A survey of the respiratory health of silica-exposed gemstone workers in Hong Kong

Occupational COPD-The most under-recognized occupational lung disease?

Chronic obstructive pulmonary disease (COPD) is caused by exposure to noxious particles and gases. Smoking is the main risk factor, but other factors are also associated with COPD. Occupational exposure to vapours, gases, dusts and fumes contributes to the development and progression of COPD, accounting for a population attributable fraction of 14%. Workplace pollutants, in particular inorganic dust, can initiate airway damage and inflammation, which are the hallmarks of COPD pathogenesis. Occupational COPD is still underdiagnosed, mainly due to the challenges of assessing the occupational component of the disease in clinical settings, especially if other risk factors are present. There is a need for specific education and training for clinicians, and research with a focus on evaluating the role of occupational exposure in causing COPD. Early diagnosis and identification of occupational causes is very important to prevent further decline in lung function and to reduce the health and socio-economic burden of COPD. Establishing details of the occupational history by general practitioners or respiratory physicians could help to define the occupational burden of COPD for individual patients, providing the first useful interventions (smoking cessation, best therapeutic management, etc.). Once patients are diagnosed with occupational COPD, there is a wide international variation in access to specialist occupational medicine and public health services, along with limitations in workplace and income support. Therefore, a strong collaboration between primary care physicians, respiratory physicians and occupational medicine specialists is desirable to help manage COPD patients' health and social issues.

Lung Function and Respiratory Health of Populations Living Close to Quarry Sites in Palestine: A Cross-Sectional Study

Environmental exposure to dust from quarrying activities could pose health dangers to the population living nearby. This study aimed to investigate the health effects of dust exposure on people living close to quarry sites and compared them with those who live far from the quarry sites. A cross-sectional comparative study was conducted among 79 exposed participants, who lived less than 500 m away from the quarry sites, and 79 control participants who lived more than 500 m away. All participants answered a questionnaire on dust exposure at home and health effects, as well as performed a lung function test in which both reported and measured health effects were investigated. People who live in close proximity to the quarry sites reported exposure to dust at home (98%), land destruction (85%), plant leaves covered with dust (97%), and an inability to grow crops (92%). The exposed group reported significantly higher eye and nasal allergy (22% vs. 3%), eye soreness (18% vs. 1%), and dryness (17% vs. 3%), chest tightness (9% vs. 1%), and chronic cough (11% vs. 0%) compared to the control group. Lung function parameters were significantly lower among the exposed group compared to the control group; mean forced vital capacity (FVC) was 3.35 L vs. 3.71 L (p = 0.001), mean forced expiratory volume in the first second (FEV₁) was 2.78 L vs. 3.17 L (p = 0.001). Higher levels of airway restriction were found among the exposed group. Among the exposed group, lung function parameters worsened with the increasing closeness of home to the quarry site. This study demonstrates the negative health effects of environmental dust exposure among two communities living near quarry sites in Palestine. The results highlight the importance of developing and strictly enforcing rules and regulations in Palestine to protect population health.

Smoking cessation sharply reduced lung cancer mortality in a historical cohort of 3185 Chinese silicotic workers from 1981 to 2014

BACKGROUND

Population-based studies showed an over 50% decrease in lung cancer risk after quitting smoking for 5-6 years, but the beneficial effect in silicotics remains unknown. We aimed to rectify this knowledge gap using a large historical cohort of 3185 Chinese silicotics since 1981 and followed-up till 2014.

METHODS

Baseline information on workers' socio-demographics, smoking habits, occupational history, and medical history was collected. Smoking status was reassessed during follow-up. Multiple Cox proportional hazards model was performed to evaluate the impact of smoking cessation on lung cancer mortality.

RESULTS

Overall, 1942 deaths occurred and 188 lung cancer deaths were identified. Compared with never quitters, silicotics who were new quitters had almost halved their lung cancer risk [hazard ratio (HR) = 0.51, 95%CI: 0.34-0.76], while persistent quitters had a 53% risk reduction (HR = 0.47, 95%CI: 0.33-0.66). Lung cancer mortality approximately halved after quitting smoking for 10 years. While the risk kept decreasing with years since cessation, it did not reverse back to that of never smokers. Persistent quitters with small opacities tended to have higher beneficial effects than those with large opacities.

CONCLUSIONS

Smoking cessation for 10 years halved lung cancer mortality among silicotics, while the beneficial effect was prominent for patients with small opacities.

