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Silica, Crystalline - Hazard Recognition |
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Are Other Health Effects of Silica Exposure Being
Overlooked?
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by
David F. Goldsmith, PhD
Public Health Institute
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The National Conference to Eliminate Silicosis March 23-25, 1997 in Washington DC
enjoyed a splendid turnout of over 600 attendees. In my opinion, the conference attention
on silicosis to the exclusion of discussion of other silica health effects was very
shortsighted . However, I was delighted by the opening remarks by NIOSH Director, Dr.
Linda Rosenstock, who pointed out that we now know that silica exposure is a risk factor
for several "new" conditions, and that deliberations should be expanded to
consider other health problems such as cancer, autoimmune diseases, nephritis and other
kidney diseases, and tuberculosis (TB).
What is the evidence for these other conditions? Last month the International Agency
for Research on Cancer (IARC) changed the classification of silica from 2A (probable human
carcinogen) to 1 (known human carcinogen). The change to IARC Type 1 means that
occupational silica dust exposure is considered like other known human carcinogens such as
asbestos, vinyl chloride, radon daughters, smoking, and DES. It means that companies are
likely to change their Material Data Safety Sheets (MSDS), that workers need to be
informed, and that where there are alternatives to silica (such as sandblasting) that they
need to be sought out. The change in IARC status does not mean that the controversy about
carcinogencity is over, but it does mean that the evidence is sufficient to convince a
group of IARC experts that silica increases the risk of lung cancer. Furthermore, it goes
a long way to meeting the criteria for causation we use in epidemiology. There is other
evidence to suggest that silica is linked to stomach cancer, lymphatic cancers, and skin
cancer, though the IARC focus was on pulmonary malignancies.
The other health effects are not "new," but we now have good epidemiology
studies of recent vintage showing that silica exposure (with and without silicosis) is
linked with several autoimmune conditions which previously there were only case studies:
rheumatoid arthritis, scleroderma, Sjogrens' syndrome, and lupus. There is also
accumulating epidemiology evidence that occupational silica exposure is linked with kidney
diseases such as nephritis and end-stage renal disease.
With a narrow focus on silicosis, we tend to overlook serious conditions that often
accompany silicosis--silicoTB and cor pulmonale (enlargement of the heart muscle).
Although these two secondary effects of silicosis are declining in the U.S. (as is
silicosis), they remain killers of relatively young workers in developing countries and in
China and former Soviet Union. Sadly we also must acknowledge the epidemic of acute and
accelerated silicosis that descended upon Mexican workers in the Midland-Odessa, Texas
area in the early part of the 1990s, some 60(!!) years after the Gauley Bridge disaster.
These men were vastly overexposed to silica, without any protection, in several oil pipe
sandblasting operations, and they have many of the autoimmune ailments as well as fatal
silicosis.
Thus, the silicosis prevention we all hope to achieve should include these other
diseases: cancer, autoimmune illnesses, kidney diseases, and TB. Furthermore, the
employees we need to communicate with about this hazard must receive information in
languages of the workers at risk, not in English only.
David F. Goldsmith, PhD
Public Health Institute
2001 Addison Street, 2nd Floor
Berkeley, CA 94704-1103 USA
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