Midori N. Courtice, Sihao Lin, Xiaorong Wang

Transcription

1 Review An updated review on asbestos and related diseases in China Midori N. Courtice, Sihao Lin, Xiaorong Wang School of Public Health and Primary Care at Chinese University of Hong Kong, Hong Kong SAR, China Background: Asbestos is an industrial mineral that can cause diseases such as asbestosis, lung cancer, and mesothelioma. Asbestos consumption in China has increased steadily since the 1960s and is currently at half a million tonnes per year. Work conditions in the asbestos-related industries are poor and exposure levels frequently exceed the occupational exposure limit. Objective: To provide an updated overview on asbestos production and consumption in China and discuss what is known about the resulting burden of asbestos-related diseases. Findings: China is the world s top chrysotile consumer and second largest producer. Over a million people may be occupationally exposed, yet reliable disease statistics are unavailable and the national burden of asbestos-related disease (ARD) is not well known. Nevertheless, ARD prevalence, incidence, and mortality are expected to be high and will increase for many decades due to the volume of asbestos consumed historically, and a long latency period. Conclusions: Government policies to prevent ARD have been implemented but more actions are necessary to ensure compliance and ultimately, the complete elimination of asbestos to prevent a heavy future disease burden. Keywords: Chrysotile, China, Occupational health, Occupational exposure, Asbestos-related diseases Introduction In 2010, the People s Republic of China became the second largest economy in the world. A consequence of the rapid industrialization has been an increase in problems related to occupational health and safety. 1 The consumption of asbestos, as an inexpensive, versatile industrial mineral has often shadowed industrial growth. However, little is known about how the ever increasing use of asbestos has impacted the health of occupationally exposed workers in China. The purpose of this article is to provide an updated overview on asbestos production and consumption in China and discuss what is known about the resulting burden of asbestos-related diseases. Asbestos Production, Consumption and Trade China ranks second after Russia in worldwide asbestos production, but first in resources ( reserves are legally, economically, and technically extractable minerals, while resources are estimated deposits that are potentially valuable and for which reasonable prospects exist for economic extraction). 58 China s asbestos resources are estimated at million Correspondence to: X R Wang, School of Public Health and Primary Care at Chinese University of Hong Kong, Hong Kong SAR, China. xrwang@cuhk.edu.hk tonnes, of which accessible reserves are estimated at million tonnes. Asbestos is ubiquitous across China and two-thirds of the reserves are located in the northwestern provinces of Qinghai, Xinjiang, Gansu, and Sichuan, with the first three accounting for over half. The mountainous terrain, isolation, and severe climate of these northwestern provinces make access a challenge but readily-accessible reserves in the east have mostly been mined. 2 4 Chrysotile accounts for 99% of reserves and is the only form of asbestos currently being mined. Actinolite and tremolite, found mainly in Anhui Province, account for 0.7% and crocidolite, 85% of which is located in Yunnan Province, accounts for 0.1% of China s asbestos reserves. However, tremolite impurities have been detected in chrysotile deposits to varying degrees and the relative purity of Chinese chrysotile appears to vary geographically. Tremolite was found to range from 0.002% to 0.310% by weight across six chrysotile mines in Sichuan, Qinghai, Xinjiang, and Liaoning; 5 less than 0.001% (limit of detection (LOD) with X-ray diffraction) tremolite contamination was reported in bulk chrysotile samples from two Sichuan mines; 6 less than 0.1% (LOD with JIS method A-1481:2008 Determination of asbestos in building material products ) was found in Mangya mine bulk samples from Qinghai Province. 7 ß W. S. Maney & Son Ltd 2012 DOI / Z International Journal of Occupational and Environmental Health 2012 VOL. 18 NO

2 Figure 1 Chinese chrysotile domestically mined and total consumed (data sources: British Geological Survey; 10 UN Comtrade; 11 US Geological Survey ) Domestic production of chrysotile started in the 1950s and has increased steadily since then. In the early 2000s, China overtook Canada as the world s second largest producer of chrysotile and may eventually replace Russia as top global producer. 