Respirable Silica Research Articles

Surface sites and unrelaxed surface energies of tetrahedral silica polymorphs and silicate

Surface properties of respirable silica, which represents a major occupational safety concern, were investigated computationally, and a model for quantitative characterization of crystalline silica surface sites was developed. It was found that the surface energy of crystalline solids, such as silica and silicates, can be calculated as a product of the surface site density and site energy. The energies of sites formed by faceting tetrahedral silica polymorphs and aluminosilicate were determined by parametric fitting ab initio surface energies to site densities. Boltzmann’s statistics was used to describe the distribution of faces as an exponential function of unrelaxed surface energy in the comminuted crystalline solids. Using these findings, crystallographic face distributions on fractured quartz, coesite, tridymite, and cristobalite were derived and average silanol hydroxyl densities in fractured particulate of these materials were estimated as 0.070, 0.059, 0.058, and 0.055 Å −2, respectively. The proposed method of quantitative characterization of the surface bridges the gap between microscopic simulations and measurable observables, such as cytotoxicity of respirable silica.

A Comparative Study of Unrelaxed Surfaces on Quartz and Kaolinite, Using the Periodic Density Functional Theory

To investigate surface properties of fractured silica particles, which are commonly connected to the etiology of silica toxicity, models of low-index unrelaxed surfaces of quartz and kaolinite were constructed and analyzed using the periodic density functional theory calculations. The models were used to investigate surface sites that emerge in the processes of heterolytic and homolytic cleavage of quartz. It is found that the quartz surface is stabilized by two types of interactions. One, due to a more even charge distribution of sites, was characterized by surface energies of up to 0.025 eV x A(-2) and the other, due to a more even oxygen distribution between complementary surfaces, was up to 0.036 eV x A(-2). The total specific surface energies of unrelaxed surfaces ranged from 0.161 to 0.200 eV x A(-2) for quartz and from 0.017 to 0.158 eV x A(-2) for kaolinite. For the conchoidal fracture of quartz an average specific surface energy of 0.187 eV x A(-2) was obtained. These results provide a foundation for further characterization of the surface properties of mechanically comminuted respirable silica particulate and for reduction of occupational health hazards due to pulverized silica.

Evaluation of Misting Controls to Reduce Respirable Silica Exposure for Brick Cutting

It is estimated that more than 1.7 million workers in the United States are potentially exposed to respirable crystalline silica, with a large percentage having been exposed to silica concentrations higher than the limits set by current standards and regulations. The purpose of this study is to characterize the use of water-misting engineering controls to reduce exposure to respirable crystalline silica for construction workers engaged in the task of brick cutting. Since data concerning the efficacy of engineering controls collected at worksites is often confounded by factors such as wind, worker skill level, the experiments were conducted in a laboratory environment. A completely enclosed testing chamber housed the brick-cutting saw. Respirable dust concentrations were measured using the Model 3321 Aerodynamic Particle Sizer. Specifically, the laboratory experiment was designed to compare dust suppression through water misting using conventional freely flowing water techniques. Brass atomizing nozzles with three flow rates were used for making this comparison: low (5.0 ml s(-1) or 4.8 gal h(-1)), medium (9.0 ml s(-1) or 8.6 gal h(-1)) and high (18 ml s(-1) or 17.3 gal h(-1)). The flow rate for freely flowing water, using manufacturer-supplied equipment, was 50 ml s(-1) (48 gal h(-1)). The experiment consisted of five replications of five samples each (low-misting, medium-misting, high-misting, freely flowing water and no control). The order of sampling within each replicate was randomized. Estimates of dust reduction showed that low-misting nozzles reduced the respirable mass fraction of dust by about 63%, medium-misting nozzles by about 67%, high-misting nozzles by about 79% and freely flowing water by about 93%. Based on these results, it may be feasible to use misting to control respirable silica dust instead of freely flowing water. This strategy is of practical interest to the construction industry which must frequently limit the amount of water used on construction sites.

