Exposure to silica and silicosis among tin miners in China: exposure-response analyses and risk assessment
W Chena, Z Zhuangb, M D Attfieldb, B T Chenb, Pi Gaob, J C Harrisonb, C Fua, J-Q Chena, W E Wallaceb
a Tongji Medical
University, School of Public Health, Department of Labor Health and
Occupational Diseases, 13 Hang Kong Lu, Wuhan, Hubei, People's
Republic of China, b National Institute for Occupational Safety and
Health (NIOSH), 1095 Willowdale Road, Morgantown, WV 26505, USA
Correspondence to: Dr W Chen weihong.chen{at}uni.essen.de
Accepted 30 August 2000
OBJECTIVES
To
investigate the risk of silicosis among tin miners and to investigate
the relation between silicosis and cumulative exposure to dust (Chinese
total dust and respirable crystalline silica dust).
METHODSA cohort study
of 3010 miners exposed to silica dust and employed for at least 1 year
during 1960-5 in any of four Chinese tin mines was conducted.
Historical total dust data from China were used to create a job
exposure matrix for facility, job title, and calendar year. The total
dust exposure data from China were converted to estimates of exposure
to respirable crystalline silica for comparison with findings from
other epidemiological studies of silicosis. Each worker's work history
was abstracted from the complete employment records in mine files.
Diagnoses of silicosis were based on 1986 Chinese pneumoconiosis
Roentgen diagnostic criteria, which classified silicosis as stages
I-IIIsimilar to an International Labour Organisation (ILO)
classification of 1/1 or greater.
RESULTSThere were
1015 (33.7%) miners identified with silicosis, who had a mean age of
48.3 years, with a mean of 21.3 years after first exposure (equivalent
to 11.0 net years in a dusty job). Among those who had silicosis, 684 miners (67.4%) developed silicosis after exposure ended (a mean of 3.7 years after). The risk of silicosis was strongly related to cumulative
exposure to silica dust and was well fitted by the Weibull
distribution, with the risk of silicosis less than 0.1% when the
Chinese measure of cumulative exposure to total dust (CTD) was under 10 mg/m3-years (or 0.36 mg/m3-years of respirable
crystalline silica), increasing to 68.7% when CTD exposure was 150 mg/m3-years (or 5.4 mg/m3-years of respirable
crystalline silica). Latency period was not correlated to the risk of
silicosis or cumulative dose of exposure. This study predicts about a
36% cumulative risk of silicosis for a 45 year lifetime exposure to
these tin mine dusts at the CTD exposure standard of 2 mg/m3, and a 55% risk at 45 years exposure to the current
United States Occupational Safety and Health Administration and Mine
Safety and Health Administration standards of 0.1 mg/m3
100% respirable crystalline silica dust.
CONCLUSIONSA clear
exposure-response relation was detected for silicosis in Chinese tin
miners. The study results were similar to most, but not all, findings
from other large scale exposure-response studies.
Keywords: silicosis; exposure to silica; dose-response relation
© 2001 by Occupational and Environmental Medicine
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