Exposure-response analysis of mortality among coal miners in the United States

Increased odds of mortality from non-malignant respiratory disease and lung cancer are highest among US coal miners born after 1939

OBJECTIVES

Coal miners suffer increased mortality from non-malignant respiratory diseases (NMRD), including pneumoconioses and chronic obstructive pulmonary disease, compared with the US population. We characterised mortality trends from NMRD, lung cancer and ischaemic heart disease (IHD) using data from the Federal Black Lung Program, National Coal Workers' Health Surveillance Program and the National Death Index.

METHODS

We compared mortality ORs (MORs) for NMRD, lung cancer and IHD in former US coal miners to US white males. MORs were computed for the study period 1979-2017 by birth cohort (<1920, 1920-1929, 1930-1939, ≥1940), with a subanalysis restricted to Central Appalachia.

RESULTS

The study population totalled 235 550 deceased miners, aged >45 years. Odds of death from NMRD and lung cancer across all miner birth cohorts averaged twice those of US males. In Central Appalachia, MORs significantly increased across birth cohorts. There was an eightfold increase in odds of death from NMRD among miners born after 1940 (MORBC≥1940 8.25; 95% CI 7.67 to 8.87). Miners with progressive massive fibrosis (PMF) were younger at death than those without PMF (74 vs 78 years; p<0.0001). We observed a pattern of reduced MORs from IHD in coal miners compared with national and regional counterparts.

CONCLUSION

US coal miners have excess mortality from NMRD and lung cancer compared with total US and Appalachian populations. Mortality is highest in the most recent birth cohorts, perhaps reflecting increased rates of severe pneumoconiosis.

Coal Miners and Lung Cancer: Can Mortality Studies Offer a Perspective on Rat Inhalation Studies of Poorly Soluble Low Toxicity Particles?

Inhalation studies involving laboratory rats exposed to poorly soluble particles (PSLTs), such as carbon black and titanium dioxide, among others, have led to the development of lung cancer in conditions characterized as lung overload. Lung overload has been described as a physiological state in which pulmonary clearance is impaired, particles are not effectively removed from the lungs and chronic inflammation develops, ultimately leading to tumor growth. Since lung tumors have not occurred under similar states of lung overload in other laboratory animal species, such as mice, hamsters and guinea pigs, the relevance of the rat as a model for human risk assessment has presented regulatory challenges. It has been suggested that coal workers' pneumoconiosis may reflect a human example of apparent "lung overload" of poorly soluble particles. In turn, studies of risk of lung cancer in coal miners may offer a valuable perspective for understanding the significance of rat inhalation studies of PSLTs on humans. This report addresses whether coal can be considered a PSLT based on its composition in contrast to carbon black and titanium dioxide. We also review cohort mortality studies and case-control studies of coal workers. We conclude that coal differs substantially from carbon black and titanium dioxide in its structure and composition. Carbon black, a manufactured product, is virtually pure carbon (upwards of 98%); TiO2 is also a manufactured product. Coal contains carcinogens such as crystalline silica, beryllium, cadmium and iron, among others; in addition, coal mining activities tend to occur in the presence of operating machinery in which diesel exhaust particles, a Type I Human carcinogen, may be present in the occupational environment. As a result of its composition and the environment in which coal mining occurs, it is scientifically inappropriate to consider coal a PSLT. Despite coal not being similar to carbon black or TiO2, through the use of a weight of evidence approach-considered the preferred method when evaluating disparate studies to assess risk- studies of coal-mine workers do not indicate a consistent increase in lung cancer risk. Slight elevations in SMR cannot lead to a reliable conclusion about an increased risk due to limitations in exposure assessment and control of inherent biases in case-control studies, most notably confounding and recall bias. In conclusion, the weight of the scientific literature suggests that coal mine dust is not a PSLT, and it does not increase lung cancer risk.

Cancer and mortality in coal mine workers: a systematic review and meta-analysis

Coal mine workers are exposed to a number of workplace hazards which may increase the risk of cancer and mortality. We conducted a systematic review and meta-analysis to investigate cancer and mortality in coal mine workers We searched in Ovid Medline, PubMed, Embase and Web of Science databases using keywords and text words related to coal mines, cancer and mortality and identified 36 full-text articles using predefined inclusion criteria. Each study's quality was assessed using the Newcastle-Ottawa Scale. We performed random-effect meta-analyses including 21 of the identified articles evaluating cancer and/or mortality of coal mine workers. The meta-analysis showed an increased risk of all-cause mortality (SMR 1.14, 95% CI 1.00 to 1.30) and mortality from non-malignant respiratory disease (NMRD) (3.59, 95% CI 3.00 to 4.30) in cohorts with coal workers' pneumoconiosis (CWP). We found a somewhat increased risk of stomach cancer (1.11, 95% CI 0.97 to 1.35) and of mortality from NMRD (1.26, 95% CI 0.99 to 1.61) in the cohorts of coal miners with unknown CWP status. The meta-analysis also showed a decreased risk of prostate cancer and cardiovascular and cerebrovascular mortality among coal miners. This may be a result of the healthy worker effect and possible lower smoking rates, and perhaps also reflect the physically active nature of many jobs in coal mines. The meta-analysis for lung cancer did not show increased risk in coal miners with CWP (1.49, 95% CI 0.70 to 3.18) or for coal miners of unknown CWP status (1.03, 95% CI 0.91 to 1.18). Lower smoking rates in coal mine workers could explain why case-control studies where smoking was controlled for showed higher risks for lung cancer than were seen in cohort studies. Coal mine workers are at increased risk of mortality from NMRD but decreased risk of prostate cancer and cardiovascular and cerebrovascular mortality. Studies of coal mine workers need long-term follow-up to identify increased mortality and cancer incidence.

[Quality of life of silicotic former miners]

BACKGROUND

The aim of this study was to assess the respiration-related quality of life (QoL) of former miners with silicosis and to determine the factors that could affect QoL (socio-demographic and professional parameters, toxic habits, co-morbidities, and degree of respiratory disability).

METHODS

This cross-sectional study involved 104 people who came for routine periodic consultation and included the medical records file and a questionnaire.

RESULTS

The average age was 66.3±5.4 years. Functional respiratory symptoms were exertional dyspnoea (97.2%), cough (73.1%), sputum (59.6%) and wheezing (25%). Associated respiratory illnesses were asthma (29.8%), COPD (18.3%), persistent rhinitis (13.5%) and tuberculosis (5.8%). 3/4 of the miners had at least one comorbidity. The most common were cardiovascular (43.3%), metabolic (27.9%) and musculo-skeletal (25%). The ventilatory defects were mild in 27.9%, moderate in 57.7% and severe in 14.4%. The radiological lesions exceeded four zones of the pulmonary parenchyma in 81.8%. The average scores for "symptoms", "activities », « impacts" and "total" were 49.1±14%, 77.8±12%, 66.5±16% and 67±16%, respectively. Age, duration of exposure, comorbidities, moderate to severe ventilatory defects, and significant to severe impairment were correlated with altered QoL.