Silicosis prevalence and risk factors in semi-precious stone mining in Brazil

BACKGROUND

Underground mining generates large amounts of dust and exposes workers to silica. This study aims to determine the prevalence and predictor factors for the development of silicosis among semi-precious-stone mineworkers in southern Brazil working in a self-administered cooperative.

METHODS

In a cross-sectional study of 348 current workers and retirees, demographic data, medical, and occupational history were collected through an interview performed by a nurse and medical record review. Risk factor associations were studied by Poisson multivariate regression.

RESULTS

The overall prevalence of silicosis was 37%, while in current miners it was 28%. Several risk factors for silicosis were identified in the univariate analysis. Inadequate ventilation in the underground galleries combined with dry drilling, duration of silica exposure, and (inversely) education remained significant in the multivariate analysis (P < 0.05).

CONCLUSION

This study is unusual in studying semi-precious stone mineworkers in a self-administered worker cooperative with limited resources. The prevalence of silicosis was very high. A number of recommendations are made-including technical support for worker cooperatives, surveillance of silica exposure and silicosis, exposure reduction measures, and benefits allowing impaired miners to leave the industry.

Silica exposure and disease in semi-precious stone craftsmen, Minas Gerais, Brazil

BACKGROUND

Brazil is an exporter of precious stones and craftsmen often work in poor conditions. We assessed silica-related diseases among crystal craftsmen and the complexity of its control.

METHODS

Case-series including 118 subjects evaluated from 2006 to 2015, based on medical interviews, chest X-rays, spirometry, and respirable silica samples.

RESULTS

Median age and length of exposure were 32 and 13 years, respectively. Silicosis, with 1/0 as a threshold, was diagnosed radiologically in 57 individuals (48.3%). Respirable silica concentrations were 0.9-29.3 times greater than the Brazilian occupational exposure limit. A Receiver Operating Characteristic (ROC) curve with the same diagnosis threshold showed best discrimination at a cut point of 12.5 years of exposure, corresponding to 4.85 mg-y/m³ of cumulative silica exposure. There was a significant decline in FEV₁ across radiological and cumulative silica exposure categories. Eleven individuals (9.3%) had mycobacterial diseases at baseline or follow-up.

CONCLUSION

Crystal craftsmen continue to suffer from silicosis, lung function impairment, comorbidity, and death due to silicosis. To date collective protection in some work sheds has not diminished silica levels. Long-term follow-up is needed to evaluate further improvements in preventive measures. Am. J. Ind. Med. 60:239-247, 2017. © 2017 Wiley Periodicals, Inc.

A silicose e o perfil dos lapidários de pedras semipreciosas em Joaquim Felício, Minas Gerais, Brasil

Para conhecer a prevalência de silicose, descrever os perfis clínico, epidemiológico e ocupacional, e estudar as condições de trabalho das oficinas de lapidação, realizou-se estudo transversal de setenta lapidários de pedras semipreciosas de Joaquim Felício, Minas Gerais, Brasil, de abril a dezembro de 2002. Utilizaram-se história ocupacional com questionário respiratório, radiografia de tórax e espirometria. A prevalência de silicose foi de 7,1%. Todos eram do sexo masculino, com média de idade de 21,5 anos e tempo médio de exposição à sílica de 7,1 anos. Todos pertenciam ao setor da economia informal e trabalhavam em oficinas pequenas e rudimentares, sendo o maquinário improvisado e havendo maciça exposição à sílica. Segundo a Classificação Radiológica da Organização Internacional do Trabalho, dos cinco casos de silicose, quatro foram classificados na categoria 1, e um na 3. A silicose em lapidários constitui um sério problema de saúde pública que requer esforços para minimização do risco de adoecimento, por meio da ação de equipes multidisciplinares provenientes de instituições governamentais e não-governamentais, com inserção ativa dos trabalhadores.

Mortality from non-malignant respiratory diseases among people with silicosis in Hong Kong: exposure-response analyses for exposure to silica dust

OBJECTIVES

To examine the exposure-response relationships between various indices of exposure to silica dust and the mortality from non-malignant respiratory diseases (NMRDs) or chronic obstructive pulmonary diseases (COPDs) among a cohort of workers with silicosis in Hong Kong.

METHODS

The concentrations of respirable silica dust were assigned to each industry and job task according to historical industrial hygiene measurements documented previously in Hong Kong. Exposure indices included cumulative dust exposure (CDE) and mean dust concentration (MDC). Penalised smoothing spline models were used as a preliminary step to detect outliers and guide further analyses. Multiple Cox's proportional hazard models were used to estimate the dust effects on the risk of mortality from NMRDs or COPDs after truncating the highest exposures.

