Presence of Stable Coal Radicals in Autopsied Coal Miners' Lungs and Its Possible Correlation to Coal Workers' Pneumoconiosis

Stable coal radicals (SCRs) were detected by electron spin resonance (ESR) spectroscopy in the lung tissue of autopsied coal miners. The SCR concentrations were measured in the lung tissues from 98 coal miners with and without (a) coal workers' pneumoconiosis (CWP), (b) cancer, and (c) a history of cigarette smoking. Concentrations of SCRs were also determined in the lungs of nonminer controls. The SCR concentration was related to longer mining tenure, CWP disease severity, lung cancer, and cigarette smoking. The mean concentration of SCRs in the lung tissues of miners with 30 ± 1.4 y of coal mining exposure was 5.3 ± 1.3 × 10¹⁷ spins/g versus controls who had a nondetectable level (< 10¹⁵ spins/g). An increase in disease severity was accompanied by a progressive increase in SCR concentration. A SCR concentration of 4.8 ± 0.7 × 10¹⁷ spins/g was found for simple CWP (with moderate coal macules) versus 7.8 ± 4.6 spins/g lung tissue for complicated CWP (with progressive massive fibrosis). Significantly higher (i.e., 10 × 10¹⁷) concentrations of SCR in the coal miners' lung tissues were associated with an exposure history in the anthracite regions of northeastern Pennsylvania. These results indicate a possible role for SCRs in the disease process. Furthermore, ESR appears to be an adequate methodology for the quantitation of coal dust retained in the lung and for distinguishing exposures to anthracite and/or bituminous coal.     

Detection of reactive free radicals in fresh coal mine dust and their implication for pulmonary injury

Freshly ground and aged anthracite and bituminous coal samples were investigated by electron spin resonance (ESR) spectroscopy to detect the presence, concentration and reactivity of free radicals. Freshly ground anthracite coal produced greater concentration of free radicals than the bituminous coal, and the radical reactivity was also greater for the anthracite. The reactivity of the newly produced free radicals in the anthracite dust correlated with the dust's toxicity. Furthermore, similar coal-based free radicals were detected in the lung tissue of autopsied coal miners, suggestive of persistent reactivity by the embedded coal dust leading to the progressive disease process. Results of the studies on the severity of coal workers' pneumoconiosis (CWP) and free radical concentration in lung tissue support this hypothesis.     

An investigation into the relationship between coal workers' pneumoconiosis and dust exposure in U.S. coal miners.

The National Study of Coal Workers' Pneumoconiosis (NSCWP) is a large, continuing epidemiologic study of the respiratory health of U.S. coal miners. By using information from the study, prevalence of coal workers' pneumoconiosis (CWP) was related to indexes of dust exposure obtained from research and compliance sampling data. Clear relationships between prevalences of both simple CWP and progressive massive fibrosis (PMF) and estimated dust exposure were seen. Additional effects independently associated with coal rank (% carbon) and age were also seen. Logistic model fitting indicated that between 2% and 12% of miners exposed to a 2-mg/m3 dust environment in bituminous coal mines would be expected to have Category 2 or greater CWP after a 40-yr working life; PMF would be expected for between 1.3% and 6.7%. The risks for anthracite miners appeared to be greater. There was a suggestion of a background level of abnormality, not associated with dust exposure, but increasing with age. Although there are certain weaknesses in the data used to derive these exposure estimates, the results are in general agreement with, but somewhat greater than, some recent findings for British coal miners.     

Pneumoconiosis and advanced occupational lung disease among surface coal miners--16 states, 2010-2011

Coal workers' pneumoconiosis (CWP) is a chronic occupational lung disease caused by long-term inhalation of dust, which triggers inflammation of the alveoli, eventually resulting in irreversible lung damage. CWP ranges in severity from simple to advanced; the most severe form is progressive massive fibrosis (PMF). Advanced CWP is debilitating and often fatal. To prevent CWP, the Coal Mine Health and Safety Act of 1969 established the current federal exposure limit for respirable dust in underground and surface coal mines. The Act also established a surveillance system for assessing prevalence of pneumoconiosis among underground coal miners, but this surveillance does not extend to surface coal miners. With enforcement of the exposure limit, the prevalence of CWP among underground coal miners declined from 11.2% during 1970-1974 to 2.0% during 1995-1999, before increasing unexpectedly in the last decade, particularly in Central Appalachia. Exposure to respirable dust is thought to be less in surface than underground coal miners. Although they comprise 48% of the coal mining workforce, surface coal miners have not been studied since 2002. To assess the prevalence, severity, and geographic distribution of pneumoconiosis among current surface coal miners, CDC obtained chest radiographs of 2,328 miners during 2010-2011 through the Coal Workers' Health Surveillance Program of the National Institute for Occupational Safety and Health (NIOSH). Forty-six (2.0%) of 2,257 miners with >1 year of surface mining experience had CWP, including 37 who had never worked underground. Twelve (0.5%) had PMF, including nine who had never worked underground. A high proportion of the radiographs suggested silicosis, a disease caused by inhalation of crystalline silica. Surface coal mine operators should monitor worker exposures closely to ensure that both respirable dust and silica are below recommended levels to prevent CWP. Clinicians should be aware of the risk for advanced pneumoconiosis among surface coal miners, in addition to underground coal miners, to facilitate prompt disease identification and intervention.     