8 In 2009, t were mined, accounting for 20% of world production (Russian chrysotile made up 54%), while total production in 2010 was t, down 15% from the previous year. 9 It was not until the 1960s that chrysotile in China was used in industrial quantities with demand for chrysotile growing steadily from then until the early 1990s at approximately 5000 to t a year, at which point, consumption skyrocketed to current levels (Fig. 1). In 1970, Asia accounted for 19% of worldwide chrysotile consumption and Japan accounted for 50% of that (Fig. 2). By 2010, Asia s share of worldwide chrysotile consumption had risen to 60% with India and China making up 85% of Asian consumption, or 51% of worldwide consumption. China and India are currently two of the fastest growing economies worldwide. Not coincidentally, they are also the two greatest consumers of chrysotile. On a per capita consumption basis in 2010, China consumed 0.45 kg chrysotile. It may appear moderate due to its large population, but this equates to high absolute consumption at t. Domestically mined chrysotile could not keep up with the significant increase in demand of the early 1990s and chrysotile imports have increased steadily since then. Imports, mostly from Russia, rose nearly 150-fold from 1083 t in 1990 to t in 2003, doubling again to t by Imports have averaged t over the last 10 years, with Russia supplying more than 80% and the remainder coming from Kazakhstan, Brazil, Canada, and Zimbabwe. In 2010, t were imported, up 15% compared to the previous year. 9 China is currently the top consumer of chrysotile in the world and its demand shows little signs of slowing down. A report from Natural Resources Canada in 2006 estimated that consumption in China would continue to increase at an average of seven percent annually. 19 China s chrysotile exports consist of a small surplus of shorter and less valuable fibers to Indonesia, Vietnam, Thailand, North Korea, and Myanmar. The annual exports to these countries over the last 10 years averaged t. Although there are approximately 3000 different types of asbestos products, asbestos cement accounts for most of China s chrysotile consumption at 70 80%, followed by asbestos friction products, sealing/ gasket products, heat-insulating products, and textiles or others. 9,20 In 2005, asbestos-cement corrugated sheets and flat sheets accounted for 92% of all fibercement roof and wall material sales. 21 Asbestos product exports consist mainly of cement, averaging t, or USD 12.5 million during 2000 and Figure 2 Comparison of Asian chrysotile consumption in 1970 and 2010 (data sources: Virta, 2006; Virta, 2009a; Virta, 2009b; US Geological Survey 13,15,16,18 ) 248 International Journal of Occupational and Environmental Health 2012 VOL. 18 NO. 3

3 Workforce and Occupational Exposure The total number employed in asbestos-related industries is estimated to be over a million. There are an estimated 598 mining and milling enterprises employing and 169 asbestos product enterprises employing , which equates to workers directly mining or processing asbestos. 3,22 The difference is made up by those employed in smaller mining, milling, or processing enterprises, such as home-based manual spinning, many of which may belong to the vast informal sector of town and village enterprises, and others employed in asbestosassociated industries, such as construction, shipbuilding, automotive repair, plumbing, and other repair or remediation works. Work conditions in the asbestos-related industries are generally poor and the levels of workers exposure to asbestos are high. Currently, the Chinese occupational exposure limit (OEL) for an 8-hour time weighted average of airborne asbestos fibers is 0.8 fibers/ml. Before 2002, it was 2 f/ml or 2 mg/m 3. Pang et al. reported dust concentrations in an asbestos products factory of 415 mg/m 3 in the 1960s, which decreased to 35 mg/m 3 in the 1980s and 17 mg/m 3 in the 1990s. 23 A more recent study has included airborne fiber measurements in an asbestos products factory, and reported geometric mean concentrations from five departments, which ranged from 0.1 to 12.6 fibers/ml. 24 Although airborne asbestos concentrations in workplaces have steadily decreased over time, they often still exceed the OEL. Asbestos-related Diseases In China, one million workers are estimated to be exposed to asbestos, many of them at exposures exceeding the OEL. Annual consumption is at half a million tonnes and nearly 14 million tonnes of chrysotile have been consumed since However, the overall burden of asbestos-related malignancies in the country is unknown, and asbestosis is likely subject to under-reports. Asbestos-related diseases (ARDs) being experienced today are associated with exposures that took place years ago when annual consumption was already at t. Reliable disease statistics, in terms of the incidence, prevalence, or mortality of asbestos-related malignancies are not readily available and there is no centralized national cancer registry or large-scale system of surveillance for ARD. Nevertheless, information about ARD in China can be found in research publications and from some government sources; available information is summarized in the following sections. Asbestosis The first case of asbestosis in China was diagnosed in Asbestosis has been eligible for compensation since 1957 as one of 13 diseases now classified under pneumoconioses according to the Occupational Diseases Prevention and Control Act of the People s Republic of China (ODPC-Act). 