RESULTS

371 of the 853 (43.49%) deaths occurring among 2789 workers with silicosis during 1981-99 were from NMRDs, and 101 (27.22%) NMRDs were COPDs. Multiple Cox's proportional hazard models showed that CDE (p = 0.009) and MDC (p<0.001) were significantly associated only with NMRD mortality. Subgroup analysis showed that deaths from NMRDs (p<0.01) and COPDs (p<0.05) were significantly associated with both CDE and MDC among underground caisson workers and among those ever employed in other occupations with high exposure to silica dust. No exposure-response relationship was observed for surface construction workers with low exposures. A clear upward trend for both NMRDs and COPDs mortality was found with increasing severity of radiological silicosis.

CONCLUSION

This study documented an exposure-response relationship between exposure to silica dust and the risk of death from NMRDs or COPDs among workers with silicosis, except for surface construction workers with low exposures. The risk of mortality from NMRDs increased significantly with the progression of International Labor Organization categories, independent of dust effects.

High-resolution CT in silicosis: correlation with radiographic findings and functional impairment

OBJECTIVE

To assess high-resolution computed tomography (HRCT) findings in silicosis and to better define the role of HRCT in early detection of parenchymal abnormalities in silica-exposed workers.

METHODS

Forty-one stone carvers were evaluated with chest radiographs (CR), HRCT, and pulmonary function tests (PFT). Inter-reader agreement was calculated using the kappa statistic (k). Correlation between radiographic and HRCT profusion scores and PFT was assessed using the Spearman correlation coefficient.

RESULTS

The most common HRCT findings were branching centrilobular structures, seen in 28/41 workers (68.3%). Nodules consistent with silicosis were detected in 53.7% workers on CR and in 56.1% workers on HRCT. Inter-reader agreement for diagnosis of silicosis was better on HRCT (k = 0.84) than on CR (k = 0.54). Small opacity profusion on HRCT correlated inversely with total lung capacity and FVC%.

CONCLUSION

Profusion of opacities on HRCT correlates with functional impairment. The presence of branching centrilobular structures may be helpful in early recognition of silicosis.

High prevalence of silicosis among stone carvers in Brazil

BACKGROUND

In the city of Petrópolis, Brazil, artisans carve souvenirs from a variety of silica-containing minerals. The finding of pulmonary massive fibrosis in one of the workers motivated an investigation of the prevalence of silicosis in this group.

METHODS

Between January 2000 and June 2002, a cross-sectional study was performed. We obtained clinical and occupational histories, spirometry, lung volumes, and carbon monoxide diffusion capacity measurements. Chest radiographs and high-resolution computed tomographies (HRCT) were evaluated. Personal air samples were analyzed.

RESULTS

Forty-two stone carvers were examined. The prevalence of silicosis was 53.7%. HRCT better characterized silicotic lesions compared to chest radiographs. Early coalescence of small opacities was associated with lung function impairment. The concentration of dust exceeded permissible limits in 91% of the workplaces.

CONCLUSIONS

Exposure to high levels of silica dust was associated with an increased prevalence of silicosis among stone carvers. Am. J. Ind. Med. 45:194-201, 2004.

Silicosis in 76 men: qualitative and quantitative CT evaluation--clinical-radiologic correlation study

PURPOSE

To use qualitative and quantitative computed tomography (CT) to test the hypothesis that impaired lung function with silicosis is due to progressive massive fibrosis (PMF) and associated emphysema.

MATERIALS AND METHODS

Seventy-six men with silicosis underwent volumetric and thin-section CT of the thorax. Lung function, Borg scale dyspnea grade, silica exposure duration, and cigarette consumption were determined. Nodular profusion (NP) at chest radiography was graded according to the International Labor Organization radiographic classification system; NP and PMF at CT were visually graded by using five-point (ie, grades 0-4) and four-point (grades 0-3) scales, respectively. Emphysema and NP, which together are defined as the NP index, were quantified by using attenuation threshold values of less than -950 HU and greater than -100 HU, respectively. Mean lung attenuation was also determined. Relationships among the CT, chest radiographic, and clinical parameters were analyzed by using Spearman correlation.

