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1.  Classification of progressive massive fibrosis of coalminers by type of radiographic appearance. 
In a pilot study the chest radiographic appearances of 112 coalminers who developed progressive massive fibrosis (PMF) over an 11 year period have been classified into six types based on the appearances of the large radiographic opacities. The most common type of PMF was one or more large shadows of homogeneous radiodensity. Less common types included markedly rounded shadows usually less than 3 cm in diameter, non-homogeneous shadows appearing to consist of conglomerations of small rounded opacities, and condensations of linear or streaky shadows. Good reproducibility by one reader between two readings were obtained. The lifetime exposures to mixed respirable coal mine dust, and to its quartz component, of these 112 men were compared with those of control subjects matched for age and starting category of simple pneumoconiosis but without PMF. Overall, the men with PMF had been exposed to more mixed dust than controls, confirming that one of the reasons some men with simple pneumoconiosis develop PMF is that they have inhaled more dust than others. Eleven of the 112 cases had large opacities that were not homogeneous and appeared to consist of conglomerations of "r" type small rounded opacities. The average quartz exposures of these men were much higher than in control subjects, suggesting that in this type of PMF quartz was an important causative factor.
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PMCID: PMC1069354  PMID: 6743580
2.  Risks of respiratory disease in the heavy clay industry 
OBJECTIVES: Little information is available on the quantitative risks of respiratory disease from quartz in airborne dust in the heavy clay industry. Available evidence suggested that these risks might be low, possibly because of the presence in the dust of other minerals, such as illite and kaolinite, which may reduce the harmful effects of quartz. The aims of the present cross sectional study were to determine among workers in the industry (a) their current and cumulative exposures to respirable mixed dust and quartz; (b) the frequencies of chest radiographic abnormalities and respiratory symptoms; (c) the relations between cumulative exposure to respirable dust and quartz, and risks of radiographic abnormality and respiratory symptoms. METHODS: Factories were chosen where the type of process had changed as little as possible during recent decades. 18 were selected in England and Scotland, ranging in size from 35 to 582 employees, representing all the main types of raw material, end product, kilns, and processes in the manufacture of bricks, pipes, and tiles but excluding refractory products. Weights of respirable dust and quartz in more than 1400 personal dust samples, and site histories, were used to derive occupational groups characterised by their levels of exposure to dust and quartz. Full size chest radiographs, respiratory symptoms, smoking, and occupational history questionnaires were administered to current workers at each factory. Exposure-response relations were examined for radiographic abnormalities (dust and quartz) and respiratory symptoms (dust only). RESULTS: Respirable dust and quartz concentrations ranged from means of 0.4 and 0.04 mg.m-3 for non-process workers to 10.0 and 0.62 mg.m-3 for kiln demolition workers respectively. Although 97% of all quartz concentrations were below the maximum exposure limit of 0.4 mg.m-3, 10% were greater than this among the groups of workers exposed to most dust. Cumulative exposure calculations for dust and quartz took account of changes of occupational group, factory, and kiln type at study and non-study sites. Because of the importance of changes of kiln type additional weighting factors were applied to concentrations of dust and quartz during previous employment at factories that used certain types of kiln. 85% (1934 employees) of the identified workforce attended the medical surveys. The frequency of small opacities in the chest radiograph, category > or = 1/0, was 1.4% (median reading) and seven of these 25 men had category > or = 2/1. Chronic bronchitis was reported by 14.2% of the workforce and breathlessness, when walking with someone of their own age, by 4.4%. Risks of having category > or = 0/1 small opacities differed by site and were also influenced by age, smoking, and lifetime cumulative exposure to respirable dust and quartz. Although exposures to dust and to quartz were highly correlated, the evidence suggested that radiological abnormality was associated with quartz rather than dust. A doubling of cumulative quartz exposure increased the risk of having category > or = 0/1 by a factor of 1.33. Both chronic bronchitis and breathlessness were significantly related to dust exposure. CONCLUSIONS: Although most quartz concentrations at the time of this study were currently below regulatory limits in the heavy clay industry, high exposures regularly occurred in specific processes and occasionally among most occupational groups. However, there are small risks of pneumoconiosis and respiratory symptoms in the industry, although frequency of pneumoconiosis is low in comparison to other quartz exposed workers.
 
PMCID: PMC1757705  PMID: 10448318
3.  THEORY AND MEASUREMENT OF VISUAL MECHANISMS  
The Journal of General Physiology  1944;27(4):287-313.
