Luo S, Liu X, Mu S, Tsai S P, Wen C P
Department of Occupational Health, School of Public Health, West China University of Medical Sciences, Chengdu, Sichuan, China.
Occup Environ Med. 2003 Jan;60(1):35-41; discussion 41-2. doi: 10.1136/oem.60.1.35.
Scattered patches of crocidolite, one form of asbestos, were found in the surface soil in the rural county of Da-yao in southwestern China. In 1983, researchers from the West China University of Medical Sciences (WCUMS) discovered that residents of two villages in Da-yao had hyperendemic pleural plaques and excessive numbers of pleural mesotheliomas.
To review and summarise epidemiological studies, along with other relevant data, and to discuss the potential contribution to environmental risk assessment.
This report is based on a review of several clinical/epidemiological studies conducted by WCUMS researchers since 1984, which included one cross sectional medical examination survey, one clinical/pathological analysis of 46 cases of mesothelioma, and three retrospective cohort mortality studies. Additional information acquired from reviewing original data first hand during a personal visit along with an interview of medical specialists from Da-yao County Hospital was also incorporated.
The prevalence of pleural plaque was 20% among peasants in Da-yao over 40 years of age in the cross sectional survey. The average number of mesothelioma cases was 6.6 per year in the 1984-95 period and 22 per year in the 1996-99 period, in a population of 68 000. For those mesothelioma cases that were histology confirmed, there were 3.8 cases/year in the first period and 9 cases/year in the second. Of the 2175 peasants in this survey, 16 had asbestosis. Lung cancer deaths were significantly increased in all three cohort studies. The annual mortality rate for mesothelioma was 85 per million, 178 per million, and 365 per million for the three cohort studies, respectively. The higher exposed peasants had a fivefold increased mesothelioma mortality compared to their lower exposed counterparts. There were no cases of mesothelioma in the comparison groups where no crocidolite was known to exist in the environment. In the third cohort study, almost one of five cancer deaths (22%) was from mesothelioma. The ratio of lung cancer to mesothelioma deaths was low for all three studies (1.3, 3.0, and 1.2, respectively).
The observation of numerous mesothelioma cases at Da-yao was a unique finding, due mainly to their lifetime exposure to crocidolite asbestos. The finding of cases dying at a younger age and the relatively high ratio of mesothelioma cases to lung cancer could also be another unique result of lifetime environmental exposure to crocidolite asbestos. Although the commercial use of crocidolite has been officially banned since 1984, the incidence of mesothelioma has continued to show a steady increase, particularly among peasants. Since the latency of mesothelioma is approximately 30-40 years, the ban had little effect in the 1990s. The increased awareness and changes in diagnosis over time may also contribute to the increase. Furthermore, exposure to asbestos stoves and walls continued. The government implemented reduction of these exposures. However, from a public health standpoint, the most important issue is the complete avoidance of further exposure to asbestos.
在中国西南部的大姚县农村地区，表层土壤中发现了零散的青石棉斑块，青石棉是石棉的一种形式。1983年，华西医科大学的研究人员发现，大姚县两个村庄的居民患有高度地方性胸膜斑，且胸膜间皮瘤数量过多。
回顾和总结流行病学研究以及其他相关数据，并讨论其对环境风险评估的潜在贡献。
本报告基于对华西医科大学研究人员自1984年以来开展的多项临床/流行病学研究的回顾，其中包括一项横断面医学检查调查、对46例间皮瘤病例的临床/病理分析以及三项回顾性队列死亡率研究。还纳入了在个人走访期间亲自查阅原始数据以及对大姚县医院医学专家进行访谈所获取的额外信息。
在横断面调查中，大姚县40岁以上农民的胸膜斑患病率为20%。在1984 - 1995年期间，在68000人的人群中，间皮瘤病例平均每年有6.6例；在1996 - 1999年期间，每年有22例。对于那些经组织学确诊的间皮瘤病例，第一阶段每年有3.8例，第二阶段每年有9例。在本次调查的2175名农民中，有16人患有石棉肺。在所有三项队列研究中，肺癌死亡率均显著增加。三项队列研究中间皮瘤的年死亡率分别为每百万85例、每百万178例和每百万365例。与暴露程度较低的农民相比，暴露程度较高的农民间皮瘤死亡率高出五倍。在已知环境中不存在青石棉的对照组中未发现间皮瘤病例。在第三项队列研究中，几乎五分之一（22%）的癌症死亡病例是间皮瘤。在所有三项研究中，肺癌与间皮瘤死亡病例的比例都较低（分别为1.3、3.0和1.2）。
在大姚观察到大量间皮瘤病例是一个独特的发现，主要是因为他们终生接触青石棉。病例在较年轻时死亡以及间皮瘤病例与肺癌的相对高比例这一发现，也可能是终生环境暴露于青石棉的另一个独特结果。尽管自1984年起已正式禁止商业使用青石棉，但间皮瘤的发病率仍持续稳步上升，尤其是在农民中。由于间皮瘤的潜伏期约为30 - 40年，该禁令在20世纪90年代几乎没有效果。随着时间的推移，意识的提高和诊断的变化也可能导致发病率上升。此外，接触石棉炉灶和墙壁的情况仍在继续。政府已采取措施减少这些暴露。然而，从公共卫生的角度来看，最重要的问题是完全避免进一步接触石棉。