26,27 There are cases of pneumoconiosis reported annually 1 and there were cumulative cases by the end of 2007, accounting for 90.8% of all reported occupational disease cases in China. 28 The vast majority of pneumoconiosis cases is coal worker s pneumoconiosis, and expected to remain this way because coal is the country s major source of energy. 29 It is less clear how many pneumoconiosis cases are classified as asbestosis. Data for asbestosis suffer from under-reporting and under-diagnosis. The potential for under-diagnosis of asbestosis may be partially due to the use of a Chinese standard, the 1986 Roentgeno-Diagnostic Criteria of Pneumoconiosis of China, instead of the ILO Classification of Pneumoconiosis. There are several key differences in Chinese standard from ILO Classification: an internal set of standard films is used instead of the ILO set, deciphered by a panel of experts instead of specially trained B-readers, and the disease cut-off point is not as inclusive as the ILO standards, leading to fewer cases being diagnosed as asbestosis. 29,30 Asbestosis prevalence estimates from epidemiological studies of Chinese asbestos workers range from 10 to 30%. 25,30 32 Applying the more conservative estimate of 10% prevalence to the estimate of one million exposed workers would result in current asbestosis cases. This estimate would not include the workers who have already died from this disease with a latency as short as 10 years and may even be an underestimate due to the differences in diagnostic standards discussed above. However, by the end of 2004, only 8237 cumulative cases of asbestosis had ever been reported nationwide. 3,33 Asbestos-related lung cancer Overall, lung cancer rates in China have been increasing from 5.46 (all lung cancer rates per ) in , to in , to in For males, lung cancer rates for the same time periods were 7.13, 24.03, and 41.43, respectively. For females, they were 3.70, 10.66, and 19.84, respectively. Smoking prevalence rates have remained relatively stable since the 1980 s at 4% for females and 60% for males. Only recently have rates among women started to increase. Although overall smoking rates for women are low, the rates in the north to northeast are four times higher than in the south and southeast, i.e. 10.2% versus 2.5%. Among men, smoking rates were the highest in the southwest. More than 70% of male farmers, factory workers, service people, private company employees, those self-employed, and those with no fixed residence were smokers. Female smoking rates by occupation were International Journal of Occupational and Environmental Health 2012 VOL. 18 NO

4 Table 1 Cohort studies on occupationally exposed asbestos workers in China Lung cancer Study Follow-up period Industry type Number of subjects Cases RR or SMR 95% CI or P value Wang Chrysotile mines M: Wang * Chrysotile products M: Chen Asbestos products M: 254 M: ,0.001 F: 184 F: (1 Meso) Sun Manual chrysotile spinning F: Wang Asbestos products M: 275 M: 34z(1 Meso) M: 7.7 M: P,0.01 F: 269 F: 4 F: 2.6 F: n/a Pang * Asbestos products Total: 530 Total: 9 Overall: M: 160 M: 3 M: 5.1,0.01 for both F: 370 F: 6 F: 6.8 Zhang Asbestos products M: 160 M: 3 M: 5.09,0.01 for both F: 370 F: 6 F: 6.82 Zhu * Seven factories Total: 5893 Total: 67 Overall: M { : M: 51 M: 5.8,0.01 for both F { : F: 16 F: 11.7 Cheng Chrysotile products Total: 1132 Overall: 21 Overall: 3.15,0.05 for all M: 662 M: 14 M: 2.78 F: 510 F: 7 F: 4.27 Note: *Prospective cohort studies, the others being retrospective. { Person-years. highest among retired persons (11%) and those working at home (8%). 35 As smoking rates have stayed relatively stable, the increase in lung cancer rates has been attributed to an aging population, pollution and westernization. Nevertheless, industrialization and associated increases in occupational exposures to carcinogens, such as asbestos, during the same time period could be another factor. Asbestosrelated lung cancer is detected on average 20 years after initial exposure to asbestos. In 1970, few incident lung cancer cases would have been attributable to asbestos; however, in subsequent years, asbestos exposure would have made an increasingly significant contribution. Incident cases in 2004 with a history of asbestos exposure, though the number is unknown, would have been exposed in the 1980s when consumption was averaging t a year. Epidemiological studies on lung cancer in chrysotile exposed workers were initiated in China as early as the 1950s, an indication that future ARD had been expected, even before chrysotile consumption started to gain momentum. Several of these studies have observed excess lung cancer risks attributable to chrysotile exposure (Table 1). A unique factor in China is a large number of females in the asbestos products workforce; since the majority of females did not smoke, asbestos-related lung cancer may be more clearly attributable to chrysotile exposure in Chinese studies than in the mostly male cohorts from the west. The Chinese OEL of 0.8 fibers/ml is considered a relatively safe level of exposure for workers, yet according to Stayner et al., excess lifetime risk for lung cancer in white men exposed for 45 years at 0.1 fibers/ml is 5/1000 chrysotile exposed workers, meaning that an excess risk of even greater magnitude may be expected for the Chinese workforce since exposures frequently exceed the current OEL. 36 Chinese male asbestos workers also have a high prevalence of smokers. For example, smokers accounted for 78% of a male asbestos cohort, 37 higher than the already high national male smoking prevalence of 60%. 