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Karen B. Mulloy, DO, MSCH
Program in Occupational and Environmental Health
University of New Mexico Health Sciences Center
Ken Silver, PhD
Department of Environmental Health
East Tennessee State University
- Crystalline silica occurs naturally in the earth’s crust
- Earth’s most abundant mineral
- Three most common forms
- Cristobalite
- Tridymite
- Quartz – most abundant component of soil & rock
- Respirable particles of silica (<5 µ in diameter) produced when crystalline silica-containing rock and sand is used or processed
- Mining, milling, and stone work
- Quarrying and tunnel operations
- Foundry and boiler work
- Sandblasting and drilling
- Pottery and glass making
- Occupational exposure associated with respiratory diseases
- Silicosis (chronic, accelerated, acute)
- Progressive pulmonary fibrosis
- Chronic obstructive pulmonary diseases
- Lung cancer
- Increased risk for TB
- Occupational exposure associated with other diseases
- Systemic autoimmune diseases
- Rheumatoid arthritis, SLE, scleroderma, small vessel vasculitides
- Renal Disease
- Glomerulonephritis, nephrotic syndrome, end-stage renal disease
- Silicosis
- First reported by ancient Greeks
- Prevalence
- Peaked in the industrial countries in the last half of the 19th century
- Disease still prevalent in the developing world and not eliminated from the developed world
- Largest industrial disaster in US history
- Gauley Bridge, WV – 1930-1932
- Tunnel construction
- Silica content of the rock - >90%
- >475 workers died
- 1,500 were disabled from chronic silicosis
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View of Gauley Bridge, WV circa 1930
Source: The Hawk’s Nest Incident, Cherniak M, 1986
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View of Hawk’s Nest tunnel interior, March 13, 1932
Source: The Hawk’s Nest Incident, Cherniak M, 1986
Silicosis: Crude mortality rates by state, U.S. residents age 15 and over, 1987-1996 |
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- A pulmonary disease caused by inhalation of dust particles of respirable size
- Three presentations and severity of the disease
- Classic silicosis
- Accelerated silicosis
- Acute silicosis
- Chronic (classic) silicosis
- 20+ years of exposure to low-medium dust levels
- Accelerated silicosis
- 5-10 years of higher dust exposure
- Acute silicosis
- <1-3 years exposure to extremely high levels of free crystalline silica
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Source: ACCP Pathology Slide Set, No. 36-2
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Source: Silicosis. Weber and Banks. In: Textbook of Clinical Occupational & Environmental Medicine. Rosenstock & Cullen, eds., 1994, page 270.
-
- Development predominantly in the upper lobes
- Rounded opacities < 1cm in diameter seen on chest x-ray
- Enlarged hilar lymph nodes with peripheral calcification - eggshell calcification
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-
- A massing of small rounded opacities in upper lobes
- Large opacities > 1 cm
- Hila retract upward & lower zones become hyper-inflated & appear emphysematous
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Source: Pathology of Occupational Lung Disease, 2nd ed. A Churg, FHY Green, 1998, pg. 163
- Characterized by same features as chronic classic silicosis
- Time from initial exposure and development of radiographic findings and symptoms and change in pulmonary function much shorter
- Rapid progression to PMF with severe respiratory impairment
- Radiographic Evidence
- Diffuse alveolar infiltrate
- Air bronchograms
- Ground glass appearance
- Hilar & mediastinal lymphadenopathy
- Bullae formation
- Air trapping
- Volume loss
- Cavity formation
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Source: Environmental & Occupational Medicine, 2nd ed., Rom W, 1992, pg. 353.
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Source: Diagnosis of Diseases of the Chest, Fraser & Pare, 1970, pg. 923.
Simple silicosis
- Symptoms
- Often no symptoms
- Chronic productive cough may be due to industrial bronchitis from dust exposure
- Physical exam
- Normal breath sounds
- Course breath sounds with co-existing bronchitis
Progressive Massive Fibrosis
- Symptoms
- Range from chronic productive cough to exertional dyspnea
- Physical exam
- Diminished breath sounds
- Prolonged expiration
- Clubbing rare
- Symptoms
- Irritative cough - sometimes productive
- Weight loss
- Fatigue
- Dyspnea
- Physical exam
- Crackles heard on auscultation
Pulmonary Function Testing
- Simple silicosis
- PMF
- Severe restriction
- Mixed obstructive/restrictive defect
- Loss of pulmonary compliance
- Hypoxemia
The Occupational History
- What kind of work do you do?
- Do you think your health problems are related to your work?
- Are your symptoms better or worse when you are at home or at work?