1. When there is projected on the retina (man, monocularly) the shadow of a grid which forms a visual field in several distinct pieces (not including the fovea in the present tests), the ordinary properties of the flicker recognition contour (F vs. log I) as a function of the light-time cycle fraction (tL) can be markedly disturbed. In the present experiments flicker was produced by the rotation of a cylinder with opaque vertical stripes. In the absence of such a grid shadow the "cone" segments of the contours form a set in which Fmax. and the abscissa of inflection are opposite but rectilinear functions of tL, while the third parameter of the probability integral (σ'log I) remains constant. This is the case also with diverse other animals tested. In the data with the grid, however, analysis shows that even for low values of tL (up to 0.50) there occurs an enhancement of the production of elements of neural effect, so that Fmax. rises rather than falls as ordinarily with increase of tL, although σ'log I stays constant and hence the total number of acting units is presumed not to change. This constitutes valid evidence for neural integration of effects due to the illumination of separated retinal patches. Beginning at tL = 0.75, and at 0.90, the slope of the "cone" curve is sharply increased, and the maximum F is far above its position in the absence of the grid. The decrease of σ'log I (the slope constant) signifies, in terms of other information, an increase in the number of acting cone units. The abscissa of inflection is also much lowered, relatively, whereas without the grid it increases as tL is made larger. These effects correspond subjectively to the fact that at the end-point flicker is most pronounced, on the "cone" curve, along the edges of the grid shadow where contrast is particularly evident with the longer light-times. The "rod" portion of the F - log I contour is not specifically affected by the presence of the grid shadow. Its form is obtainable at tL = 0.90 free from the influence of summating "cone" contributions, because then almost no overlapping occurs. Analysis shows that when overlapping does occur a certain number of rod units are inhibited by concurrent cone excitation, and that the mean contribution of elements of neural action from each of the non-inhibited units is also reduced to an extent depending on the degree of overlap. The isolated "rod" curve at tL = 0.90 is quite accurately in the form of a probability integral. The data thus give a new experimental proof of the occurrence of two distinct but interlocking populations of visual effects, and experimentally justify the analytical procedures which have been used to separate them. 2. The changing form of the F - log I contour as a function of tL, produced in man when the illuminated field is divided into parts by a shadow pattern, is normally found with the bird Taeniopygia castenotis (Gould), the zebra finch. The retina has elements of one general structural type (cones), and the F - log I contour is a simplex symmetrical probability integral. The eye of this bird has a large, complex, and darkly pigmented pecten, which casts a foliated shadow on the retina. The change in form of the F - log I curve occurs with tL above 0,50, and at tL = 0.90 is quite extreme. It is more pronounced than the one that is secured in the human data with the particular grid we have used, but there is no doubt that it could be mimicked completely by the use of other grids. The increase of flicker acuity due to the pecten shadow is considerable, when the dark spaces are brief relative to the light. The evidence thus confirms the suggestion (Menner) drawn from comparative natural history that the visual significance of the avian pecten might be to increase the sensory effect of small moving images. It is theoretically important that (as in the human experiment) this may be brought about by an actual decrease of effective retinal area illuminated. It is also significant theoretically that despite the presence of shadows of pecten or of grid, and of the sensory influences thus introduced, the probability integral formulation remains effective.
PMCID: PMC2238017  PMID: 19873387
4.  Pulmonary disease from occupational exposure to an artificial aluminium silicate used for cat litter. 
All available workers engaged in bagging an artificial crystalline aluminium silicate--the kiln-dried residue from the calcining and water extraction of alunite (a hydrated sulphate of aluminium and potassium) that is currently classified as a nuisance dust--were studied after a complaint of respiratory and systemic symptoms, including arthritis, by an employee of the factory, who showed physiological and radiographic evidence of diffuse pulmonary fibrosis and in whom lung biopsy showed diffuse fibrosis with granulomas. Inhalation challenge produced a transient decrease in transfer factor and transfer factor standardised for alveolar volume. Twenty-five subjects were known to have been exposed at some time to the dust of alunite-residue. Of the 17 who could be contacted, all agreed to attend for respiratory questionnaire and occupational history, pulmonary function testing (spirometry, lung volumes, gas transfer), and posteroanterior chest radiograph. Six subjects considered that occupational exposure to the dust was responsible for respiratory symptoms. Three subjects had abnormality of the chest radiograph consistent with pulmonary fibrosis. The mean percentage of predicted transfer factor standardised for effective alveolar volume was 71.1% in subjects with abnormal chest radiographs and 86.6% in subjects with normal radiographs (p = 0.10). There was a trend in the correlation between the percentage of predicted transfer factor standardised for effective alveolar volume and total dust exposure (sum of the products of grade of severity of each exposure period and duration of each exposure period in months) (r = 0.40 p = 0.10). This study suggests that there may be a relation between inhalation of the dust of this form of aluminium silicate and pulmonary fibrosis.
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PMCID: PMC1008753  PMID: 7448131
5.  Hut lung: a domestically acquired pneumoconiosis of mixed aetiology in rural women. 
Thorax  1991;46(5):334-340.
A form of pneumoconiosis in rural African women termed "Transkei silicosis" has been thought to be due to silica particles inhaled while they are hand grinding maize between rocks. Twenty five women were studied who were considered to have this condition according to the following criteria: rural domicile, radiographic and lung biopsy evidence of pneumoconiosis, no exposure to mining or industry and no evidence of active tuberculosis. They were assessed for radiological, pathological, physiological and bronchoalveolar lavage fluid features. Potential aetiological factors were assessed by determining levels of exposure to respirable quartz and non-quartz containing dusts and smoke in rural dwellings during maize grinding and cooking. Most of the women were symptomless. Radiological findings ranged from a miliary pattern to extensive fibrosis resembling progressive massive fibrosis. Histological features included simple "anthracosis" in 12, anthracosis with macules in six, and mixed dust fibrosis in seven. Cell numbers and their proportions in lavage fluid were normal. More than 60% of macrophages were heavily laden with inorganic inclusions. Respirable quartz concentrations and calculated cumulative time weighted exposures were below those recommended for industry during grinding with sandstone (100% quartz) and they were even lower during grinding with dolerite containing no quartz despite the presence of an appreciable amount of quartz in the ground maize. Total respirable dust and smoke concentrations were greater than the recommended safe levels. Three women had no exposure to maize grinding. It is concluded that the inhalation of non-quartz containing dust and smoke from biomass fuelled fires is more important in the aetiology of this condition than exposure to quartz dust. The term "hut lung" may be more appropriate.
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PMCID: PMC463130  PMID: 2068688
6.  Baritosis: a benign pneumoconiosis. 
Thorax  1976;31(1):30-39.
Baritosis is one of the benign pneumoconioses in which inhaled particulate matter lies in the lungs for years without producing symptoms, abnormal physical signs, incapacity for work, interference with lung function, or liability to develop pulmonary or bronchial infections or other thoracic disease. Owing to the high radio-opacity of barium, the discrete shadows in the chest radiograph are extremely dense. Even in the most well-marked cases with extreme profusion of the opacities, massive shadows do not occur. When exposure to barium dust ceases the opacities begin slowly to disappear. Nine cases of baritosis occurring in a small factory in which barytes was crushed, graded, and milled are described. Two of the cases occurred after only 18 and 21 month's exposure, and 9 of the 10 men employed for more than one and a half years had baritosis. Five of the affected men examined at intervals since their exposure to barytes ceased in 1964 showed marked clearing of their radiological abnormalities.
