Transcript INORGANIC DUSTS - AOEC

INORGANIC DUSTS
AOEC Teaching Module
2007
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 for
Toxic 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.
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)
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
Libby Mine Site
Asbestos (tremolite)containing Vermiculite
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
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
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
Toxicological Considerations
for Inorganic Dusts
•
•
•
•
Asbestos
Silica
Fiberglass
Vermiculite
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
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
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
Potential Health Effects
• Nonmalignant
– Asbestosis
• Malignant
– Lung Cancer (bronchogenic carcinoma)
– Mesothelioma
– Possible association with non-pulmonary
Asbestosis related deaths by state:
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
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
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
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”
Asbestosis
• Note:
– Pleural plaques
– Fibrosis
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
Mesothelioma
• Cancer arising from the epithelium or subepithelium 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
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
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
Electron micrograph of tumor showing
several characteristics of mesothelioma
Dvorak A. N Engl J Med 2001;345:424
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
Toxicological Considerations
for Inorganic Dusts
•
•
•
•
Asbestos
Silica
Fiberglass
Vermiculite
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)
Silica - Occurrence
• Common
component of soil
and rock
– Crystalline silica is a
component of nearly
every mineral
deposit
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
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
Classical Silicosis
• Irreversible fibrotic
disease of lungs
• May develop only
after decades
(chronic) of
occupational
exposure to silica
• Preventable with
proper precautions
Silicosis with Fibrosis
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)
Accelerated silicosis
• Accelerated silicosis
– Develops more rapidly (in the range of 15
years)
– Follows more intense exposure
– Similar radiographic appearance
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
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
Silicosis Treatment
• Avoidance of
exposure
• Inhaled
corticosteroids
• Supportive care
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
Other manifestations
• Pulmonary tuberculosis
– Occurs more frequently
in silicosis patients
• Some have posited
association with
autoimmune disease
– Rheumatoid arthritis (RA)
– Scleroderma
– Progressive systemic
sclerosis
Toxicological Considerations
for Inorganic Dusts
•
•
•
•
Asbestos
Silica
Fiberglass
Vermiculite
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
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
Toxicological Considerations
for Inorganic Dusts
•
•
•
•
Asbestos
Silica
Fiberglass
Vermiculite
Vermiculite
• Naturally occurring
mineral
– Expands when
heated
– Light-weight
– Fire-resistant
– Absorbent
– Odorless
Vermiculite Uses
• Attic insulation
• Packing material
• Garden products
Health Issues
• May be contaminated with amphibole
(tremolite) asbestos
• Health effects determined by degree of
amphibole exposure
General Principles of
Inorganic Dust Exposure
• Determining exposure
• Anticipation of health effects
• Reducing exposure and preventing
disease
Exposure/Dose
• EXPOSURE is simply the opportunity for
contact with a chemical or substance
• DOSE is how much of a material actually
enters the body
• Some mistake the concept of exposure
thinking it is synonymous with dose
• There is a clear difference between
EXPOSURE and DOSE
Exposure
• Determined by:
– Degree of aerosolization of
particles and fibers
• Sanding, dusting,
demolition, construction
– Adequacy of ventilation
• Closed spaces result in
greater levels of exposure
– Proper use of personal
protective equipment (PPE)
• Masks and filters decrease
exposure
Principles of Dust-Related
Disease
• Inorganic dusts only cause pulmonary
disease following long-term, high
intensity exposure
• Confounding factors may include:
– Exposure to multiple other agents
– Concomitant exposure to carcinogens
– Tobacco use
– Genetic issues
Disease Prevention
• Identify populations
potentially at-risk
– Workers
– Those near uncontrolled,
heavy use
– Families of workers
• Evaluation of working
environment
– Air quality evaluation
– Wet work versus dry work
– Use of proper PPE
Clinical Problem Solving
Scenario
• Two male workers, ages 67 and 52,
present to a local clinic following
diagnosis with pleural mesothelioma
Relevant History
• What are the key features of an
appropriate:
– History of present illness (HPI)?