CONCLUSION

Improvement of QoL requires comprehensive care with the management of complications, co-morbidities, better patient awareness, and better consideration of the feelings of patients.

Association between Coalmine Dust and Mortality Risk of Lung Cancer: A Meta-Analysis

Background

Evidence on the carcinogenicity of coalmine dust in occupational settings is still conflicting. Therefore, we conducted this research to evaluate the mortality risk of lung cancer for coalminers exposed to occupational dust when compared to population with no or low dust exposure.

Methods

Databases of PubMed and Chinese National Knowledge Infrastructure as well as reference lists were searched updated to September 18, 2020. The enrolled articles should report lung cancer mortality risk for coalminers exposed to occupational dust. Basic information was extracted such as the author and publication year, area and ethnicity, the type and estimates of outcome, duration of follow-up, and the study design. The checklists from Agency for Healthcare Research and Quality and the Newcastle-Ottawa Scale were used for the assessment of quality and bias risk for descriptive studies, cohort studies, and case control studies, respectively. The overall relative risks were calculated while Begg's and Egger's tests and sensitivity analysis were performed to explore potential heterogeneity sources. Metaregression and subgroup analyses were also conducted to give more detailed information for the correlation between dust exposure and lung cancer mortality.

Results

A total of 19 articles with 22 different studies (descriptive study, case control study, and cohort study) including 8909 observed deaths from 1964 to 2017 were enrolled with a significant heterogeneity (I ² = 95%, P < 0.001). The pooled relative risk of mortality from lung cancer was 1.16 (1.03-1.30) for coalminers. Results of metaregression analysis indicated that the high heterogeneity among these enrolled studies might be caused by the ethnicity differences (P = 0.011). Subgroup analysis also indicated that the pooled estimate for Asian population in China was 4.94 (3.95-6.17) with I ² = 39.3% and P = 0.192. All these results suggested that exposure to occupational dust would significantly increase the mortality risk of lung cancer, especially for Asian population in China, which should be measured and controlled more strictly. Discussion. This systematic review and meta-analysis provides high-quality evidence that exposure to occupational dust might increase the mortality risk of lung cancer, especially for Asian populations in China. The magnitude of this effect is of major public health importance in view of the ubiquitous existence of coalmining industry in China and even in the world. However, these pooled estimates should be interpreted cautiously because of the high heterogeneity among these publications. Other. This study was supported by the National Key Research and Development Program of China (Grant No. 2016YFC1302501).

Mortality among workers employed in the mining industry in the United States: A 29-year analysis of the National Health Interview Survey-Linked Mortality File, 1986-2014

BACKGROUND

Working in the mining industry increases the risk of chronic diseases and mortality. We investigated overall and cause-specific mortality rates among workers employed in the mining sector in the United States.

METHODS

We pooled 29 years of National Health Interview Survey (NHIS) public-use data from 1986 to 2014, with mortality follow-up until 31 December 2015. We grouped respondents into the mining and nonmining sectors based on the responses given at the time of the NHIS interview. We compared the overall and cause-specific mortality rates using standardized mortality ratios (SMR) and 95% confidence interval (CI) adjusted for the competing cause of death.

RESULTS

From 1986 to 2014, an estimated 14 million deaths were recorded among subjects eligible for mortality follow-up. Of these, an estimated 50,000 deaths occurred among those working in the mining sector. A significantly higher overall mortality (SMR = 1.26, 95% CI: 1.17-1.36), and mortality from heart diseases (adjusted SMR = 1.56, 95% CI: 1.31-1.83), cancer (adjusted SMR = 1.30, 95% CI: 1.14-1.48) and unintentional injuries (adjusted SMR = 1.41, 95%CI: 1.03-1.85) were observed among those employed in the mining sector. When the analyses were restricted to men, only the SMRs for heart disease and cancer remained statistically significant. No elevated SMR for deaths from chronic lower respiratory disease was observed in the study.

CONCLUSION

Workers employed in the mining sector have a significantly increased total death rate and death rates from heart disease, cancer, and unintentional injuries.

Progressive Massive Fibrosis Resurgence Identified in U.S. Coal Miners Filing for Black Lung Benefits, 1970-2016

RATIONALE

There has been a resurgence of progressive massive fibrosis (PMF) in the United States, particularly among central Appalachian miners.

OBJECTIVES

We characterized the proportion of PMF among former U.S. coal miners applying for Federal Black Lung Program benefits, 1970-2016.

METHODS

Data from the U.S. Department of Labor were used to characterize trends in proportion of PMF cases, defined as an approved black lung claim with a determination of PMF, among all miners who filed for federal benefits between January 1, 1970, and December 31, 2016. Joinpoint, logistic, and linear regression models were used to identify changes in the proportion of claimants with PMF over time.

RESULTS

There were 4,679 unique PMF cases among claimants for federal black lung benefits between 1970 and 2016, with 2,474 miners determined to have PMF since 1996. The number of PMF cases among Federal Black Lung Program claimants fell from 404 (0.5% of claimants) in 1978 to a low of 18 cases (0.6%) in 1988, and then increased to 353 cases (8.3%) in 2014. The proportion of federal black lung benefits claimants with PMF has been increasing since 1978 (0.06% annual percent change [APC]; 95% confidence interval [CI], 0.05-0.07%; P < 0.0001), and began increasing at a significantly increased rate after 1996 (0.26% APC; 95% CI, 0.25-0.28%; P < 0.0001). Most miners with PMF (84%) last mined in West Virginia, Kentucky, Pennsylvania, or Virginia. Since 1970, the proportion of claimants with PMF has increased significantly among miners who last worked in Kentucky (16.6% APC; 95% CI, 16.5-16.7%), Pennsylvania (4.7% APC; 95% CI, 4.6-4.8%), Tennessee (16.1% APC; 95% CI, 15.7-16.4%), West Virginia (16.8% APC; 95% CI, 16.6-16.9%), and most sharply among miners last working in Virginia (31.5% APC; 95% CI, 31.2-31.7%), where in 2009, more than 17% of claimants received a PMF determination. The proportion of PMF determinations for the rest of the United States has not exceeded 4%.

