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.     

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.     

肺癌病因研究中接尘量计算的真实性评价

为评价肺癌病例对照研究中接尘剂量估算方法的真实性,对广西锡矿病因研究对象进行了重新计算。广西锡矿队列发现男性肺癌死者１３０例,配对照６２７例。共７５７人。其中接法工人５７２名,发现各期矽肺共２４３例,根据在斩工业卫生监测资料估算所有接尘工人的累积总粉尘接触量,再计算不同接尘水平下矽肺的发病率。结果显示,随接尘水平上升,矽肺发病率升高,两者存在明显的接触剂量反应关系。完全符合矽肺发病特点。从而间接证     

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.     

Indirect validation of a retrospective method of exposure assessment used in a nested case-control study of lung cancer and silica exposure.

Validations of retrospective methods of assessment used in occupational epidemiological studies have rarely been published. This study is an indirect validation of a quantitative retrospective assessment of exposure to silica used in a nested case-control study of lung cancer among workers at 29 metal mines and pottery factories in China. Indices of cumulative total dust and cumulative respirable dust were calculated by merging work histories with the historical exposure profile for each subject. To validate indirectly the methods of exposure assessment used in the study of lung cancer, trends for exposure response relation between the two indices of exposure to silica and risk of silicosis were evaluated with 376 patients with silicosis from the study population as the cases, and 1262 controls without silicosis for comparison. Age adjusted odds ratios (ORs) as a measure of risk of silicosis showed striking trends with both indices of exposure to silica. For cumulative respirable dust, the OR (95% confidence interval) rose from 7.6 (5.1-11.4) for low exposure to 20.0 (13.2-30.6) for medium exposure, and to 51.7 (31.0-86.8) for high exposure. The strength of the association between exposure to silica and risk of silicosis suggests that the retrospective assessment of exposure used in the case-control study of lung cancer would accurately reflect an exposure response relation between silica and lung cancer, if it existed.     

Estimating historical exposure to silica among mine and pottery workers in the people's Republic of China

A quantitative retrospective exposure assessment method was developed for use in a nested case-control study of lung cancer among mine and pottery workers exposed to silica dust in the People's Republic of China. Exposure assessment was carried out in 20 mines (10 tungsten, 6 iron/copper, and 4 tin) and nine pottery factories. A job title dictionary was developed and used in both the collection of historical exposure information and work histories of 1,668 (316 cases and 1,352 controls) study subjects. Several data abstraction forms were developed to collect historical and current exposure information and employees' work histories, starting in 1950. A retrospective exposure matrix was developed on the basis of facility/job title/calendar year combinations using available historical exposure information and current exposure profiles. Information on the amount of respirable, thoracic, and free silica content in total dust was used in estimating exposure to silica. Starting in 1950, 6,805 historical estimates had been carried out for 14 calendar-year periods. We estimated the average total dust concentration to be 9 mg/M³, with a range from 28 mg/M³ in earlier years to 3 mg/M³ in recent years. Several exposure indices [such as cumulative dust, average dust, cumulative respirable (<5 μ in particle size) and thoracic (<10 μ in particle size) silica dust, average respirable and thoracic silica dust, exposure-weighted duration, and the highest/longest exposure] were calculated for individuals by merging work history and historical exposure matrix for each study subject. We developed these various measures of exposure to allow investigators to compare and contrast different indices of historical exposure to silica. © 1993 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Respiratory effects of exposure to low levels of concrete dust containing crystalline silica

BACKGROUND: Dusts containing crystalline silica are generated in mining, construction, glass, granite and concrete production industries. The association between exposure to low levels of concrete dust containing crystalline silica and reduction in lung function, was evaluated in a cross-sectional study. METHODS: The study was carried out among 144 concrete workers, from two factories, with exposure assessment of respirable dust and silica by personal samplers. Results of respiratory questionnaires and standardized measurements of lung function were compared with the results in a control population. Multiple linear regression analysis was used in selecting factors that predict (age and standing height standardized residual) lung function. RESULTS: The average concentration of respirable dust in both factories was 0.8 mg/m(3) and 0.06 mg/m(3) for respirable silica. The average silica content of the dust was 9%. The average cumulative dust exposure was 7.0 mg/m(3) year and cumulative silica exposure was 0.6 mg/m(3) year. Significant associations between exposure to concrete dust and a small lung function (FEV(1)/FVC ratio, MMEF) loss were found, independent of smoking habits and of a history of allergy. CONCLUSIONS: Our results indicate that, concrete workers with chronic obstructive pulmonary symptoms and/or work-related lower respiratory symptoms are at risk of having a reduction in lung function (FEV&(1)/FVC ratio) outside the 5th percentile of the external reference population, and therefore, of mild chronic obstructive pulmonary disease, at respirable concrete dust levels below 1 mg/m(3) with a respirable crystalline silica content of 10% (TWA, 8 hr).     