– Past medical history?
– Past surgical history?
– Occupational history?
– Social history?
– Family history?
Relevant HPI
• Presence of cardiopulmonary
complaints
– Dyspnea
– Chest pain
• Systemic complaints
– Weight-loss
– Night sweats
Past Medical History
• History of:
– Asthma
– COPD
– Cancer, especially lung cancer
– Pulmonary disease
• Tuberculosis
• Sarcoidosis
Past Surgical History
• Identify previous thoracic surgery
– Pneumonectomy
– Radiation to thorax
– Previous lung biopsy
Occupational and
Environmental History
• Current occupation
– Job description
– Length of employment
– Job specifics, time spent at each activity
• Use of personal protective equipment
– Type/level of PPE
– How frequently is PPE used
– Is PPE supplied and/or required by employer
• Previous employment
– Construction, demolition, military service, foreign
travel etc.
Social History
• Thorough tobacco use history
– Accurate assessment of smoking history
• Ethanol use
– Evaluation of nutritional and immune status
• Illicit drug use
– Especially inhaled drugs (e.g. marijuana, crack,
solvent inhalants, etc)
• Hobbies/home environment
– Radon in home, hobbies that may result in
pulmonary exposure
Family History
•
•
•
•
Lung cancer
Mesothelioma
Asthma/COPD
Sarcoidosis
Important Physical Exam
Findings
• Presence or absence of:
– Abnormal lung sounds
– Clubbing of digits
– Cyanosis
– Abnormal heart sounds
– Peripheral edema
– Wasting/cachexia
Appropriate Work-up
• Consider:
– Laboratory Testing
– Radiographic Evaluation
– Lung Function Testing
Laboratory Testing
• Screening labs as indicated by history
• Possibly pre-operative labs if thoracic
surgery is being considered
• Stool guaiac
– Important consideration in this age group
• Urinalysis for blood
– If indicated by history
Radiographic Evaluation
• Chest radiography
– Standard part of evaluation of patients with
exposure history
– May be evaluated according to several reading
protocols
– Possibly serial X-rays to look for progression
• Computed tomography
– As necessary, possibly to confirm diagnosis or
follow response to treatment
Lung Function Testing
• Spirometry
• Full pulmonary function testing
– May identify element of reversible
bronchospasm amenable to treatment
Assessment and Plan
• How should these patients be treated?
• How should these patients be followed?
• Is this an unusual event?
– Clusters of unusual cases need close evaluation
• Does this represent an occupational
exposure?
• Should the work-place be investigated
– Which is the responsible agency?
• Should other workers be screened or
monitored?
References
• Camus M et al. Nonoccupational Exposure to
Chrysotile Asbestos and the Risk of Lung
Cancer N Engl J Med 1998
• Beckett WS. Current Concepts: Occupational
Respiratory Diseases. N Engl J Med 2000
• Steele JPC. Prognostic Factors for
Mesothelioma. Hematol Oncol Clin N Am.
2005
• West SD, Lee YCG. Management of
Malignant Pleural Mesothelioma. Clin Chest
Med 2006
References
• Krug LM. An overview of the
chemotherapy for mesothelioma.
Hematol Oncol Clin N Am 2005
• Hessel PA et al. Asbestos, asbestosis,
and lung cancer: a critical assessment
of the epidemiological evidence. Thorax
2005
References
• http://www.atsdr.cdc.gov/DT/fibrousglass.html
• http://www.osha.gov/SLTC/etools/silica/silicos
is/silicosis.html
• Calvert et al. Occupational silica exposure
and risk of various diseases: an analysis
using death certificates from 27 states of the
United States. Occup Environ Med. 2003;
60(2):122-9.
References
• Occupational, Industrial, and
Environmental Toxicology. M Greenberg
(ed.). Mosby, Inc 2003
• Yarborough. Chrysotile as a cause of
mesothelioma: An assessment based
on epidemiology. Crit Rev Toxicol. 36:
165-187. 2006