CONCLUSIONS

There has been a resurgence of PMF, particularly in central Appalachian miners. The resurgence of this preventable disease points to the need for improved primary and secondary prevention of dust-related lung disease in U.S. coal miners.

Coal mine dust lung disease in the modern era

Coal workers' pneumoconiosis (CWP), as part of the spectrum of coal mine dust lung disease (CMDLD), is a preventable but incurable lung disease that can be complicated by respiratory failure and death. Recent increases in coal production from the financial incentive of economic growth lead to higher respirable coal and quartz dust levels, often associated with mechanization of longwall coal mining. In Australia, the observed increase in the number of new CWP diagnoses since the year 2000 has necessitated a review of recommended respirable dust exposure limits, where exposure limits and monitoring protocols should ideally be standardized. Evidence that considers the regulation of engineering dust controls in the mines is lacking even in high-income countries, despite this being the primary preventative measure. Also, it is a global public health priority for at-risk miners to be systemically screened to detect early changes of CWP and to include confirmed patients within a central registry; a task limited by financial constraints in less developed countries. Characteristic X-ray changes are usually categorized using the International Labour Office classification, although future evaluation by low-dose HRCT) chest scanning may allow for CWP detection and thus avoidance of further exposure, at an earlier stage. Preclinical animal and human organoid-based models are required to explore potential re-purposing of anti-fibrotic and related agents with potential efficacy. Epidemiological patterns and the assessment of molecular and genetic biomarkers may further enhance our capacity to identify susceptible individuals to the inhalation of coal dust in the modern era.

Mortality in Miners with Coal-Workers' Pneumoconiosis in the Czech Republic in the Period 1992-2013

While working underground, miners are exposed to a number of risk factors that have a negative impact on their health and may be a cause of an increased mortality in miners. The aim of the study was to compare total and specific mortality in black coal miners with acknowledged coal-workers’ pneumoconiosis (CWP) and without CWP, and the mortality of the general male population in the Czech Republic in the period 1992–2013. The sample consisted of 3476 coal miners with CWP and 6687 ex-coal miners without CWP, who were removed after achieving the maximum permissible exposure (MPE). The mortality risk differences were analyzed with the use of the standardized mortality ratio (SMR) and 95% confidence interval. Significantly higher total mortality (SMR = 1.10; 95% CI: 1.02–1.17), and mortality from malignant neoplasm (SMR = 1.16; 95% CI: 1.03–1.30), lung cancers (SMR = 1.70; 95% CI: 1.41–2.04), and non-malignant respiratory diseases (SMR = 2.78; 95% CI: 2.32–3.31) were found in the sample of coal miners with CWP. In this sample, the severity of CWP was assessed, and the SMR increased with the severity of CWP. The total (SMR = 0.86; 95% CI: 0.82–0.91) and specific mortality of miners without CWP were not higher compared with the general population. In the case where the miners were removed from underground work after achieving the MPE (without CWP), their mortality was not higher than that of the general population, but the mortality of miners with CWP was higher compared to the general population. This mortality was affected by malignant and non-malignant respiratory diseases.

An approach to adjust standardized mortality ratios for competing cause of death in cohort studies

Purpose

The calculation of standardized mortality ratios (SMRs) is a standard tool for the estimation of health risks in occupational epidemiology. An increasing number of studies deal with the analysis of the mortality in employees suffering from an occupational disease like silicosis or coal-worker pneumoconiosis (CWP). Their focus lies not on the mortality risk due to the occupational disease itself, but on other diseases such as lung cancer or heart diseases. Using population-based reference rates in these studies can cause misleading results because mortality rates of the general population do not reflect the elevated mortality due to the occupational disease investigated. Hence, the purpose of the present paper is to develop an approach to adjust the risk estimates for other causes of death with respect to the effect of an occupational disease as a competing cause of death in occupational mortality cohort studies.

Methods

To overcome the problems associated with SMRs, the paper makes use of proportional mortality ratios (PMR), which are a further approach for the estimation of health risks in occupational epidemiology. The cause-specific SMR can be rewritten as a product of PMR times the overall SMR. The PMR can be adjusted by ignoring the competing cause of death. Hence, an adjusted cause-specific SMR can be derived by multiplying this adjusted PMR with the overall SMR. This approach is applied to studies concerning lung cancer risk in coal miners suffering from CWP.

Results and conclusions

The usual approach for calculating SMRs leads to an underestimation of the real lung cancer risk in subgroups of miners suffering from CWP. The same effect can be observed in workers exposed to respirable silica already suffering from silicosis. The presented approach results in more realistic risk estimation in mortality cohort studies of employees suffering from an occupational disease. It is easily calculable on the basis of usually published values of observed cases and the corresponding cause-specific SMR.

Lung cancer among coal miners, ore miners and quarrymen: smoking-adjusted risk estimates from the synergy pooled analysis of case-control studies

OBJECTIVES

Working in mines and quarries has been associated with an elevated lung cancer risk but with inconsistent results for coal miners. This study aimed to estimate the smoking-adjusted lung cancer risk among coal miners and compare the risk pattern with lung cancer risks among ore miners and quarrymen.

METHODS

We estimated lung cancer risks of coal and ore miners and quarrymen among 14 251 lung cancer cases and 17 267 controls from the SYNERGY pooled case-control study, controlling for smoking and employment in other at-risk occupations.

RESULTS

Ever working as miner or quarryman (690 cases, 436 controls) was associated with an elevated odds ratio (OR) of 1.55 [95% confidence interval (95% CI) 1.34-1.79] for lung cancer. Ore miners (53 cases, 24 controls) had a higher OR (2.34, 95% CI 1.36-4.03) than quarrymen (67 cases, 39 controls; OR 1.92, 95% CI 1.21-3.05) and coal miners (442 cases, 297 controls; OR 1.40, 95% CI 1.18-1.67), but CI overlapped. We did not observe trends by duration of exposure or time since last exposure.

CONCLUSIONS

This pooled analysis of population-based studies demonstrated an excess lung cancer risk among miners and quarrymen that remained increased after adjustment for detailed smoking history and working in other at-risk occupations. The increase in risk among coal miners were less pronounced than for ore miners or quarrymen.