38 A large number of asbestos-related lung cancers would be expected to develop due to the classically described multiplicative interaction between asbestos and smoking exposure. This interaction was demonstrated in the Chongqing study: compared to non-chrysotile exposed non-smokers, the relative risk of lung cancer in non-chrysotile exposed smokers, chrysotile exposed non-smokers, and chrysotile exposed smokers, was 6.03, 7.52, and 17.35, respectively. 37 Mesothelioma and other cancers While statistics on mesothelioma do not exist in China at the national level, some data are available at the municipal level, as well as from individual epidemiological studies. In 2000, the Centre for Disease Control (CDC) in Qingdao, an industrial centre with a history of asbestos products manufacturing and shipbuilding until the late 1990s, initiated a computerized health data system including death certificates for over 7.5 million people. From this database, 94 cases of mesothelioma from 2000 to 2007 or about 1.57 cases/ million/year were documented, of which 65.6% were seen in females, and one case was reportedly seen in a 12-year-old. The authors attributed the higher proportion of female cases to the high proportion of female factory workers and from lung cancer as a competing cause of death in male smokers, since Chinese females tend not to smoke. 30,45 From 2008 until the end of 2010, the Qingdao CDC documented 36 additional 250 International Journal of Occupational and Environmental Health 2012 VOL. 18 NO. 3

5 cases of mesothelioma. 46 The average age was 69 years for males and 75 years for females. There was no discernible trend over the 10-year span. Shanghai, Harbin, and Wuhan CDC branches have initiated similar computerized data collection systems, 47 although data from these branches have not been made publicly available. From individual epidemiological studies, three cases of mesothelioma were reported in 1227 Laiyuan chrysotile miners, 31 two in 1264 Shenyang chrysotile product factory workers, 30 two out of 515 Chongqing chrysotile product factory workers, and one additional case in a young man exposed as a child while spinning chrysotile at home. 24,48 The case of the home chrysotile spinner highlights a problem unique to China. Most employees remain at their jobs, possibly even performing the same task for their entire working lives, and their whole families live together in dormitories near the asbestos factories or mines. The families could be exposed as workers bring home asbestos on their clothing, or as overtime work to be completed at home. Household exposures of workers families have been described before but typically only as fibers being brought home inadvertently on the clothes of workers. 49 The relatively high levels of asbestos exposure being experienced and the fact that China is the world s greatest user of chrysotile are not reflected in the reported incidences of ARD, in particular, mesothelioma. One possibility is that the labor force experiences a lower life expectancy than higher income nations and workers may die of other illnesses before mesothelioma has a chance to develop. Another factor could be the poor quality of diagnosis as illustrated by the questionable 12-year-old with mesothelioma, 47 a disease which typically takes several decades to develop. As of 2002, mesothelioma diagnosis in China required: 1. cytopathological evidence; 2. cumulative asbestos exposure of at least 1 year; 3. latency of at least 15 years. Many cases may simply be misdiagnosed as lung cancer as there is no mandatory requirement for tissue verification or radiographs and experienced pathologists are still not available in many parts of the country. 30 In 2010, Park et al. estimated the global magnitudes of reported and unreported cases of mesothelioma for the 15-year period between 1994 and China was estimated to have 5107 (95% CI: ) cumulative cases of mesothelioma for that time period. Estimates were based on cumulative asbestos use from 1920 to 1970 when, for the sake of the calculation, asbestos exposure was assumed to have stopped. Asbestos exposures did not stop in 1970; however; worldwide cumulative use has nearly doubled since then and in China, cumulative use has risen to 14.4 million by the end of 2010 from 1.8 million by the end of Some Chinese researchers believe annual incidence of mesothelioma may already be at 1500 cases per year and even greater rates are expected in the future. 