CT和高分辨CT对煤工尘肺小阴影和阴影融合及肺气肿诊断的价值

目的 探讨CT和高分辨CT(HRCT)早期检测煤工尘肺小阴影、阴影融合与肺气肿的敏感性和准确性.方法 77例煤工尘肺患者、36例无尘肺煤工和37例健康非煤工接受多层螺旋CT机无间隔胸部容积扫描及HRCT扫描,对所获得的CT图像进行煤工尘肺小阴影密集度分级、平均肺密度值和肺气肿指数测定,并与其X线胸片诊断结果对照.结果 对77例煤工尘肺患者CT和HRCT诊断的尘肺小阴影密集度分级与X线胸片尘肺分期一致性较好(Kappa=0.771,P＜0.01).CT和HRCT诊断尘肺的敏感性达到98.70％,在X线胸片确诊的77例煤工尘肺患者中,CT和HRCT评估76例为煤工尘肺,可疑1例.CT和HRCT从36例X线胸片无尘肺煤工中检出8例(22.22％)达到小阴影密集度1级;从73例Ⅰ～Ⅱ期煤工尘肺患者中,检出26例(35.62％)阴影密集度≥3级,其中3级密集度阴影20例,4级密集度阴影6例;对4例X线胸片Ⅲ期煤工尘肺患者,CT和HRCT与X线胸片诊断结果相同.从113例煤工中,X线胸片检出肺气肿7例(6.19％),CT检出36例(31.86％).CT尘肺小阴影密集度1～2级组的CT平均肺密度值最高,明显高于健康对照组、无尘肺组和小阴影密集度4级组,差异有统计学意义(F1=-45.73、F2=-23.00和F3=57.72,P＜0.01或P＜0.05).结论 从多层螺旋CT获得的CT和HRCT影像,与X线胸片比较,对煤工尘肺小阴影、阴影融合与肺气肿识别的敏感性和准确性均较高,可为煤工尘肺及其并发症的早期诊断提供更先进的手段.     

Life Expectancy of Pennsylvania Coal Miners Compensated for Disability

From December 1965 through December 1967, 13,000 Pennsylvania coal miners were awarded compensation for complete disability due to coal workers’ pneumoconiosis (CWP). Standardized mortality ratios compare all deaths occurring in a sample of 4,004 of these men with deaths expected (1959 to 1961) of white men in Pennsylvania; similar ratios are shown for anthracite and bituminous miners by category and stage of CWP and, in some cases, according to whether the ratio of forced expiratory volume during the first second of a forced exhalation after maximum inhalation to vital capacity (FEV₁/FVC) was greater or less than 55%. Excess deaths were found primarily in subjects with a reduced ventilatory capacity, and secondarily with complicated CWP of stage C or, for anthracite miners, stage B. No excess deaths were found for simple CWP or stage A complicated with FEV₁/FVC more than 55%.     

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.     

Advanced cases of coal workers' pneumoconiosis--two counties, Virginia, 2006

This report describes 11 newly identified cases of advanced coal workers' pneumoconiosis (CWP), including progressive massive fibrosis (PMF), in working coal miners from Lee and Wise counties in southwestern Virginia. PMF is a disabling and potentially fatal form of CWP, an occupational lung disease caused by the inhalation of coal mine dust. The continuing occurrence of advanced forms of CWP emphasizes the importance of comprehensive measures to control coal mine dust effectively and reduce the potential for inhalation exposures in coal mining.     