COPD and levels of Hsp70 (HSPA1A) and Hsp27 (HSPB1) in plasma and lymphocytes among coal workers: a case-control study

This case-control study aimed to investigate whether the levels of Hsp70 (HSPA1A) and Hsp27 (HSPB1) in plasma and lymphocytes were associated with the risk of chronic obstructive pulmonary disease (COPD) among coal workers. A total of 76 COPD cases and 48 age-matched healthy controls from a group of coal workers were included. The case group consisted of 35 COPD patients whose condition was complicated with coal workers' pneumoconiosis (CWP) and 41 COPD patients without CWP. Heat shock proteins (Hsps) in plasma and lymphocytes were detected by ELISA and flow cytometry, respectively. Multiple logistic regression models were applied to estimate the association between Hsp levels and COPD risk. Our results showed that plasma Hsp70 and lymphocyte Hsp27 levels were significantly higher and plasma Hsp27 levels were significantly lower in COPD cases than in controls (p < 0.01). No significant differences in lymphocyte Hsp70 levels were found between COPD cases and the matched subjects. Higher plasma Hsp70 levels (odds ratio (OR) = 13.8, 95 % confidence interval (CI) = 5.7-33.5) and lower plasma Hsp27 levels (OR = 4.6, 95 % CI = 2.0-10.5) were significantly associated with an increased risk of COPD after adjusting for confounders. Higher lymphocyte Hsp27 levels were only associated with an increased risk of COPD with CWP (OR = 6.6, 95 % CI = 2.0-22.1) but not with an increased risk of COPD without CWP (OR = 3.0, 95 % CI = 0.9-8.9). Additionally, there were strong joint effects of different Hsps on COPD risk. These results showed that higher levels of plasma Hsp70 and lower levels of plasma Hsp27 might be associated with an increased risk of COPD among coal workers. They may have the potential to serve as monitoring markers for COPD in coal workers.

Respiratory disease mortality among US coal miners; results after 37 years of follow-up

OBJECTIVES

To evaluate respiratory related mortality among underground coal miners after 37 years of follow-up.

METHODS

Underlying cause of death for 9033 underground coal miners from 31 US mines enrolled between 1969 and 1971 was evaluated with life table analysis. Cox proportional hazards models were fitted to evaluate the exposure-response relationships between cumulative exposure to coal mine dust and respirable silica and mortality from pneumoconiosis, chronic obstructive pulmonary disease (COPD) and lung cancer.

RESULTS

Excess mortality was observed for pneumoconiosis (SMR=79.70, 95% CI 72.1 to 87.67), COPD (SMR=1.11, 95% CI 0.99 to 1.24) and lung cancer (SMR=1.08; 95% CI 1.00 to 1.18). Coal mine dust exposure increased risk for mortality from pneumoconiosis and COPD. Mortality from COPD was significantly elevated among never [corrected] smokers and former smokers (HR=1.84, 95% CI 1.05 to 3.22; HRK=1.52, 95% CI 0.98 to 2.34, respectively) but not current smokers (HR=0.99, 95% CI 0.76 to 1.28). Respirable silica was positively associated with mortality from pneumoconiosis (HR=1.33, 95% CI 0.94 to 1.33) and COPD (HR=1.04, 95% CI 0.96 to 1.52) in models controlling for coal mine dust. We saw a significant relationship between coal mine dust exposure and lung cancer mortality (HR=1.70; 95% CI 1.02 to 2.83) but not with respirable silica (HR=1.05; 95% CI 0.90 to 1.23). In the most recent follow-up period (2000-2007) both exposures were positively associated with lung cancer mortality, coal mine dust significantly so.

CONCLUSIONS

Our findings support previous studies showing that exposure to coal mine dust and respirable silica leads to increased mortality from malignant and non-malignant respiratory diseases even in the absence of smoking.

Population cancer risks associated with coal mining: a systematic review

Background

Coal is produced across 25 states and provides 42% of US energy. With production expected to increase 7.6% by 2035, proximate populations remain at risk of exposure to carcinogenic coal products such as silica dust and organic compounds. It is unclear if population exposure is associated with increased risk, or even which cancers have been studied in this regard.

Methods

We performed a systematic review of English-language manuscripts published since 1980 to determine if coal mining exposure was associated with increased cancer risk (incidence and mortality).

Results

Of 34 studies identified, 27 studied coal mining as an occupational exposure (coal miner cohort or as a retrospective risk factor) but only seven explored health effects in surrounding populations. Overall, risk assessments were reported for 20 cancer site categories, but their results and frequency varied considerably. Incidence and mortality risk assessments were: negative (no increase) for 12 sites; positive for 1 site; and discordant for 7 sites (e.g. lung, gastric). However, 10 sites had only a single study reporting incidence risk (4 sites had none), and 11 sites had only a single study reporting mortality risk (2 sites had none). The ecological study data were particularly meager, reporting assessments for only 9 sites. While mortality assessments were reported for each, 6 had only a single report and only 2 sites had reported incidence assessments.

Conclusions

The reported assessments are too meager, and at times contradictory, to make definitive conclusions about population cancer risk due to coal mining. However, the preponderance of this and other data support many of Hill’s criteria for causation. The paucity of data regarding population exposure and risk, the widespread geographical extent of coal mining activity, and the continuing importance of coal for US energy, warrant further studies of population exposure and risk.

The classic pneumoconioses: new epidemiological and laboratory observations

The purpose of this article is to provide an update on selected issues of current interest and recent developments related to 3 types of inorganic mineral dust exposures causing classic forms of pneumoconiosis: coal mine dust, crystalline silica, and asbestos. Common themes include new imaging modalities, emerging exposures, and evolving appreciation of additional adverse health effects associated with exposure to these inorganic mineral dusts.

Coal mining is associated with lung cancer risk in Xuanwei, China

BACKGROUND

Xuanwei, China, experiences some of the highest rates of lung cancer in China. While lung cancer risk has been linked to the household use of bituminous coal, no study has comprehensively evaluated the risk of lung cancer associated with the mining of this coal in Xuanwei. In Xuanwei, coal is typically extracted from underground mines, without ventilation, and transported to the surface using carts powered by manpower or electricity.

METHODS

We evaluated the risk of lung cancer and working as a coal miner, in the absence of diesel exhaust exposure, in a population-based case-control study of 260 male lung cancer cases and 260 age-matched male controls with information on occupational histories. Odds ratios (ORs) and 95% confidence intervals (CIs) for working as a coal miner and years of working as a coal miner were calculated by conditional logistic regression, adjusting for potential confounders, such as smoking and household coal use.

RESULTS

We observed an increased risk of lung cancer among coal miners (OR = 2.7; 95%CI = 1.3-5.6) compared to noncoal miners. Further, a dose-response relationship was observed for the risk of lung cancer and the number of years working as a coal miner (P(trend)  = 0.02), with those working as miners for more than 10 years experiencing an almost fourfold increased risk (OR = 3.8; 95%CI = 1.4-10.3) compared to noncoal miners.