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

BACKGROUND: 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). METHODS: 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. RESULTS: 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. CONCLUSION: 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.     

Exposure to silica and silicosis among tin miners in China: exposure-response analyses and risk assessment

OBJECTIVES—To investigate the risk of silicosis among tin miners and to investigate the relation between silicosis and cumulative exposure to dust (Chinese total dust and respirable crystalline silica dust).
METHODS—A cohort study of 3010 miners exposed to silica dust and employed for at least 1 year during 1960-5 in any of four Chinese tin mines was conducted. Historical total dust data from China were used to create a job exposure matrix for facility, job title, and calendar year. The total dust exposure data from China were converted to estimates of exposure to respirable crystalline silica for comparison with findings from other epidemiological studies of silicosis. Each worker''s work history was abstracted from the complete employment records in mine files. Diagnoses of silicosis were based on 1986 Chinese pneumoconiosis Roentgen diagnostic criteria, which classified silicosis as stages I-III—similar to an International Labour Organisation (ILO) classification of 1/1 or greater.
RESULTS—There were 1015 (33.7%) miners identified with silicosis, who had a mean age of 48.3 years, with a mean of 21.3 years after first exposure (equivalent to 11.0 net years in a dusty job). Among those who had silicosis, 684 miners (67.4%) developed silicosis after exposure ended (a mean of 3.7 years after). The risk of silicosis was strongly related to cumulative exposure to silica dust and was well fitted by the Weibull distribution, with the risk of silicosis less than 0.1% when the Chinese measure of cumulative exposure to total dust (CTD) was under 10 mg/m³-years (or 0.36 mg/m³-years of respirable crystalline silica), increasing to 68.7% when CTD exposure was 150 mg/m³-years (or 5.4 mg/m³-years of respirable crystalline silica). Latency period was not correlated to the risk of silicosis or cumulative dose of exposure. This study predicts about a 36% cumulative risk of silicosis for a 45 year lifetime exposure to these tin mine dusts at the CTD exposure standard of 2 mg/m³, and a 55% risk at 45 years exposure to the current United States Occupational Safety and Health Administration and Mine Safety and Health Administration standards of 0.1 mg/m³ 100% respirable crystalline silica dust.
CONCLUSIONS—A clear exposure-response relation was detected for silicosis in Chinese tin miners. The study results were similar to most, but not all, findings from other large scale exposure-response studies.


     

1817名铸造厂工人缺血性心脏病的队列研究

目的研究铸造作业工人缺血性心脏病发病风险及其与铸造作业、矽尘累积接触量之间的剂量-反应关系,并对缺血性心脏病的发病风险进行预测。方法采用队列研究方法,选择某铸造厂1980年1月1日-1996年12月31日在册一年以上的铸造作业工人建立研究队列,观察终止日期为2009年12月31日。以浇注、配砂、清理、熔炼、天车、造型和制芯等工种工人作为铸造组,电工、钳工和检查工等辅助工作为对照组。使用SPSS软件Cox回归模型分析缺血性心脏病发病风险及其与铸造作业、矽尘累积接触量之间的剂量-反应关系,并使用logistic回归建立缺血性心脏病发病风险的预测模型。结果本研究共随访30年,1817人,45 553.05人年,缺血性心脏病156例,人-年发病率为342.46/10万,平均发病年龄51.46岁,发病工龄21.61年。男性、吸烟、饮酒、年龄和工龄分别都是缺血性心脏病发病的危险因素。缺血性心脏病发病风险与矽尘累积接触量呈正相关,调整吸烟的影响后,工人矽尘年累积接触量每增加1mg/m3,缺血性心脏病发病风险增加75.8%(RR=1.758,95%CI1.221～2.532)。铸造组工人缺血性心脏病发病风险显著增加,调整吸烟的影响后,与对照组工人相比,配砂工、清理工、熔炼工、造型工、制芯工分别增加1.048倍、1.395倍、70.4%、97.0%和1.270倍。根据预测模型,工人缺血性心脏病发病概率随日接触矽尘浓度的增加、接尘工龄的延长而增加。结论铸造作业工人面临较大的缺血性心脏病发病风险。不同工种工人缺血性心脏病发病风险不同,其中,配砂、清理、熔炼、造型、制芯工人较高。铸造作业、矽尘累积接触量是缺血性心脏病的独立危险因素。缺血性心脏病预测模型表明,发病概率与日接触矽尘浓度和接尘工龄呈明显的剂量-反应关系。     

