[The correction of the status of the pulmonary surfactant system as a method for preventing experimental pneumoconiosis]

Using a model of experimental pneumoconiosis in albino rats, induced by breathing in a rock dust, we attempted correction of the pulmonary surfactant system, for which purpose we tried choline chloride as a drug preparation. The action of the above drug was found out to be depended upon the moment of its administration and time during which it is being administered, and is that of influence on both the concentration and mechanism of absorbtion of surface-active fractions of the surfactant in the liquid-gas interface. Early administration of choline chloride (during the dust factor exposure) increases concentration of those surfactants notable for their surface-active properties being maintained, and improves the processes of diffusion of surface-active substances, which observation is accompanied by decrease in intensity of the processes of fibroformation in the lung tissue. Choline chlorid employed on the discontinuation of the dust exposure has adverse effects leading to changes in the lipid composition, impairing the surface-active properties and processes of diffusion of the pulmonary surfactant, which fact may contribute to aggravation of fibrosis in the lungs.

The pneumoconioses

The stringent industrial hygiene regulations that have been introduced in North America, Europe, and Australasia have led to a decline in the incidence and prevalence of silicosis, coal workers' pneumoconiosis, and asbestosis. Although new cases of asbestosis are not occurring, an appreciable number of mesotheliomata are still being diagnosed, and there has yet been little, if any, decline in the latter tumor. These new cases are nearly entirely due to exposure to amphiboles in the 1940s and 1950s. It is expected that by about the year 2000 the incidence of mesothelioma will begin to decrease in the United States and Canada. Meanwhile there is an undue preoccupation with more and more sensitive methods of detecting asbestosis, silicosis, and coal workers' pneumoconiosis, eg, magnetic resonance imaging, bronchoalveolar lavage, and so forth. Much effort is being made in trying to detect disease in groups of workers with extremely low exposures and no symptoms. Smaller and smaller effects are being detected, with the ultimate aim appearing to be detecting nothing at all. Efforts should be made at surveying other populations exposed to agents that have recently been introduced and that could conceivably have long-term effects.

Occupational exposure to carbon black in its manufacture: data from 1987 to 1992

Carbon black is a very pure form of very finely divided particulate carbon used mainly in the automotive tyre industry. Its carbonaceous nature and submicron size (unpelleted) have raised concerns with regard to its ability to affect respiratory morbidity. This paper describes the exposure to carbon black dust in the first and second phase of a large multi-national epidemiological study investigating the magnitude of these exposure-related effects. In Phase I, 1278 respirable dust samples were taken (SIMPEDS cyclone) which increased to 2941 in Phase II with a similar rise in the number of total inhalable dust samples (IOM head) from 1288 in Phase I to 3433 Phase II. Exposure dropped markedly between the two phases with total inhalable dust showing a bigger reduction (49.9%) than respirable dust (42%), although the mean exposure for certain factories and job categories dropped more than others. The data are presented by the 14 job titles/numbers (21-34). The highest mean exposure in both phases and for both dust fractions is experienced by the warehouse packers and they are also most likely to exceed the OES of 3.5 mg m-3 (35.1% of samples in Phase I and 12.0% in Phase II).

Fiber exposure assessment in the Swedish rock wool and slag wool production industry in 1938-1990

OBJECTIVE

A multiplicative model was developed to assess past exposure to respirable fibers among rock wool and slag wool production workers in Sweden in 1938-1990.

METHODS

Information on the job titles, work tasks and employment times of 1487 workers exposed to man-made vitreous fibers was obtained from company records and interviews with older employees. A mathematical model developed earlier for assessing historical fiber exposure, based on factory averages, was further developed. Matrices of multipliers for each plant that were specific for job title were modified to assess fiber exposure with respect to job title and calendar period. The model was based on measurements made in 1977. Two methods of exposure assessment were compared, cumulative exposure based on factory average (model I) and cumulative exposure based on job title (model II).

RESULTS

The exposure changed considerably in the two factories during the period 1938-1990, and it varied also between job titles. The estimated average fiber (f) exposure level at the two plants in the middle of the 1940s was 1.32 and 0.78 f.ml-1. These values are 26 and 16 times higher, respectively, than the exposure in 1980. Process changes, as well as the addition of binders and oil, reduced the exposure drastically around 1950. The mean cumulative respirable fiber exposure for the 1487 subjects was 1.44 (range 0.05-18.40) f.ml-1.year. The cleaners had 14 times higher annual fiber exposure than the preproduction workers.