RESULTS

NP at chest radiography correlated (r > 0.50) with all CT parameters of nodularity. CT PMF had the highest correlation with emphysema (r = 0.58, P <.001). NP at chest radiography and all CT parameters were inversely related to lung function. At multiple regression analysis, PMF and emphysema index (both at CT) were significant determinants of forced expiratory volume in 1 second (FEV1) (P =.006 and.03, respectively) and FEV1 to forced vital capacity (FVC) ratio (P =.007 and.02, respectively). Mean lung attenuation remained related to FVC (P =.03), diffusing capacity of lung for carbon monoxide (P =.04), and Borg scale grade (P =.01). Cigarette consumption and silica exposure duration had no independent effects on lung function.

CONCLUSION

Qualitative and quantitative CT parameters can be used as indirect measures of functional impairment in silicosis. PMF and emphysema are independently related to airflow obstruction, whereas mean lung attenuation is related to clinical dyspnea and reduced lung volume.

Pneumoconiosis among workers in a Vietnamese refractory brick facility

BACKGROUND

Vietnam is a rapidly industrializing country with increasing needs for building materials, including refractory bricks. The manufacture of refractory bricks results in high levels of free silica, a recognized occupational hazard.

METHODS

A cross-sectional survey was conducted among 158 employees using a respiratory symptom questionnaire and ILO classification of radiographs for pneumoconiosis.

RESULTS

The prevalence of radiographic silicosis (ILO category 1/0 and greater) was 10% in all workers with evidence of a dose-response gradient. Pneumoconiosis prevalence increased from 0% in workers employed < 10 years at the plant to 18% for workers employed > 20 years (trend test P = 0.01 for each year increment after adjusting for gender and tobacco use).

CONCLUSIONS

Workers in this plant demonstrate a consistent pattern of radiographic evidence of pneumoconiosis, which appears to be related to duration of work. Future studies should assess exposure control measures that are appropriate to countries undergoing rapid industrialization such as Vietnam.

Nitrogen dioxide exposure from domestic gas cooking and airway response in asthmatic women

BACKGROUND

Previous studies have not found a consistent association between exposure to domestic cooking using gas appliances and exacerbation of asthma. We investigated the immediate airflow response to acute exposure from single episodes of gas cooking, and peak airflow variability from continued exposure to repeated episodes of gas cooking in a group of non-smoking asthmatic women.

METHODS

Sixteen adult non-smoking women with mild to severe persistent asthma were studied. The acute short term level of nitrogen dioxide (NO2) during gas cooking episodes and the mean exposure to NO2 from repeated gas cooking episodes were measured over a 2 week period, as well as proxy measures of frequency of cooking on each day and the length of time spent cooking each day. Their asthma status was monitored using peak expiratory flow rates (PEFR) before and after cooking, 2 week self-recorded serial readings of PEFR, respiratory symptom severity score, and use of rescue bronchodilators for acute asthma attacks.

RESULTS

Cooking was significantly associated with an immediate mean fall in PEFR of 3.4% (p=0.015, paired t test). The acute short term NO2 level during cooking was significantly correlated with the fall in PEFR (r=–0.579; p=0.019). The frequency of cooking over a 2 week period was positively correlated with the mean exposure to NO2(r=0.529; p=0.042). Continued exposure to NO2 over a 2 week period was associated significantly with increased frequency of rescue bronchodilator usage for asthma attacks (r=0.597; p=0.031). However, it was negatively associated with PEFR variability (r=–0.512; p=0.051) and respiratory symptom severity score (r= –0.567; p=0.043), probably due to the masking effects of bronchodilator treatment.

CONCLUSIONS

Acute short term exposure to NO2 from single episodes of gas cooking is associated with immediate airflow limitation. Continued exposure from repeated episodes of gas cooking in asthmatic women is associated with greater use of rescue bronchodilators.

Nitrogen dioxide exposure from domestic gas cooking and airway response in asthmatic women

BACKGROUND

Previous studies have not found a consistent association between exposure to domestic cooking using gas appliances and exacerbation of asthma. We investigated the immediate airflow response to acute exposure from single episodes of gas cooking, and peak airflow variability from continued exposure to repeated episodes of gas cooking in a group of non-smoking asthmatic women.

METHODS

Sixteen adult non-smoking women with mild to severe persistent asthma were studied. The acute short term level of nitrogen dioxide (NO2) during gas cooking episodes and the mean exposure to NO2 from repeated gas cooking episodes were measured over a 2 week period, as well as proxy measures of frequency of cooking on each day and the length of time spent cooking each day. Their asthma status was monitored using peak expiratory flow rates (PEFR) before and after cooking, 2 week self-recorded serial readings of PEFR, respiratory symptom severity score, and use of rescue bronchodilators for acute asthma attacks.