CONCLUSIONS

These findings suggest that coal mining in Xuanwei may be a risk factor for lung cancer.

Coal dust exposure and mortality from ischemic heart disease among a cohort of U.S. coal miners

BACKGROUND

Particulate exposure from air pollution increases the risk of ischemic heart disease (IHD) mortality. Although coal miners are highly exposed to coal dust particulate, studies of IHD mortality risk among coal miners have had inconsistent results. Previous studies may have been biased by the healthy worker effect.

METHODS

We examined the dose-response relationship between cumulative coal dust exposure, coal rank, and IHD mortality among a cohort of underground coal miners who participated in the National Study of Coal Workers' Pneumoconiosis.

RESULTS

After adjusting for age, smoking, and body mass index, risk of IHD mortality increased at higher levels of coal dust exposure. Mortality risk was also associated with coal rank region.

CONCLUSION

There was an increased risk of mortality from IHD associated with cumulative exposure to coal dust, and with coal rank. The effect of coal rank may be due differences in the composition of coal mine dust particulate. The association of risk of IHD mortality with cumulative particulate exposure is consistent with air pollution studies.

Cytogenetic monitoring of coal workers and patients with coal workers' pneumoconiosis in Turkey

Occupational exposure to coal dust causes coal workers' pneumoconiosis (CWP), which is a chronic inflammatory and fibrotic lung disease. Recently, chronic inflammation has been accepted as a crucial factor in the pathogenesis of neoplasia. The chronic inflammation provides dynamic setting for oxidative stress and formation of free radicals. Interaction of reactive oxygen species (ROS) with DNA augments the likelihood of DNA structural and transcriptional errors. The purpose of this study was to investigate the genotoxic risk in pneumoconiotic patients and in those with occupational exposure to coal dust. Therefore, sister chromatid exchange (SCE) and micronucleus (MN) tests were performed in Turkish CWP patients, coal workers, and an unexposed control group. Both SCE and MN frequencies in CWP patients were found significantly higher than in coal worker and unexposed groups. There were no differences between SCE and MN frequencies of coal worker and unexposed groups. On the other hand, no correlation between SCE frequency, duration of exposure, and age was observed in all three groups. There was also no effect of smoking on the frequencies of SCE and MN in the groups. Based on these results, it might be suggested that development of CWP leads to a significant induction of cytogenetic damage in peripheral lymphocytes of CWP patients. This is the first report on CWP patients with elevated cytogenetic endpoints. Further, a larger follow-up study is warranted.

Mortality among U.S. underground coal miners: a 23-year follow-up

BACKGROUND

The mortality experience over 22-24 years of 8,899 working coal miners initially medically examined in 1969-1971 at 31 U.S. coal mines was evaluated.

METHODS

A cohort life-table analysis was undertaken on underlying causes of death, and proportional hazards models were fitted to both underlying, and underlying and contributing causes of death.

RESULTS

Elevated mortality from nonviolent causes, nonmalignant respiratory disease (NMRD), and accidents was observed, but lung cancer and stomach cancer mortality were not elevated. Smoking, pneumoconiosis, coal rank region, and cumulative coal mine dust exposure were all predictors of mortality from nonviolent causes and NMRD. Mortality from nonviolent causes and NMRD was related to dust exposure within the complete cohort and also for the never smoker subgroup. Dust exposure relative risks for mortality were similar for pneumoconiosis, NMRD, and chronic airways obstruction.

CONCLUSIONS

The findings confirm and enlarge upon previous results showing that exposure to coal mine dust leads to increased mortality, even in the absence of smoking.

Understanding the chemical properties of macerals and minerals in coal and its potential application for occupational lung disease prevention

Recent increases in oil price further strengthen the argument that coal and coal products will play an increasingly important role in fulfilling the energy needs of our society. Coal is an aggregate of heterogeneous substances composed of organic (macerals) and inorganic (minerals) materials. The objective of this review was to assess whether some chemical parameters in coal play a role in producing environmental health problems. Basic properties of coal--such as chemical forms of the organic materials, structure, compositions of minerals--vary from one coal mine region to another as well as from coals of different ranks. Most importantly, changes in chemical properties of coals due to exposure to air and humidity after mining--a dynamic process--significantly affect toxicity attributed to coal and environmental fate. Although coal is an extremely complex and heterogeneous material, the fundamental properties of coal responsible for environmental and adverse health problems are probably related to the same inducing components of coal. For instance, oxidation of pyrite (FeS2) in the coal forms iron sulfate and sulfuric acid, which produces occupational lung diseases (e.g., pneumoconiosis) and other environmental problems (e.g., acid mine drainage and acid rain). Calcite (CaCO3) contained in certain coals alters the end products of pyrite oxidation, which may make these coals less toxic to human inhalation and less hazardous to environmental pollution. Finally, knowledge gained on understanding of the chemical properties of coals is illustrated to apply for prediction of toxicity due to coal possibly before large-scale mining and prevention of occupational lung disease during mining.

Comparative pathology of environmental lung disease: an overview

Environmental factors play a major role in a majority of lung diseases. Asthma, chronic obstructive pulmonary disease (COPD), lung cancer, and many interstitial lung diseases are influenced or caused by environmental factors. Animals and humans may respond differently to the same agent, and a study of the comparative pathology between the two is useful for optimizing animal models of environmental lung disease and for evaluating their predictive value in carcinogenicity studies. This overview describes the most common nonneoplastic pathologic pulmonary responses to inhaled environmental agents in the human and contrasts them with the responses observed in rats exposed to the same agents. We show both similarities and difference in response to the same agents; furthermore, both species have unique responses to some agents (for example, progressive massive fibrosis in the human and proliferative squamous lesions in the rat). Quantitative analysis of the grades of response to three environmental particulate dusts revealed differences between the 2 species at the cellular level. Specifically, acute intra-alveolar inflammation, alveolar epithelial hyperplasia, and alveolar lipoproteinosis were all greater in rats than in humans exposed to the same agents. These differences may account for differences between the 2 species in carcinogenic response to nonfibrous particulates.

Decline in lung function and mortality: implications for medical monitoring

AIM

To investigate the risk of death associated with selected cut-off points for rate of decline of forced expiratory volume in one second (FEV(1)).

METHODS

Mortality rates of a cohort of 1730 coal miners who had performed two pulmonary function tests 12.8 years apart were followed up for an additional 12 years. Based on previous studies, cut-off points for FEV(1) rate of decline (ml/year) were selected as 30, 60 and 90 ml/year. Cox proportional hazard regression was used to estimate multivariate risk ratio of death in each category.