煤尘职业接触者和早期煤工尘肺BAL液中表面活性物质研究

目的 探讨煤尘职业接触者和早期煤工尘肺患者BAL液中表面活性物质含量改变特点及其意义。方法 采煤工人23人,按X线诊断煤工尘肺期别分为0期（煤尘接触者）组7人、0^ 组8人和I期组8人,并取健康农民7人为对照组。经纤维支气管肺泡灌洗（BAL）收集BAL液,测定表面活性蛋白A(SP－A）和磷脂（PL）及其组分含量。结果 0期组BAL液中SP－A含量、SP－A／PL和PG／PI明显高于对照组（P＜0．01）,且随煤工尘肺期别增加而有降低趋势。结论 BAL液中SP－A含量、SP－A／PL和PG／PI升高可能是煤尘接触的早期效应指标。     

Does Coal Workers Pneumoconiosis Predict to Lung Cancer? Some Evidence from a Case-Control Study

Previous reports on the relationship between coal workers' pneumoconiosis(CWP) and lung cancer mortality have shown widely differingresults. Concern has centred especially around whether or notthere is an aggregation of complicated CWP, or Progressive MassiveFibrosis (PMF), with lung cancer. This paper evaluates, amongUS coal miners, the CWP-lung cancer relationship by computingthe lung cancer mortality risk of simple and complicated CWPas well as the interactions with cigarette smoking and ventilatoryfunction. Two case-control studies based on 317 white male lungcancer mortality cases are presented. A one-to-one matched-casedesign allows examination of the lung cancer mortality riskof CWP and cigarette smoking. A two-to-one matched-case designcontrols on smoking status. Based upon these data, no evidenceof a CWP-lung cancer risk was found, although the expected increasedrisk for lung cancer mortality in cigarette smokers was observed.No relationship was found between PMF and lung cancer mortalityrisk. Finally, no evidence was found of interaction effectsbetween cigarette smoking or ventilatory function and CWP aspredictors of lung cancer mortality risk. Requests for reprints should be addressed to: R. G. Ames, Appalachian Laboratory, US National Institute for Occupational Safety and Health, 944 Chestnut Ridge Road, Morgantown, West Virginia 26505, USA.     

煤工尘肺患者肺通气功能障碍的影响因素

目的分析煤工尘肺(CWP)患者肺功能障碍的可能影响因素。方法采用病例-对照研究,分别选择141名CWP患者为病例组,200名非CWP的接尘矿工为接尘组,75名非从事接尘作业的健康者为对照组,均为男性。对研究对象调查接尘工种、接尘工龄、肺部疾病、吸烟及职业卫生防护情况等,并测定肺通气功能,根据对照人群特征建立相应肺功能指标的预计回归方程计算预计值,以各指标的实测值和预计值之比对肺功能障碍进行分型,采用非条件Logistic回归模型对影响因素进行分析。结果病例组及接尘组FVC、FEV_(1.0)实测值及FVC、FEV_(1.0)实测值与其预测值的比值均明显低于对照组,差异有统计学意义(P<0.05);随煤工尘肺分级增加,限制性和混合性通气功能障碍发生率明显增高(x~2=67.46,51.19,P<0.05);佩戴口罩情况、CWP分期、吸烟程度、接尘工龄等指标均被选入非条件Logistic回归模型。结论影响煤工尘肺患者肺功能障碍的因素可能有CWP晋级、是否坚持佩戴口罩、吸烟、接尘工龄等。     

Gallium-67 citrate imaging in underground coal miners

Twenty-two underground coal workers with 27 or more years of coal dust exposure were studied with gallium-67 citrate (Ga-67) imaging. Radiographic evidence of coal workers pneumoconiosis (CWP) was present in 12 subjects. The Ga-67 scan was abnormal in 11 of 12 with, and 9 of 10 without, CWP. The Ga-67 uptake index was significantly correlated with total dust exposure (p less than 0.01) and approached significant correlation with the radiographic profusion of the nodules (0.10 greater than p greater than 0.05). There was no correlation between Ga-67 uptake and spirometric function, which was normal in this group of patients; furthermore, increased lung uptake of gallium did not indicate a poor prognosis in subjects no longer exposed to coal dust. While coal dust exposure may be associated with positive Ga-67 lung scan in coal miners with many years of coal dust exposure, the scan provided no information not already available from a careful exposure history and a chest radiograph. Since Ga-67 scanning is a relatively expensive procedure we would recommend that its use in subjects with asymptomatic CWP be limited to an investigative role and not be made part of a routine evaluation.     

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.     

