Introduction
Asbestos is a group of naturally occurring fibrous minerals with extraordinary tensile strength, poor heat conduction, and relative resistance to chemical. For these reasons, asbestos was widely used in construction of buildings and as an ingredient in a number of products, such as roofing shingles, water supply lines, and fire blankets, as well as clutches and brake linings for automobiles.
In Hong Kong, the Air Pollution Control Ordinance, Cap. 311, banned the import and sale of the more hazardous types of asbestos, amosite and crocidolite, since 1996. A total ban on the import, transhipment, supply and use of all forms of asbestos was introduced in 2014. However, buildings built before the mid 1980s may have asbestos containing materials (ACM). Some examples of ACM are corrugated asbestos cement sheet, lagging materials for hot water pipes, electrical insulation cable tray. For more information about asbestos control and common ACM in Hong Kong, please refer to the webpage of the Environmental Protection Department (EPD) (http://www.epd.gov.hk/epd/english/environmentinhk/air/asbestos/asbestos.html).
Sources of Exposure to Asbestos
The asbestos fibres go into our body mainly through inhalation and the source of exposure can be broadly categorized into occupational and environmental exposure.
Occupational Exposure
In Hong Kong, to protect worker's health in relation to asbestos work, the Factories and Industrial Undertakings (Asbestos) Regulation (Cap. 59AD) has banned work with any type of asbestos in industrial undertakings, except the removal and disposal of asbestos. Hence, occupational exposure may arise during the removal and disposal of asbestos, particularly if adequate preventive and control measures are not taken. The Labour Department has issued a Code of Practice (http://www.labour.gov.hk/eng/public/os/B/asbestos.pdf) to provide guidance on the necessary measures, such as adopting dust suppression work methods and using protective clothing and approved respirators, for protecting workers from exposure to asbestos dust at work.
Environmental Exposure
Because of its natural occurrence and widespread use in the built environment and certain industries in the past, asbestos fibres are present in minute quantities in air which urban and rural dwellers are breathing in.
Some people may have concern about ACM, namely corrugated asbestos cement sheet and grilles, present in their home environment. Asbestos fibres in these ACM are generally bound into the base material matrix and can only release extremely small quantity of asbestos fibres, if any, under normal circumstances.
Potential Health Effects
According to the World Health Organization, exposure to asbestos can cause lung cancer and mesothelioma (a rare cancer of the pleural and peritoneal linings). Asbestos exposure is also responsible for other diseases such as asbestosis (fibrosis of the lungs), and plaques, thickening and effusion in the pleura.
Workers engaging in asbestos removal and disposal work have a higher risk of exposure to asbestos dust at work and this is particularly true if they do not take proper protection. Through inhalation, asbestos fibres may get trapped and remain in the lungs and affect health. The type and severity of health effects depends on a number of factors such as the level and duration of asbestos exposure and smoking habit.
Some diseases related to the exposure of asbestos are briefly described below.
a. Asbestosis
Asbestosis is a chronic lung disease which is due to high level and prolonged period of asbestos exposure. Generally speaking, a brief exposure to asbestos would not lead to asbestosis. In asbestosis, inhaled asbestos fibres cause the lung tissues to scar, leading to fibrosis or asbestosis. The scarring makes it more difficult to breathe. The latency period for the onset of asbestosis is typically 10-20 years after the initial exposure of asbestos. Asbestosis generally progresses slowly, and its presentation can vary from asymptomatic (no symptoms) to disabling.
b. Pleural Abnormalities
Persons with significant exposure to asbestos are at higher risk for developing various types of pleural (membranes lining the lung and the inside of the chest cavity) abnormalities, such as pleural effusion and thickening. Nevertheless, there are many causes of pleural abnormalities. Most people will not have symptoms, but some may have decreased lung function and shortness of breath.
c. Mesothelioma
Mesothelioma is a rare cancer, which affects the membranes lining the lungs and the inside of the chest cavity (pleura) or the abdominal cavity (peritoneum). Although most mesotheliomas are caused by exposure to asbestos, brief exposure to asbestos carries a very low risk of developing mesothelioma. The latency period between the time of initial exposure to asbestos and development of mesothelioma is commonly more than 30 years.
d. Lung Cancer
Lung cancer is a malignant tumor of the lung and is more common in men, particularly over the age of 40. There are many risk factors for lung cancer, including cigarette smoking or exposure to secondhand smoke (also known as passive smoking), exposure to radon gas, air pollution, radiation exposure and occupational exposure to certain chemicals or substances, such as asbestos, arsenic and chromium. Generally speaking, a brief exposure to asbestos carries a very low risk of lung cancer.
Health Advice
Ambient air usually has a very low level of asbestos fibres, which poses a very low health risk. Unlike occupational exposure to asbestos, the chance of adverse heath effect for inadvertent environmental exposure to asbestos fibres in daily life is very low. Nevertheless, one may consult a family doctor if one wishes to learn more about possible health effects of asbestos exposure or if specific symptoms (such as shortness of breath and chest pain) develop.
Everyone is encouraged to adopt healthy lifestyles including no smoking and drinking, healthy diet as well as regular exercise.