A 13C CP/MAS and 31P NMR study of the interactions of dipalmitoylphosphatidylcholine with respirable silica and kaolin

The interaction of silica and kaolin with dipalmitoylphosphatidylcholine (DPPC) has been studied using 13C and 31P solid state nuclear magnetic resonance spectroscopy. These studies explore the molecular interactions of these respirable dusts with a model lung surfactant species to characterize silica toxicity in mixed systems. The choline head group of DPPC was found to remain mobile when adsorbed on kaolin, in contrast to an immobile head group on silica. Further, glycerol carbon intensities were greatly diminished relative to that of choline carbons, a result attributed to broadening effects. These preliminary findings suggest that silica toxicity may not be related to choline mobility as previously noted [J. Colloid Interface Sci. 172 (1995) 536–538].

Risk of silicosis in cohorts of Chinese tin and tungsten miners and pottery workers (II): Workplace-specific silica particle surface composition

It is hypothesized that surface occlusion by alumino-silicate affects the toxic activity of silica particles in respirable dust. In conjunction with an epidemiological investigation of silicosis disease risk in Chinese tin and tungsten mine and pottery workplaces, we analyzed respirable silica dusts using a multiple-voltage scanning electron microscopy-energy dispersive X-ray spectroscopy (MVSEM-EDS). Forty-seven samples of respirable sized dust were collected on filters from 13 worksites and were analyzed by MVSEM-EDS using high (20 keV) and low (5 keV) electron beam accelerating voltages. Changes in the silicon-to-aluminum X-ray line intensity ratio between the two voltages are compared particle-by-particle with the 90th percentile value of the same measurements for a ground glass homogeneous control sample. This provides an index that distinguishes a silica particle that is homogeneously aluminum-contaminated from a clay-coated silica particle. The average sample percentages of respirable-sized silica particles alumino-silicate occlusion were: 45% for potteries, 18% for tin mines, and 13% for tungsten mines. The difference between the pottery and the metal mine worksites accounted for one third of an overall chi-square statistic for differences in change in measured silicon fraction between the samples. The companion epidemiological study found lower silicosis risk per unit cumulative respirable silica dust exposure for pottery workers compared to metal miners. Using these surface analysis results resolves differences in risk when exposure is normalized to cumulative respirable surface-available silica dust.

Risk of silicosis in cohorts of Chinese tin and tungsten miners, and pottery workers (I): An epidemiological study

Epidemiological evaluations of the risk of silicosis in relation to exposure to crystalline silica have raised the question of whether different types of silica dust exposures vary with respect to their ability to cause silicosis. The aim of this study is to compare the risk of silicosis among cohorts of silica dust-exposed Chinese tin miners, tungsten miners, and pottery workers and to assess whether gravimetric measurements of respirable silica dust sufficiently determine the risk of silicosis or whether other factors of exposure may play a significant role. Cohorts were selected from 20 Chinese mines and potteries. Inclusion criteria were starting employment after January 1, 1950 and being employed for at least 1 year during 1960-1974 in one of the selected workplaces. Radiological follow-up for silicosis onset was from January 1, 1950 through December 31, 1994. Silicosis was assessed according to the Chinese radiological criteria for diagnosis of pneumoconiosis (as suspect, Stage I, II, or III). Exposure-response relationships were estimated for silicosis of Stage I or higher. Silica dust exposure was estimated in terms of cumulative total dust exposure, calculated from a workplace, job title, and calendar year exposure matrix, and individual occupational histories. Cumulative total dust exposure was converted in two steps into cumulative respirable dust exposure and cumulative respirable silica dust exposure using conversion factors estimated from side-by-side measurements conducted in 1988-89. The male cohorts included 4,028 tin miners, 14,427 tungsten miners, and 4,547 pottery workers who had similar onset of employment and duration of follow-up. For a given exposure level, the risk of silicosis was higher for the tin and tungsten than the pottery workers. The observed differences in the risk of silicosis among the three cohorts suggest that silica dust characteristics, in addition to cumulative respirable silica dust exposure, may affect the risk of silicosis.

Historical cohort study of U.S. man-made vitreous fiber production workers IX: summary of 1992 mortality follow up and analysis of respiratory system cancer among female workers.