Erythrocyte antioxidant enzyme activities in coal miners from three French regions

This study investigated whether differences in the prevalence and severity of coal workers' pneumoconiosis (CWP) between three coal mines could be related to differences in oxidative stress exposure as evaluated in vivo through red-blood-cell antioxidant enzyme activities. Blood samples were obtained from 229 miners selected according to their occupation and their pneumoconiotic status. The following biomarkers were evaluated: erythrocyte catalase, Cu²⁺/Zn²⁺ superoxide dismutase (Cu²⁺/Zn²⁺ SOD), and glutathione peroxidase activities. Antioxidant enzyme activities did not differ significantly between the group of surface workers in Lorraine and the group of underground miners without CWP in Lorraine and in the other coal mines. Erythrocyte Cu²⁺/Zn²⁺ SOD activity was slightly decreased in the group of active underground miners with simple pneumoconiosis as compared with the group of miners without CWP in Nord/Pas-de-Calais. No effect was seen between retired miners at different stages of CWP. Our findings indicate that differences in the prevalence and severity of CWP do not seem to be related to various oxidative activities of coal dust particles, at least as reflected by measurements of antioxidant enzyme activities in circulating erythrocytes in this study. Received: 3 March 1997 / Accepted: 14 October 1997     

Relations between occupational exposure to coal mine dusts,erythrocyte catalase and Cu++/Zn++ superoxide dismutase activities,and the severity of coal workers' pneumoconiosis

OBJECTIVES: To better understand the relations between occupational exposure, blood antioxidant enzyme activities, total plasma antioxidant concentration, and the severity of coal workers'' pneumoconiosis (CWP). METHODS: Blood samples were obtained from miners without CWP exposed to low dust concentrations for > or = 4 years at the time of the study (n = 105), or exposed to high dust concentrations for > or = 14 years at the time of the study (n = 58), and from retired miners with CWP (n = 19). Miners without CWP were classified into three subgroups according to their estimated cumulative exposure to dust. Chest x ray films were obtained for each miner. Miners were classified in five subgroups according to their International Labour Organisation (ILO) profusion grades. Univariate tests were completed by multiple linear regression analyses. RESULTS: The estimated cumulative exposure to dust was strongly positively related to erythrocyte catalase activity and strongly negatively related to Cu++/Zn++ SOD activity only in miners exposed to high dust concentrations for > or = 14 years at the time of the study (F tests p = 0.006 and p = 0.004 respectively). Moreover, catalase activity was strongly related to the severity of CWP expressed as five subgroups of ILO profusion grades (F test p = 0.003); the greatest difference in the mean values was found between the group of 1/1 to 1/2 ILO profusion grades and the group of 2/1 to 3/3 ILO profusion grades. CONCLUSION: These results are in good agreement with the hypothesis that production of reactive oxygen species may be an important event in the exposure to coal mine dusts and the severity of CWP. Erythrocyte catalase and Cu++/Zn++ SOD activities are more closely related to recent exposure to high dust concentrations than to cumulative exposure, and could be considered as biological markers of exposure rather than as markers of early adverse biological effect.       

Basic mechanisms leading to focal emphysema in coal workers' pneumoconiosis

Coal miners develop focal emphysema characterized by dilatation of second- and third-order respiratory bronchioles with coal mine dust-laden macrophages infiltrating the wall. A reticulin network with small amounts of collagen and atrophy of smooth muscle occurs. To evaluate the mechanisms of lung injury associated with this lesion, 17 long-term non- or ex-smoking West Virginia underground coal miners underwent bronchoalveolar lavage (BAL) and were compared to healthy nonsmoker and smoker controls. The coal miners had evidence of an alveolar macrophage-neutrophil alveolitis with a significant increase in neutrophils/microliter of epithelial lining fluid and an increased gallium lung scan index (206 +/- 26 units). Alveolar macrophages lavaged from coal miners spontaneously released exaggerated amounts of superoxide anion and hydrogen peroxide in vitro compared to nonsmoking controls. Coal workers had significantly elevated levels of neutrophil elastase in BAL fluid complexed with alpha 1-antitrypsin (P less than 0.01) and normal levels of alpha 1-antitrypsin. An accumulation of activated, dust-laden inflammatory cells with increased release of oxidants and elastase may contribute to the development of focal emphysema identified at postmortem in miners with coal workers' pneumoconiosis.     

