Risk of silicosis in a cohort of white South African gold miners

The risk of silicosis was investigated in a cohort of 2,235 white South African gold miners who had, on average, 24 years of net service from 1940 to the early 1970s and who were followed up to 1991 for radiological signs of onset of silicosis (ILO category 1/1 or more). There were 313 (14%) miners who developed signs of silicosis at an average age of 55.9 years. The latency period was largely independent of the cumulative dust exposure. In 57% of the silicotics, the radiological signs developed, on average, 7.4 years after mining exposure ceased. The risk of silicosis increased exponentially with the cumulative dust dose, the accelerated increase being after 7 mg/m³-years. At the highest exposure level of 15 mg/m³-years, which represents approximately 37 years of gold mining at an average respirable dust concentration of 0.4 mg/m³, the cumulative risk for silicosis reached 77%. In conclusion, the risk of silicosis was strongly dose dependent; however, the latency period was largely independent of the dose. © 1993 Wiley-Liss, Inc.     

Exposure to silica and silicosis among tin miners in China: exposure-response analyses and risk assessment

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).
METHODS—A 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-III—similar to an International Labour Organisation (ILO) classification of 1/1 or greater.
RESULTS—There 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.
CONCLUSIONS—A 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.


     

Continued exposure to silica after diagnosis of silicosis in Brazilian gold miners

BACKGROUND: There is a paucity of studies analyzing the effect of continued silica exposure after the onset of silicosis with regard to disease progression. The present study investigates differences in clinical and radiological presentation of silicosis among former workers with a diagnosis of silicosis, and compares workers who continued to be exposed to silica with those who stopped silica exposure after having received their diagnosis. METHODS: A sample of 83 former gold miners with a median of 21 years from the first diagnoses of silicosis, had their clinical and occupational histories taken and underwent both chest radiography (International Labor Organization standards) and spirometry. Their silica exposure was assessed and an exposure index was created. The main outcome was the radiological severity of silicosis and tuberculosis (TB). The statistical analysis was done by multiple logistic regression. RESULTS: Among the 83 miners, 44 had continued exposed to silica after being diagnosed with silicosis. Continuation of silica exposure was associated with advanced radiological images of silicosis (X-ray classification in category 3, OR = 6.42, 95% CI = 1.20-34.27), presence of coalescence and/or large opacities (OR = 3.85, CI = 1.07-13.93), and TB (OR = 4.61, 95% CI = 1.14-18.71). CONCLUSIONS: Differential survival is unlikely to explain observed differences in silicosis progression. Results reinforce the recommendation that silica exposure should be halted at an early stage whenever X-ray is suggestive of the disease.     

Time-weighted averages, peaks, and other indices of exposure in occupational epidemiology.

Dose surrogates commonly used in occupational epidemiology are exposure intensity, exposure duration, and cumulative exposure. The appropriateness of any of these measures as dose indicators depends on the nature of the induction process for the disease under consideration. Peak exposure intensity is often associated with acute health outcomes, whereas cumulative exposure is generally more relevant for diseases with long induction times, i.e., "chronic" diseases. However, there may be situations where peak exposure is etiologically relevant in chronic disease induction, such as might occur with nonlinear rates of damage during brief intervals of very high exposure. An approach is described for evaluating the effect of peak exposures in which peaks may be defined on a relative basis for each worker, or with respect to an absolute value, such as the permissible occupational exposure limit. The analytic strategy is illustrated with data from a case-control study of silicosis in relation to quantitative estimates of silica exposure. In this example, relative peak exposures and average non-peak exposures appear to be better predictors of silicosis risk than cumulative exposure.     