We report the 1946-1992 mortality experience of 4008 females employed in any of 10 U.S. fiberglass manufacturing plants between 1945 and 1978 relative to external population rates. We also examine respiratory system cancer (RSC) mortality as a function of estimated exposure to respirable fibers (RFib), formaldehyde (FOR), silica, phenolics, urea, and other agents based on internal cohort comparisons. No statistically significantly elevated standardized mortality ratios were observed for all-cause mortality (930 deaths), any of the 25 nonmalignant causes considered, all malignant neoplasms (266 deaths), or any of the 27 malignant causes considered. Internal cohort comparisons revealed no significant positive associations between RSC mortality (53 cases) and exposure to RFib, FOR, or any of the other agents considered, although exposure levels were generally low. Some demographic subgroups appear to be at relatively increased risk of RSC.

Assessment of silica exposure and engineering controls during tuckpointing.

Exposures to crystalline silica in the construction industry are widespread. This report documents exposures to crystalline silica and describes the effectiveness of a commercially available dust collection system designed for tuckpointing tools. Exposure to respirable crystalline silica (quartz) can result in silicosis, a serious and often fatal disease with symptoms including shortness of breath, weight loss, weakness, and the onset of autoimmune diseases. The American Conference of Governmental Industrial Hygienists (ACGIH©R ) regards silica as a suspected human carcinogen, and the National Toxicology Program (NTP) and the National Institute for Occupational Safety and Health (NIOSH) have designated crystalline silica as a potential occupational carcinogen. NIOSH estimates that more than one million workers are at risk for silicosis, with the majority of them in construction trades.(1) The NIOSH Recommended Exposure Limit (REL) and ACGIH©R Threshold Limit Value (TLV©R ) for respirable quartz are 0.05 mg/m3. The Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) for respirable dust containing crystalline silica for the construction industry is measured in millions of particles per cubic foot (mppcf) and is calculated using the following formula: PEL = 250 mppcf/% silica + 5.(2) However, OSHA compliance officers use the general industry PEL for respirable silica to test for compliance on construction sites, calculating the allowable exposure based on the measured quartz percentage for each sample in accordance with the following equation: 10 mg/m3/(% quartz + 2).(1) In this article, we used the NIOSH REL and the ACGIH TLV as the evaluation criteria, as these values reflect more current research on the health effects of silica exposure. Construction workers are routinely exposed to silica-containing dust without any engineering controls. One study showed that tuckpointing workers were exposed to silica-containing dust at levels 17 to 116 times higher than the OSHA PEL and 212 to 4300 times higher than the NIOSH REL.(3) According to NIOSH, non-powered air purifying respirators are not recommended for workers who are exposed to greater than 10 times the NIOSH REL.(4) In cases such as this, engineering controls, not only respirators, are required to reduce the exposure to the workers. OSHA also requires that engineering controls be used to the extent feasible for reducing exposures to regulated agents.(5) Exposures in construction are closely related to task.(6) For the grinding process during tuckpointing, personal silica exposures can vary substantially between the component tasks a worker conducts. Exposure assessment and the design of effective control technology require knowledge of each task component’s relative contribution to the total exposure. Detailed work task–exposure analysis using a combination of direct reading monitor and videotaping is well suited to assess the exposure associated with each task component in the mortar grinding process.(7) The goals of this study were as follows: 1) to evaluate the efficiency of engineering controls by calculating the respirable dust reduction as the ratio of exposure, both with and without the engineering control; 2) to determine the contribution of each component task to the total exposure in the grinding process based on the detailed task-exposure analysis; 3) to suggest improvements to the engineering control based on the data analysis and the comments of the journeyman bricklayers participating in the evaluation; and, 4) to evaluate the suitability of the disposable half-mask respirators typically used in this process.

Excessive exposure to silica in the US construction industry.