Occupational exposure assessment for crystalline silica dust: approach in Poland and worldwide

Crystalline silica is a health hazard commonly encountered in work environment. Occupational exposure to crystalline silica dust concerns workers employed in such industries as mineral, fuel-energy, metal, chemical and construction industry. It is estimated that over 2 million workers in the European Union are exposed to crystalline silica. In Poland, over 50 thousand people work under conditions of silica dust exposure exceeding the occupational exposure limit. The assessment of occupational exposure to crystalline silica is a multi-phase process, primarily dependent on workplace measurements, quantitative analyses of samples, and comparison of results with respective standards. The present article summarizes the approaches to and methods used for assessment of exposure to crystalline silica as adopted in different countries in the EU and worldwide. It also compares the occupational limit values in force in almost 40 countries. Further, it points out the consequences resulting from the fact that IARC has regarded the two most common forms of crystalline silica: quartz and cristobalite as human carcinogens. The article includes an inter-country review of the methods used for air sample collection, dust concentration measurements, and determination of crystalline silica. The selection was based on the GESTIS database which lists the methods approved by the European Union for the measurements and tests regarding hazardous agents. Special attention has been paid to the methods of determining crystalline silica. The author attempts to analyze the influence of analytical techniques, sample preparation and the reference materials on determination results. Also the operating parameters of the method, including limit of detection, limit of quantification, and precision, have been compared.     

Pulmonary alveolar proteinosis induced by silica dust?

Abstract Pulmonary alveolar proteinosis (PAP) is a rare disease, with several aetiologies. This study reports the first Finnish case of PAP with possible induction by silica dust. A 58-year-old male patient had a documented history of heavy exposure to silica dust over a long period, although he himself considered the exposure to be low. The patient's cumulative exposure to silica dust was approximately 10 mg m(-3) years according to the workplace measurements. The patient developed classical symptoms and signs of PAP that closely mimicked those of acute silicosis, but he did not have any signs of classic silicosis. We conclude that significant chronic exposure to silica favours the diagnosis of PAP rather than acute silicosis in this case. PAP should be taken into account when patients exposed to silica dust complain of respiratory symptoms. A patient's assessment of his/her exposure to silica may not always be reliable.     

锡矿作业工人粉尘接触和队列死因分析

[目的]评价混合性粉尘接触对锡矿作业工人健康的影响及累积粉尘接触与主要引起工人死亡疾病的关系。[方法]建立广西4个锡矿1972~1974年在册且工作一年以上工人的研究队列,以全国城市居民年龄别死亡率为参照,标化死亡比(SMR)作为统计指标。[结果]队列共计7837人,至1994年底,共计165156.7人年,死亡1094人。影响锡矿工人健康的主要疾病按累积死亡率从高到低排序分别是:肿瘤(5.3%)、脑血管疾病(2.4%)、心血管系统疾病(1.9%)和呼吸系统疾病(1.7%),这4种疾病引起的死亡占总数的80.7%,恶性肿瘤以肺癌和肝癌最多,分别占总死亡数的12.6%和10.9%。全死因标化死亡比(SMR=0.94)接近全国平均水平,而鼻咽癌、肝癌、肺癌、白血病、尘肺和脑血管疾病的SMR较高,分别为3.41、1.97、2.49、2.31、33.89和1.15。队列中接尘工人4629名,研究发现矿尘接触导致死亡率上升,与粉尘接触存在明确剂量反应关系的疾病主要是尘肺、肺癌和肺结核。[结论]混合性粉尘明显影响工人健康,累积粉尘接触与肺癌死亡存在剂量-反应关系,可能与粉尘中高含量的砷和游离二氧化硅有关。     

