Figure 3: Lung tissue observed under polarized light microscopy containing crystalline
silica (26)
As already mentioned, the outcome of crystalline silica exposure leads to silicosis. Silicosis is a
slowly progressive disorder and usually takes more than 10 years to develop and may progress
after a workerʼs exposure to silica has ended. The majority of miners develop radiological signs of
silicosis only when they are over 50 years. Ref.(2). An exposed worker will either develop acute,
accelerated or chronic silicosis. The main determinant of the type of silicosis is however the
workerʼs level of exposure. Workers exposed to high concentrations of fine particulate matter as
crystalline silica will be more prone to develop acute or accelerated silicosis. Chronic silicosis is
3
mainly the result of long-term exposure to silica. With acute, accelerated and chronic silicosis,
death occurs after a few months, 5-10 years and more than 10 years respectively. Table 1
summarises different occupations that are know to be associated with acute, accelerated and
chronic silicosis.
Table 1: Difference types of silicosis associated with different occupations
Workers with silicosis are furthermore prone to develop other lung diseases due to the fibrotic
effect crystalline silica have on lung tissue. Other lung diseases associated with crystalline silica
exposure are increased mycobacterium infections i.e., tuberculosis, brochogenic carcinoma and
immune-mediated diseases i.e., scleroderma. A lifetime exposure to 0.1 mg.m3 increase the
likelihood to develop lung cancer by 30%. Recently there are indications that nephrotoxicity in
workers who are exposed to silica is linked with quartz exposure. There exist numerous case
reports linking acute glomerulonephritis with accelerated silicosis Ref.(11). Hotz et al. Ref.(16)
mentioned that sub clinical effects on kidney function may occur in workers who are exposed to
silica for short periods. Out of all diseases mentioned only silicosis, tuberculosis and
bronchogenic carcinoma are compensatable diseases.
A primary feature that develops in lungs of silica quartz exposed workers is nodule formation in
the upper zones of the lung Ref.(17). Nodule formation is usually the result of many years of
exposure to relatively low levels of dust that contain silica quartz Ref.(18).
Figure 4: A microscopic photo of a typical silicotic nodule containing collage fibres in a
whorled pattern (27)
4
Type of silicosis Occupation
Acute
Sandblasting, surface drilling, tunneling, silica flour milling, ceramic
making, grinding
Accelerated Silica flour mill operations, sandblasting and other mechanically
and crushing operations
Chronic
Inhalation of crystalline silica over prolonged periods, + 10 years of
exposure to dust containing 18-30% crystalline silica