Respirable Silica Research Articles

Does long-term concrete work cause silicosis?

The machining of cast concrete often produces heavy exposure to respirable silica dust. Work with concrete in general results in considerably less exposure, however, and only a few cases of silicosis due to work with concrete have been reported. Telephone interviews with detailed questions on occupational history were made with 271 construction workers specializing in concrete work for more than 20 years, and exposure data were evaluated for different work tasks. The mean cumulative exposure of subjects to silica was estimated to be 2.4 mg.years.m-3. Chest radiographs were classified according to the International Labour Office classification. There was no suspicion of silicosis for any of the workers. The risk of contracting silicosis from work with concrete in the Swedish construction industry in recent decades is considered to be slight and does not justify general, periodic chest radiographic screening.

Relation between exposure to respirable silica dust and silicosis in a tungsten mine in China.

To estimate the quantitative relation between exposure to respirable silica dust and risk of an attack of silicosis, 1151 workers exposed to silica dust and employed from 1958 to 1987 in a tungsten mine in China were investigated. The results showed that the ratio of respirable silica dust concentration to total silica dust concentration was 0.529. Then, the total silica dust concentration in historical surveillance and monitoring data was converted to respirable silica dust concentration. The free silica content in respirable dust determined by x ray diffraction averaged 24.7%. Multiple logistic regression was used for the dichotomous dependent variables (presence or absence of silicosis). The independent variables in the multiple logistic regression with presence of silicosis as the dependent variable were age when first exposed, tuberculosis (presence or absence), and cumulative exposure to respirable silica dust. The partial regression coefficient of individual cumulative exposure was estimated as 0.079. It implied a positive association between exposure to respirable silica dust and risk of an attack of silicosis. The exposure limit for respirable silica dust was estimated as 0.24 mg/m3 under given conditions.

Inhibitory action of tetrandrine on macrophage production of interleukin-1 (IL-1)-like activity and thymocyte proliferation.

Tetrandrine is a bisbenzylisoquinoline alkaloid which has been shown to exhibit antifibrotic activity against silicosis. Tetrandrine is characterized by its strong binding to alveolar macrophages and inhibition of particle-induced respiratory burst activity in these phagocytes. In contrast, tubocurine and tubocurarine are structurally similar to tetrandrine but exhibit little effect on fibrosis or activation of alveolar macrophages. The objective of the present study was to test the effect of tetrandrine on macrophage production of monokines in response to occupational dusts, and to determine tetrandrine's effect on monokine-medicated cell growth using a mouse thymocyte proliferation assay and lipopolysaccharide (LPS) as a positive control. Stimulation of alveolar macrophages by respirable silica dust resulted in a release of monokines which caused a fourfold increase in thymocyte proliferation. Coal dust, on the other hand, had no effect on macrophage production of this cytokine. Tetrandrine was found to exhibit a dose-dependent inhibition of monokine release from both silica and LPS-stimulated alveolar macrophages. In experiments where thymocytes were directly treated with tetrandrine, a dose-dependent inhibition of thymocyte proliferation was noted with both interleukin-1-(IL-1) specific and nonspecific mitogenic (concanavalin A) actions. In contrast to the inhibitory potency of tetrandrine, tubocurarine was found to have no effect on either the production of monokines by LPS-stimulated alveolar macrophages or IL-1-mediated thymocyte proliferation. These results provide a correlation between the antifibrotic effect of tetrandrine and inhibition of macrophage activation.

Characterisation of respiratory health and exposures at a sintered permanent magnet manufacturer.

Sintered permanent magnets are made from the powdered metals of cobalt, nickel, aluminium, and various rare earths. During production, exposure to respirable crystalline silica and asbestos may also occur. Reported here is a cross sectional study of 310 current and 52 retired hourly employees who worked 10 or more years making sintered magnets. Each participant had a chest radiograph, spirometry, and completed a respiratory questionnaire. Illness logs were also reviewed to calculate the incidence of recorded respiratory disorders. The prevalences of abnormalities in pulmonary function and respiratory symptoms were not higher than found in an external referent population. Although the prevalence of diffuse parenchymal opacities consistent with pneumoconiosis (four workers) was similar to the referent population, one worker had radiographic findings consistent with silicosis and two workers had profusion scores of 1/2 or above, not seen in the referent group. The incidence of reported respiratory conditions in the log, including asthma, was 10 times that of other manufacturers in the same industrial classification category. Excessive exposures to cobalt, nickel, and respirable silica were shown by environmental measurements.

