Mineral dusts and prevention of silicosis, vol 4; No.2, September 1997Pneumoconiosis in China: Current situation and countermeasures,by Zou Changqi, Gao Yun, Ma Qingyan |
China has a population of 1.2 billion. The number of workers exposed to dust may total as many as twelve million people. Silicosis has long been the most common occupational disease in China.
After the founding of the new China in 1949, the country underwent rapid economic development in the 1950s. Owing to unawareness of the hazardous effects of silica dust, however, dust control and workers' medical surveillance did not keep pace with the nation's industrialisation. Especially in the mid-1950s, the introduction of mechanical mining techniques without wet dust suppression caused exposure to high levels of dust in some workplaces, the highest dust concentrations reaching even a few thousand milligrams per cubic metre. In consequence, unfortunately, there were many cases of silicosis.
This grievous situation drew the government's attention. Preventive measures were taken and pertinent regulations for dust control were promulgated. The widespread occurrence of silicosis among heavily exposed workers has basically been under control since the late 1960s.
Since the end of the 1970s, however, economic reforms and the policy of opening China have brought vigorous development of enterprises owned by townships and villages. As a result of the irregular mining practices in some small industries, the hazard posed by dust is becoming more and more serious, making prevention of pneumoconiosis an issue of growing concern.
This paper analyses and discusses the current situation in China with regard to pneumoconiosis and the countermeasures being taken for its prevention, in response to the "ILO/WHO International Programme on Global Elimination of Silicosis", proposed during the 12th session of the ILO/WHO joint committee on occupational health in Geneva in 1995.
Pneumoconiosis situation in China
According to data on the prevalence of pneumoconiosis from 1949 to 1986, obtained from a national epidemiological survey, and to nationwide annual data on newly reported cases of occupational diseases and deaths for the period 1987 to 1996, the cumulative number of pneumoconiosis cases recorded in China between 1949 and the end of 1996 totalled 524,759. Out of these, 134,674 cases (25.7%) were fatal, while 390,085 (74.3%) patients survived. Moreover, a nationwide survey conducted in 1986 discovered that an additional 520,000 workers exposed to dusts were suspected of having silicosis.
All twelve types of pneumoconiosis included in the official list of occupational diseases issued by the Ministry of Health (i.e., silicosis, coal workers' pneumoconiosis, graphite pneumoconiosis, carbon black pneumoconiosis, asbestosis, talcosis, cement pneumoconiosis, mica pneumoconiosis, porcelain workers' pneumoconiosis, aluminosis, welders' pneumoconiosis, and foundry workers' pneumoconiosis) were detected in China. Silicosis and coal workers' pneumoconiosis were the most common types of pneumoconiosis, their respective shares being 46.8% (245,845 cases) and 39.9% (209,239 cases). Both types together accounted for 86.7% of all cases. There were in total 69,677 cases of foundry workers' pneumoconiosis, porcelain workers' pneumoconiosis, cement pneumoconiosis and asbestosis, accounting for 13.3% of all cases (Figure 1).
Geographic distribution
Most of the pneumoconiosis patients lived in provinces where mining industries (coal, metals) are located; Sichuan, Liaoning, Hunan, Shanxi, Jiangxi provinces. The cumulative number of cases in these five provinces was 217,877, amounting to about 41.6% of total cases for the entire country. The highest number of cases, 59,395, was diagnosed in Sichuan province; this figure represents 11.3% of all cases in China (Figure 2). The next highest numbers of cases occurred in Heilongjiang, Hebei and Henan provinces, each having more than 20,000 cases.
Distribution by industry
There were 212,385 cumulative cases of pneumoconiosis in the coal industry, which topped all industries and accounted for 40.3% of the total for all of China. The other two industries having the greatest occurrences of pneumoconiosis were the metallurgical industry and the non-ferrous industry, their respective number of the cases being 63,214 (12.2%) and 47,761 (9.2%). The industries with cumulative cases exceeding 10,000 cases included the building materials industry, the engineering industry, light industry, the petrochemical industry and the railway industry. In total, 82,204 cases were detected in these industries, being 15.5% of those in China (Figure 3).
