Asbestos and the Human Body
In order to create an understandable document, Scenario Learning, Inc. rewrote a
portion of the Asbestos Toxicity Case Study published by the Agency for Toxic
Substances and Disease Registry (ATSDR). The Reference section of this SafeSchools
course contains the complete ATSDR report.
How does asbestos enter the body?
Inhalation is the primary route of asbestos entry into the body. Ingestion of asbestos
fibers can occur from drinking contaminated water (or other contaminated sources)
or after swallowing fiber-containing mucus clearance from the lungs.
Experts debate the fate of ingested asbestos. Most ingested fibers will not be
absorbed and pass from the body with feces. Data do not clearly correlate
gastrointestinal (GI) tumors to direct ingestion of asbestos fibers. However, some
occupational studies report that workers exposed to asbestos by inhalation have a
twofold greater risk of colorectal cancer than unexposed workers do. Some
investigators believe that fibers removed from the lungs then swallowed causes this
malignancy.
It appears that a few ingested fibers pass through the GI wall and reach blood,
lymph, urine, and other tissues. (Fibers can also enter lymph through the lungs.)
Once in the blood and lymph, these bodily fluids transport the fibers to other areas
where they may lodge.
Lymph is an almost colorless fluid that bathes body tissues. This fluid drains into
lymph vessels that carry lymph from the body and ultimately empty into the blood
stream. Lymph nodes, located along the path and throughout the body, filter the
lymph. Research indicates that people with high levels of asbestos fibers in the lung
also had asbestos bodies in kidney, heart, liver, spleen, adrenals, pancreas, brain,
prostate, and thyroid tissues and that lymph is responsible for the movement of
asbestos fibers throughout the body.
Does the size of asbestos fibers matter?
In terms of the aerodynamics of reaching the depths of the lung, asbestos fibers act
differently from most types of inhaled particles. For most inhaled nonasbestos
particles, generally only particles between 0.5 and 5 microns in diameter with a
length-to-width ratio of 3:1 lodge in the air sacs and terminal bronchioles of the
lungs. Upper airway passages (nose, throat, and windpipe) filter most larger
particles. Smaller particles tend to remain suspended in the inspired air, and the
majority leaves the body when exhaling. However, asbestos is an exception. Fibers
ranging from 5 to 10 microns or more in length can also penetrate to the lower
respiratory regions of the lungs, where they lodge and stimulate scar tissue or
cancerous growth.
In addition, asbestos fibers can split and break down into smaller fibrils. Electron
microscopy reveals that fibrils result from asbestos fibers splitting to shorten both
length and diameter. A single asbestos fiber can fracture into hundreds of tiny fibrils.
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Copyright Scenario Learning Inc., 2001-2002
Research indicates that these uncoated fibrils might be the form that migrates into
the protective spaces around the lungs and abdomen (peritoneal and pleural spaces).
In conclusion, the lungs can retain a significant proportion of inhaled asbestos fibers.
The size and shape of asbestos fibers affect the lungs’ ability to effectively remove
them. The fibrous nature of asbestos also renders the lungs’ defense mechanisms
ineffective. Normally, macrophages (a type of white blood cell) engulf smaller,
nonfibrous, foreign particles in the lungs or remove them by lymphatic or mucus
mechanisms. However, attempts by the macrophages to engulf fibers might not
always be successful. The bottom line is that the size and shape of asbestos fibers
affect the lungs’ ability to effectively remove them.
Fiber size also appears to correlate with specific asbestos-related diseases. A 1990
study reports the following relationships between fiber size and asbestos-related
disease:

Asbestosis is most closely related to the number of fibers longer than about 2
micrometers (m) and thicker than about 0.15 m

Mesothelioma to the number of fibers longer than about 5 m and thinner
than about 0.1 m

Lung cancer to the number of fibers longer than about 10 m and thicker
than about 0.15 m
Once inside the lungs, fibers can relocate by cilia movement, lymphatic drainage, or
after ingestion the macrophages. Asbestos fibers can also penetrate a last bronchiole
and enter the space surrounding the bronchiole. Because the fibers concentrate in
the lower lungs, there is a tendency for fibrous tissue to first form in the lower lung
region.
How is scar and cancerous tissue formed?
The formation of fibrous (scar) and cancerous tissues results from the persistent
release of natural inflammatory response chemicals. It appears that the presence
asbestos fibers stimulate the secretion of these response chemicals. Stimulation for a
sufficient length of time produces one of the permanent growths.
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Copyright Scenario Learning Inc., 2001-2002