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PMCID: PMC470358  PMID: 1257935
7.  A study of Spanish sepiolite workers. 
Thorax  1993;48(4):370-374.
BACKGROUND--Sepiolite is an absorbent clay that is used as pet litter. It forms thin crystals, which are a transition between chain and layered silicates. Inhalation studies in animals have shown no evidence of pulmonary damage. This paper reports a cross sectional study of the total work force of the largest sepiolite production plant in the world. METHODS--Two hundred and eighteen workers (210 men and eight women) were studied. Height, age, and smoking history were recorded. Chest radiographs were read according to the International Labour Office (ILO) classification by two readers. Readings were used to construct a numerical score, which was then used in statistical analyses. Forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were divided by the square of the height. Casella size selective personal samplers were used in randomly selected operatives to collect dust eight years before the rest of the study was carried out. These samples were evaluated gravimetrically. Total dust samples were examined by optical and electron microscopes. Results were analysed by bivariate linear regression, chi 2 tests, and analysis of variance. RESULTS--When allowance was made for smoking habit workers exposed to dry dust showed a significantly greater decline in FEV1 with age than workers with little exposure to dry dust. A similar pattern applied to FVC. Radiographic score showed deterioration with age but no clear differences from other variables. High concentrations of dust were found in the bagging department and also in the classifier shed. CONCLUSIONS--The major finding was that lung function deteriorated more rapidly in those who had had more exposure to dust, but there was no evidence of any accompanying radiographic change.
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PMCID: PMC464435  PMID: 8511734
8.  Kaolin dust concentrations and pneumoconiosis at a kaolin mine. 
Thorax  1984;39(6):436-441.
Kaolin is removed from underground seams in the mining area to a processing area, where it is sliced, dried, and pulverised to make the finished product. A study was undertaken to determine the dust concentrations in various work areas and to assess the prevalence of radiographic and pulmonary function abnormalities in 65 workers at a Georgia kaolin mine. Respirable dust concentrations were higher in the processing area than in the mine or maintenance areas for all determinations from 1977 to 1981. The mean respirable dust level in the processing area in 1981 was 1.74 mg/m3 and 0.14 mg/m3 in the mine area. Five workers, all of whom had worked at the processing area, had radiographic evidence of kaolin pneumoconiosis. The mean values of forced vital capacity (FVC) and FEV1 of the entire group were within the normal range. When the spirometric values were expressed as a percentage of the predicted values, the FVC and FEV1 were significantly lower in the workers with kaolinosis than in other workers in the processing area. The FVC and FEV1 also declined significantly with increasing years of work in the processing area. The FEV1/FVC%, however, was not significantly altered either by the presence of kaolinosis or by an increasing number of years of work, indicating that the impairment was restrictive and hence likely to be a consequence of dust inhalation rather than smoking. In this study the highest dust concentrations occurred in the processing area, and kaolin pneumoconiosis was limited to those who had worked there. Kaolin exposure appeared to have a small but significant effect on ventilatory capacity in those with kaolin pneumoconiosis and in workers with a longer exposure. There was no association between the radiographic appearances of kaolinosis and cigarette smoking or between the presence of radiographic abnormalities and reduced arterial blood gas tensions.
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PMCID: PMC459826  PMID: 6463912
9.  Small animals in the study of pathological effects of asbestos 
The main pathological effects attributed to asbestos are carcinogenesis and fibrogenesis. Statistical studies have shown that asbestos workers may expect a higher morbidity not only from cancer of the lung and mesothelioma but also from cancer at other sites. Carcinomas have been reported in animals following the injection of asbestos, but the production of carcinomas by inhaled asbestos is less easy to demonstrate; most examples of experimental carcinogenesis with asbestos have been produced in rats. Rats and man react differently to asbestos in that rats do not produce asbestos bodies.
The fibrosis that follows inhalation of asbestos has been frequently described, but studies with specific pathogen free animals have shown that, like the fibrosis that may follow the inhalation of silica dust, gross fibrosis involving the production of abnormal amount of collagen probably requires the intervention of infection as well as asbestos.
Because of the difficulties encountered in the direct investigation of carcinogenesis and fibrogenesis resulting from the inhalation of asbestos, attention has been directed to the mechanisms by which the lung is able to protect itself against these fibrous dusts. While non-fibrous dusts and short fibers can be ingested by macrophages and removed via the bronchus, the long fibers that may also reach the alveolar regions may not be removed by this mechanism. The probability that a fiber may reach the alveoli depends largely on the fiber diameter and only to a small extent on the fiber length, so that, for example, fibers 100 μm long may reach the alveoli of a guinea pig. These long fibers may become coated with a ferroprotein derived from hemoglobin to form an asbestos body and, after morphological changes, the asbestos body may be broken up, the fragments ingested by macrophages and dissolved. The lung is thus cleared of asbestos. In the guinea pig lung, consolidated areas from which the asbestos has disappeared shows signs of return to normal.
This clearance mechanism is inhibited by other factors: quartz dust may almost completely inhibit asbestos body formation; tobacco smoke has a considerable effect, and even very heavy loads of carbon may act similarly.
The normal lung appears able to efficiently eliminate small loads of both nonfibrous and fibrous dust, including the carcinogenic asbestos fibers. The capacity is not unlimited, however, and when the load is heavy there is a much greater probability that fibers will not be detoxicated. In addition, other factors such as silica dust and tobacco smoke may remove the protective mechanism in the lungs.
