Asbestos-related Occupational Lung Diseases in NSW, Australia and Potential Exposure of the General Population

Transcription

1 Industrial Health 2008, 46, Review Article Asbestos-related Occupational Lung Diseases in NSW, Australia and Potential Exposure of the General Population Eun-Kee PARK 1, Kirsty M. HANNAFORD-TURNER 1, Rebecca A. HYLAND 1, Anthony R. JOHNSON 1 and Deborah H. YATES 1, 2 * 1 Research and Education Unit, Workers Compensation Dust Diseases Board of NSW, Level 14, 82 Elizabeth St., Sydney, NSW 2000, Australia 2 Department of Thoracic Medicine, St Vincent s Hospital, Sydney, NSW 2010, Australia Received April 2, 2008 and accepted July 16, 2008 Abstract: Asbestos is a fibrous silicate which is recognized as causing a variety of lung disorders including malignant mesothelioma of the pleura, lung cancer and asbestosis. Asbestos use has been banned in most developed countries but exposure still occurs under strict regulation in occupational settings and also occasionally in domestic settings. Although the hazards of asbestos are well known in developed countries, awareness of its adverse health effects is less in other parts of the world, particularly when exposure occurs in non-occupational settings. Experience of asbestos use and its adverse heath effects in developed countries such as Australia have resulted in development of expertise in the diagnosis and treatment of asbestos-related diseases as well as in screening and this can be used to help developing countries facing the issue of asbestos exposure. Key words: Asbestos, Mesothelioma, Asbestos-related diseases, Occupational exposure, Public health Introduction It is well established that asbestos exposure, mainly in occupational settings, can produce several lung diseases including lung malignancies. Asbestos usage has been banned in most developed countries but it is still very widely used as a raw material in developing countries as it is relatively cheap and has a wide range of uses. In this article, we review the adverse health effects caused by asbestos exposure and the existing compensation scheme in New South Wales, Australia, where the health effects of occupational asbestos exposure are well recognized, and where policies have been implemented regarding asbestos exposure. What is Asbestos? *To whom correspondence should be addressed. Asbestos is a naturally occurring fibrous mineral used extensively in a variety of applications due to its exceptional durability and resistance to heat, corrosion, cold, acids, alkalis, electricity, noise and vibration. Due to its excellent insulation properties, asbestos was commonly used as a thermal lagging, applied to boilers and pipes, and included in many different fire protection products such as fire doors and fire resistant paneling 1). The three most common types of asbestos used in industry were chrysotile (white asbestos), amosite (brown asbestos) and crocidolite (blue asbestos). Other varieties included tremolite, actinolite and anthophyllite. Crocidolite fibers are generally shorter and straighter than other types of asbestos and have been shown to be far more persistent in the lung when compared with long, thin and curly chrysotile fibers which generally disappear within about 10 yr after exposure 2). Amosite is long, thin and flexible and bends to form wide arches which break into smaller groups of sharp needle-like fibers. The ends of the fibers are flat and do not have frayed or split ends. The health risks of asbestos exposure are probably related to their biological longevity and crocidolite is recognized to be the most carcinogenic and fibrogenic of the different var-

2 536 E-K PARK et al. ieties of asbestos whereas chrysotile is thought to be the least harmful 3, 4). Health Risks and Asbestos-Related Diseases The risk to health following asbestos exposure have historically been greatest in occupational settings, probably due to the fact that this is where highest levels of exposure have been experienced as well as the longest durations of exposure. The development of asbestos-related diseases also depends on fiber type and individual differences. According to the Australian National Occupational Health and Safety Commission 5), the recommended exposure standards for asbestos in air in Australia is 0.1 fibers/ml for chrysotile, crocidolite and amosite, which is consistent with other international guidelines 6). Asbestos-related disorders include non-malignant disorders such as asbestosis, diffuse pleural thickening, pleural plaques and pleural effusions, and malignancies such as lung cancer and malignant mesothelioma 7 9). Asbestosis is pulmonary fibrosis (scarring) or fibrosis of the lung tissue itself (that part responsible for gas exchange across the lung), and people with extensive asbestosis