Silicosis

Silicosis is the commonest and one of the most serious occupational diseases. It is irreversible fibrosis of the lungs caused by inhalation of free silica dust.

Importance of Silica and Silicosis

The distribution of silicon in nature is similar to the distribution of carbon in organic matters. Silicon contributes to about 28% of the earth's crust. Silicon being very reactive does not remain in the element form but combines either with oxygen alone and forms free silica (SiO₂) or with oxygen and other elements and forms silicates, eg asbestos. Silica and silicates constitute the bulk of most kinds of rocks, clays and sands.

The term silicosis is reserved for the lung disorder caused by inhalation of free silica, which is an untreatable progressive disease and is the commonest and most widespread of all occupational diseases. Exposure to large amount of free silica can pass unnoticed because, silica is odourless, non-irritant and does not cause any immediate noticeable effect and hence is confused with ordinary dust. Silica exposure also predisposes to development of pulmonary tuberculosis, which is an important public health problem in the country.

Who is at risk

It is estimated that about 3 million people working in various types of mines, ceramics, potteries, foundries, metal grinding, stone crushing, agate grinding, slate pencil industry etc., are occupationally exposed to free silica dust and are at potential risk of developing silicosis.

Symptoms

Silicosis will often develop between 20 to 45 years after the exposure. But certain forms of the disease can occur after a single heavy dose to a very high concentration of silica in a short period of time. Workers with Silicosis may have following symptoms:

• Shortness of breath following physical excretion.
• Severe and chronic cough.
• Fatigue, loss of appetite,
• Chest pains and fevers.

Silica particles end up the air sacs of the lung, causing inflammation and scarring that damages the sacs, preventing gas exchange and normal breathing. The disease will be fatal as the inflammation spreads and lung tissue becomes damaged.

Clinical features

It is important to emphasize that there may be no symptoms even when the radiographic appearances suggest fairly advanced silicosis. Dyspnoea on exertion is considered to be the most frequent and directly related symptom of silicosis. The severity of dyspnoea increases with progress of the disease. In the absence of complicating disease (eg tuberculosis), it is rarely complained of at rest. Slight unproductive cough is a symptom at the initial stages, later on the quantity of sputum increases. The symptom complex may resemble chronic bronchitis. Excessive sputum production is due to bronchial catarrh brought about by chronic dust exposure and some times it is due to secondary bacterial infection of the devitalized lungs. Chest pain and haemoptysis indicate the possibility of complication like tuberculosis.

Diagnosis and treatment

Workers have been overexposed to silica dust should visit a doctors specializing in lung disease, a pulmonologist. Silicosis often goes untreated and undiagnosed especially chronic silicosis because its symptoms are not unique. A person’s occupational history with silica dust exposure will help doctors evaluate possible medical problems. Through medical examination using chest X-rays and lung function test can determine if a person has silicosis. Lung function tests are useful in early diagnosis of the disease, often showing poor airways and bronchitis associated with irritation from the dust.

Using tools like CT Scans, MRIs, invasive procedures are almost never required to make the diagnosis of silicosis as a simple Chest X-ray is a good tool. Patients at risk should let their doctor know, because the doctor may not think to look for the disease. There are risks of misdiagnosis. It may be misdiagnosed as pulmonary edema and Tuberculosis. Few lasting treatment are available for silicosis.

Treatment

There is no specific treatment for silicosis, therapy being directed largely at the complications of the disease. The first step is obviously stopping continuing exposure. This will not stop the gradual progression of the disease, but will prevent it form an even faster rate of progression. Patients are administered oxygen and steroids to help them breathe as the disease runs its course.

Prevention

Prevention of the disease is key action to control silicosis, because there is no way to reverse the disease.

• Industrial hygiene - Dust control measures -  elimination or suppression of dust in the work environment is the key in the control of silicosis. The general principles of dust control measures include substitution of more hazardous substances with innocuous substances, isolation and enclosure of the sources of dust, use of wet methods wherever possible, application of local and general exhaust, humidification of the work environment, etc. Frequently, the management is found to share the misconception of laymen that the use of dust mask is sufficient for the prevention of dust related occupational diseases in the industry. The personal protective equipments such as masks should be prescribed only when all available dust control measures have failed. In fact, the dust masks are of little value when the dust concentrations are high as the dust particles will clog the pores in the filter resulting in a choking sensation and discontinuance of the use of masks by workers. Moreover, the masks are not suited for hot and humid climate
• Medical surveillance : Workers at risk of exposure, such as miners or sandblasting should have lung examination at least every 3 years.
• Health education of the workers need to be taken up to sensitise the workers on occupational health.

Sources

1. Silica and diseases - NIOH bulletin
2. Silicosis - A human rights issue
3. Silicosis and silicotuberculosis in India