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PMCID: PMC1475401  PMID: 4377872
10.  Measuring Dust Exposure with the Thermal Precipitator in Collieries and Foundries 
The standard thermal precipitator has been modified for field surveys of airborne dust exposure so as to make it more portable. A microprojector is used when assessing the samples and for coal-mine dusts the counts are restricted to the range 0·5 to 5 microns.
In industrial environments the dust concentration appears to vary with a standard deviation of more than 50% of the mean. Part of this variability is due to errors of the thermal precipitator. The standard error of a count of a sample is about 10% to 15% in practical work and the combined effect of this and other errors is that the standard error of a single result is about 15%. However, in practice this can be neglected since the dust concentration itself is so variable. A more important source of error is the bias, due to overlapping among the particles on the cover glasses. The count may give a serious underestimate of the number of airborne particles if high sample densities are used.
The product of average concentration and duration of exposure is probably a good index of the dose of dust retained in a man's lungs. The duration of exposure is measured by a simple time study made at the same time as the concentration is measured.
Samples are taken near workers chosen at random to give unbiased estimates of the dust exposure. Ideally successive samples are taken alongside different workers. However, in a survey at a colliery it was not possible to do this and each day had to be spent with one collier. The mean dust exposure of the coal-getters was 2,860 particle-hours per shift, of those on stone work 2,250 particle-hours per shift, and the remainder had a mean dust exposure of 1,010 particle-hours per shift.
In a survey at a steel works successive samples could be taken alongside different workers. It was found that the dustiness was unrelated to the apparently dusty processes and as the dust was very fine it was suspected that it was the normal atmospheric pollution of the neighbourhood. This was confirmed by samples taken outside.
The cost of such surveys is found to lie between £1 and £2 per sample taken and consequently alternative instruments are being developed which can run unattended for long periods. In future research studies respiratory ventilation as well as dust exposure may be measured over many years, which, combined with periodic medical examinations, would enable the relation between dust exposure and its effects on the men to be determined.
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PMCID: PMC1037902  PMID: 13651553
11.  Respiratory health effects and exposure to superabsorbent polymer and paper dust - an epidemiological study 
BMC Public Health  2011;11:557.
Background
The primary aim of the present study was to investigate if exposure to dust from absorbent hygiene products containing superabsorbent polymer is related to symptoms from the airways and from the eyes. The secondary aim was to estimate the current exposure to superabsorbent polymer among production and maintenance workers in a plant producing hygiene products.
Methods
The cohort comprised 1043 workers of whom 689 were exposed to super absorbent polymer and 804 were exposed to paper dust (overlapping groups). There was 186 workers not exposed to either superabsorbent polymer or to paper dust They were investigated with a comprehensive questionnaire about exposure, asthma, rhinitis and symptoms from eyes and airways. The results were analyzed with logistic regression models adjusting for sex, age, atopy and smoking habits. An aerosol sampler equipped with a polytetrafluoroethylene filter with 1 μm pore size was used for personal samplings in order to measure inhalable dust and superabsorbent polymer.
Results
The prevalence of nasal crusts (OR 1.4, 95% CI 1.01-2.0) and nose-bleeding (OR 1.7, 95% CI 1.2-2.4) was increased among the paper dust exposed workers (adjusted for superabsorbent polymer exposure). There were no significant effects associated with exposure to superabsorbent polymer (adjusted for paper dust exposure). The average exposure to inhalable levels of total dust (paper dust) varied between 0.40 and 1.37 mg/m3. For superabsorbent polymer dust the average exposure varied between 0.02 and 0.81 mg/m3.
Conclusions
In conclusion, our study shows that workers manufacturing diapers in the hygiene industry have an increased prevalence of symptoms from the nose, especially nose-bleeding. There was no relation between exposure to superabsorbent polymer and symptoms from eyes, nose or respiratory tract, but exposure to paper dust was associated with nose-bleeding and nasal crusts. This group of workers had also a considerable exposure to superabsorbent polymer dust.
doi:10.1186/1471-2458-11-557
PMCID: PMC3155498  PMID: 21752269
12.  Pulmonary Fibrosis and Encephalopathy Associated with the Inhalation of Aluminium Dust 
The clinical, radiographic, pathological, and environmental features of a case of extensive aluminium fibrosis of the lungs are reported in a man of 49 years of age who had worked for 13½ years in the ball-mill room of an aluminium powder factory.
It is noteworthy that his symptoms were referable to the central nervous system, and that he died from terminal broncho-pneumonia following rapidly progressive encephalopathy, associated with epileptiform attacks. He had no presenting pulmonary symptoms, and ϰ-ray examination of the chest showed only slight abnormalities. Radiographic examination of the chests of 53 other workers in the same factory, and clinical examination with lung function tests of 23 of them revealed no other definite cases of aluminium fibrosis of the lung, nor any other cases with neurological signs and symptoms.
Estimations of the aluminium contents of the body tissues such as the lungs, brain, liver, and bone are also recorded. When compared with normal values, it was found that the lungs and brain contained about 20 times and the liver 122 times more than normal. As a contribution to the study of the aluminium content of normal tissues, and as a control series for the results given by Tipton, Cook, Steiner, Foland, McDaniel, and Fentress (1957), and Tipton, Cook, Foland, Rittner, Hardwick, and McDaniel (1958, 1959), the aluminium content of eight “normal” brains was estimated and in all cases it was found to be less than 0·6 μg. Al/g. wet weight.
The results of a survey of the dust concentrations in the factory are also given.
The use of aluminium compounds in the experimental production of epilepsy in primates is reviewed, and it is suggested that the neurological signs and symptoms with epileptiform convulsions which occurred in this case might have been related to aluminium intoxication. We hold the view, however, that the interstitial and nodular fibrosis found in the lungs was undoubtedly associated with the inhalation and retention of aluminium dust.