锡矿工人接尘与矽肺危险度评价

目的探讨粉尘暴露与矽肺危险度之间的接触效应关系。方法选择广西４个锡矿１９６０～１９６５年间工作１年以上的３０１０名接尘工人进行队列研究。用生存分析法统计累积粉尘接触量和矽肺出现的关系。结果追访到１９９４年底,检出矽肺１０１５例（３３．７％）。矽肺平均潜伏期２１．３年。总粉尘浓度７．５ｍｇ／ｍ３（ＴＷＡ）。拟合生存分析模型表明：矽肺发病危险度与累积接尘量的关系适合Ｗｅｉｂｕｌ分布。累积总粉尘接触量低于１０ｍｇ·ｍ－３·ａ－１时,矽肺危险小于１％;累积总粉尘接触量超过２０ｍｇ·ｍ－３·ａ－１时,矽肺累积危险度升高加快;累积总粉尘接触量达１５０ｍｇ·ｍ－３·ａ－１时,矽肺危险超过６８％。接尘时间与接尘量和矽肺危险度呈正相关。结论矽肺危险度与累积接尘量之间存在接触效应关系。     

Risk of pulmonary tuberculosis relative to silicosis and exposure to silica dust in South African gold miners [published erratum appears in Occup Environ Med 1999 Mar;56(3):215-6]

OBJECTIVES: To investigate the following questions. (1) Is silica dust on its own, without the presence of silicosis, associated with an increased risk of pulmonary tuberculosis (PTB) in workers exposed to silica dust? (2) In the absence of silicosis is the excess risk dose related? (3) What is the predominant chronological sequence between the development of PTB and the development of silicosis after the end of exposure to dust? METHODS: A cohort of 2255 white South African gold miners has been followed up from 1968 to 1971, when they were 45-55 years of age, to 31 December 1995 for the incidence of PTB. During the follow up 1592 (71%) men died. Of these, 1296 (81%) had a necropsy done at the National Centre for Occupational Health (NCOH) to determine the presence of silicosis and PTB. The incidence of PTB in the cohort was studied relative to cumulative exposure to dust and the onset of silicosis. For the miners with necropsy, the incidence for PTB was studied relative to the severity of silicosis found at necropsy. RESULTS: There were 115 subjects who developed PTB. The total person- years of follow up was 39,319. For the whole cohort, the factors associated with increased risk of PTB were cumulative exposure to dust (mg/m3.y) (the adjusted rate ratio (RR) 1.07; (95% confidence interval (95% CI) 1.04 to 1.10)), silicosis diagnosed radiologically (3.96 (2.59 to 6.06)), and tobacco pack-years (1.02 (1.01 to 1.03)). The RR (95% CI) for PTB increased with increasing quartiles of cumulative exposure to dust 1.0, 1.51 (0.78 to 2.91), 2.35 (1.28 to 4.32), and 3.22 (1.75 to 5.90). In miners who did not have radiologically diagnosed silicosis (n = 1934, PTB = 74), the adjusted RR (95% CI) for PTB and cumulative exposure to dust was 1.10 (1.06 to 1.13), and increased with quartiles of cumulative exposure to dust as 1.00, 1.46 (0.70 to 3.03), 2.67 (1.37 to 5.23), and 4.01 (2.04 to 7.88). For the subjects who had a necropsy (n = 1296, PTB = 70), the adjusted RR (95% CI) for PTB increased with the severity of silicosis found at necropsy; 1.0 for no silicosis, 1.88 (0.97 to 3.64) for negligible, 2.69 (1.35 to 5.37) for slight, and 2.30 (1.16 to 4.58) for moderate or marked silicosis. For subjects who had a necropsy and no silicosis (n = 577, PTB = 18), the adjusted RR (95% CI) increased slightly with quartiles of cumulative dust 1.0, 1.11 (0.31 to 4.00), 1.42 (0.43 to 4.72), and 1.38 (0.33 to 5.62). CONCLUSION: Exposure to silica dust is a risk factor for the development of PTB in the absence of silicosis, even after exposure to silica dust ends. The risk of PTB increases with the presence of silicosis, and in miners without radiological silicosis, with quartiles of exposure to dust. The severity of silicosis diagnosed at necropsy was associated with increasing risk of PTB and even < 5 nodules--that is, undetectable radiologically--was associated with an increased risk of PTB. The diagnosis of PTB was on average 7.6 years after the end of exposure to dust, at around 60 years of age. The onset of radiological silicosis preceded the diagnosis of PTB in 90.2% of the cases with PTB who had silicosis. The results have implications for medical surveillance of workers exposed to silica dust after the end of exposure.       