CONCLUSIONS

Model II was judged to be more valid than model I in assessing exposure to man-made vitreous fibers.

Prevention and treatment of pneumoconiosis in China

Silicosis is one of the most serious occupational diseases which affect many workers' health in China. Under the guidance of policies from the Chinese Government, the industries, health care institutions, scientists and workers were organized and have made great efforts in prevention and treatment of silicosis as well as pneumoconiosis. Since the 1960s, the national health standards and chest X-ray diagnosis criteria for silicosis were established and have been revised recently. A nationwide epidemiological survey revealed that the cumulative pneumoconiosis cases were about 4,800,000 (1949-1992). The high prevalence rate has been the motivation to search for anti-silicotic drugs. Several kinds of anti-silicotic drugs were studied and found to be able to retard progression of silicosis and cause changes in X-ray picture. The mechanism of drug efficiency and the development of silicosis have attracted the interest of scientists in this fields and fruitful results have been obtained. For prevention of dust hazards, the systematic design for facilities of dust collection and the isolation of dust source appropriate to township industries have been worked out and used widely. Recently, under the supervision of the Ministry of Public Health, China, a pilot study on counter-measure for industrial hazards and health care service in township industries has been instituted.

Results of pneumoconiosis examination--different trends among industries

In this report we describe yearly changes in pneumoconiosis patients and pneumoconiosis progression in each industry in Japan, using statistics of Ministry of Labour based on the results of pneumoconiosis examinations performed at plants in accordance with the Pneumoconiosis Law. We found that the number of workers exposed to mineral dust decreased yearly. The number of subjects with positive findings, the number of new cases with pneumoconiosis, the ratio of positive findings, and the incidence rate of pneumoconiosis also decreased. In particular, the number of subjects with positive signs of pneumoconiosis clearly decreased. A similar tendency was seen in the number of cases including voluntary applications. Industry-wise, however, there was a large difference among the industries. The ratio of pneumoconiosis with complications, along with the progression ratio, decreased. Subjects with progressed pneumoconiosis decreased annually, exhibiting less-serious signs and symptoms. There have been reports with a different view about the general trend of pneumoconiosis. We examine and discuss the cause of discordance between the studies.

Dust and pneumoconiosis in the South African foundry industry

The objectives of this study were to estimate the extent of occupational health monitoring for dust and pneumoconiosis in the foundry industry and to assess dust levels and the prevalence of pneumoconiosis in a group of foundries. In only 13 (16%) of the 82 foundries that responded to a postal questionnaire were regular periodic full-sized chest radiographs done. Dust levels were measured every 3 years or more frequently in 20 foundries (24%). An uncontrolled dust hazard was evident in all 9 foundries surveyed between 1983 and 1992. The prevalence of silicosis ranged from 0% to 10.3% and increased with duration of service. The study provided convincing evidence of neglect of occupational health by the foundry industry.

[Occupation-specific indicators for strategic prevention in risk groups]

Using graphical representations to compare undistorted information it was attempted to bridge the gap between medicine and concerned risk-groups. Age-standardized mortality rates in 1979-1983 for 55 occupational groups (in 11 categories) of males aged 35 to 74 years were computed and compared to the Swiss national average; simultaneously the quantitative importance and the total mortality without accidents is shown for each occupational group: as an example the figure for lung cancer is reproduced. The elevated total mortality in the upper tertile of occupational groups is significantly explained by an increased risk of dying from circulatory or respiratory diseases, liver cirrhosis or malignancies of the lung, oropharynx, oesophagus or stomach. Foreseeable decrease of high-risk occupational groups will result in a further decline in mortality due to stomach cancer and cerebrovascular diseases in Switzerland.

From explosions to black lung: a history of efforts to control coal mine dust

Highlights in the history of efforts to prevent occupational lung disease among coal miners in the United States are reviewed. The Federal Coal Mine Health and Safety Act of 1969 is summarized, and the sources and effects of its provisions to prevent coal workers' pneumoconiosis are examined. Descriptions follow of the identification of coal workers' pneumoconiosis as a disease, identification of respirable coal mine dust as its cause, and establishment and enforcement of an exposure limit. The development of prevention efforts focusing on surveillance of both exposure and outcome and of enforcement of dust control methods is examined.