RESULTS

Cooking was significantly associated with an immediate mean fall in PEFR of 3.4% (p=0.015, paired t test). The acute short term NO2 level during cooking was significantly correlated with the fall in PEFR (r=-0.579; p=0.019). The frequency of cooking over a 2 week period was positively correlated with the mean exposure to NO2 (r=0.529; p=0.042). Continued exposure to NO2 over a 2 week period was associated significantly with increased frequency of rescue bronchodilator usage for asthma attacks (r=0.597; p=0.031). However, it was negatively associated with PEFR variability (r=-0.512; p=0.051) and respiratory symptom severity score (r= -0.567; p=0.043), probably due to the masking effects of bronchodilator treatment.

CONCLUSIONS

Acute short term exposure to NO2 from single episodes of gas cooking is associated with immediate airflow limitation. Continued exposure from repeated episodes of gas cooking in asthmatic women is associated with greater use of rescue bronchodilators.

Biochemical indicators of occupational health hazards in Nkalagu cement industry workers, Nigeria

Routine diagnostic tests for some organ-system functions were adopted as biochemical probes in health screening of cement milling workers. Thirty-five volunteers from the Nkalagu cement industry, Nigeria were screened. Out of 14 biochemical parameters studied, raised levels of serum bicarbonates (HCO-), aspartic transaminase (AST) and alanine transaminase (ALT) were observed among cement milling workers compared with a control population. Elevated bicarbonate values were found to differ statistically (P < 0.05) between the quarry workers and the rest of the volunteer work population. In a similar manner, elevated ALT values differ statistically (P < 0.05) between the kilning workers and the rest of the study population. Elevated bicarbonate values are associated with chronic bronchitis, while elevated values of AST and ALT suggest susceptibility to hepatitis, particularly anicteric hepatitis as the elevated values of the transaminase were not matched by a corresponding rise in serum bilirubin. The implications of this study to occupational health screening cannot be overemphasized.

Chest radiography and high resolution computed tomography in the evaluation of workers exposed to silica dust: relation with functional findings

OBJECTIVES

To compare the usefulness of high resolution computed tomography (HRCT) with chest radiography (CR) in the diagnosis and assessment of severity of silicosis.

METHODS

27 workers exposed to silica underwent CR, HRCT, and pulmonary function tests. Two experienced readers independently evaluated CR by International Labour Office classification, and grouped the results into four categories. HRCT categories of nodule profusion and the extent of emphysema were graded on a four point scale; in 20 subjects the percentage distribution of lung densities were measured by HRCT.

RESULTS

Concordance between readers was higher for HRCT than for CR (K statistic = 0.49 and 0.29 respectively). There was poor concordance between CR and HRCT in the early stage of silicosis. No significant difference in pulmonary function tests was found among different CR categories, but forced expiratory volume in one second (FEV1), maximal expiratory flow at 50% and 75% of FVC (MEF50, MEF75), and diffusion capacity significantly decreased with increasing HRCT categories. Subjects with simple silicosis detected by HRCT had a lower FEV1 than subjects without silicosis, whereas subjects with conglomerated silicosis showed higher residual volume and functional residual capacity than subjects with simple silicosis. These relations were not affected by smoking or symptoms of chronic bronchitis. Different grades of emphysema detected by HRCT were significantly different in diffusion capacity. Only the HRCTs of the lowest and the highest categories of profusion of parenchymal opacities were significantly different in their distribution of density classes.

CONCLUSION

HRCT is more reproducible and accurate than CR, as suggested by the higher agreement between readers and the better correlation with pulmonary function tests, irrespective of smoking and chronic bronchitis; however, these data do not support the hypothesis that HRCT is more sensitive than CR in the early detection of silicosis.

Silica exposure and chronic airflow limitation in pottery workers

We assessed the relationship between exposure to silica dust and chronic airflow limitation in an epidemiological survey conducted among pottery workers and controls who were of the same socioeconomic status (average age: 35 y; 78% males). Data were collected by questionnaire for respiratory symptoms, allergy, respiratory history, smoking habits, and occupation. Lung function was measured with a computer-equipped Gauthier spirometer. We excluded subjects with silicosis or doubtful chest x-ray, and two exposure levels were defined. No differences were observed between exposed subjects and controls with respect to respiratory conditions. Mean pulmonary function values for men and women were significantly lower, after adjustment for age, height, and smoking habits, in even indirectly exposed pottery workers, compared with controls. These results suggest that exposure to silica dust is a risk factor for chronic airflow limitation and is independent of radiographic changes.