Change of exposure response over time and long-term risk of silicosis among a cohort of Chinese pottery workers

An analysis was conducted on a cohort of Chinese pottery workers to estimate the exposure-response relationship between respirable crystalline silica dust exposure and the incidence of radiographically diagnosed silicosis, and to estimate the long-term risk of developing silicosis until the age of 65. The cohort comprised 3,250 employees with a median follow-up duration of around 37 years. Incident cases of silicosis were identified via silicosis registries (Chinese X-ray stage I, similar to International Labor Organisation classification scheme profusion category 1/1). Individual exposure to respirable crystalline silica dust was estimated based on over 100,000 historical dust measurements. The association between dust exposure, incidence and long-time risk of silicosis was quantified by Poisson regression analysis adjusted for age and smoking. The risk of silicosis depended not only on the cumulative respirable crystalline silica dust exposures, but also on the time-dependent respirable crystalline silica dust exposure pattern (long-term average concentration, highest annual concentration ever experienced and time since first exposure). A long-term "excess" risk of silicosis of approximately 1.5/1,000 was estimated among workers with all annual respirable crystalline silica dust concentration estimates less than 0.1 mg/m(3), using the German measurement strategy. This study indicates the importance of proper consideration of exposure information in risk quantification in epidemiological studies.     

Historical respirable quartz exposures of industrial sand workers: 1946-1996

BACKGROUND: Besides a clear relationship to silicosis, crystalline silica-quartz-has been associated with lung cancer, nonmalignant renal disease, and auto-immune disease. To study diseases associated with crystalline silica further, NIOSH conducted a cohort mortality study of workers from 18 silica sand plants, which had quarry, crushing, and bagging operations to produce industrial sand. Twelve of these plants also had grinding mills to produce fine silica powder. The historical crystalline silica exposures of workers at these plants were estimated to facilitate exposure-response analyses in the epidemiologic study. METHODS: NIOSH obtained personal respirable dust measurement records from Mine Safety and Health Administration (MSHA) compliance inspections at all 18 plants and from the archives of seven plants which had collected samples. These samples had been analyzed for quartz content by x-ray diffraction. Although no personal samples were available before 1974, impinger dust measurements were reported for 19 silica sand plants in 1946; these data were converted and used to estimate exposures prior to 1974. Statistical modeling of the samples was used to estimate quartz exposure concentrations for workers in plant-job-year categories from the 1930s when mortality follow-up of the cohort began until 1988 when follow-up stopped. RESULTS: Between 1974 and 1996, there were 4,269 respirable dust samples collected at these 18 plants. The geometric mean quartz concentration was 25.9 microg/m(3) (GSD = 10.9) with a range from less than 1 to 11,700 microg/m(3). Samples below 1 microg/m(3) were given a value of 0.5 microg/m(3). Over one-third of the samples -37%) exceeded the MSHA permissible exposure limit value for quartz (PEL = 10 mg/m(3)/(%quartz + 2)) and half (51%) of the samples exceeded the NIOSH recommended exposure limit (REL=50 microg/m(3)). The samples were collected from workers performing 143 jobs within the 18 plants, but too few samples were collected from many of the jobs to make accurate estimates. Therefore, samples were combined into 10 categories of jobs performing similar tasks or located within the same plant area. CONCLUSIONS: The quartz concentrations varied significantly by plant, job, and year. Quartz concentrations decreased over time, with measurements collected in the 1970s significantly greater than those collected later. The modeled exposure estimates improve upon duration of employment as an estimate of cumulative exposure and reduce exposure misclassification due to variation in quartz levels between plants, jobs, and over time. Am. J. Ind. Med. 38:389-398, 2000. Published 2000 Wiley-Liss, Inc.     