An Occupational Risk Survey of a Refractory Brick Company in Ha Noi,Viet Nam

Abstract

Viet Nam has an increasing need for building materials, including refractory bricks. Little is known regarding the occupational hazards incurred in brick manufacturing. To determine the occupational health hazards posed by a refractory brick operation in Ha Noi, Viet Nam, a cross-sectional occupational risk survey was conducted, focusing on respirable dust hazards. It included an industrial hygiene walk-through and gravimetric dust analysis. Noise, heat, lack of head protection, and dust exposure were hazards identified at the brick-manufacturing site. Respiratory protection involved a three-layer cloth mask that had not been tested for efficacy. Silica dust exposure levels exceeded the Vietnamese permissible exposure level by almost fivefold based on gravimetric assessment and estimated silica content. This brick manufacturing site contains significant injury and respiratory illness hazards. Further investigations are necessary to begin to develop occupational safety measures at the site.     

Risk of silicosis in cohorts of Chinese tin and tungsten miners and pottery workers (II): Workplace-specific silica particle surface composition

BACKGROUND: It is hypothesized that surface occlusion by alumino-silicate affects the toxic activity of silica particles in respirable dust. In conjunction with an epidemiological investigation of silicosis disease risk in Chinese tin and tungsten mine and pottery workplaces, we analyzed respirable silica dusts using a multiple-voltage scanning electron microscopy-energy dispersive X-ray spectroscopy (MVSEM-EDS). METHODS: Forty-seven samples of respirable sized dust were collected on filters from 13 worksites and were analyzed by MVSEM-EDS using high (20 keV) and low (5 keV) electron beam accelerating voltages. Changes in the silicon-to-aluminum X-ray line intensity ratio between the two voltages are compared particle-by-particle with the 90th percentile value of the same measurements for a ground glass homogeneous control sample. This provides an index that distinguishes a silica particle that is homogeneously aluminum-contaminated from a clay-coated silica particle. RESULTS: The average sample percentages of respirable-sized silica particles alumino-silicate occlusion were: 45% for potteries, 18% for tin mines, and 13% for tungsten mines. The difference between the pottery and the metal mine worksites accounted for one third of an overall chi-square statistic for differences in change in measured silicon fraction between the samples. CONCLUSION: The companion epidemiological study found lower silicosis risk per unit cumulative respirable silica dust exposure for pottery workers compared to metal miners. Using these surface analysis results resolves differences in risk when exposure is normalized to cumulative respirable surface-available silica dust.     

一起严重矽尘职业危害事件的调查分析

目的了解造成本次严重矽尘危害事件的原因及危害程度,探讨小型石英粉加工企业矽尘危害的预防和控制措施。方法深入作业现场进行卫生学调查,了解作业环境职业卫生状况,对矽肺发病情况进行统计分析。结果该厂作业场所粉尘浓度全部超标,最高达187mg/m3,粉尘中游离二氧化硅高达96.28%。全部28名接尘工人中已诊断矽肺病18例,患病率为64.29%。结论硅粉生产由于粉尘中游离二氧化硅含量高、粒度细、致肺纤维化作用强,是一个职业病危害极大的行业。应加强预防性卫生监督管理,在项目立项时应避免不符合条件的企业从事硅粉生产,对已投产的矽尘危害大且整改后仍不符合职业卫生要求的企业予以关停或转产,以保护劳动者健康。     

Estimating the total number of newly-recognized silicosis cases in the United States

BACKGROUND: The US employer-based surveillance system for documenting occupational injuries and illnesses undercounts chronic diseases. We suggest a method to estimate the number of individuals who are newly-recognized with silicosis each year in the United States. METHODS: Data from US death certificates, the Michigan state-based surveillance system, and capture-recapture analysis were used to calculate national estimates of silicosis. RESULTS: From 1987 to 1996, 2,787 deaths occurred in the United States where silicosis was mentioned on the death certificates. During the same period, in Michigan 77% of death certificates with a mention of silicosis were confirmed as silicosis-related deaths and the ratio of the number of living to deceased confirmed silicosis cases was 6.44. The proportion of confirmed silicosis deaths, the ratio of the living to deceased silicosis cases and capture-recapture analysis from the Michigan surveillance system, were used to estimate that there were 3,600-7,300 cases per year of silicosis in the United States from 1987 to 1996. CONCLUSIONS: Our estimate of the annual number of newly-recognized silicosis cases is significantly larger than the estimate from the employer-based reporting system used for counting occupational disease in the United States. This employer-based surveillance system is inadequate for determining the frequency of occupational disease. Our analysis which combines a readily-available and relatively inexpensive national administrative database (i.e., death certificates) with a more costly state-based active surveillance system is a cost-effective model that could be used to provide better estimates of a number of different occupational diseases. Accurate estimates of occupational illnesses are essential to both determine temporal trends and evaluate efforts to prevent silicosis.     