RESULTS

The risk ratios (compared to "below 30 ml/year") were 1.39 (95% CI 0.99 to 1.97) in the "60 to less than 90 ml/year" category and 1.90 (95% CI 1.32 to 2.76) in the "90 ml/year and above" category. Rates of decline above 90 ml/year were consistently related to excess mortality. In non-smokers and those with neither restrictive nor obstructive patterns at the first survey, rates of decline above 60 ml/year were significantly associated with increased mortality.

CONCLUSIONS

Risk of death increases in individuals with rates of decline above about 60 ml/year and is statistically significant with declines of 90 ml/year or more. These results should be useful to healthcare providers in assessing lung function declines observed in individuals.

A critical assessment of studies on the carcinogenic potential of diesel exhaust

After decades of research involving numerous epidemiologic studies and extensive investigations in laboratory animals, a causal relationship between diesel exhaust (DE) exposure and lung cancer has not been conclusively demonstrated. Epidemiologic studies of the transportation industry (trucking, busing, and railroad) show a small elevation in lung cancer incidence (relative risks [RRs] generally below 1.5), but a dose response for DE is lacking. The studies are also limited by a lack of quantitative concurrent exposure data and inadequate or lack of controls for potential confounders, particularly tobacco smoking. Furthermore, prior to dieselization, similar elevations in lung cancer incidence have been reported for truck drivers, and in-cab diesel particulate matter (DPM) exposures of truck drivers were comparable to ambient highway exposures. Taken together, these findings suggest that an unidentified occupational agent or lifestyle factor might be responsible for the low elevations in lung cancer reported in the transportation studies. In contrast, underground miners, many of whom experience the highest occupational DPM exposures, generally do not show elevations in lung cancer. Laboratory studies must be interpreted with caution with respect to predicting the carcinogenic potential of DE in humans. Tumors observed in rats following lifetime chronic inhalation of very high levels of DPM may be attributed to species-specific overload mechanisms that lack relevance to humans. Increased tumor incidence was not observed in other species (hamsters or mice) exposed to DPM at very high levels or in rats exposed at lower levels (</=2000 mug/m3). Although DPM contains mutagens, mutagenicity studies in which cells were exposed to concentrated extracts of DPM also have limited application to human risk assessment, because such extracts can be obtained from DPM only by using strong organic solvents, agitation, and heat. Most studies have shown that whole DPM itself is not mutagenic because the adsorbed organic compounds are minimally bioavailable in aqueous-based fluids. In the past two decades, dramatic changes in diesel engine technology (e.g., low-sulfur fuel and exhaust after-treatment) have resulted in >99% reduction in DPM and other quantitative and qualitative changes in the chemical and physical characteristics of diesel exhaust. Thus, the current database, which is focused almost entirely on the potential health effects of traditional diesel exhaust (TDE), has only limited utility in assessing the potential health risks of new-technology diesel exhaust (NTDE). To overcome some of the limitations of the historical epidemiologic database on TDE and to gain further insights into the potential health effects of NTDE, new studies are underway and more studies are planned.

Apoptosis and Bax expression are increased by coal dust in the polycyclic aromatic hydrocarbon-exposed lung

BACKGROUND

Miners inhaling respirable coal dust (CD) frequently develop coal workers' pneumoconiosis, a dust-associated pneumoconiosis characterized by lung inflammation and variable fibrosis. Many coal miners are also exposed to polycyclic aromatic hydrocarbon (PAH) components of diesel engine exhaust and cigarette smoke, which may contribute to lung disease in these workers. Recently, apoptosis was reported to play a critical role in the development of another pneumoconiosis of miners, silicosis. In addition, CD was reported to suppress cytochrome P450 1A1 (CYP1A1) induction by PAHs.

METHODS

We investigated the hypothesis that apoptosis plays a critical role in lung injury and down-regulation of CYP1A1 induction in mixed exposures to CD and PAHs. We exposed rats intratracheally to 0.0, 2.5, 10.0, 20.0, or 40.0 mg/rat CD and, 11 days later, to intraperitoneal beta-naphthoflavone (BNF) , a PAH. In another group of rats exposed to CD and BNF, caspase activity was inhibited by injection of the pan-caspase inhibitor Q-VD-OPH [quinoline-Val-Asp (OMe) -CH2-OPH].

RESULTS

In rats exposed to BNF, CD exposure increased alveolar expression of the proapoptotic mediator Bax but decreased CYP1A1 induction relative to BNF exposure alone. Pan-caspase inhibition decreased CD-associated Bax expression and apoptosis but did not restore CYP1A1 activity. Further, CD-induced lung inflammation and alveolar epithelial cell hypertrophy and hyperplasia were not suppressed by caspase inhibition.

CONCLUSIONS

Combined BNF and CD exposure increased Bax expression and apoptosis in the lung, but Bax and apoptosis were not the major determinants of early lung injury in this model.

The genotoxic risk of underground coal miners from Turkey

A cytogenetic monitoring study was carried out on a group of workers from a bituminous coal mine in Zonguldak province of Turkey, to investigate the genotoxic risk of occupational exposure to coal mine dust. Cytogenetic analysis, namely sister chromatid exchanges (SCEs), chromosomal aberrations (CAs) and micronucleus (MN) tests were performed on a strictly selected group of 39 workers and compared to 34 controls matched for gender, age, and habit. Smoking and age were considered as modulating factors. Both SCE and CA frequencies in coal miners appeared significantly higher than in controls. Similarly, there was a significant increase in the frequency of total micronuclei in exposed group as compared to control group. The effect of smoking on the level of SCE and MN was significant in the control group. A positive correlation between the age and the level of SCE was also found in controls. The frequencies of both SCE and CA were significantly enhanced with the years of exposure. The results of this study demonstrated that occupational exposure to coal mine dust leads to a significant induction of cytogenetic damage in peripheral lymphocytes of workers engaged in underground coal mining.

The global burden of non-malignant respiratory disease due to occupational airborne exposures

BACKGROUND

Occupational non-malignant respiratory disease arises from exposure of workers to airborne agents, mostly particulate or dusts. We describe the worldwide mortality and morbidity from asthma, chronic obstructive pulmonary disease (COPD), and pneumoconioses arising from these occupational exposure and focus on cases reported in the year 2000.

METHODS

The proportions of workers exposed to the agents, and their levels of exposure, were estimated using workforce data and the CAREX (CARcinogen EXposure) database. These were combined with relative risk measures (for asthma and COPD) or absolute risk measures (for the pneumoconioses) to develop estimates of deaths, disability-adjusted life years (DALYs) and attributable fraction (for asthma and COPD).