Exposures to respirable dust and silica were investigated among 36 construction sites in the USA. Personal measurements (n = 151) were analyzed from 80 workers in four trades, namely bricklayers, painters (while abrasive blasting), operating engineers and laborers. Painters had the highest exposures (median values for respirable dust and silica: 13.5 and 1.28 mg/m(3), respectively), followed by laborers (2.46 and 0.350 mg/m(3)), bricklayers (2.13 and 3.20 mg/m(3)) and operating engineers (0.720 and 0.075 mg/m(3)). Mixed models were fitted to the log-transformed air levels to estimate the means and within- and between-worker variance components of the distributions in each trade. We refer to the likelihood that a typical worker from a given trade would be exposed, on average, above the occupational exposure limit (OEL) as the probability of overexposure. Given US OELs of 0.05 mg/m(3) for respirable silica and 3 mg/m(3) for respirable dust, we estimated probabilities of overexposure as between 64.5 and 100% for silica and between 8.2 and 89.2% for dust; in no instance could it be inferred with certainty that this probability was <10%. This indicates that silica exposures are grossly unacceptable in the US construction industry. While engineering and administrative interventions are needed to reduce overall air levels, the heterogeneous exposures among members of each trade suggest that controls should focus, in part, upon the individual sites, activities and equipment involved. The effects of current controls and workplace characteristics upon silica exposures were investigated among operating engineers and laborers. Silica exposures were significantly reduced by wet dust suppression (approximately 3-fold for laborers) and use of ventilated cabs (approximately 6-fold for operating engineers) and were significantly increased indoors (about 4-fold for laborers). It is concluded that urgent action is required to reduce silica exposures in the US construction industry.

Sandblasting under uncontrolled and primitive conditions in Turkey.

Journal of Occupational HealthVolume 45, Issue 1 p. 66-69 Case StudyFree Access Sandblasting under Uncontrolled and Primitive Conditions in Turkey Can Sevinc, Can Sevinc Dokuz Eylul University School of Medicine Division of Pulmonary DiseasesSearch for more papers by this authorArif H. Cimrin, Arif H. Cimrin Dokuz Eylul University School of Medicine Division of Pulmonary DiseasesSearch for more papers by this authorMetin Manisali, Metin Manisali Division of RadiodiagnosticSearch for more papers by this authorErcument Yalcin, Ercument Yalcin Dokuz Eylul University Faculty of Engineering Department of Mining EngineeringSearch for more papers by this authorYasar Alkan, Yasar Alkan Regional Laboratory of Work Health and Safety Office, Izmir, TurkeySearch for more papers by this author Can Sevinc, Can Sevinc Dokuz Eylul University School of Medicine Division of Pulmonary DiseasesSearch for more papers by this authorArif H. Cimrin, Arif H. Cimrin Dokuz Eylul University School of Medicine Division of Pulmonary DiseasesSearch for more papers by this authorMetin Manisali, Metin Manisali Division of RadiodiagnosticSearch for more papers by this authorErcument Yalcin, Ercument Yalcin Dokuz Eylul University Faculty of Engineering Department of Mining EngineeringSearch for more papers by this authorYasar Alkan, Yasar Alkan Regional Laboratory of Work Health and Safety Office, Izmir, TurkeySearch for more papers by this author First published: 21 May 2003 https://doi.org/10.1539/joh.45.66Citations: 15 Corresponding to: C. Sevinc, Mithatpasa Caddesi No:259/2 Gurup Apt. 35330 Balcova, Izmir, Turkey AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL References 1 National Institute for Occupational Safety and Health Alert: Request for assistance in preventing silicosis and deaths from sandblasting. Cincinnati, Ohio: US Department of Health and Human Services, Public Health Service, CDC; DHHS publication no. (NIOSH) 1992; 92– 102 2T Koga, K Hirano, M Masuzaki, Y Komiya and S Tsuiki: Three patients with typical sandblaster's silicosis proven by mineralogical analysis. Nippon Kyobu Shikkan Gakkai Zasshi 28, 1098– 1105 (1990) 3BG Ferris: Recommended respiratory disease questionnaire for use with adults and children in epidemiological research. Epidemiology Standardisation Project. Am Rev Respir Dis 118, 1– 35 (1978) 4Guidelines for the use of ILO International Classification of Radiographs of Pneumoconiosis Revised Edition, Safety and Health Series, Genova 22, 1– 17 (1980) 5CL Bergin, NL Müller, S Vedal, C Staples, RT Abboud and M Chan-Yeung. CT in silicosis: Correlation with plain films and pulmonary function tests. AJR 1986; 46: 477– 483. 6KD Rosenman, MJ Reilly, DJ Kalinowsky and FC Watt. Silicosis in the 1990s. Chest 1997; 111: 779– 786. 7D Shaman. Silicosis: the occupational disease that shouldn't exist. Am Lung Assoc Bull 1983; 69: 6– 12. 8A Migliozzi and K Gromen. Silicosis among workers involved in abrasive blasting- Cleveland, Ohio, 1995. Mor Mortal Wkly Rep CDC Surveill Summ 46, 744– 747 (1997) 9B Samimi, H Weill and M Ziskind. Respirable silica dust exposure of sandblasters and associated workers in steel fabrication yards. Arch Environ Health 29, 61– 66 (1974) 10G Wagner. The inexcusable persistence of silicosis [editorial]. Am J Public Health 85, 1346– 1347 (1995) 11JL Abraham and SL Wiesenfeld. Two cases of fatal PMF in an ongoing epidemic of accelerated silicosis in oilfield sandblasters: Lung pathology and mineralogy. Ann Occup Hyg 41, 440– 447 (1997) 12HW Glindmeyer and YY Hammad. Contributing factors to sandblasters' silicosis: Inadequate respiratory protection equipment and standards. J Occup Med 30, 917– 921 (1988) Citing Literature Volume45, Issue1January 2003Pages 66-69 ReferencesRelatedInformation