四川省23家石英砂企业职业危害因素检测结果

目的调查、检测、评价四川省23家石英砂企业职业危害因素及防护效果,为企业职业危害防护措施改进提供依据。方法依据相关法律法规进行现场卫生学调查,按照国家职业卫生标准和规范进行采样和分析。结果①现场卫生学调查结果:23家石英砂企业绝大多数属于微小型企业,80%企业生产工艺采用了湿法生产,存在的主要职业病危害因素有粉尘(矽尘)和噪声。②职业危害因素检测结果:总粉尘共检测53个作业点,范围在0.50～27.4 mg/m3,平均3.84 mg/m3;18个作业点在职业卫生标准限值内,合格率为34.0%。呼吸性粉尘共检测53个作业点,范围在0.40～10.84 mg/m3;平均2.35 mg/m3,21个作业点在职业卫生标准限值内,合格率为39.6%。分析48个作业点粉尘中的游离二氧化硅(SiO2)含量只有13个点(27.1%)在10%以下。噪声共测量102个作业点,强度范围在72.2～104.0 dB(A),平均86.3 dB(A);66个作业点在职业卫生标准限值内,合格率为66.7%。结论四川省23家洗选、加工石英砂为主的生产企业中职业危害因素粉尘浓度超标严重,72.9%的作业场所中游离SiO2含量大于10%,属于高度危害作业场所,个别噪声岗位超限严重。因此,必须加强防护措施的设置与防护用品使用监督,才能有效预防职业病的发生。     

Polymorphisms of the IL-1 gene complex in coal miners with silicosis

BACKGROUND: Silicosis is characterized by fibrosing nodular lesions that eventually develop into progressive pulmonary fibrosis. Pro-inflammatory cytokines, such as interleukin-1 (IL-1), play a key role in the development of silicosis by regulating mediators which are responsible for lung injury, inflammation, and potentially fibrosis. To study whether functional single nucleotide polymorphisms (SNPs) located in the regulatory elements of genes coding for the IL-1alpha, IL-1beta, and IL-1 receptor antagonist (RA) cytokines are associated with silicosis, we examined 318 Caucasian cases confirmed histopathologically with pulmonary silicosis and 163 controls without any apparent inflammation or other pulmonary disease. METHODS: Genotyping was carried out by polymerase chain reaction-restriction fragment length polymorphism technique. RESULTS: The proportion of the IL-1RA (+ 2018) allele 2 genotype was increased in miners with silicosis (0.27) compared to controls (0.16). The odds of being a case were 2.15 (CI = 1.4-3.3) times higher for subjects with at least one copy of allele 2. No statistically significant differences in the allelic frequencies or genotype distributions for IL-1alpha (+ 4845) or IL-1beta (+ 3953) were found between the control and disease groups. CONCLUSIONS: This is the first report showing an association between the IL-1RA (+ 2018) polymorphism and silicosis, and suggests that this polymorphism may confer increased risk for the development of the disease.     

Previously undetected silicosis in New Jersey decedents

BACKGROUND: Despite a reported decline in mortality and hospitalizations associated with silicosis [U.S. Department of Health and Human Services, 1999], this decline may be artifactual, stemming in part from underdiagnosis by physicians. METHODS: This study estimates, through radiological confirmation, the prevalence of unrecognized silicosis in a group of silica-exposed New Jersey decedents whose cause of death was chronic obstructive pulmonary disease (COPD), tuberculosis, or cor pulmonale. Two expert readers re-evaluated the chest X-rays of this group to determine the presence or absence of silicosis. The study population was considered to be presumptively exposed to silica dust by virtue of their usual industry of employment as listed on the death certificate. RESULTS: Radiographic evidence of silicosis was found in 8.5% of this population, and evidence of asbestosis was found in another 10.7%, for a total of 19.2%. CONCLUSIONS: The existence of previously unrecognized silicosis and asbestosis in 19.2% of this study group suggests that occupational lung disease is under-recognized and, hence, undercounted.     