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PMCID: PMC1038218  PMID: 13932137
13.  Long-Term Exposure to Silica Dust and Risk of Total and Cause-Specific Mortality in Chinese Workers: A Cohort Study 
PLoS Medicine  2012;9(4):e1001206.
A retro-prospective cohort study by Weihong Chen and colleagues provides new estimates for the risk of total and cause-specific mortality due to long-term silica dust exposure among Chinese workers.
Background
Human exposure to silica dust is very common in both working and living environments. However, the potential long-term health effects have not been well established across different exposure situations.
Methods and Findings
We studied 74,040 workers who worked at 29 metal mines and pottery factories in China for 1 y or more between January 1, 1960, and December 31, 1974, with follow-up until December 31, 2003 (median follow-up of 33 y). We estimated the cumulative silica dust exposure (CDE) for each worker by linking work history to a job–exposure matrix. We calculated standardized mortality ratios for underlying causes of death based on Chinese national mortality rates. Hazard ratios (HRs) for selected causes of death associated with CDE were estimated using the Cox proportional hazards model. The population attributable risks were estimated based on the prevalence of workers with silica dust exposure and HRs. The number of deaths attributable to silica dust exposure among Chinese workers was then calculated using the population attributable risk and the national mortality rate. We observed 19,516 deaths during 2,306,428 person-years of follow-up. Mortality from all causes was higher among workers exposed to silica dust than among non-exposed workers (993 versus 551 per 100,000 person-years). We observed significant positive exposure–response relationships between CDE (measured in milligrams/cubic meter–years, i.e., the sum of silica dust concentrations multiplied by the years of silica exposure) and mortality from all causes (HR 1.026, 95% confidence interval 1.023–1.029), respiratory diseases (1.069, 1.064–1.074), respiratory tuberculosis (1.065, 1.059–1.071), and cardiovascular disease (1.031, 1.025–1.036). Significantly elevated standardized mortality ratios were observed for all causes (1.06, 95% confidence interval 1.01–1.11), ischemic heart disease (1.65, 1.35–1.99), and pneumoconiosis (11.01, 7.67–14.95) among workers exposed to respirable silica concentrations equal to or lower than 0.1 mg/m3. After adjustment for potential confounders, including smoking, silica dust exposure accounted for 15.2% of all deaths in this study. We estimated that 4.2% of deaths (231,104 cases) among Chinese workers were attributable to silica dust exposure. The limitations of this study included a lack of data on dietary patterns and leisure time physical activity, possible underestimation of silica dust exposure for individuals who worked at the mines/factories before 1950, and a small number of deaths (4.3%) where the cause of death was based on oral reports from relatives.
Conclusions
Long-term silica dust exposure was associated with substantially increased mortality among Chinese workers. The increased risk was observed not only for deaths due to respiratory diseases and lung cancer, but also for deaths due to cardiovascular disease.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Walk along most sandy beaches and you will be walking on millions of grains of crystalline silica, one of the commonest minerals on earth and a major ingredient in glass and in ceramic glazes. Silica is also used in the manufacture of building materials, in foundry castings, and for sandblasting, and respirable (breathable) crystalline silica particles are produced during quarrying and mining. Unfortunately, silica dust is not innocuous. Several serious diseases are associated with exposure to this dust, including silicosis (a chronic lung disease characterized by scarring and destruction of lung tissue), lung cancer, and pulmonary tuberculosis (a serious lung infection). Moreover, exposure to silica dust increases the risk of death (mortality). Worryingly, recent reports indicate that in the US and Europe, about 1.7 and 3.0 million people, respectively, are occupationally exposed to silica dust, figures that are dwarfed by the more than 23 million workers who are exposed in China. Occupational silica exposure, therefore, represents an important global public health concern.
Why Was This Study Done?
Although the lung-related adverse health effects of exposure to silica dust have been extensively studied, silica-related health effects may not be limited to these diseases. For example, could silica dust particles increase the risk of cardiovascular disease (diseases that affect the heart and circulation)? Other environmental particulates, such as the products of internal combustion engines, are associated with an increased risk of cardiovascular disease, but no one knows if the same is true for silica dust particles. Moreover, although it is clear that high levels of exposure to silica dust are dangerous, little is known about the adverse health effects of lower exposure levels. In this cohort study, the researchers examined the effect of long-term exposure to silica dust on the risk of all cause and cause-specific mortality in a large group (cohort) of Chinese workers.
What Did the Researchers Do and Find?
The researchers estimated the cumulative silica dust exposure for 74,040 workers at 29 metal mines and pottery factories from 1960 to 2003 from individual work histories and more than four million measurements of workplace dust concentrations, and collected health and mortality data for all the workers. Death from all causes was higher among workers exposed to silica dust than among non-exposed workers (993 versus 551 deaths per 100,000 person-years), and there was a positive exposure–response relationship between silica dust exposure and death from all causes, respiratory diseases, respiratory tuberculosis, and cardiovascular disease. For example, the hazard ratio for all cause death was 1.026 for every increase in cumulative silica dust exposure of 1 mg/m3-year; a hazard ratio is the incidence of an event in an exposed group divided by its incidence in an unexposed group. Notably, there was significantly increased mortality from all causes, ischemic heart disease, and silicosis among workers exposed to respirable silica concentrations at or below 0.1 mg/m3, the workplace exposure limit for silica dust set by the US Occupational Safety and Health Administration. For example, the standardized mortality ratio (SMR) for silicosis among people exposed to low levels of silica dust was 11.01; an SMR is the ratio of observed deaths in a cohort to expected deaths calculated from recorded deaths in the general population. Finally, the researchers used their data to estimate that, in 2008, 4.2% of deaths among industrial workers in China (231,104 deaths) were attributable to silica dust exposure.
What Do These Findings Mean?
