qts Aspirin 2 tablets 90 tablets Table Salt 3 tsp. 60 tsp. Cyanide in Lima Beans 0.5 cups 11 cups Toxicity is the adverse effect caused when a chemical reaches a sufficient dose—threshold. 6 Asbestos Types Chrysotile Asbestos Crocidolite Asbestos The Three Ds of Fiber Toxicology Dose - Amount reaching the deep lung Dimension - Thin fibers deposit in the deep lung; long fibers are more toxic Durability - Dissolution and breakage; more durable fibers are more toxic Hesterberg and Hart., Inhal. Tox., 2001 8 Biopersistence Determines Toxic Potential of Fibers Long Fiber (> 20 µm) Incongruent Dissolution Congruent Dissolution Transverse Breakage Complete Altered Biological Translocation Dissolution Reactivity Macrophage Uptake Mucociliary Clearance Epithelial Cell Uptake Intracellular Degradation Translocation to Interstitium Hesterberg and Hart., Inhal. Tox., 2001 9 Important to Link Exposure and Dose and to the Lung’s Response to Asbestos Fibers Exposure Dose At High Doses: Response Inflammation Fibrosis Mesothelioma Lung cancer 10 What happens to fibers in the lung? Movement Up the Mucociliary Escalator Macrophage with fiber Asbestos in the Lung Macrophage Exposure Early Clearance of Short Fibers Soluble Long Fibers Rapid Recovery of Normal Durable Long Fibers Chronic Inflammation Chromosomal Effects of Fibers in Cells Grown in Culture Dishes 17 Asbestos Fibers are Taken Up by Cells Grown in Culture and Accumulate in the Perinuclear Region of the Cell Hesterberg, Oshimura, Brody and Barrett, 1986 Asbestos Induces Anaphase Abnormalities in Syrian Hamster Embryo (SHE) Cells in Culture Dishes Hesterberg and Barrett, 1985 Asbestos and Fiber Glass Induce Cytogenetic Effects in SHE Cells in Culture Dishes Hesterberg et al., 1985 But Asbestos Does Not Induce Cytogenetic Effects in Primary Cultures of Human Bronchial Epithelial Cells Grown in Culture Dishes Kodama et al., 1993 Toxicity of Asbestos to Primary Cultures of Mesothelial Cells Untreated Mesothelial Cells Apoptosis in Asbestos-Treated Mesothelial Cells Broaddus et al., 1996 22 Toxicity of Asbestos to Primary Cultures of Human Mesothelial Cells • Induced apoptosis, not chromosome effects Broaddus et al., 1996: • All cells die within one week Yang et al., 2006 • Programmed necrosis Yang et al., 2010 How can asbestos cause mesothelioma if human mesothelial cells exposed to asbestos die? Yang et al., 2006 23 Fibers With the Same Length Have the Same Toxicity to CHO Cells in Culture Hart et al., 1994 No Correlation Between Cell Culture Chromosomal Effects and Inhalation Toxicity of Fibers In Vitro Toxicity Rat Inhalation Toxicity Fiber Chromosome Effects Fibrosis Tumors Crocidolite Yes Yes Yes Chrysotile Yes Yes Yes RCF1 Yes Yes Yes 475 Fiber Glass Ye s Yes No MMVF 22 (Slag Wool) Yes No No X607 Fiber Yes No No MMVF10 (Fiber glass) Yes No No MMVF22 (Mineral wool) Yes No No Hesterberg and Hart, 2001 Hart et al., 1994 25 Fiber Dissolution and Biopersistence Studies 26 Measurement of In Vitro Dissolution of Fibers Simulated Lung Fluid Fibers Analyze Solutes: Outflow Na +,Ca +2 , etc. Leaching of the Outer Layer of a Fiber Glass Fiber Leaching of Metals From Fibers Leaving Weakened Silicon Dioxide Matrix Na+ Ca+2 Mg+2 K+ B+3 SiO2 Matrix Vitreous Fibers Dissolve and Break Glass Fibers Lung Macrophage After 3 Days in Lung Fluid with Fiber 30 Asbestos Physical/Chemical Structure Determines Biopersistence Chrysotile Asbestos Crocidolite Asbestos 31 Inhalation Biopersistence Study Protocol 32 Biopersistence of Fibers in the Lung 120 100 80 60 % of Day 1 Day of % Amosite 40 Fibers/Lung >20 µm >20 Fibers/Lung E Glass 20 475 Glass Cert. Glass 901 Glass 0 0 90 180 270 360 Recovery Days Biopersistence of Amosite and Chrysotile Bernstein and Hoskins, 2006 34 Rodent Studies of Lung Disease 35 Advantages of Rodent Inhalation Studies • Respirable fibers used • Exposure determined • Dose = Lung burdens • Fibrosis, lung cancer, and mesothelioma • Biopersistence • Determine threshold • Relationship between fibrosis and tumors 36 Lungs 14 Days After Similar Exposures to Tremolite or Chrysotile Tremolite Chrysotile Bernstein, 2003 Chronic Inhalation Studies of Fiber Toxicity and Tumorigenicity At Risk Animals Inhalation Exposure Recovery 3 Mo 6 Mo 12 Mo 18 Mo 24 Mo 20% Recovery Lung Histopathology and Burden Rodent Chronic Fiber Inhalation Studies Fiber Type Species Fibrosis Lung Cancer Meso Air Control R - 1-3.7 0 Asbestos Amosite H + 0 26* Asbestos Amosite R + 38* 5 Asbestos Crocidolite R + 13.2* 0.9 Asbestos Chrysotile R + 18.5* 1.4 Asbestos Chrysotile H + 0 0 FG-SA MMVF32 R + 23* 4.7 Ceramic RCF1 R + 12.4* 1.6 Ceramic RCF1 H + 0 41* FG-SA MMVF33 H + 0 1.2 Rock MMVF21 R + 4.4 0 FG-BI MMVF10 R - 5.8 0 Hybrid X607 R - 0 0 FG-BI MMVF11 R - 2.6 0 Slag MMVF22 R - 2.6 0 HT MMVF34 R - 0 0 Hesterberg and Hart, CRT, 2001 39 If Chrysotile is Biosoluble in the Lung, then Why did it Produce Lung Disease in the Animal Studies? 