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INORGANIC DUSTS

INORGANIC DUSTS. AOEC Teaching Module 2007.

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INORGANIC DUSTS

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  1. INORGANIC DUSTS AOEC Teaching Module 2007

  2. This educational module was produced by Michael Greenberg, MD, MPH, Arthur Frank, MD, PhD, and John Curtis, MD for The University of Texas Health Science Center at San Antonio (UTHSCSA) Environmental Medicine Education Program and South Texas Environmental Education and Research Program (STEER-San Antonio/Laredo/Harlingen,Texas)Administrative support was provided by the Association of Occupational and Environmental Clinics through funding to UTHSCSA by the Agency forToxic Substances and Disease Registry (ATSDR), U.S. Department of Health and Human Services.Use of this program must include acknowledgement of the authors,UTHSCSA and the funding support.For information about other educational modules contact the UTHSCSA STEER office, Mail Code 7796, 7703 Floyd Curl Drive, San Antonio,Texas 78229-3900,(210)567-7407.

  3. HISTORICAL PERSPECTIVE • Dusty trades such as mining have been linked to potential health problems since antiquity • Pliny described problems associated with mining nearly 2 thousand years ago • A key recognition was that the dust itself could lead to lung problems (pneumoconioses)

  4. Libby, Montana • Vermiculite mining began in Libby in the 1920’s • The vermiculite ore was contaminated with tremolite asbestos • W.R. Grace Company controlled the mines beginning in the 1960’s

  5. Libby Mine Site

  6. Asbestos (tremolite)-containing Vermiculite

  7. Why are we concerned about Libby, MT? • Materials mined from the Libby area were actually shipped throughout USA • Texas and other border areas did receive materials mined at Libby

  8. From Libby to Texas • More than 675,000 tons of vermiculite were sent from Libby area mines to dozens of locations in Texas between 1963 and 1992 > 327,000 tons to Dallas > 193,000 tons to Houston > 103,000 tons to San Antonio

  9. Health Effects • Some studies have reported increased rates of lung cancer, asbestosis and mesothelioma in vermiculite exposed populations in and around Libby, MT • Miners • Families of those employed in the mines • Local population surrounding the mines

  10. Toxicological Considerations for Inorganic Dusts • Asbestos • Silica • Fiberglass • Vermiculite

  11. Asbestos • A group of hydrates silicates found as mineral fibers in natural rock formations • 2 major groups (6 distinct types) • Serpentine • Chrysotile • Amphibole • Amosite, anthophyllite, crocidolite, actinolite, tremolite

  12. Asbestos - Occurrence • Exists in natural deposits • Harmless if undisturbed • Used in industry • Thousands of uses including: • Fire-proofing • Construction • Automobile parts • Durable and persistent in the environment Tremolite Asbestos

  13. Exposure • Construction (now less frequent) • Demolition of asbestos containing structures may result in aerosolization of fibers • Drinking water may contain asbestos • Natural deposits • Cement pipes containing asbestos

  14. Potential Health Effects • Nonmalignant • Asbestosis • Malignant • Lung Cancer (bronchogenic carcinoma) • Mesothelioma • Possible association with non-pulmonary

  15. Asbestosis related deaths by state:

  16. Asbestosis • When asbestos is deposited in the lungs • Biopersistence in lungs varies with specific type of asbestos • A fibrotic response may arise from retained fibers • This may cause pulmonary problems in some cases • Usually develops over 20-40 years

  17. Active Fibrosis at the Edge of a Scar (Hematoxylin and Eosin, x125) Asbestos body Rajagopol J and Mark E. N Engl J Med 2002;347:1262-1268

  18. Asbestosis - Clinical • Symptoms may include dyspnea and cough • Pulmonary function tests may reveal: • Reduced diffusing capacity • Restrictive pattern on PFTs • Radiographic abnormalities may be seen Histopathologic view of asbestosis

  19. Asbestosis - Radiographic Findings • Chest radiography: • Small irregular opacities in lower lobes • Upper lobe disease less likely • Pleural plaques • Indication of exposure ONLY • Does NOT indicate clinical disease • Only 10-15% of plaques are visible radiographically • Pleural Effusions • Fibrosis • Curvilinear plural lines • Thickened inter- and intra-lobular lines • CT scan may show “honeycombing”

  20. Asbestosis • Note: • Pleural plaques • Fibrosis

  21. Amphibole Asbestos and Cancer • Increased risk of bronchogenic carcinoma - up to 5 times relative risk in some studies • SYNERGISTIC effect with tobacco smoking that may increase relative risk up to almost 50 Scanning electron micrograph of lung cancer cells

  22. Mesothelioma • Cancer arising from the epithelium or sub-epithelium of pleura, peritoneum or pericardium • May have increased incidence in populations with long-term, high concentration amphibole asbestos exposure • Reported odds ratios vary in different trades • No excess risk from chrysotile asbestos • Some exposures may involve multiple types of asbestos with co-existent amphibole and chrysotile forms