Reconstruction of Silica Exposure at a Foundry for Evaluation of Exposure–Response

The reconstruction of working lifetime exposures to silica at a large foundry was described. Through the use of interviews with long-term employees, a history of the facility was developed for the years 1960–90, areas of similar work activities were identified and work locations for those with various job titles were documented over time. Two thousand and seventy historical industrial hygiene measurements of exposure collected during these three decades were linked to work area and an estimate of average respirable silica concentration was calculated for each area, by year. Overall, exposures declined between 1960 and 1990; however, substantial differences in exposure were estimated across work areas. Exposure at a specific job was calculated from the estimates of work-area respirable silica concentration, weighted by the amount of time persons with that job were in the area. These job-related exposure estimates were used to calculate three exposure metrics for persons employed in the foundry: cumulative, working lifetime average and highest daily exposure.

Crystalline Silica Exposure and Major Health Effects in Western Australian Gold Miners

We have re-analysed a cohort study of Western Australian goldminers using quantitative silica exposure estimates. The results indicate strong and separate dose–response effects for both duration and intensity of exposure to respirable silica and the incidence of compensated silicosis. There were significant increases in mortality from both autoimmune diseases and lung cancer among those with silicosis. There was a small non-significant increase in lung cancer mortality associated with cumulative silica exposure, which was similar in magnitude to that found in other studies. Propensity score adjustment indicated that, in contrast to asbestos and asbestosis, the increase in risk of lung cancer was restricted to subjects with silicosis.

Exposure to respirable crystalline silica in eastern North Carolina farm workers.

Occupational exposure to crystalline silica has been linked to silicosis, some forms of cancer, and certain autoimmune diseases. Little information exists on exposure levels of respirable silica in the agricultural industry. This study assessed respirable silica exposure of farm workers in eastern North Carolina. Sandy soils in this region have been shown to contain high levels of respirable silica. Personal breathing zone samples (n = 37) were collected from 27 workers at seven farms during various agricultural activities. The highest respirable silica concentrations were measured during sweet potato transplanting (3.91 +/- 2.07 mg/m3). Respirable silica exposure was observed to be associated with agricultural activity, soil moisture, relative humidity, and wind speed. Most of the variation in exposure (79%) was explained by agricultural activity and soil moisture. The observed percentage of silica levels (mean 34.7%) were almost twice as high as was reported in studies of California agriculture. This may be due to the loamy sand and sandy loam soil types in the regions in this study. In agriculture, respirable silica exposure is highly variable, but the potential for exposures above the threshold limit value of 0.05 mg/m3 exists during particular agricultural activities.

Airborne respirable silica near a sand and gravel facility in central California: XRD and elemental analysis to distinguish source and background quartz.