RESULTS

There were an estimated 386,000 deaths (asthma: 38,000; COPD: 318,000; pneumoconioses: 30,000) and nearly 6.6 million DALYS (asthma: 1,621,000; COPD: 3,733,000, pneumoconioses: 1,288,000) due to exposure to occupational airborne particulates.

CONCLUSIONS

Occupational airborne particulates are an important cause of death and disability worldwide.

Rapidly progressive coal workers' pneumoconiosis in the United States: geographic clustering and other factors

BACKGROUND

Despite significant progress made in reducing dust exposures in underground coal miners in the United States, severe cases of coal workers' pneumoconiosis (CWP), including progressive massive fibrosis (PMF), continue to occur among coal miners.

AIMS

To identify US miners with rapidly progressive CWP and to describe their geographic distribution and associated risk factors.

METHODS

Radiographic evidence of disease progression was evaluated for underground coal miners examined through US federal chest radiograph surveillance programmes from 1996 to 2002. A case of rapidly progressive CWP was defined as the development of PMF and/or an increase in small opacity profusion greater than one subcategory over five years. County based prevalences were derived for both CWP and rapidly progressive cases.

RESULTS

A total of 886 cases of CWP were identified among 29 521 miners examined from 1996 to 2002. Among the subset of 783 miners with CWP for whom progression could be evaluated, 277 (35.4%) were cases of rapidly progressive CWP, including 41 with PMF. Miners with rapidly progressive CWP were younger than miners without rapid progression, were more likely to have worked in smaller mines (<50 employees), and also reported longer mean tenure in jobs involving work at the face of the mine (in contrast to other underground mining jobs), but did not differ with respect to mean underground tenure. There was a clear tendency for the proportion of cases of rapidly progressive CWP to be higher in eastern Kentucky, and western Virginia.

CONCLUSIONS

Cases of rapidly progressive CWP can be regarded as sentinel health events, indicating inadequate prevention measures in specific regions. Such events should prompt investigations to identify causal factors and initiate appropriate additional measures to prevent further disease.

Respirable Coal Dust Particles Modify Cytochrome P4501A1 (CYP1A1) Expression in Rat Alveolar Cells

Cytochrome P4501A1 (CYP1A1) metabolizes polycyclic aromatic hydrocarbons in cigarette smoke to DNA-binding reactive intermediates associated with carcinogenesis. Epidemiologic studies indicate that the majority of coal miners are smokers but have a lower risk of lung cancer than other smokers. We hypothesized that coal dust (CD) exposure modifies pulmonary carcinogenesis by altering CYP1A1 induction. Therefore, male Sprague Dawley rats were intratracheally instilled with 2.5, 10, 20, or 40 mg CD/rat or vehicle (saline); and 11 d later, pulmonary CYP1A1 was induced by intraperitoneal injection of beta-naphthoflavone (BNF; 50 mg/kg). Fourteen days after CD exposure, CYP1A1 protein and activity were measured by Western blot and 7-ethoxyresorufin-O-deethylase activity, respectively. CYP1A1 and the alveolar type II markers, cytokeratins 8/18, were localized and quantified in lung sections by dual immunofluorescence with morphometry. The area of CYP1A1 expression in alveolar septa and alveolar type II cells in response to BNF was reduced by exposure to 20 or 40 mg CD compared with BNF alone. CD exposure significantly inhibited BNF-induced 7-ethoxyresorufin-O-deethylase activity in a dose-responsive manner. By Western blot, induction of CYP1A1 protein by BNF was significantly reduced by 40 mg CD compared with BNF alone. These findings indicate that CD decreases BNF-induced CYP1A1 protein expression and activity in the lung.

Quantitative exposure-response for silica dust and lung cancer in Vermont granite workers

BACKGROUND

Excess lung cancer mortality among the exposed Vermont granite workers has been reported. These studies were based on job and tenure surrogates, with the potential for misclassification and inability to evaluate quantitative exposure-response.

METHODS

Industrial hygiene data collected from 1924 to 1977 was analyzed in conjunction with mortality data to examine quantitative exposure-response for silica, lung cancer, and other lung diseases. A person-years analysis was undertaken by cumulative exposure group, including lagged and unlagged tabulations. Poisson models were fitted to untransformed and log transformed exposure.

RESULTS

The results indicated a clear relationship of lung cancer, tuberculosis, pneumoconiosis, non-malignant lung disease, and kidney cancer with cumulative exposure. An exposure to 0.05 mg/m(3) from age 20 to 64 was associated with a lifetime excess risk of lung cancer for white males of 27/1,000.

CONCLUSIONS

The results of this study of workers exposed almost exclusively to silica and no other major occupational confounding exposures indicate a clear exposure-response for lung cancer.

Update on respiratory disease from coal mine and silica dust

Coal mine and silica dust cause significant respiratory disease in spite of modern dust control regulations. Susceptible individuals in exposed populations may develop fibrosing lung disease, obstructive airways disease, including chronic bronchitis and emphysema, or lung cancer. A careful occupational history that elicits exposure to respiratory hazards is the cornerstone of an accurate diagnosis. Treatment involves removal from exposure, supportive care, pulmonary rehabilitation, and when disabling disease is present, assistance obtaining compensation.

A biomathematical model of particle clearance and retention in the lungs of coal miners. II. Evaluation of variability and uncertainty

The objective of this study is to investigate the sources of variability and uncertainty in a previously developed human lung dosimetry model. That three-compartment model describes the retention and clearance kinetics of respirable particles in the gas-exchange region of the lungs. It was calibrated using exposure histories and lung dust burden data in U.S. coal miners. A multivariate parameter estimation and optimization method was developed for fitting the dosimetry model to these human data. Models with various assumptions about overloading of alveolar clearance and interstitialization (sequestration) of particles were evaluated. Variability in the estimated clearance rate coefficients was assessed empirically by fitting the model to groups' and to each miner's data. Distributions of lung and lymph node particle burdens were computed at working lifetime exposures, using the variability in the estimated individual clearance rate coefficients. These findings confirm those of the earlier analysis; i.e., the best-fitting exposure-dose model to these data has substantial interstitialization/sequestration of particles and no dose-dependent decline in alveolar clearance. Among miners with different characteristics for smoking, disease, and race, the group median estimated alveolar clearance rate coefficients varied by a factor of approximately 4. Adjustment for these group differences provided some improvement in the dosimetry model fit to all miners (up to 25% reduction in MSE), although unexplained interindividual differences made up the largest source of variability. The predicted mean lung and lymph node particle burdens at age 75 after exposure to respirable coal mine dust at 2 mg/m(2) for a 45-year working lifetime were 12 g (5th and 95th percentiles, 3.0-26 g) and 1.9 g (0.26-5.3), respectively. This study provides quantitative information on variability in particle retention and clearance kinetics in humans. It is useful for risk assessment by providing estimated lung dust burdens associated with occupational exposure to respirable particles.