experience severe shortness of breath and even die from this disease. The development of asbestosis normally follows high asbestos exposures (approximately 25 fiber/ml/yr) with a latency of yr 2, 10). Diffuse pleural thickening is the development of fibrosis of the pleura over a wide area. It involves both layers of the pleura, particularly the inner lining. It is seen less commonly than pleural plaques but produces more symptoms due to the larger area affected. It may cause shortness of breath and chest pain and usually develop yr after exposure 2, 11). Pleural plaques are small patches of scarring usually involving the parietal pleura which frequently calcify and can usually be visualized on chest radiographs. Pleural plaques are an indicator of past asbestos exposure and can develop following low exposures. Pleural plaques generally do not in themselves cause respiratory symptoms but may be associated with other asbestos-related diseases such as asbestosis, malignant mesothelioma or lung cancer. Benign asbestos-related pleural effusion can develop after asbestos exposure with a latency of yr. Chest pain and shortness of breath are the main symptoms although often there are no symptoms 2, 12). Heavy asbestos exposure may also result in lung cancer with a long latency period of 20 or more years, and the risk of lung cancer is much higher if the individual has smoked cigarettes. Lung cancer is accepted as due to asbestos exposure if asbestosis has developed 13, 14), but the attribution is less clear with lower levels of asbestos exposure. Symptoms include chronic cough, breathlessness and chest pain as well as haemoptysis (coughing up blood), hoarseness of the voice and wheezing. Malignant mesothelioma (MM) is an aggressive and fatal cancer of the parietal pleura that is primarily caused by asbestos exposure in occupational settings 15, 16). Approximately 85% of cases of MM are estimated to be secondary to asbestos exposure, and the risks of MM developing are much greater after crocidolite exposure than other asbestos varieties. There is some debate as to whether chrysotile actually causes MM or whether cases described after chryostile exposure are in fact due to contamination with tremolite. MM has also been described after domestic exposure to naturally occurring asbestos form minerals which occur in Turkey 17). The latency period between first exposure to asbestos and the development of MM ranges from yr 18, 19). Individuals with MM have a very short survival time of less than 18 months after diagnosis 20 22). Currently, there is no proven treatment which cures MM, although some treatments may prolong survival. When compared with other countries, Australia has one of the highest incidences of MM in the world due to its substantial usage of asbestos products throughout the 1900 s. The number of MM cases in Australia between 1986 and 2000 was 5,176 with an incidence of 40 cases per million for the total population, predicted to peak in , 24). However, more recent predictions for New South Wales suggest a slightly later peak in ). The incidence of MM throughout Europe is expected to peak in , 27) and MM has probably already peaked in the United States 3, 28, 29). In the United States, defendant companies have paid 54 billion dollars in compensation claims up to 2001 and estimated future liabilities are 210 billion dollars 30). The predicted compensation costs for mesothelioma in Australia and Europe are 5 and 80 billion U.S. dollars, respectively 27). The incidence of mesothelioma has increased world wide due to increased asbestos usage in developing countries 22, 31 33). However, accurate determination of numbers of cases of MM and asbestos-related diseases in developing countries is not easy due to lack of experienced medical doctors, absence of surveillance systems (such as a MM registry system), and less attention from the government and public sectors. Asbestos Consumption and Occupational Exposure in Australia Asbestos usage in Australia remained high until the early 1980 s when legislation was introduced to restrict these products because asbestos had become recognized as a potent carcinogen 34). In Australia, the top five industry groups from which the highest numbers of cases arise are the building industry, the transport equipment manu- Industrial Health 2008, 46,