51 Other cancers considered causally related to asbestos include laryngeal and ovarian cancers, and possible associations with stomach and colorectal cancers. 52 Gastrointestinal (including stomach and colorectal) and other cancer mortality has been reported in Chinese studies. A standardized mortality ratio (SMR) of 1.66 (95% CI: ) was reported for gastrointestinal cancers in male Qinghai chrysotile miners; 7 an SMR of 7.9 was reported for stomach cancer in male asbestos workers in Qingdao when compared to the general male population (P,0.001); 23 an SMR of 2.4 (P,0.05) for stomach cancer was reported in workers from a study of seven asbestos products factories when compared to controls. 43 Other studies have observed no excess risk. 37,40,41,44 Steps Taken towards the Prevention of ARD The Chinese government has implemented several policies towards ARD prevention. An occupational disease reporting network has been in place since the 1980s and ARD are recognized by the Chinese Ministry of Health as occupational diseases eligible for compensation under the ODPC-Act. Over the last 10 years, legislation has been passed to restrict asbestos use (Table 2), including a revision of the asbestos OEL which was lowered in Health data collection has also been initiated in some regions. 53 China has been slow to embrace asbestos substitutes but research into alternatives including metal fibers, mineral fibers, plant fibers such as cotton and Table 2 Year Timeline of asbestos regulations in China over the recent decade Regulation 2002 Occupational exposure limit revised from 2 to 0.8 f/ml (GBZ2-2002) 2003 The use of asbestos is banned in automotive friction materials 2005 The import and export of amphibole asbestos was completely banned 2007 The Ministry of Health issued a new regulation entitled Criterion for the Control and Prevention of Occupational Hazards in Asbestos Processing (GBZ/T ) Asbestos was forbidden in building projects for the 2008 Beijing Olympics and the 2010 Asian Games 2011 On 1 June 2011, a new industry standard was implemented in China, prohibiting the use of asbestos in siding and wall materials for construction; the prohibition is part of a Chinese national standard (GB ) International Journal of Occupational and Environmental Health 2012 VOL. 18 NO

6 flax, and synthetic fibers such as glass, ceramic, and para-aramid (Kevlar) was initiated as early as the 1980s. As restrictions on asbestos have increased in recent years, there has been a slow but steady increase in demand. 20 Over the last 10 years, and t of mineral wool and glass wool products, respectively, have been produced annually, mostly for roofing materials, insulating materials, friction materials, and noise dampeners. 54 China is also the largest producer of chemical fibers in the world, producing 24 t a year, or 60.7% of global production. 55 Despite these positive steps towards occupational health and safety promotion, working conditions in Chinese industries remain characteristic of a quickly growing economy with few regulatory systems in place: heavy exposures, few engineering controls and unenforced use of personal protective equipment. In regard to receiving compensation for ARD, hurdles exist in recognizing disease and making a claim, such as the requirement of several rounds of diagnosis by various authorized provincial and municipal health institutes. The ODPC-Act mandates employers to be responsible for the workers compensation and medical care with insurance companies, and to communicate the compensation program to employees. 1 Employers, particularly those in the informal sector, are less likely to provide information and education about occupational diseases or the system of compensation, and they may even withhold documentation or deny employment when claims are made. 56 Migrant workers would likely receive even less occupational health and safety training, as they frequently move between employment settings and would find the process of making a worker s compensation claim nearly impossible. Finally, even with the best of intentions on the part of the government, a complete ban on chrysotile is unlikely to proceed if commercial asbestos interest groups, such as the Chinese Non-metallic Material Industrial Association, the industry s main lobby group, continue to pressure the government to promote controlled use policies instead. 20 Conclusions As the world s greatest consumer of chrysotile, the incidence of ARD in China is expected to rise over the next few decades. The European Agency for Safety and Health at Work has projected annual Chinese fatalities from ARD at by 2035 while other experts estimate current ARD deaths are at per year already. 57 Increasing awareness of ARD and its prevention among the government, employers, and workers through research, training, and education programs is of utmost importance. 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