Distribution among different types of work
According to the data collected in 1986, the majority of pneumoconioses occurred in the mining industry, which accounted for 79.7% of all cases. Workers involved in quarrying, ore mining and carrying in metal mines, and coal cutting in coal mines had high occurrences of pneumoconiosis, amounting to 72.2% of all pneumoconiosis cases detected in mining industries. Cases among factory workers occurred mainly in the grinding of quartz, metal foundries and casting; these accounted for 32.6% of all cases in factories. The findings indicate that those exposed to high concentrations of free silica face the greatest risk of contracting silicosis.
Trends in the occurrence of pneumoconiosis over the years
Figure 4 shows that the occurrence of pneumoconiosis in China has increased year by year. The number of new cases diagnosed each year increased from hundreds of cases in the early 1950s to thousands of cases in 1956, and further to some 10,000 new cases in 1974. The highest number of new cases for one year was over 20,000, diagnosed in 1986. The trend has been a declining one since 1987, the number of new cases being below 10,000 each year after 1995, while the number of fatal cases has remained at 5,000 every year (Figure 5). The falling occurrence of new cases may partly be attributed to under-reporting by some State-owned and township-owned enterprises.
Nevertheless, the number of surviving patients is still near 400,000, and about 10,000 new cases are diagnosed each year. It is estimated that the total number of cumulative cases of pneumoconiosis for all of China will reach 600,000 at the beginning of next century.
Countermeasures
Legislation and health standards
As early as in the mid-1950s, when the number of patients was rising rapidly, the Chinese government started to pay attention to the prevention and control of silicosis. Since then, a series of regulations was promulgated and managerial measures have been taken.
"The Decision for preventing the silica dust hazard in mines" was promulgated by the State Council in 1956. "The scope of occupational diseases and the management for patients with occupational diseases", which lists silicosis as one of the officially recognized occupational diseases, was promulgated by the Ministry of Health in 1957. "The temporary provisions of the medical preventive measures for workers with silica dust exposure" was also promulgated by the Ministry of Health. (Table 1)
The Ministry of Health charged experts in academic institutions with the tasks of devising health standards for dusts in the air at workplaces and of establishing diagnostic criteria for pneumoconiosis. To strengthen the monitoring and inspection of dusts, to enhance the health surveillance of exposed workers, and to improve the working conditions in workplaces, the Ministry of Health and the National Committee of Construction jointly issued "The Temporary Health Standards for the Design of Industrial Premises (101 56)" in 1956. After trials had been carried out and amendments made, in 1979 six government ministries including the Ministry of Health jointly promulgated a formal regulation, namely "The Health Standards for the Design of Industrial Premises (TJ36 79)". According to this standard, any enterprise being newly set up or expanded and reconstructed must meet the requirement of a maximum allowable concentration (MAC) of dust (2 mg/m3) in workplaces when the content of free silica in the dust is 10% or higher. In 1989, the MAC of workplace dust was set at 1.5 mg/m3 for dusts having a free silica content exceeding 50 80% (GB112724 89), and 1 mg/m3 for those exceeding 80% (GB112725 89). Furthermore, the "National Standard of Working Classification in Dust Environment (GB5817 86)" and "The Radiological Diagnostic Criteria of Pneumoconiosis and Principles for Management of Pneumoconiosis (GB5906 86)" were also formulated. (Table 2)
The above-mentioned regulations and health standards have played a key role in the prevention and control of the hazards posed by dusts, and in reduction of the occurrence of silicosis. In some industrial enterprises, dust concentrations which were very high in the mid-1950s decreased remarkably within three to five years, and nearly reached the health standards set in China. This drop in dust levels has prevented an increase in silicosis patients, and measures for the prevention and control of pneumoconiosis have gradually been put on the right track.
Implementation of comprehensive measures for dust control
At the end of the 1950s, comprehensive measures intended for the purpose of dust control in industries where silica dust posed a hazard were put forward and disseminated throughout the country. These comprehensive measures are symbolised as "Eight Words", the "Eight Words" being: water; wind; airtight; innovation; protection; propaganda; management; and inspection. They represent the following concepts: wet operation; sufficient ventilation; air-tightness to dust; technical innovation of dust control; personal protection; health education and propaganda; management; and enforcement of regulations. The "Eight Words" campaign was implemented first in the metallurgical and non-ferrous industries, with successful results.
Dust control was then expanded to other sectors of industry. Only in the mid-1960s did the serious situation of heavy exposure to dust and a rapid increase in the number of silicosis patients come more or less under control.
