Department of Epidemiology, School of Basic Medicine, Peking Union Medical College, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing 100005, China.
Biomed Environ Sci. 2010 Apr;23(2):121-9. doi: 10.1016/S0895-3988(10)60041-4.
The purposes were to determine the relationship between silicosis among foundry workers and their cumulative exposure to silica dust, and to establish a regression model to predict the risk for developing silicosis by a given length of employment and air concentrations of silica at worksites.
A 29-year cohort study was conducted, including all those employed for more than one year during January 1, 1980 to December 31, 1996 and all members of the cohort were followed-up to December 31, 2008. In total, 2009 workers of an automobile foundry in Shiyan, Hubei province were recruited in the study, 1300 at eight worksites including sand preparation, cast shakeout, and finishing, melting, moulding, core-making, overhead crane operation and pouring as exposed group, and the other 709 auxiliary workers at the same factory, such as electricians, inspectors, fitters, and so on, as control group. Person-years of observation were calculated by persons observed and years followed-up for each of them. Person-year incidence of silicosis and its relative risk (RR) or odds ratio (OR) and 95% confidence intervals (CI) among the workers were estimated, adjusted for relevant factors with logistic regression model using SPSS version 15.0 software.
Totally, 2009 workers were followed-up for 37 151 person-years and 48 cases of silicosis were found, with an overall incidence of 1.34 per thousand, 2.02 per thousand in exposed group, and 0.15 per thousand in control one. Risk of silicosis was significantly higher in the exposed group than that in the control one (RR = 13.13, 95% CI 3.18-54.13), higher in men than that in women (RR = 13.92, 95% CI 1.92-100.93). Risks of silicosis varied by job, highest in those exposed to cast shakeout and finishing (RR = 28.14, 95% CI 6.43-123.11), followed by those exposed to pouring (RR = 22.23, 95% CI 5.01-98.55) in the foundry. Average length of employment at onset of silicosis was 25.94 years, and silicosis incidence increased with length of employment. Average age at onset of silicosis was 47.83 years old. The risk of silicosis in workers with pulmonary tuberculosis was 2.57 folds as those without it (P < 0.01). Ten deaths were recorded in those with silicosis, with a case-fatality rate of 20.83 percent three of them died of lung cancer, three of liver cancer, two of ischemic heart disease, and two of other diseases as their immediate causes of death. Incidence of silicosis in foundry workers positively correlated with their cumulative silica exposure (OR = 3.00, 95% CI 2.34-3.83). Risks of silicosis increased by 4.38 folds with an increase of 1 mg/m3-year of cumulative silica exposure, and by 3.79 folds with smoking, respectively, adjusted for alcohol drinking and age. Based on a logistic regression model fitted, incidence of silicosis is expected to be 44.6 per thousand for those with daily exposure to silica of 4.18 mg/m3 in average for 30 years, and if incidence of silicosis is expected to be less than 1 per thousand, daily exposure to silica should be controlled below 0.2 mg/m3 for those with 20 years of employment, or below 0.1 mg/m3 for those with 30 or 40 years of silica exposure.
At present, foundry workers in China still face high risk of developing silicosis. For lowering occurrence of silicosis in exposed workers, it seems necessary that current occupational exposure limits for silica at worksites in China should be reexamined and silica dust control measures be strengthened.
确定铸造工人矽肺与其累积矽尘暴露之间的关系，并建立一个回归模型，预测在给定的工作年限和工作场所空气中的矽浓度下，发生矽肺的风险。
进行了一项为期 29 年的队列研究，包括 1980 年 1 月 1 日至 1996 年 12 月 31 日期间工作年限超过一年的所有工人，并对所有队列成员进行随访至 2008 年 12 月 31 日。总共招募了湖北省十堰市一家汽车铸造厂的 2009 名工人，其中 1300 名在包括砂准备、铸件清理、整理、熔化、造型、制芯、天车操作和浇注等八个工作场所暴露，其余 709 名辅助工人在同一工厂工作，如电工、检验员、钳工等，作为对照组。通过每个工人的观察时间和随访时间计算观察人数年。使用 SPSS 版本 15.0 软件，通过逻辑回归模型，对工人矽肺的发病情况进行了估计，并对相关因素进行了调整。
共对 2009 名工人进行了 37151 人年的随访，发现 48 例矽肺，总发病率为千分之 1.34，暴露组为千分之 2.02，对照组为千分之 0.15。暴露组矽肺发病风险明显高于对照组（RR=13.13，95%CI 3.18-54.13），男性高于女性（RR=13.92，95%CI 1.92-100.93）。矽肺发病风险因工作而异，铸件清理和整理最高（RR=28.14，95%CI 6.43-123.11），其次是浇注（RR=22.23，95%CI 5.01-98.55）。矽肺发病的平均工龄为 25.94 年，矽肺发病率随工龄的增加而增加。矽肺发病的平均年龄为 47.83 岁。患有肺结核的工人矽肺发病风险是没有肺结核的 2.57 倍（P<0.01）。10 例死亡，矽肺死亡率为 20.83%，其中 3 例死于肺癌，3 例死于肝癌，2 例死于缺血性心脏病，2 例死于其他疾病。铸造工人矽肺发病率与累积矽尘暴露呈正相关（OR=3.00，95%CI 2.34-3.83）。随着累积矽尘暴露增加 1mg/m3 年，矽肺发病风险增加 4.38 倍，吸烟增加 3.79 倍，调整饮酒和年龄因素后。根据拟合的逻辑回归模型，对于每天暴露于 4.18mg/m3 矽尘 30 年的工人，矽肺发病率预计为 44.6/千，而如果预计矽肺发病率低于 1/千，则应控制暴露于矽尘的工人每天的暴露量低于 0.2mg/m3，对于工作 20 年的工人，或低于 0.1mg/m3，对于工作 30 年或 40 年的工人。
目前，中国的铸造工人仍面临较高的矽肺发病风险。为了降低暴露工人矽肺的发生，似乎有必要重新审查中国目前工作场所的矽尘职业接触限值，并加强矽尘控制措施。