The efficacy of local exhaust ventilation for controlling dust exposures during concrete surface grinding

This study assessed the effectiveness of a commercially available local exhaust ventilation (LEV) system for controlling respirable dust and crystalline silica exposures during concrete grinding activities. Surface grinding was conducted at six commercial building construction sites in Seattle, WA, by cement masons. Time-integrated filter samples and direct reading respirable dust concentrations were collected using a cyclone in line with a direct reading respirable dust monitor. Personal exposure levels were determined with and without LEV, one sample directly after the other. A total of 28 paired samples were collected in which three different dust collection shroud configurations were tested. Data obtained with a direct reading respirable dust monitor were adjusted to remove non-work task-associated dust exposures and was subsequently used to calculate the exposure reduction achieved. The application of LEV resulted in a reduction in the overall geometric mean respirable dust exposure from 4.5 to 0.14 mg/m(3), a mean exposure reduction of 92%. Despite the effective control of dust generated during surface grinding, 22 and 26% of the samples collected while LEV was being used were greater than the 8 h time-weighted average permissible exposure limit (Occupational Safety and Health Administration) and threshold limit value (American Congress of Governmental Industrial Hygienists) for respirable crystalline silica, respectively.     

Respirable crystalline silica dust exposure during concrete finishing (grinding) using hand-held grinders in the construction industry

Studies reporting the findings of exposure to crystalline silica dust during concrete finishing in construction settings are scarce due to the dynamic nature of the activity and the existence of many confounding factors. This study was initiated to explore the issue. A total of 49 personal respirable dust samples were collected during concrete finishing while workers used hand-held grinders. Only 15 (31%) of the grinders were equipped with local exhaust ventilation (LEV) systems. The confounding factors (e.g. wind velocity, wind direction, relative humidity and ambient temperature) were determined. To make the sampling task-specific, air sampling was activated only during actual grinding. Task-specific sampling times during each work shift ranged from 10 to 200 min. The concentration of total respirable particulate ranged from 0.34 to 81 mg/m3, with a mean +/- SD of 18.6 +/- 20.4 mg/m3, and the concentration of crystalline silica in the samples ranged from 0.02 to 7.1 mg/m3, with a mean +/- SD of 1.16 +/- 1.36 mg/m3. LEV on the grinders reduced the silica dust level significantly (P < 0.01) compared to grinders without LEV. Increased wind velocity also reduced the silica dust concentration significantly (P < 0.03). Working upwind reduced the exposure to silica dust compared to working downwind, but the difference was not statistically significant. The time-weighted average concentration of silica dust in 69% of the samples exceeded the current recommended threshold limit value of 0.05 mg/m3, indicating a strong need to devise methods for controlling workers' exposure to crystalline silica dust during concrete finishing activities.     

Occupational exposure and analysis of microcrystalline cristobalite in mullite operations

Three analytical methods currently used for crystalline free silica determination in occupational exposure samples were evaluated for their applicability to ceramic materials containing synthetic mullite. X-ray powder diffraction is the only method that can be used with sufficient precision and potentially adequate accuracy for occupational exposure monitoring. Personal respirable dust exposure samples were collected in two foundries. The results of exposure evaluations in Plant A showed overexposure to the dust, particularly in the shakeout area. The cristobalite concentration in the respirable dust exceeded that in the original material for this particular area. This may be related to the preheating of molds to more than 1100 degrees C for the pouring of stainless steel castings, causing conversion of some of the colloidal silica binder to cristobalite, and related to high vibration fracture of the material during removal of castings from molds. In Plant B, quartz was sometimes present along with cristobalite in personal samples. Respirable dust levels exceeded the Occupational Safety and Health Administration's (OSHA) permissible exposure limit (PEL) and the National Institute for Occupational Safety and Health's (NIOSH) recommended time-weighted average (TWA) for crystalline free silica, indicating a need for better engineering controls to reduce dust levels. The inadequacy of reference standards currently available for cristobalite analysis in these types of materials is cited. The need for more toxicological research is emphasized.