ASSESSMENT OF INDUSTRIAL VACUUM CLEANERS OF BOTH WET AND DRY TYPES FOR USE IN POTTERIES<xref ref-type="fn" rid="fn1"><sup>*</sup></xref>

The efficiency of vacuum cleaners of both wet and dry types has been assessed in terms of the quality of the air returned to the atmosphere. Tests were carried out in the laboratory and on-site at potteries, using apparatus designed to contain the air issuing from the cleaner, so that it could be analysed with a real-time dust sampling instrument. Examination of the dust collected by a dry vacuum cleaner during on-site tests, or the slurry collected by a wet cleaner, enables test material to be specified for use in laboratory measurements of efficiency. Dry cleaners have the potential of achieving higher efficiency than wet cleaners, provided that good filters are used. Wet cleaners achieve a higher standard of floor cleaning than dry cleaners, but the quality of air that they return is not, in general, as good, since the filtration system that they employ is simple. A large fraction of the cleaners tested returned dust to the atmosphere at a concentration equivalent to a respirable silica concentration of approximately 0.1 mgm−3.

Respirable Dust Exposures in U.S. Surface Coal Mines (1982–1986)

Exposure of miners to respirable coal mine dust and to respirable quartz silica at surface coal mines in the United States during 1982-1986 were evaluated by job category using data collected by coal mine operators and Mine Safety and Health Administration (MSHA) inspectors. Average coal mine dust concentrations were usually well below the MSHA Permissible Exposure Limit (PEL) for all job categories, but at least 10% of the samples obtained from some coal preparation plant job areas and most drilling job areas had concentrations that exceeded the 2.0 mg/m3 limit. In contrast, a very high proportion of samples from surface mine driller areas exceeded the quartz PEL. Of all samples collected for highwall drill operators and helpers, 78% and 77%, respectively, were greater than the 0.1 mg/m3 quartz exposure limit (average concentrations were .32 and .36 mg/m3, respectively). Although MSHA compliance data may not be entirely adequate for assessing chronic exposure to quartz, these data and the results of other NIOSH studies nonetheless indicate excessive exposure to silica in a group of surface coal miners.

Surface and Bulk Infrared Modes of Crystalline and Amorphous Silica Particles: A Study of the Relation of Surface Structure to Cytotoxicity of Respirable Silica

Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity.

Surface and bulk infrared modes of crystalline and amorphous silica particles: a study of the relation of surface structure to cytotoxicity of respirable silica.

Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity.

Silica Exposure and Lung Cancer in Ceramic Workers: A Case-Control Study

The results are presented from a case-control study, concerning the possible relation between silica exposure in the Dutch fine ceramic industry and lung cancer. For this purpose 381 male, age-matched pairs of primary lung cancer cases and controls were selected from the pathology department of the University Hospital in the region, where two large ceramic companies are located. Information about employment in the ceramic industry was obtained from the personnel and financial administration departments of the two companies. On the basis of job titles a panel of occupational hygiene experts reached consensus about the qualitative exposures of each individual worker. Twenty one per cent of the cases were employed in the ceramic industry, compared with 19% of the controls (odds ratio 1.11; 95% Cl: 0.77-1.61). Although the average employment period of cases and their relative silica exposure surpassed those of controls, odds ratios for long duration of employment and considerable exposure to respirable silica dust did not reach statistical significance. After constructing a qualitative exposure index, based on the amount and duration of exposure, a tendency towards a positive correlation with lung cancer emerged. No relation between specific histological tumour cell types and working in the ceramic industry emerged. Although the study does not suggest a consistent cause-effect relation between silica exposure in the regional, Dutch fine ceramic industry and lung cancer, an increased risk for the high exposure group in the past can not be totally excluded.

Cancer incidence among Danish stone workers.

The lung cancer incidence of 2071 Danish stone workers was followed for a 42-year period. The expected numbers of cancer cases were based on the incidence rates for all Danish men after adjustment for region, and the data were analyzed separately for skilled and unskilled stone workers. The standardized incidence ratio (SIR) for lung cancer was 200 (44 observed, 22.0 expected) for all skilled stone workers, 808 (7 observed, 0.9 expected) for skilled sandstone cutters in Copenhagen, 119 (8 observed, 6.5 expected) for skilled granite cutters in Bornholm, 181 (24 observed, 13.2 expected) for all unskilled stone workers, 246 (17 observed, 6.9 expected) for unskilled workers in the road and building material industry, and 111 (7 observed, 6.3 expected) for unskilled workers in the stonecutting industry. Smoking was unlikely alone to explain the excess risk, and the available data on levels of exposure in the Danish stone industry point to a possible dose-response relationship between exposure to respirable silica dust and the incidence of lung cancer.