- Are you now or have you previously been exposed to dust, fumes, chemicals, radiation or loud noises?
- History of silica exposure
- Radiographic evidence consistent with silicosis
- Absence of other illnesses that mimic silicosis
(LS Newman. N Engl J Med 1995; 333:1129)
- Prevalence
- 5.3% in workers with x-ray evidence of silicosis
- 25% in workers with acute or accelerated silicosis
- As high as 75% among South African gold miners
- Diagnosis difficult
- TB infection can be walled off in the lung by the silica induced fibrosis
- False negative acid-fast-staining sputum smear may occur
- Radiographic changes seen with TB infections can mimic advanced cases of silicosis
- Diagnosis
- Presence of chest x-ray changes of a worker with silicosis over a short period of time indicates superimposed TB infection until proven otherwise
- Annual PPD
- If results become positive without clinical evidence of active TB, the patient should be treated with 1 year of INH
- Crystalline silica deposited in lungs causes epithelial & macrophage injury and activation and persistent inflammation
- Human subjects exposed to dust containing crystalline silica showed an increase in the levels of sister chromatid exchange and chromosomal aberrations in peripheral blood lymphocytes
- Animal studies have shown gene mutations and tumor formation as a result of marked and persistent inflammation and epithelial proliferation
- IARC
- Crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans (Group 1)
- First described in 1953 by Caplan
- Unusual radiologic changes in the lungs of Welsh coal miners who had pneumoconiosis
- Since then the autoimmune disease linked with crystalline silica exposure
- Rheumatoid arthritis, scleroderma, SLE, some small vessel vasculitides
- Inhalation of crystalline silica particles leads to chronic immune activity and fibrosis
- Studies have shown that crystalline silica can be mobilized from lungs to other organs - lymph nodes, spleen, and kidney
- Silicosis has been linked to an increase in autoantibodies, immune complexes, and excess production of immunoglobulins, even in the absence of a specific autoimmune disease
- Possible Mechanisms
- May be result of adjuvant (a substance that enhances an immune response to an antigen) effect on antibody production
- Cell death by necrosis and apotosis (an active process involved in gene regulation)
- Host susceptibility and genetic differences may explain why all workers exposed to silica do not develop immune disorders may
- Epi studies
- Statistical significance between silica exposure and several renal diseases
- An increasing standardized rate ratio for acute and chronic renal disease with increasing cumulative crystalline silica exposure and an excess of end-stage renal disease incidence (highest for glomerulonephritis)
- Intensity of exposure to silica dust may be more important than cumulative exposure or duration in the development of autoimmune diseases
- Study crystalline silica exposure most strongly associated with ESRD and median exposure was below the OSHA permissible exposures levels
- Prevention/ Prevention/Prevention
- Workers at risk for progression of disease and TB infection
- Yearly chest x-ray and PPD Flu and pneumococcal vaccine
- Aggressive treatment of TB infections
- Dyspnea treated with inhaled bronchodilators
- O2 for cor pulmonale, hypoxemia, pulmonary hypertension
- Occupational Health Surveillance
- Gather information on cases of occupational illness and injury and workplace exposures
- Condense, refine, and analyze the data
- Disseminate analyzed data to workers, unions, employers, governmental agencies, public
- Plan and execute interventions - primary prevention - based on the analyzed data
- Occupational Sentinel Health Event
- "A disease, disability, or untimely death which is occupationally related and whose occurrence may: 1) provide the impetus for epidemiologic or industrial hygiene studies; or 2) serve as a warning signal that materials substitution, engineering control, personal protection, or medical care may be required"
- State-based Surveillance
- Sentinel Event Notification Systems for Occupational Risk (SENSOR)
- Many state based silicosis surveillance projects
- May help in case investigations
- Many states have a legal requirement to report a case of silicosis to the appropriate state agency
- Hierarchy of Controls
- Engineering
- Substitution, control hazard at source (wet process), improved ventilation
- Administrative
- Personal Protective Equipment
- Federal Coal Mine Health and Safety Act of 1969 (Coal Act)
- Federal Mine Safety and Health Act of 1977 (Mine Act)
- Occupational Safety and Health Act of 1970
- Current OSHA PEL for respirable silica
- 10 mg/m3 / %SiO2 + 2 for 8-hour TWA
- Current NIOSH REL for respirable silica
- 50 µg/m3 TWA for up to 10 hours/day during a 40 hour workweek
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Any Questions?
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"The way to dusty death. Out, out, brief candle!
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more."
- Shakespeare,
Macbeth,
Act V, Scene V
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