  23. Clinical and Computed Tomographic (CT) Features of Malignant Mesothelioma Subcutaneous extension of mesothelioma Mesothelioma presenting as a pleural mass Mesothelioma encircling the intrathoracic space Robinson B and Lake R. N Engl J Med 2005;353:1591-1603

  24. Mesothelioma • Does occur in patients with no asbestos exposure • May be difficult to diagnose • Long latency period • Averages 30-40 years following exposure • Difficult to treat/poor prognosis • Chemotherapy • Radical thoracic surgery

  25. Electron micrograph of tumor showing several characteristics of mesothelioma Dvorak A. N Engl J Med 2001;345:424

  26. Mesothelioma • Survival from time of diagnosis varies according to several prognostic factors • Usually less than 20 months • No effective curative therapy • Surgery is mainly palliative • Chemotherapy may prolong survival

  27. Toxicological Considerations for Inorganic Dusts • Asbestos • Silica • Fiberglass • Vermiculite

  28. Silica • Refers to the chemical compound silicon dioxide • Crystalline silica exists in several forms • Alpha quartz (often simply referred to as quartz) • Other forms (beta quartz, keatite, coesite etc.) less common • Noncrystalline (amorphous)

  29. Silica - Occurrence • Common component of soil and rock • Crystalline silica is a component of nearly every mineral deposit

  30. Silica Exposure • NIOSH indicates that > 1.7 million U.S. workers may be exposed to silica • Various occupations may result in exposure • Construction • Sandblasting • Mining • Most exposures are to mixed dust with variable silica content

  31. Health Consequences • Estimated 200-300 deaths per year due to silica exposure • In some cases silica exposure may result in: • Silicosis • Some have suggested an association between silica and other medical conditions including • Lung cancer • Increased risk of tuberculosis • Autoimmune disease Mycobacterium tuberculosis

  32. Classical Silicosis • Irreversible fibrotic disease of lungs • May develop only after decades (chronic) of occupational exposure to silica • Preventable with proper precautions

  33. Silicosis with Fibrosis

  34. Chronic (classic) silicosis • Develops over many years (as long as 45 yrs or longer) • Radiographic findings include: • Nodular opacities in upper lobes • Lymph node calcification (egg-shell pattern) • Lower-lobe hyperinflation or bullae • Restrictive pattern seen on pulmonary function tests (PFTs)

  35. Accelerated silicosis • Accelerated silicosis • Develops more rapidly (in the range of 15 years) • Follows more intense exposure • Similar radiographic appearance

  36. Acute silicosis • Extremely uncommon • Requires SUBSTANTIAL exposure over relatively short time frame • May develop in less than 1 year • Symptoms: dyspnea, fever, weight-loss, chest pain, rapidly progressive respiratory failure • Radiographic appearance: • Ground-glass appearance • Linear opacities • Hilar lymph node enlargement • Biological mechanisms for the development of this disease may differ from other forms

  37. Hawk’s Nest Disaster • 1931-1932; near Gauley Bridge, West Virginia • Largest American epidemic of acute silicosis • More than 400 workers died • Federal hearings determined that rock blasting was conducted at this site through rock > 90% pure silica

  38. Silicosis Treatment • Avoidance of exposure • Inhaled corticosteroids • Supportive care

  39. Silica and Lung Cancer • There is evidence of carcinogenicity in some animal models • Controversial in human populations - • Current IARC classification • 1 (known human carcinogen) • Other reviews report no evidence of causation between silicosis and lung cancer

  40. Other manifestations • Pulmonary tuberculosis • Occurs more frequently in silicosis patients • Some have posited association with autoimmune disease • Rheumatoid arthritis (RA) • Scleroderma • Progressive systemic sclerosis

  41. Toxicological Considerations for Inorganic Dusts • Asbestos • Silica • Fiberglass • Vermiculite

  42. Fiberglass • Colloquial term/trade name for fibrous glass products made from molten glass or sand • Used as thermal and sound insulation • Known to cause irritative symptoms of the skin, upper airways, mucous membranes following unprotected exposure

  43. Health Effects • Limited animal evidence of carcinogenicity • Usually at doses and routes of exposure not expected to be clinically relevant, i.e. extraordinarily high exposures for long time period • IARC (2001) states fibrous glass is “not classifiable” as to carcinogenicity

  44. Toxicological Considerations for Inorganic Dusts • Asbestos • Silica • Fiberglass • Vermiculite

  45. Vermiculite • Naturally occurring mineral • Expands when heated • Light-weight • Fire-resistant • Absorbent • Odorless

  46. Vermiculite Uses • Attic insulation • Packing material • Garden products

  47. Health Issues • May be contaminated with amphibole (tremolite) asbestos • Health effects determined by degree of amphibole exposure

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