3 ADVERSE HEALTH EFFECTS OF ASBESTOS 537 facturing industry (which includes shipbuilding and railway locomotive building and maintenance), asbestos product manufacturing, steelworks and power stations. Asbestos based products can be found in many public buildings, including hospitals and schools. Following World War II, many private dwellings were built out of asbestos as a consequence of a brick shortage in NSW, and most of these homes still exist. During demolition or renovation of these buildings, asbestos exposure may occur and appropriate dust-control measures and/or personal protective equipment usage are recommended. However, there is limited information about such asbestos exposures in residents homes particularly when home renovations occur, and this may also occur inadvertently in a public sector environment. As an example, more than 2000 fire fighters may have been exposed to asbestos-contaminated dust during emergency response training programs held at the Holsworthy army base in NSW in Australia since ). Subsequently, ambient airborne asbestos levels were monitored to determine the potential for asbestos exposure exceeding the exposure limits, and all staffs were screened. Those with confirmed exposure will presumably be monitored for life to ensure early detection of asbestos-related disease. An investigation of this sort is expensive, time consuming and labor intensive and also causes anxiety and worry in those who have been exposed regardless of exposure intensity. The result is that fear of asbestos is spread throughout the local population, government, workers unions, and family members of those exposed. Trends in Malignant Mesothelioma in New South Wales, Australia The state of New South Wales in Australia has experience with many cases of MM due to high asbestos product consumption following the industrial and residential boom of the 1950 and 1960s. The Workers Compensation (Dust Diseases) Board of NSW (DDB) is a statutory authority which was set up in 1961 to compensate workers with occupational lung diseases and which keeps detailed records of cases of occupational asbestos-related diseases. Recent studies show that after diagnosis the median survival for MM is 8.5 months for men and 10.4 months for women in New South Wales 22), and predicted numbers of MM in NSW will peak in 2014, with an annual incidence of 196 cases 25). A total of 2,147 MM deaths were registered between 1970 and 2006 at the DDB. The majority (97.0%) of the MM population was male (n=2,083) with only 3.0% female (n=64). MM is relatively uncommon in women. The mean age (SD) of all at death was 68.0 (9.9) yr of age. There were 115 peritoneal types (5.4%), with 2,032 pleural types (94.6%) of MM. Although seasonal variation in deaths from lung cancer has been reported with mortality peaking in autumn 36), this does not appear to be the case for MM. The seasonal pattern in MM deaths in this period was similar for spring (n=520), summer (n=553), autumn (n=561) and winter (n=513) which showed no overall significant difference. Surveillance Program of Asbestos-Related Diseases in New South Wales, Australia All occupational lung diseases are preventable when the appropriate precautions are taken to avoid exposure to toxic products. The Surveillance of Australian Workplace Based Respiratory Events (SABRE) scheme is a voluntary, anonymous notification scheme of occupational lung diseases that has been operating in NSW since June Individuals who notify cases to SABRE are respiratory physicians, occupational physicians or WorkCover accredited general practitioners with a special interest in occupational medicine. To date, 157 medical doctors in NSW have participated in the scheme. Every two months, participating doctors who see new cases of occupational lung diseases in their normal practice notify SABRE of these new cases. SABRE collects information on all occupational lung diseases including asbestos-related diseases and MM. Information collected by the scheme includes age, gender, smoking history, the causal agents, and the occupation and industry thought to be responsible for exposure to an agent. Since June 2001, 3,151 new cases of occupational lung disease have been reported to SABRE. There are more diagnoses than cases because some individuals have developed more than one occupational lung disease. Many of the diseases notified to SABRE have been caused by exposure to asbestos. To date, a total of 1,006 (30.1%) cases with pleural plaques have been reported followed by 790 MM cases (23.7%), diffuse pleural thickening (22.3%, n=746), asbestosis (10.2%, n=341) and lung cancer (5.2%, n=173) 37). The SABRE scheme plays an important role in determining which occupations and industries are likely to cause the lung diseases. Once known, positive strategies can be developed to prevent lung diseases in these industries and occupations. SABRE has the potential to decrease the incidence of the occupational lung disease and to be of significant public health benefit. Compensation for Workers with Asbestos- Related Diseases in New South Wales, Australia The DDB provides a no-fault statutory compensation system for workers disabled by dust diseases resulting