Respiratory health of brickworkers in Cape Town, South Africa. Appropriate dust exposure indicators and permissible exposure limits.

The predictive value for respiratory abnormalities of dust indicators was assessed for 268 brickworkers. The subjective/objective correlations were poor (r = 0.09). The subjective indicators were found to be predictive of early/mild abnormalities, while the objective indicators were better for more severe abnormalities. The respirable/total dust correlations were high (r = 0.99). Length of service was a good proxy predictor for most respiratory abnormalities, while respirable dust was a good proxy for respirable free silica. Simple screening measures with potential application in less-developed settings, like subjective questionnaire responses and total dust measurement, are suggested. The American Conference of Governmental Industrial Hygienists' threshold limit values for free silica and "nuisance" particulates appear to be too high to prevent the occurrence of abnormalities. The World Health Organization's health-based limit for respirable free silica (1 mg/m3) and hygienic standards of well below 5 mg/m3 would have prevented much of the respiratory abnormality found. Hygienic standards for dust and the concept of "nuisance" dust need to be reevaluated by further research.

Silica exposure and silicosis among Ontario hardrock miners: II. Exposure estimates.

An epidemiological investigation was carried out to determine the relationship between silicosis in hardrock miners in Ontario and cumulative exposure to silica (free crystalline silica--alpha quartz) dust. This second report describes a side-by-side air-sampling program used to derive a konimeter/gravimetric silica conversion curve. A total of 2,360 filter samples and 90,000 konimeter samples were taken over 2 years in two mines representing the ore types gold and uranium, both in existing conditions as well as in an experimental stope in which dry drilling was used to simulate the high dust conditions of the past. The method of calculating cumulative respirable silica exposure indices for each miner is reported.

Contributing factors to sandblasters' silicosis: inadequate respiratory protection equipment and standards.

National concordance standards for respiratory protection during abrasive blasting have existed for more than 50 years; however, these standards have not kept pace with advances in blast equipment, have not provided realistic estimates of expected protection in the workplace, and have been misused by manufacturers and distributors of respiratory protective equipment who have assured, through sales literature, that the equipment is acceptable for conditions under which they have never been tested. This situation has contributed to exposure of sandblasters to hazardous levels of respirable free silica, and is reviewed here to prevent a continuation of the incompatibility of these and other standards for respiratory protection with the actual exposures to various noxious inhalants in the workplace.

Evaluation of a Water-Type Dust Collector at an Underground Crushing Operation

A self-induced wet dust collector operating at 8.7 m3/sec was evaluated at a crushing station in an underground hard rock mine. The new dust collector replaced a baghouse dust collector. The unit was evaluated for dust removal efficiency as a function of particle size. Performance also was assessed by comparing airborne respirable dust in the general area prior to and after installation of the new collector system. The use of cascade impactors and optical particle counters at the intake and the exhaust of the dust collector revealed a high efficiency (>90%) for particles greater than 2.0 µm in size. The efficiency dropped to approximately 70% and 25% for 1.0 µm and 0.5 µm particles, respectively. The overall respirable dust reduction in the immediate crusher vicinity was measured with 10-mm nylon cyclones and another type of personal dust sampler designed by the Mining Research Laboratory in Elliot Lake, Ontario. The results showed an average respirable dust reduction of 51% with a maximum of 64% in some areas. For respirable silica dust, the average reduction was higher at 70% with maxima of up to 79%.

Evaluation of a Water-Type Dust Collector at an Underground Crushing Operation

A self-induced wet dust collector operating at 8.7 m3/sec was evaluated at a crushing station in an underground hard rock mine. The new dust collector replaced a baghouse dust collector. The unit was evaluated for dust removal efficiency as a function of particle size. Performance also was assessed by comparing airborne respirable dust in the general area prior to and after installation of the new collector system. The use of cascade impactors and optical particle counters at the intake and the exhaust of the dust collector revealed a high efficiency (>90%) for particles greater than 2.0 µm in size. The efficiency dropped to approximately 70% and 25% for 1.0 µm and 0.5 µm particles, respectively. The overall respirable dust reduction in the immediate crusher vicinity was measured with 10-mm nylon cyclones and another type of personal dust sampler designed by the Mining Research Laboratory in Elliot Lake, Ontario. The results showed an average respirable dust reduction of 51% with a maximum of 64% in some areas. For respirable silica dust, the average reduction was higher at 70% with maxima of up to 79%.