40 Lung Dose = Deposited Dose – Amount Cleared Lung Burdens of Chrysotile and Other Fibers During a Chronic Inhalation Study Two Year 6 Month Lung Burden Recovery Percent Retained Produced Fiber Exposure Fibers/Lung Fibers/Lung After 6 Mo Lung Type Fibers/cc (X 106) (X 106) Recovery Disease X607 174 58 15 26% No RCF 187 143 61 58% Yes Chrysotile 10,600 1,600 216 14% Yes Hesterberg et al., 1998 Lung Burdens of Chrysotile and Other Fibers During a Chronic Inhalation Study Two Year 6 Month Lung Burden Recovery Percent Retained Produced Fiber Exposure Fibers/Lung Fibers/Lung After 6 Mo Lung Type Fibers/cc (X 106) (X 106) Recovery Disease X607 174 58 15 26% No RCF 187 143 61 58% Yes Chrysotile 10,600 1,600 216 14% Yes Hesterberg et al., 1998 Chrysotile Does Not Cause Mesotheloimas in Hamsters Num ber Lun g Mesoth elial Group Animals Fibrosis Hyperplasia Meso thelioma Control 83 No No No MMVF 10a 81 No No No Chrysotile 49 Yes No No MMVF 33 83 Yes Yes Yes RCF 1 102 Yes Yes Yes Amosite 83 Yes Yes Yes McConnell et al., 1995 Hesterberg et al., 1999 McConnell et al., 1999 Chronic Bioassays of Chrysotile Asbestos • Chronic exposure resulted in lung fibrosis, cancer and a single mesothelioma in rats • Chrysotile exposure levels were very high — 10,600 f/cc • This is 100,000 times the OSHA PEL of 0.1 f/cc • Massive dose to the lung target tissues • Lung clearance likely impaired due to “overload” Hesterberg et al., 1993 45 Threshold for Chrysotile-Induced Lung Disease is Above 500 f/cc • Three month rat inhalation study of chrysotile • Exposure to 536 WHO fiber/cc • No lung fibrosis was observed at this level • 200-fold lower than tumorigenic exposure of 10,500 f/cc • Lack of fibrosis suggests no lung cancer or mesothelioma • This study indicates a threshold of > 500 f/cc Bernstein et al., 2006. 46 Fiber Biopersistence Correlates with Inhalation Toxicity of Fibers Biopersistence Rat Inhalation Toxicity Fiber Half-Life (Days) Fibrosis Tumors Crocidolite 817 + + Amosite 418 + + MMVF32 79 + + RCF1 55 + + MMVF33 49 + - MMVF21 67 + - MMVF 10 (Fiber glass) 14.5 - - X607 9.8 - - MMVF11 (Fiber glass) 9 - - MMVF22 (Mineral wool) 9 - - MMVF34 (Mineral wool) 6 - - Hesterberg and Hart, 2001 47 Fiber Biopersistence Correlates with Inhalation Toxicity of Fibers Biopersistence Rat Inhalation Toxicity Fiber Half-Life (Days) Fibrosis Tumors Crocidolite 817 + + Amosite 418 + + MMVF32 79 + + RCF1 55 + + MMVF33 49 + - MMVF21 67 + - MMVF 10 (Fiber glass) 14.5 - - Chrysotile (Canada) 11.3 X607 9.8 - - MMVF11 (Fiber glass) 9 - - MMVF22 (Mineral wool) 9 - - MMVF34 (Mineral wool) 6 - - Chrysotile (Brazil and CA) 1.3, 0.3 Hesterberg and Hart, 2001 48 Lung Fibrosis Occurs Before Lung Cancer and Mesothelioma in Rodents Hesterberg and Hart, 2001 Airborne TWA Fiber Concentrations from Drywall Workers (fibers/cc ≥5 µm) Study TWA Contemporary Studies Brorby et al. (2013) (respirable PCM 0.26 (median) fibers, enclosed space) Brorby et al. (2013) (respirable PCM 0.078 (median) fibers, nonenclosed space) Contemporary Estimates of Historical Exposures Brorby et al. (2013) 0.11 (median) Historic Studies Rhodes and Ingalls (1976) 0.1 to 0.9 Rhodes and Spencer (1977) 0.005 to 0.3 (personal TWAs) Verma and Middleton (1980) 2.1 to 4.5 Verma and Middleton (1981) 4.2 National Loss Control Service None Corporation, 1972 Soule (1973) None Rohl et al. (1975)/Fischbein et al. (1979) None PCM=phase contrast microscopy 50 Low Exposures to Chrysotile Do Not Result in Lung Disease 12000 10000 8000 6000 4000 Exposure Levels in Fibers/cc in Levels Exposure 2000 0 Lung Disease in No Lung Disease in Drywall Installers Animals Animals 51 Summary and Conclusions • In vitro studies in non-lung rodent cells and cell lines have shown chromosomal effects, but – These effects are not seen in primary cultures of human lung cells – In vitro chromosome studies were invalidated by chronic animal inhalation studies • Chrysotile is very biosoluble in the lung • Threshold for chrysotile disease > 500 f/cc • Low chrysotile exposures do not cause disease 52 Does Low Exposure to Chrysotile Pose a Health Risk? Dr.
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