According to a statistical report published in 1996, the dust concentration in the air of 66% of workplaces (46% in township enterprises) on average had been in compliance with the national standard. The latency of the development of silicosis had been prolonged significantly from 9.5 years in the 1950s to 26.3 years in the 1980s. The average age of patients being diagnosed with silicosis had risen from 35.3 years in the 1950s to 51.3 years in the 1980s. Among the 393,797 cumulative cases of silicosis (up to the end of 1986), 95.7% had a working history of exposure to dust before 1964. In another words, only 5% of the patients diagnosed as having silicosis had a history of exposure to dust after 1964. These figures are believed to indicate effective prevention by means of comprehensive dust control measures.
Analysis of the relationships between the dust concentration measured yearly, on the one hand, and the detection rate of silicosis and the average age at occurrence of grade I silicosis, on the other hand, confirm this conclusion in a metallurgical mine and a refractory brick factory (Figures 67). Additionally, no case of silicosis has been detected among workers employed at some mines and factories in the past 20 30 years. There is thus an optimal basis for nationwide elimination of silicosis, although dust pollution remains a serious issue in some industries, such as coal mining and the building materials industry and in township-owned enterprises. In these sectors, the occurrence of new cases of pneumoconiosis is still increasing.
Health surveillance and therapeutic management
"The temporary provisions of medical prevention measurements for workers with silica dust exposure", issued by the Ministry of Health in 1963, stipulated periodic health examinations of workers exposed to dusts. The time intervals of periodic health examination for pneumoconiosis, which vary in accordance with the free silica content of the dust, were also specified in detail in 1991 (Table 3). New workers must undergo pre-placement medical examination before starting work. These examinations should be conducted by physicians working in the local occupational disease hospitals or anti-epidemic sanitation stations, which are situated throughout the country.
Those who have been diagnosed as having silicosis receive free medical care and/or undergo rehabilitation. A comprehensive treatment regimen has been suggested for improving their clinical symptoms, enhancing their physical strength, reducing complications and for prolonging their lives. Positive results have already been observed.
On the basis of widespread implementation of the comprehensive measures for dust control, conducted throughout the country in the early 1970s, some academic institutions and public schools of medical colleges cooperated in studying the mechanism of silicosis and in screening medicines for treating the disease. As the result of much animal experimentation and clinical studies, several medicines including poly vinyl pyrimidine n-oxide, tetrandrine, quinoly piperazine hydroxyl phosphate and aluminium citrate have proved to be promising (Table 4). These drugs have been well accepted by the patients, and they have eased patients' symptoms and slowed down the progression of silicosis lesions. Further observation is underway to determine the effects of implementing comprehensive treatments based on a combination of the above drugs.
Conclusion
Pneumoconiosis is the most common occupational disease in China. By the end of 1996, the number of cumulative cases of pneumoconiosis totalled 524,359. In all, 134,674 pneumoconiosis patients have died, and 390,085 are still alive. A series of preventive measures for silicosis incorporating legislation and comprehensive dust control measures, medical surveillance of workers at risk and therapeutic management has been adopted by the government since the late 1950s. The high prevalence of silicosis among heavily exposed workers has basically been brought under control. The trend of new cases has been declining year by year since the 1980s. We have proved that silicosis can be prevented and controlled; the challenge, however, is still present. The hazards posed by silica dust remain serious, and new cases are still emerging in some industries. The government must continue to take effective actions to control the dust hazard and to reduce the occurrence of pneumoconiosis, and ultimately to eliminate the occurrence of silicosis in China.
References
1. Ministry of Health, Proceedings of Epidemiological Survey of Pneumoconiosis in China. Publishing House of Peking Union Medical College and Beijing Medical University, Beijing, 1992.
2. Sub-committee for Occupational Health Standards, China National Technical Committee of Health Standards, Ministry of Health, P. R. China. Maximum Allowable Concentration for Chemical Substances and Permissible Exposure Limits for Physical Agents at the Workplaces (1979 1989), Beijing, 1990.
3. Department of Health Inspection, Ministry of Health, PR China. Annual Bulletin of Health Inspection (1990 1996), Beijing.
Zou Changqi, Gao Yun, Ma Qingyan
Institute of Occupational Medicine
Chinese Academy of Preventive Medicine
Beijing 100050, P.R. China