Chest x ray films from construction workers: International Labour Office (ILO 1980) classification compared with routine readings

The extent of agreement between International Labour Office (ILO) and clinical readings of chest x ray films from construction workers was studied. From a survey of 5898 workers 258 subjects with a profusion of small opacities of > or = 1/1 and a stratified sample of subjects with profusion < 1/1 were selected. Only 41% of the films classified as ILO profusion category > or = 1/1 were clinically recorded as non-normal for the parenchyma. The proportion of films recorded as pneumoconiotic (or possibly so) was especially low for irregular opacities (22%), but increased with the profusion category (both rounded and irregular) as well as with the size of rounded opacities (p 3/11, q 12/25, r 3/4). Only with the profusion category > or = 2/1 were most of the films recorded as pneumoconiotic. The specificity and sensitivity were highest in the geographical areas where a few clinical readers had assessed many films each. The proportion of false negative clinical reports was low for circumscribed pleural thickening of the chest wall (9%) and diaphragmatic pleural thickening (6%). For calcified pleural changes and for the combination of diffuse pleural thickening and obliteration of the costophrenic angle, false negative reports were absent. The present study shows an unsatisfactory sensitivity for clinical compared with ILO readings as a means for screening the parenchyma of workers with a risk of pneumoconiosis.

Epidemiological data on US coal miners' pneumoconiosis, 1960 to 1988

OBJECTIVES

Statistics on prevalence of pneumoconiosis among working underground coal miners based on epidemiologic data collected between 1960 and 1988 are presented. The main intent was to examine the time-related trend in prevalence, particularly after 1969, when substantially lower dust levels were mandated by federal act.

METHODS

Data from studies undertaken between 1960 and 1968 were collected and compared. Information for the period 1969 to 1988 was extracted from a large ongoing national epidemiologic study. Tenure-specific prevalence rates and summary statistics derived from the latter data for four consecutive time intervals within the 19-year period were calculated and compared.

RESULTS

The results indicate a reduction in pneumoconiosis over time. The trend is similar to that seen in a large radiologic surveillance program of underground miners operated concurrently.

CONCLUSIONS

Although such factors as x-ray reader variation, changes in x-ray standards, and worker self-selection for examination may have influenced the findings to some extent, adjusted summary rates reveal a reduction in prevalence concurrent with reductions in coal mine dust levels mandated by federal act in 1969.

Surveillance data on US coal miners' pneumoconiosis, 1970 to 1986

OBJECTIVES

Statistics on prevalence of pneumoconiosis among working underground coal miners from data collected as part of a large national radiographic surveillance program between 1970 and 1986 are presented. The main intent was to examine the time-related trend in prevalence over this period, which coincides with historically low dust levels mandated by federal act.

METHODS

Tenure-specific prevalence rates and summary statistics derived from them for four consecutive time intervals within the 16-year period were calculated and compared.

RESULTS

The results indicate a reduction in pneumoconiosis over the life of the program. This trend is similar to that seen in epidemiologic studies undertaken concurrently.

CONCLUSIONS

Although low participation in the surveillance program and other problems complicate the findings, it appears that reductions in dust exposure mandated by federal act in 1969 have led to lower prevalence of pneumoconiosis among underground coal miners.

British data on coal miners' pneumoconiosis and relevance to US conditions

OBJECTIVES

The current primary federal dust standard for US underground coal miners of 2 mg/m3 respirable dust is based on British epidemiological information on exposure-response derived in 1969. Since then, much new information has become available. This paper reviews and compares the available information as it relates to the US mining situation.

METHODS

Recent exposure-response information on pneumoconiosis and dust exposure derived by British researchers was employed to estimate working-life risks of pneumoconiosis for miners exposed to 2 mg/m3.

RESULTS

It is estimated that close to 9% of underground coal miners who work for 40 years in a 2 mg/m3 environment would develop pneumoconiosis (category 1 or greater). Progressive massive fibrosis would develop in 0.7%.

CONCLUSIONS

There are unresolved questions relating to the validity of extrapolating findings on British mines and miners to the US and also in predicting disease levels at the low end of the dust exposure spectrum. Given the data available, current information suggests miners who are employed for a working life-time at the current federal dust limit of 2 mg/m3 are still at risk of developing pneumoconiosis.