Nested case-control study of lung cancer among pulp and paper workers in relation to exposure to dusts

BACKGROUND

Numerous studies have indicated an increased risk of lung cancer in pulp and paper industry workers. In a 1990 survey, standardized mortality ratio (SMR) was found to be 122 (95% CI:96-153) for lung cancer in Polish male workers in the pulp and paper industry, and 166 (95% CI:95-270) among workers engaged in paper production.

METHODS

A nested case-control design within a cohort of pulp and paper workers was applied. Seventy-nine lung cancer cases and 237 "healthy" controls were selected from the cohort of 10,460 workers employed during the years 1968-1990, and observed until the end of 1995. Based on personnel files, occupational exposure was reconstructed by experts. Using a questionnaire, data on smoking habits were collected. ORs unadjusted and adjusted for smoking were calculated applying the model of conditional logistic regression.

RESULTS

Occupational exposure to inorganic dusts (kaolin, lime, cement, brick, grindstone) adjusted for smoking was a significant lung cancer risk factor, with a 4.0-fold risk (95% CI:1.3-12.6), and a dose-response by cumulative dose index. Among organic dusts only wood dust increased albeit insignificantly the risk for those exposed (adjusted for smoking OR = 2.1, 95% CI:0.9-4.9), but without dose-response relationship.

CONCLUSIONS

Exposure to occupational dust with relatively low content of silica, but at high concentrations may be considered as a factor increasing lung cancer risk. However, the observation made in this study should be viewed with caution as it was based on a small number of cases, and further evidence is needed to confirm or refute the authors' hypothesis.

Silicosis and coal workers' pneumoconiosis

Exposure to coal mine dust and/or crystalline silica results in pneumoconiosis with initiation and progression of pulmonary fibrosis. This review presents characteristics of simple and complicated coal workers' pneumoconiosis (CWP) as well as pathologic indices of acute and chronic silicosis by summarizing results of in vitro, animal, and human investigations. These results support four basic mechanisms in the etiology of CWP and silicosis: a) direct cytotoxicity of coal dust or silica, resulting in lung cell damage, release of lipases and proteases, and eventual lung scarring; b) activation of oxidant production by pulmonary phagocytes, which overwhelms the antioxidant defenses and leads to lipid peroxidation, protein nitrosation, cell injury, and lung scarring; c) activation of mediator release from alveolar macrophages and epithelial cells, which leads to recruitment of polymorphonuclear leukocytes and macrophages, resulting in the production of proinflammatory cytokines and reactive species and in further lung injury and scarring; d) secretion of growth factors from alveolar macrophages and epithelial cells, stimulating fibroblast proliferation and eventual scarring. Results of in vitro and animal studies provide a basis for proposing these mechanisms for the initiation and progression of pneumoconiosis. Data obtained from exposed workers lend support to these mechanisms.

Molecular epidemiological study of non-small-cell lung cancer from an environmentally polluted region of Poland

The p53 mutation spectrum can generate hypotheses linking carcinogen exposure to human cancer. Although it is well-documented that tobacco smoking is a major cause of lung cancer, the contribution of air pollution is less well-established. We determined the molecular and immunohistochemical changes (p53 gene mutations, p53 protein accumulation and WAF1 protein expression) and genetic polymorphisms of GSTM1, CYP1A1 and CYP2D6 genes in a case series of non-small-cell lung cancers from Silesia. This region of southern Poland is highly industrialized with considerable environmental pollution. More than 50% of lung cancers (90/164) contained p53 mutations and 75% showed the combined alteration of the p53 gene and protein accumulation. Males occupationally exposed to coal-derived substances showed a relatively high frequency of squamous and large-cell carcinomas, relatively frequent mutations in codon 298 of p53 and a low frequency of p53 immunohistochemically positive tumours. Codon 298 GAG-->TAG mutations have rarely been found in lung cancers in other populations. We found no correlation between WAF1 protein expression and mutations in the p53 gene or p53 protein accumulation. No statistically significant relationship was found between p53 mutations and GSTM1, CYP1A1, CYP2D6 genotypes. Never smokers with lung cancers from Silesia had a higher frequency of G:C-->T:A transversions than previously reported of the p53 mutation spectrum in never smokers (6/15 vs 4/34; P = 0.06 by chi2). These data are a tentative indication that occupational and environmental exposure to polycyclic aromatic hydrocarbons, such as benzo(a)pyrene, in polluted air contributes to the molecular pathogenesis of lung cancer in never smokers.

Mortality of Dutch coal miners in relation to pneumoconiosis, chronic obstructive pulmonary disease, and lung function

OBJECTIVES

To analyse the mortality patterns of former Dutch coal miners, focusing on coal workers' pneumoconiosis (CWP) and chronic obstructive pulmonary diseases (COPD) in relation to pre-existing impairment of lung function.

METHODS

3790 selected miners, medically examined between 1952 and 1963, were followed up to the end of 1991 with the municipal population registries and the causes of death from the death certificates were ascertained and converted to the codes from the ninth revision of the international classification of diseases (ICD-9). Mortality comparisons were made with the male population in The Netherlands, resulting in standardised mortality ratios (SMRs). 3367 miners had radiological manifestation of CWP at medical examinations.

RESULTS

80% of the miners died during the follow up period. Excess mortalities from CWP (SMR 4523) and COPD (SMR 179) were found. Coal miners without CWP also showed an increased mortality from COPD (SMR 2913). A diminished lung function (forced expiratory volume in one second (FEV1), or FEV1/FVC (forced vital capacity) ratio) at medical examination resulted in a significantly increased SMR for COPD (322 and 212 respectively) whereas normal lung function yielded expected mortalities from COPD. A positive correlation also emerged between diminished lung function and the SMR due to CWP. The body mass index (BMI) at the moment of medical examination was correlated with the risk of dying of COPD and CWP: a decreasing BMI resulting in an increased SMR.

CONCLUSIONS

Not only infectious diseases and CWP but also COPD is an important cause of occupational mortality in miners with extensive exposure to coal mine dust. No obvious connection between pre-existing CWP and the COPD mortality exists. Impaired FEV1 and FEV1/FVC ratios are predictors of an increased risk of COPD death. The BMI seems to indicate the severity of the COPD, resulting in premature death.