These findings indicate that long-term silica dust exposure is associated with substantially increased mortality among Chinese workers. They confirm that there is an exposure–response relationship between silica dust exposure and a heightened risk of death from respiratory diseases and lung cancer. That is, the risk of death from these diseases increases as exposure to silica dust increases. In addition, they show a significant relationship between silica dust exposure and death from cardiovascular diseases. Importantly, these findings suggest that even levels of silica dust that are considered safe increase the risk of death. The accuracy of these findings may be affected by the accuracy of the silica dust exposure estimates and/or by confounding (other factors shared by the people exposed to silica such as diet may have affected their risk of death). Nevertheless, these findings highlight the need to tighten regulations on workplace dust control in China and elsewhere.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001206.
The American Lung Association provides information on silicosis
The US Centers for Disease Control and Prevention provides information on silica in the workplace, including links to relevant US National Institute for Occupational Health and Safety publications, and information on silicosis and other pneumoconioses
The US Occupational Safety and Health Administration also has detailed information on occupational exposure to crystalline silica
What does silicosis mean to you is a video provided by the US Mine Safety and Health Administration that includes personal experiences of silicosis; Dont let silica dust you is a video produced by the Association of Occupational and Environmental Clinics that identifies ways to reduce silica dust exposure in the workplace
The MedlinePlus encyclopedia has a page on silicosis (in English and Spanish)
The International Labour Organization provides information on health surveillance for those exposed to respirable crystalline silica
The World Health Organization has published a report about the health effects of crystalline silica and quartz
doi:10.1371/journal.pmed.1001206
PMCID: PMC3328438  PMID: 22529751
14.  Piezoelectric Driving of Vibration Conveyors: An Experimental Assessment 
Sensors (Basel, Switzerland)  2013;13(7):9174-9182.
Vibratory feeders or vibratory conveyors have been widely used for the transport and orientation of individual parts and bulk materials in many branches of industrial activity. From the designer's standpoint, the current endeavor is to conceive efficient vibratory feeders, satisfying constraints of power consumption, vibration transmission and noise emission. Moreover, the interest in the reduction of maintenance cost is always present. In this context, this paper investigates experimentally the concept of vibratory conveying based on the use of piezoelectric materials for motion generation. A small-size prototype of a linear conveyor, in which lead-zirconate-titanate (PZT) patches are bonded to the resilient elements, is described. One of the main design goals is that the prototype is intended to be fed directly from the electric network, aiming at avoiding the use of electronic equipment for driving. To comply with this feature and, at the same time, enable to adjust the transport velocity, a mechanical device has been conceived in such a way that the first natural frequency of the conveyor can be changed. It is shown that the transport velocity is determined by the proximity between the excitation frequency and the first natural frequency of the conveyor. The experimental tests performed to characterize the dynamic behavior of the prototype are described and the range of transport velocities is determined.
doi:10.3390/sl30709174
PMCID: PMC3758643  PMID: 23867743
vibratory feeder; vibratory conveyor; automation; piezoelectricity
15.  Studies in chronic allergic bronchopulmonary aspergillosis. 2. Radiological findings. 
Thorax  1977;32(3):262-268.
The characteristics and the incidence of changes in plain chest radiographs were analysed in detail in 50 asthmatic patients with chronic allergic bronchopulmonary aspergillosis in whom the diagnosis had been made from 2 to 25 years previously (mean duration 10-9 years). One thousand two hundred and forty-two chest radiographs, an average of about two per year per patient, were reviewed. Two hundred and sixty-seven acute episodes of transient shadows (a mean of 5-3 per patient), mostly homogeneous consolidations and band-like shadows, were recorded throughout the period of follow-up. Features of overinflation were present in 21 patients in the first radiograph and in 17 in the last, the decrease being attributed to the effects of permanent lung damage due to the allergic aspergillosis. Permanent changes, such as tubular and ring shadows, loss of vascular shadows, and lobar shrinkage were recorded in 41 patients at the start and in 49 at the end of the follow-up. The tubular shadows were found in 28 patients in the first radiograph and in 45 in the last, whereas ring shadows were seen in 18 and 30 patients respectively. Half of the episodes of consolidation and atelectasis left permanent changes, mainly ring shadows, as seen in the last radiograph. Of the band-like shadows, 32% were found to be followed by the subsequent appearance of tubular shadows. Statistically significant correlations were found between the duration of aspergillosis, the number of transient shadows throughout the period of follow-up, the extent of the permanent shadows, and the reduction of gas transfer factor at the time of the final follow-up.
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PMCID: PMC470594  PMID: 882940
16.  Respiratory diseases in hard metal workers: an occupational hygiene study in a factory. 
A hygiene study of a hard metal factory was conducted from 1981 to 1984. All workers exposed to hard metal were medically examined and their exposure to cobalt measured. Eighteen employees had occupational asthma related to exposure to hard metal, a prevalence rate of 5.6%. Nine had a positive bronchial provocation test to cobalt and reactions of the immediate, late, or dual type were elicited. Exposure measurements suggest that asthma may be caused by cobalt at a mean time weighted average concentration below 0.05 mg/m3. Only two of the nine individuals with cobalt asthma had a positive patch test to cobalt. Chest radiographs of three workers showed diffuse shadows of category 1 or over. X ray microanalysis of lung biopsy specimens from two of these three workers showed the presence of tungsten, titanium, cobalt, nickel, and some minerals. One of the two was diagnosed as having pneumoconiosis due to exposure to silica in a steel industry and the other was suspected of having pulmonary fibrosis caused by dust generated from the carborundum wheels used to grind hard metal. There were no cases with interstitial pneumonitis in the factory.
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PMCID: PMC1007687  PMID: 3718895
17.  Respiratory disorders associated with heavy inhalation exposure to dolomite dust 
Background
Although dolomite is classified as a relatively non-toxic, nuisance dust, little information exists as to its potential to produce respiratory disorders following occupational exposure. The purpose of this study was, therefore, to evaluate the possible effects, if any, of heavy inhalation exposure to this chemical on the prevalence of respiratory symptoms, functional impairments and radiographic abnormalities of the lungs.