Pneumoconiosis prevalence among working coal miners examined in federal chest radiograph surveillance programs--United States, 1996-2002

Coal workers' pneumoconiosis (CWP) is a chronic lung disease caused by inhalation of coal mine dust. To characterize the prevalence of CWP, the National Institute for Occupational Safety and Health (NIOSH) analyzed recent radiographic information from the U.S. National Coal Workers' X-ray Surveillance Program (CWXSP). Established under the Federal Coal Mine Health and Safety Act of 1969, CWXSP is administered by NIOSH under federal regulations. NIOSH is responsible for approving coal miner examination plans, submitted approximately every 5 years by companies that operate underground coal mines. This report summarizes the results of the analysis, which indicate that the overall prevalence of CWP among participating miners continues to decline; however, new cases are occurring among miners who have worked exclusively under current dust exposure limits. An evaluation of the mining conditions that have resulted in these cases is underway.     

Respiratory outcomes among South African coal miners at autopsy

BACKGROUND: Studies of dose-response relationships between respiratory outcomes at autopsy and coal dust exposure are limited. The Pathology Automation System (PATHAUT) database of South African miners, is one of the largest autopsy databases of occupational lung disease. This study described the prevalence of respiratory outcomes among South African coal miners at autopsy, and determined whether dose response relationships existed between emphysema and exposure. METHODS: Autopsies conducted from 1975 to 1997 on coal miners with exclusive coal mining exposure and having exposure duration information (n = 3,167) were analyzed from PATHAUT. Logistic regression was used to determine relationships between exposure and outcomes, controlling for race, smoking and age on a subset for whom smoking history was available (n = 725). RESULTS: The mean duration of exposure was 11.0 years. Most were black miners (75.3%) with significant differences in the mean ages of black and white miners (37.9 and 55.3 years, respectively). Only 22.9% of cases had information on smoking. The prevalence of silicosis, tuberculosis (TB), coal workers' pneumoconiosis (CWP), and moderate and marked emphysema were 10.7%, 5.2%, 7.3%, and 6.4%, respectively. All diseases, except TB, were associated with exposure duration. Black miners had 8.3 and 1.2 fold greater risks for TB and CWP, respectively, than white miners. White miners had an increased risk of 1.4 and 5.4 for silicosis and moderate to marked emphysema, respectively. In models unadjusted for age, and including smoking, moderate to marked emphysema was strongly associated with exposure duration (OR = 3.4; 95% CI = 1.9-5.9 for highest tercile of exposure duration). Exposure-related risk estimates were reduced when age was introduced into the model. However, age and duration of exposure were highly correlated, (r = 0.68) suggesting a dilution of the exposure effect by age. CONCLUSIONS: There were significant dose related associations of disease, including emphysema, with coal dust exposure.     

Identification and classification of high risk groups for Coal Workers' Pneumoconiosis using an artificial neural network based on occupational histories: a retrospective cohort study

Background  

Coal workers' pneumoconiosis (CWP) is a preventable, but not fully curable occupational lung disease. More and more coal miners are likely to be at risk of developing CWP owing to an increase in coal production and utilization, especially in developing countries. Coal miners with different occupational categories and durations of dust exposure may be at different levels of risk for CWP. It is necessary to identify and classify different levels of risk for CWP in coal miners with different work histories. In this way, we can recommend different intervals for medical examinations according to different levels of risk for CWP. Our findings may provide a basis for further emending the measures of CWP prevention and control.     

Oxidative DNA damage in peripheral blood lymphocytes of coal workers

Reactive oxygen species are important mediators of both mineral dust-induced (malignant) lung disease and in vitro DNA damage. Therefore, we studied in vivo oxidative DNA damage in coal workers who had been chronically exposed to silica-containing dust. In peripheral blood lymphocytes of 38 retired coal miners (eight with coal workers pneumoconiosis, 30 references) and 24 age-matched, non-dust-exposed controls 7-hydro-8-oxo-2-deoxyguanosine (8-oxodG) was determined by reversed phase high-performance liquid chromatography with electrochemical detection. The ratio of 8-oxodG residues to deoxyguanosine (dG) was related to individual cumulative dust exposure estimates and pneumoconiotic stage as established by chest radiography. The ratio of 8-oxodG to dG(x 10^–5) in lymphocytes did not differ between miners with coal workers' pneumoconiosis (2.61 ± 0.44) and miners without coal workers' pneumoconiosis (2.96 ± 1.86). However, oxidative DNA damage in all miners was higher than in the non-dust-exposed controls (1.67 ± 1.31). 8-oxodG/dG ratio was not related to individual cumulative coal dust exposure, age or smoking (pack years) when evaluated by multiple linear regression. We suggest that oxidative damage to the DNA of peripheral blood lymphocytes may be introduced by increased oxidative stress responses in subjects chronically exposed to mineral dusts. Whether this is an important pathway in the suggested carcinogenicity of silica is still an open question.