LISA: a new aerosol generation system for sampler evaluation.

A Large Inorganic Sampler Assembly (LISA) system has been built for the evaluation of particulate sampling devices, including the device used in the NIOSH method for respirable silica (Method 7500). Significant features of LISA are the following: 1) The accommodation of up to 30 filter cassettes or 12 cyclone samplers; 2) high precision of particulate deposition (Sr = 2.2%); 3) micro-computerized reduction of optical particle counter data; and 4) special design features to facilitate ease of operation. The system has been used to evaluate sampler systems for a number of different airborne dusts.

Silica and Glomerulonephritis: Case Report and Review of the Literature

A 54-year-old foundry worker with extensive silica exposure, but no pulmonary disease, developed the nephrotic syndrome and renal failure over a 3-month period. Renal biopsy demonstrated a proliferative glomerulonephritis; energy dispersive x-ray analysis detected silicon within the renal tubules. Measurements of respirable silica at the foundry revealed levels up to 2.5 times the current occupational standard. Similar glomerular disease has been reported in silica-exposed animals and workers with silicosis. This case suggests that clinicians should include silica exposure in the differential diagnosis of unexplained diffuse proliferative glomerulonephritis, renal disease may occur without clinically evident pulmonary disease in silica exposure, and silica-induced glomerulonephritis warrants further clinical and epidemiologic research.

An Investigation of the Performance of the 10-mm Nylon Cyclone

Abstract The sampling device recommended by the National Institute for Occupational Safety and Health for the determination of respirable silica is a 10-mm nylon cyclone and 37-mm cassette loaded with a PVC-type filter and operated at 1.7 lpm. The device has been subjected to a statistically rigorous determination of the sampling precision under controlled laboratory conditions using a silica-rich mine dust in a laboratory-built generation system. The statistical design used in the investigation eliminated contributions to the precision estimate from run and position effects. The precision of the device over the deposition range 826–1800 μg/sample was found to be 2.18%. In a follow-up study of air leaks in the device, five possible locations of leaks were selected. A set of sampling devices was made with air leaks of varying magnitude in the selected locations. The devices were tested using a vacuum leak testing apparatus. They were then placed in a generation system and challenged with a uniform concentr...

Optimization of overburden drill dust control systems on surface coal mines

ABSTRACT A significant problem at U.S. surface mining operations is complying with more stringent dust standards resulting from high respirable free silica concentrations. In areas where potentially harmful concentrations of silica-bearing dust exist, more stringent dust standards are applied to limit the amount of respirable free silica to which the workers are exposed. According to U.S. Mine Safety and Health Administration (MSHA) data, overburden drilling occupations have the greatest exposure to silica Worker exposure may be reduced by reducing the amount of dust produced by the drill. This can be accomplished with either dry collection or wet suppression systems. Both of these systems were evaluated in the field, results of this testing are the subject of this paper. This work was performed under a U.S. Bureau of Mines contract by PEI Associates, Inc. A special study of dry and wet systems was conducted to determine the proper operating parameters for each type of system. Shroud height was evaluated ...

DETERMINANTS OF PROGRESSION IN SANDBLASTERS' SILICOSIS

Abstract Chest roentgenograms and pulmonary function studies were completed on 83 silicotic sandblasters; 61 returned for longitudinal study, with follow-up ranging from 1 to 7 yr. Estimates of respirable free silica concentrations were based on extensive measurements of airborne dust and protective equipment used. Sixty-three percent exhibited X-ray evidence of disease progression between initial and latest films. Probability of progression increased as duration and level of past silica dust exposure increased and was higher among blacks than whites. Those with large opacities and/or certain symbols (ILO U/C classification) on initial X-ray had a higher probability of progression than those with only small opacities. Declines in pulmonary function were associated with average concentration of silica dust exposure. Those in the lowest category (≤ 1.25 mg m-3) experienced normal mean annual rates of decline (29 ml for FEV1 although 50% (5/10) had exhibited X-ray progression over the same period. Mean annual decline in FEV for the middle and upper (> 3.0 mg m-3) concentration categories were 87 and 166 ml, respectively; 59 and 100% of these categories, respectively, exhibited X-ray progression. Antibody prevalences and immunoglobulin levels were high but unrelated to disease state, X-ray progression or pulmonary function decline.