Methods
The study population consisted of a group of 39 exposed subjects engaged in digging and excavating activities that were in operation for building a local dam, as well as 40 healthy non-exposed employees that served as the referent group. Subjects were interviewed and respiratory symptoms questionnaires, as suggested by the American Thoracic Society (ATS), were completed for them. Thereafter, they underwent chest X-ray and lung function tests. Additionally, using routine gravimetric techniques, personal dust monitoring for airborne inhalable and respirable dust was carried out at different dusty work sites. Finally to determine the chemical composition of the dust, it was analyzed by X-ray fluorescence (XRF) technique.
Results
XRF revealed that the major component (50.52%) of the dust was calcium magnesium carbonate, dolomite. Additionally, levels of exposure to inhalable and respirable dust were estimated to be 51.7±24.31 and 23.0±18.11mg/m3, respectively. Statistical analysis of the data showed that symptoms such as regular cough, phlegm, wheezing, productive cough and shortness of breath were significantly (p<0.05) more prevalent among exposed workers. Similarly, the ratio of FEV1/FVC in exposed subjects was significantly different from that of non-exposed individuals. In contrast, no significant abnormalities were observed in the chest radiographs of both groups.
Conclusions
In conclusion, while these data cast doubt on the notion that dolomite is a harmless chemical, they provide evidence in favour of the proposition that exposure to high atmospheric concentrations of this compound is likely to be associated with respiratory symptoms.
PMCID: PMC3482327  PMID: 23115717
Dolomite dust; Occupational exposure; Respiratory symptoms; Functional impairments of the lungs
18.  Wood Dust Sampling: Field Evaluation of Personal Samplers When Large Particles Are Present 
Annals of Occupational Hygiene  2010;55(2):180-191.
Recent recommendations for wood dust sampling include sampling according to the inhalable convention of International Organization for Standardization (ISO) 7708 (1995) Air quality—particle size fraction definitions for health-related sampling. However, a specific sampling device is not mandated, and while several samplers have laboratory performance approaching theoretical for an ‘inhalable’ sampler, the best choice of sampler for wood dust is not clear. A side-by-side field study was considered the most practical test of samplers as laboratory performance tests consider overall performance based on a wider range of particle sizes than are commonly encountered in the wood products industry. Seven companies in the wood products industry of the Southeast USA (MS, KY, AL, and WV) participated in this study. The products included hardwood flooring, engineered hardwood flooring, door skins, shutter blinds, kitchen cabinets, plywood, and veneer. The samplers selected were 37-mm closed-face cassette with ACCU-CAP™, Button, CIP10-I, GSP, and Institute of Occupational Medicine. Approximately 30 of each possible pairwise combination of samplers were collected as personal sample sets. Paired samplers of the same type were used to calculate environmental variance that was then used to determine the number of pairs of samples necessary to detect any difference at a specified level of confidence. Total valid sample number was 888 (444 valid pairs). The mass concentration of wood dust ranged from 0.02 to 195 mg m−3. Geometric mean (geometric standard deviation) and arithmetic mean (standard deviation) of wood dust were 0.98 mg m−3 (3.06) and 2.12 mg m−3 (7.74), respectively. One percent of the samples exceeded 15 mg m−3, 6% exceeded 5 mg m−3, and 48% exceeded 1 mg m−3. The number of collected pairs is generally appropriate to detect a 35% difference when outliers (negative mass loadings) are removed. Statistical evaluation of the nonsimilar sampler pair results produced a finding of no significant difference between any pairing of sampler type. A practical consideration for sampling in the USA is that the ACCU-CAP™ is similar to the sampler currently used by the Occupational Safety and Health Administration for purposes of demonstrating compliance with its permissible exposure limit for wood dust, which is the same as for Particles Not Otherwise Regulated, also known as inert dust or nuisance dust (Method PV2121).
doi:10.1093/annhyg/meq075
PMCID: PMC3037778  PMID: 21036895
ACCU-CAP™; Button sampler; CIP10-I sampler; GSP sampler; inhalable sampling; IOM sampler; wood dust
19.  Bronchial disease in ulcerative colitis. 
Thorax  1980;35(8):581-585.
Ten patients with ulcerative colitis, all of whom were non-smokers, presented with a productive cough. In six, the chest radiography was normal and cough was the only symptom; three of these patients had a minor obstructive ventilatory defect on testing. Four patients complained of exertional dyspnoea and had both an abnormal chest radiograph with bilateral pulmonary shadows and a mixed obstructive and restrictive ventilatory defect. Bronchial epithelial biopsies from four patients (two with and two without pulmonary shadows) revealed basal reserve cell hyperplasia, basement membrane thickening, and submucosal inflammation, changes more usually associated with cigarette smoking. Inhaled beclomethasone diproprionate relieved cough in seven patients. The occurrence of airway epithelial disease in association with ulcerative colitis raises the possibility of a systemic mechanism affecting both bronchial and colonic epithelium. It does not seem likely that sulphasalazine was the cause of the pulmonary syndrome in these subjects.