Victoria M. Trasko: champion of state-based surveillance of occupational diseases in the United States, 1937 to 1971

Victoria M. Trasko (1907-1979), a relatively unknown figure to many currently practicing occupational health specialists, was a pioneer in state-based surveillance of occupational diseases in the United States. To highlight her accomplishments during her career with the United States Public Health Service from 1937 to 1971, this report briefly reviews her publications on occupational disease surveillance. Her span of work includes guidelines for state industrial hygiene programs, numbers of workers in state occupational health programs, compilation of state and local laws related to industrial hygiene, proposals for standardized reporting of occupational disease, and analysis of trends in workers' compensation and mortality statistics for occupational diseases. She pilot tested the first state-based model system for occupational disease reporting in the United States. She documented the great difficulty experienced by states in getting physicians to report cases of occupational diseases, and pointed out that surveillance of other existing data sources was worthwhile, at least for some occupational diseases. She was the first to report on the distribution of silicosis cases in the United States by state, industry, and job title. She was the first to comment on mortality trends for the pneumoconioses and to document problems in comparability between different International Classification of Disease (ICD) periods.

Grain dust and lung function. Dose-response relationships

Grain dust exposure has been associated with both acute and chronic respiratory abnormalities. We sought to answer two questions with regard to this exposure: (1) is there a dose-response relationship between grain dust and respiratory abnormalities, and (2) is there evidence to suggest that the allowable exposure (currently 10 mg/m3 in Canada) be lowered? We compared respiratory symptoms and lung function among 454 grain elevator workers and 55 civic workers to estimates of lifetime average grain dust exposure. A total of 781 personal air samples representing 20 different job titles over a 15-yr period were used to construct a job title-time period matrix for average dust exposure levels. The matrix was applied to each worker's detailed job history to obtain a value for estimated cumulative and average dust exposure. Significant dose-response relationships were seen for chronic phlegm production, breathlessness on exertion, FEV1, and FVC; and dose-response trends were evident for the longitudinal change in both FEV1 and FVC. Workers with estimated average exposure between 4 and 9 mg/m3 were found to have significantly lower values for FEV1 and FVC compared to both grain workers exposed to less than 4 mg/m3 on average and civic workers, despite no difference in duration of employment among these groups. The results indicate a strong dose-response relationship between grain dust exposure and both respiratory symptoms and lung function and also suggest that the current Canadian allowable exposure level of 10 mg/m3 is too high.

[Substantiation of the mean working day maximum allowable concentrations of dusts with differing degrees of fibrogenesis]

On the basis of developed by the author mathematical models of pneumoconiosis morbidity and of methodological techniques of dusts dividing according to the degree of fibrogenesis under exposure to various concentrations of dusts differing in fibrogenesis. In the author's opinion, working conditions can be considered safe if the probability of pneumoconiosis does not exceed 0.1% for the 40 years length of working. On this basis mean working day concentrations, at which the probability of the development of the mentioned disease does not exceed 0.1%, are proposed as mean working day MACs. Average working day MACs for the whole range of dusts fibrogenesis have been calculated. The obtained in this way average working day MACs for the least fibrogenic dusts equal 6 mg/m3, and for the most fibrogenic dusts - 0.2 mg/m3.

[Artificial mineral fibers and the risk of cancer]

The cancer risk can be reduced by replacing crocidolite and amosite by chrysotile asbestos, by replacing asbestos by man-made mineral fibres that produce less dust, and by nonfibrous materials. MMMF have been found to be carcinogenic in experiments in animals. All respirable mineral fibres that are retained in the lungs are suspected to increase the lung cancer risk, the fibre length and surface properties appearing to be the decisive factors. For most of these fibres, data so far collected in humans are still insufficient to permit definite conclusions to be drawn. There is a certain amount of evidence to suggest that rock/slag wool may be carcinogenic in humans: lung cancer in workers in the production area in the USA was found to be significantly increased (SMR 134%), and in the early phase of European production an SMR of 257% was observed. In the area of glass wool production, exposure to fibre and lung cancer rates were lower, but showed an increasing tendency with increasing time elapsed since the first exposure to respirable fibres. Methodological problems associated with published epidemiological studies are reviewed, and prevention strategies--which need to give consideration to the possibility that the carcinogenicity per fibre could be higher in the case of MMMF than in chrysotile asbestos--are discussed.