Despite the potential toxicity of respirable quartz to humans, little is known about the transport of airborne quartz from sources to receptors and how to distinguish anthropogenically generated quartz from natural background in a receptor sample. Airborne quartz emissions near a sand and gravel facility were determined using PM10 and PM2.5 filter samples collected at four downwind sites (D1: 22 m, D2: 62 m, D3: 259 m, and D4: 745 m from the facility) as well as one upwind site (U1: 1495 m) during summer sampling. X-ray diffraction was used to determine quartz concentration and elemental composition was analyzed using PIXE, XRF, PESA, and HIPS techniques. Elemental composition of the PM samples was used to determine the X-ray mass absorption coefficients that are essential for accurate quartz quantification by XRD. Elemental composition was found to be a useful tool to distinguish source and background crystalline silica. Both PM10 and PM2.5 samples collected at the D1, D2, and D3 sites contained more Si, Al, and Fe and less H, Na, and S, compared to those at the U1 site, whereas site D4 sample compositions were similar to those at the U1 site. A composite variable, SOIL/(H+Na+S), where SOIL = 2.20Al + 2.49Si + 1.63Ca + 1.94Ti + 2.42Fe, was used to distinguish source materials from background. Average dry season quartz concentrations in replicate PM10 samples were 4.6 +/- 0.9) microg m(-3) at U1, 60.6 (+/- 5.4) microg m(3) at D1, 62.4 (+/- 3.6) at D2, 32.6 (+/- 2.1) microg m(-3) at D3, and 9.41 (+/- 0.9) microg m(-3) at D4. The mass fraction of quartz was the highest at the D1 site and decreased with increasing distance from the facility. The mass of PM2.5 samples was too low to determine quartz concentrations. These results identify the facility as the main source of quartz and other silicate minerals downwind of the plant and that the air quality of the most remote sampling site, located approximately 750 m downwind, was still impacted by the facility's activity.

Total dust, respirable dust, and microflora toxin concentrations in Colorado corn storage facilities.

To aid in the process of characterizing corn dust exposures on farms and in elevators in northeastern Colorado, several parameters were examined. Total dust and respirable dust samples were collected and evaluated. Potentially dangerous dust components evaluated were respirable silica, endotoxin, and mycotoxin levels. Many of the total dust samples (58%) would have exceeded 8-hour time-weighted average (TWA) had sampling been conducted for 8 hours; on farms the operation takes between two and four hours. The same statement may be made for respirable dust samples collected for this project. Nearly 33 percent of the respirable dust samples collected would have exceeded the Occupational Safety and Health Administration (OSHA) TWA had sampling been conducted over an 8-hour period. Respirable silica standards were exceeded at 25 percent of the sampling locations. Presence of mycotoxins at all sites was confirmed by the use of ELISA kits. The most significant finding of this study was high levels of endotoxin at several of the sampling sites. Eighty-five percent of the sampling locations had endotoxin levels above 500 EU/m3. One location, Farm 4, had endotoxin levels of above 1.7 million EU/m3.

Mortality from non-malignant respiratory disease in the fibreglass manufacturing industry

Objectives: To investigate the question of whether there is an association between workplace exposures and sociodemographic factors and mortality from non-malignant respiratory disease excluding influenza and pneumonia (NMRDxIP) among workers...

Mortality from lung cancer among silicotic patients in Sardinia: an update study with 10 more years of follow up

OBJECTIVESTo evaluate the association between silica, silicosis and lung cancer, the mortality of 724 patients with silicosis, first diagnosed by standard chest x ray film between 1964 and 1970, has...

Lung cancer risk, silica exposure, and silicosis in Chinese mines and pottery factories: The modifying role of other workplace lung carcinogens*

Aims of our study were to explore whether and to what extent exposure to other lung carcinogens, or staging and clinical features of silicosis modify or confound the association between silica and lung cancer. We used data from a nested case-control study, conducted in the late 1980s in 29 Chinese mines and potteries (10 tungsten mines, 6 copper and iron mines, 4 tin mines, 8 pottery factories, and 1 clay mine), that included 316 lung cancer cases and 1,356 controls, matched by decade of birth and facility type. The previous analysis of these data presented results by type of mine or factory. In our study, pooling all 29 Chinese work sites, lung cancer risk showed a modest association with silica exposure. Risk did not vary after excluding subjects with silicosis or adjusting the risk estimates by radiological staging of silicosis. Strong correlation among exposures prevented a detailed evaluation of the role of individual exposures. However, lung cancer risk was for the most part absent when concomitant exposure to other workplace lung carcinogens, such as polycyclic aromatic hydrocarbons (PAHs), nickel or radon-daughters, was considered. The cross classification of lung cancer risk by categories of exposure to respirable silica and total respirable dust did not show an independent effect of total respirable dust. Silicosis showed a modest association with lung cancer, which did not vary by severity of radiological staging, or by radiological evidence of disease progression, or by level of silica exposure. However, among silicotic subjects, lung cancer risk was significantly elevated only when exposure to cadmium and PAH had occurred. Our results suggest that, among silica-exposed Chinese workers, numerous occupational and non-occupational risk factors interact in a complex fashion to modify lung cancer risk. Future epidemiological studies on silica and lung cancer should incorporate detailed information on exposure to other workplace lung carcinogens, total respirable dust, and on surface size and age of silica particles to understand whether and to what extent they affect the carcinogenic potential of silica.