某有色金属企业1980～1999年职业伤害的流行病学研究

目的 掌握有色金属企业职业伤害分布特征，探索职业伤害发生规律和影响职业伤害发生的因素，为最大限度地控制和减少职业伤害提供科学依据。方法 用回顾性流行病学调查方法，调查某有色金属企业1980～1999年职业伤害发生情况和分布规律。结果 某有色金属企业1980～1999年发生职业伤害3831例。矿山3000例，工厂831例；男性3592例，女性239例；轻伤3630例，重伤104例，死亡57例。职业伤害在时间分布上有季节性特征。昼时分布有明显的集中趋势，高发于中班，圆形分布检验差异有显著性。人群分布以20～30岁年龄为高发人群，构成占40％以上，以20～25岁为最高点。工龄分布以1～10年工龄者为高发，最高点在1～5年工龄段。轻伤和重伤的年龄差别有统计学意义(Z=-2.184，P=0．029)，职业伤害程度与年龄呈正相关(r=0．041，P=0.011)。职业伤害主要分布在打眼、出矿、钳工、起重、支柱五大工种，易受伤部位是手、脚、头、四肢、五官，易受伤类型是物击、车辆、高坠。结论 某有色金属企业职业伤害发生率逐年下降，综合干预收到了效果，职业伤害是可以预防和控制的。     

Case-control study of silicosis, silica exposure, and lung cancer in white South African gold miners

A case-control study was undertaken to assess the association between lung cancer and silicosis or silica dust exposure in white South African gold miners. Cases and controls were identified from deaths reported to the Gold Miners Provident Fund for the period January, 1979-October, 1983. Two controls were matched to each case by year of birth (+/- 2 years) and by smoking (+/- 5 cigarettes or equivalents per day) assessed 10 years (+/- 2 years) prior to death. One hundred thirty-three matched triplets were identified. The results showed no overall association between lung cancer and radiological silicosis (OR = 1.08, p = 0.92). Autopsy data indicated no overall associations between lung cancer and silicosis of the lung parenchyma (OR = 1.49, p = 0.11), the pleura (OR = 0.72, p = 0.30), or the hilar glands (OR = 0.85, p = 0.72). A trend toward increased severity of silicosis of the parenchyma was evident; however, this was not statistically significant (p = 0.08). Odds ratios for lung cancer and silicosis were higher at lower levels of cumulative silica dust exposure (ORs = 2.43, 1.72, 1.35 and 0.62 for lung cancer and autopsy silicosis of the parenchyma for the lowest, second, third, and highest quartiles of dust exposure, respectively; all p greater than 0.05). Cases did not differ from controls for total silica dust exposure, length of exposure, weighted average intensity of exposure, or number of shifts at high dust (all p greater than 0.20). The data do not support the hypothesis of a carcinogenic role for silica dust and no statistically significant associations were found between lung cancer and silicosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

中药“热毒清”对矽肺防治效应的实验研究

为探讨中药“热毒清”对矽肺的防治效应,本文取提纯的不同培养阶段的四组小鼠腹腔巨噬细胞,用形态学和细胞化学的方法,对细胞的形态及ACP和SDH活性进行了动态观察。结果表明,SiO_3组巨噬细胞吞噬SiO_2粉尘后远较中药和P_(204)组迅速死亡、崩解。细胞内ACP和SDH活性也大大地低于中药和P_(204)组(P<0.01),但中药与P_(204)组间无显著差异(P>0.05)。认为“热毒清”有明显的防治矽肺效应。