4 538 E-K PARK et al. from exposure to asbestos while employed in NSW. Under the legislation, the DDB is required to determine eligibility and award compensation to workers and dependants of deceased workers. An award is made after the diagnosis has been established by the DDB Medical Authority, a panel of at least 3 respiratory physicians specializing in occupational lung disease. Detailed clinical and pathological information are available to the Medical Authority. Lifetime occupational histories are also assessed. These are collected by face-to-face interviews between workers and DDB industrial history officers, and in a minority of cases interviews are conducted with the next of kin. The DDB regularly screens a large number of workers with previous asbestos exposure for potential respiratory disease. The routine examination includes a standardized questionnaire, radiology, lung function and a clinical examination by a thoracic physician. New cases of asbestosis, diffuse pleural thickening, pleural plaques, and MM notified at the DDB from were 290, 663, 4,315 and 816, respectively 38). Other diseases due to dust exposure (e.g. silicosis) are also covered by the DDB, but are not relevant to this review. Workers with pleural plaques alone are not eligible for compensation, but those with asbestosis and/or diffuse pleural thickening are awarded compensation based on the extent of their disablement as assessed using American Medical Association (AMA V) criteria 39). Many cases of lung cancer have been related to smoking and thus it can often be very difficult to determine if the lung cancer is due to asbestos exposure. Lung cancer is accepted as being attributable to asbestos exposure if asbestosis or diffuse pleural thickening is present, using the American Thoracic Society (ATS) criteria for establishing such a diagnosis 40). In the absence of asbestosis, the criteria currently used at the DDB are based on the Helsinki criteria 41). These criteria are not universally accepted 42), and may require revision in the future. The Helsinki criteria require: (1) an estimated cumulative exposure to mixed (amphibole plus chrysotile) asbestos fibers of 25 fibers per milliliter per year (fiber-years), as assessed by an experienced occupational hygienist; (2) retained fiber levels of 2 million amphibole fibers (> 5 µm) per gram of dry lung tissue or 5 million amphibole fibers (> 1 µm) per gram of dry lung tissue, as determined by electron microscopic analysis (3) a high lung asbestos fiber count, within the range recorded for asbestosis in the same laboratory, performed on lung tissue using Transmission Electron Microscopy (TEM) and Energy Dispersive Spectroscopy (EDS) to identify the asbestos fibers; (4) Asbestos body concentrations determined by light microscopic analysis greater than 10,000 per gram of dry lung tissue. The DDB has established reference values for asbestos-related diseases which are being objectively evaluated against other laboratories and occupational hygiene assessments 43). Asbestos in the future There is ample evidence that asbestos as a carcinogenic material may threaten public health in terms of social and economical stress. Use of asbestos has been banned in many developed countries but secondary asbestos exposure from asbestos-containing building materials may still be a concern to the general population. When asbestoscontaining materials are damaged or deteriorate with age they can release fibers into the atmosphere which may cause public health concerns, although firm data regarding adverse health effects are limited. In consequence, systematic and effective surveillance programs are needed to raise social awareness and to target potential problem areas, not just medical screening and workplace exposure measurements. Summary Asbestos has proven carcinogenic properties when inhaled and particularly in smokers. The use of asbestos had been banned in many countries but secondary asbestos exposure in the population may still occur, producing a public health risk. In many developing countries, awareness of adverse health effects related to asbestos exposure is still not high, and systematic and effective surveillance programs are lacking. To protect the public from asbestos exposure, effective surveillance plans at a national level need to be explored with labor unions, government and non-governmental organizations, and specialists. Although the health risks vary according to the type of asbestos, the final goal of such plans should be eventual cessation of exposure of all forms of asbestos from the public and domestic arena. Acknowledgements The authors are also grateful to Ms Amanda Ellis for her valuable comments on this manuscript. The present study was supported by Workers Compensation Dust Diseases Board, Sydney, NSW, Australia. 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