Estimating historical respirable crystalline silica exposures for Chinese pottery workers and iron/copper, tin, and tungsten miners

Collaborative studies of Chinese workers, using over four decades of dust monitoring data, are being conducted by the National Institute for Occupational Safety and Health (NIOSH) and Tongji Medical University in China. The goal of these projects is to establish exposure–response relationships for the development of diseases such as silicosis or lung cancer in cohorts of pottery and mine workers. It is necessary to convert Chinese dust measurements to respirable silica measurements in order to make results from the Chinese data comparable to other results in the literature.This article describes the development of conversion factors and estimates of historical respirable crystalline silica exposure for Chinese workers. Ambient total dust concentrations (n>17000) and crystalline silica concentrations (n=347) in bulk dust were first gathered from historical industrial hygiene records. Analysis of the silica content in historical bulk samples revealed no trend from 1950 up to the present. During 1988–1989, side-by-side airborne dust samples (n=143 pairs) were collected using nylon cyclones and traditional Chinese samplers in 20 metal mines and nine pottery factories in China. These data were used to establish conversion factors between respirable crystalline silica concentrations and Chinese total dust concentrations. Based on the analysis of the available evidence, conversion factors derived from the 1988–1989 sampling campaign are assumed to apply to other time periods in this paper. The conversion factors were estimated to be 0.0143 for iron/copper, 0.0355 for pottery factories, 0.0429 for tin mines, and 0.0861 for tungsten mines. Conversion factors for individual facilities within each industry were also calculated. Analysis of variance revealed that mean conversion factors are significantly different among facilities within the iron/copper industry and within the pottery industry. The relative merits of using facility-specific conversion factors, industry-wide conversion factors, or a weighted average of the two are discussed. The exposure matrix of the historical Chinese total dust concentrations was multiplied by these conversion factors to obtain an exposure matrix of historical respirable crystalline silica concentrations.

Estimating historical respirable crystalline silica exposures for Chinese pottery workers and iron/copper, tin, and tungsten miners

Collaborative studies of Chinese workers, using over four decades of dust monitoring data, are being conducted by the National Institute for Occupational Safety and Health (NIOSH) and Tongji Medical University in China. The goal of these projects is to establish exposure-response relationships for the development of diseases such as silicosis or lung cancer in cohorts of pottery and mine workers. It is necessary to convert Chinese dust measurements to respirable silica measurements in order to make results from the Chinese data comparable to other results in the literature. This article describes the development of conversion factors and estimates of historical respirable crystalline silica exposure for Chinese workers. Ambient total dust concentrations (n>17000) and crystalline silica concentrations (n=347) in bulk dust were first gathered from historical industrial hygiene records. Analysis of the silica content in historical bulk samples revealed no trend from 1950 up to the present. During 1988-1989, side-by-side airborne dust samples (n=143 pairs) were collected using nylon cyclones and traditional Chinese samplers in 20 metal mines and nine pottery factories in China. These data were used to establish conversion factors between respirable crystalline silica concentrations and Chinese total dust concentrations. Based on the analysis of the available evidence, conversion factors derived from the 1988-1989 sampling campaign are assumed to apply to other time periods in this paper. The conversion factors were estimated to be 0.0143 for iron/copper, 0.0355 for pottery factories, 0.0429 for tin mines, and 0.0861 for tungsten mines. Conversion factors for individual facilities within each industry were also calculated. Analysis of variance revealed that mean conversion factors are significantly different among facilities within the iron/copper industry and within the pottery industry. The relative merits of using facility-specific conversion factors, industry-wide conversion factors, or a weighted average of the two are discussed. The exposure matrix of the historical Chinese total dust concentrations was multiplied by these conversion factors to obtain an exposure matrix of historical respirable crystalline silica concentrations.