The mineral dust diseases

The mineral dust diseases, also called the pneumoconioses, comprise a wide spectrum of conditions ranging from diseases characterized by diffuse collagenous pulmonary reactions to relatively small lung burdens of bioactive dusts (e.g. silicosis, asbestosis) to diseases characterized by largely non-collagenous reactions in the face of heavy lung dust burdens (e.g. coal workers pneumoconiosis). According to information submitted to the International Labour Office, which is however incomplete, substantial numbers of individuals are still at risk for the mineral dust diseases in the workplaces of the world. An overview of their epidemiology in industrialized and industrializing countries reveals more commonalities than contrasts. Commonalities include the major determinants of disease (including exposure level, intensity and particle size distribution), their clinical manifestations and, probably, secular trends towards less clinically severe disease, at least in the larger, better controlled workplaces. Still a risk however, in both industrializing as well as industrialized countries, are the small, uncontrolled workplaces, often the source of mini-epidemics. Contrasts relate to the incidence and/or prevalence rates of tuberculosis amongst workforces at risk for the mineral dust diseases. Rates, which are invariably higher in industrializing than in industrialized economies, usually reflect the background tuberculosis rates in the populations which furnish the industrial workforces and they should be the target for control measures. Research in the industrialized countries should focus on disease mechanisms and on the bioactivity of workplace contaminants, old and new, and in the industrializing countries on the distribution and determinants of mineral dust diseases in their workplaces.(ABSTRACT TRUNCATED AT 250 WORDS)

Silicosis among gemstone workers in South Africa: tiger's-eye pneumoconiosis

Six cases of silicosis in workers involved in the processing of semiprecious gem stones have been seen in our clinic since 1976. They had been employed as stone sculptors in lapidaries where they processed tiger's-eye, rose quartz, amethyst, quartz crystal, and a variety of other locally occurring semiprecious stones. In five of the cases, exposure was in small and poorly regulated lapidaries without specific dust control measures. The sixth was detected during the course of a health and hygiene survey (including dust sampling) that was conducted in one of two lapidaries still operating in our area. Progressive massive fibrosis (PMF) or accelerated silicosis was noted in four of the six cases, three of whom had progression of their disease after cessation of exposure. With the development of PMF, the initial restrictive pulmonary function abnormalities were followed by steadily worsening airflow obstruction. Lung biopsies confirmed silicosis in three cases. Tuberculosis was confirmed in two cases and suspected and treated in a third. Workmen's Compensation was awarded in five cases. The survey confirmed that in semiprecious gem stone processing, the risk of silicosis appears to be confined to stone sculptors. Tried and proven techniques of general and local exhaust ventilation combined with water or oil to control dust at source were capable of effectively reducing dust emission to acceptable levels.

Lung function in silica-exposed workers. A relationship to disease severity assessed by CT scan

To investigate the relationship of lung function, airflow limitation, and lung injury in silica-exposed workers, we analyzed the clinical, functional, and radiologic data of 94 long-term workers exposed in the granite industry or in foundries. The subjects were divided into four subsets based on chest roentgenogram and CT scan of the thorax: group 1 consisted of 21 subjects with category 0 chest roentgenogram and category 0 CT scan; group 2, 28 subjects with category E 1 on both chest roentgenogram and CT scan; group 3, 18 subjects with category E 1 on chest roentgenogram but with coalescence or conglomeration or both seen only on CT scan; and group 4, 27 subjects with category E 1 and coalescence or conglomeration or both on roentgenogram and CT scan. The groups did not differ in terms of age, height, cigarette smoking, or years of exposure. Lung volumes were significantly reduced only in group 4 (p less than 0.05). Lung compliance, diffusion capacity, and the rest-exercise P(A-a)O2 gradient were reduced in groups 3 and 4 (p less than 0.05). Expiratory flow rates were significantly reduced in groups 2, 3, and 4, with the lowest values in group 4. The expiratory flow rates in group 3 were significantly lower in group 3 than in group 2. These results support the concept that airflow in silica-exposed workers is significantly reduced when the disease is detectable on simple chest roentgenogram; coalescence or conglomeration or both on chest roentgenogram or CT scan is associated with significant loss of lung volumes, gas exchange function, and increased airflow obstruction.