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PMCID: PMC471338  PMID: 7444824
20.  Respiratory health effects of opencast coalmining: a cross sectional study of current workers. 
OBJECTIVE: To identify whether there is evidence of pneumoconiosis and other respiratory health effects associated with exposure to respirable mixed dust and quartz in United Kingdom opencast coalmines. METHODS: A cross sectional study of current workers (1224 men, 25 women) was carried out at nine large and medium sized opencast sites in England, Scotland, and Wales. To characterise a range of occupational groups within the industry, full shift measurements of personal exposures to respirable dust and quartz were taken. Up to three surveys were carried out at each site, covering all four seasons. For the purposes of comparisons with health indices these groups were further condensed into five broad combined occupational groups. Full sized chest radiographs, respiratory symptoms, occupational history questionnaires, and simple spirometry were used to characterise the respiratory health of the workforce. Logistic or multiple regression techniques were used to examine relations between indices of exposure and respiratory health. RESULTS: None of the group geometric mean dust concentrations, based on 626 valid dust samples, exceeded 1 mg.m-3, and 99% of all quartz concentrations were below 0.4 mg.m-3, the current maximum exposure limit. The highest quartz concentrations were experienced by the rock drilling team and drivers of bulldozers (used to move earth and stone from layers of coal). There were clear differences in mean respirable dust and quartz concentrations between occupational groups. These were consistent across the different sites, but depended in part on the day of measurement. The variations between sites were not much greater than between days, suggesting that differences between sites were at least partly explained by differences in conditions at the time of the measurements. The prevalence of radiographic small opacities profusion category > or = 1/0, based on the median of three readings, was 4.4%. Five men had category 2 pneumoconiosis and two men (including one of these five) had progressive massive fibrosis category A. From regression analyses, the relative risk of attaining a profusion of category > or = 0/1 was estimated to be doubled for every 10 years worked in the dustiest, preproduction opencast jobs, after allowing for age, smoking, and site effects. Risk was not associated with time worked in any other occupation within the industry, nor with previous employment in underground mining or other dusty jobs. Symptoms of chronic bronchitis were present in 13% of the men. Frequency of chronic bronchitis was influenced by years worked in dusty jobs outside opencast mining, but not by time spent in occupations within the industry. Asthmatic symptoms were reported by 5% of the workforce, close to the mean frequency found in adult men. No positive associations were found between asthma and occupational exposures. Lung function on average was close to predicted value and showed no relation to time worked in opencast occupations. CONCLUSIONS: Frequency of (mostly mild) chest radiographic abnormalities is associated with working in the dustier, preproduction jobs in the industry. Although some of these mild abnormalities may be non-occupational (due to aging or smoking), the association with exposure indicates a small risk of pneumoconiosis in these men, and the need to monitor and control exposures, particularly in the high risk occupations.
PMCID: PMC1128802  PMID: 9245948
21.  Radiographic abnormalities and the risk of lung cancer among workers exposed to silica dust in Ontario. 
OBJECTIVE: To determine whether workers in Ontario who had been exposed to silica dust and who have radiographic abnormalities are at increased risk of lung cancer. DESIGN: Cohort and case-control studies of rates of death from lung cancer and cancer incidence rates; data were obtained from the Ontario Silicosis Surveillance Registry. Follow-up was through linkage to the Ontario mortality and cancer registries. SETTING: Ontario. PARTICIPANTS: A total of 523 workers with radiographic abnormalities and 1568 control subjects with normal radiographic findings who had been exposed to silica dust. Matching criteria were year of birth and the requirement that the control subject have a normal radiographic finding either later than or in the same year that the radiographic abnormality was identified in the silicosis subject. OUTCOME MEASURES: Standardized mortality ratios (SMRs), standardized incidence ratios (SIRs) and odds ratios for lung cancer. RESULTS: In the cohort analysis, with the Ontario population rates as reference, the all-cause SMR was 0.96 among the workers with radiographic abnormalities and 0.51 among the control subjects. The corresponding SIRs for lung cancer were 2.49 and 0.87 (p < 0.001). In the case-control analysis the workers with silicosis were more likely than the control subjects to have been smokers, but this difference likely accounted for only a small part of the difference in the incidence of lung cancer. The relative risk of lung cancer was elevated among the workers with silicosis from the foundry, mining and nonmetallic-minerals industries; however, the number of subjects was too small for a significant difference to be detected. Among the miners exposure to radon daughters did not affect the risk of lung cancer attributable to radiographic abnormalities. CONCLUSIONS: Radiographic abnormalities suggestive of exposure to silica dust are markers for increased risk of lung cancer. Physicians might thus wish to warn their patients with silica-associated radiographic abnormalities about the increased risk and to counsel those who smoke to stop.
PMCID: PMC1337491  PMID: 7804920
22.  Ventilatory responses of normal subjects to flax dust inhalation: the protective effect of autoclaving the flax. 
A homogeneous batch of dew retted hackled flax was divided into two portions. One was untreated and the other was steamed for 45 minutes at 125 degrees C in three pressure/vacuum cycles in an autoclave. Dust was collected when the two flaxes were separately processed by industrial doubler and stapler machines. From untreated flax 7.2 g of dust was collected per kilogram of flax after two processing operations. From the steamed flax 4.4 g of flax was obtained per kilogram after four operations. A method was devised to disperse the dust in a room to produce dust levels similar to those encountered in a dusty mill (4.5-5.7 mg/m3). Twelve normal volunteers from the managerial staff of the linen industry of Northern Ireland inhaled the dust over six hour periods. With the untreated flax decreases were obtained in mean forced expiratory measurements of 7.6% in FEV1 and 4.5% in FVC (p less than 0.01). A double blind crossover comparison of similar levels of untreated and steamed flax dusts showed 30% less impairment of the forced expirations with steamed than with untreated flax (p less than 0.05). If these responses reflect the long term airway effects of flax dust then the steaming of flax may help in reducing byssinosis.
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PMCID: PMC1007450  PMID: 3970886
23.  Respiratory Function and Disease among Workers in Alkaline Dusts* 
Little is known of the possible effects of sodium carbonate dust on the lower respiratory passages. A large alkali industry, with a number of works, was used for an investigation of lime and soda ash dusts evolved during the process. The physical and chemical characteristics of these dusts and details of the type of work and environmental conditions are described. In 1954 and 1956 a survey was made of respiratory sickness absence, chest radiographic appearance, and respiratory function in workers employed in areas with exposure to soda ash, lime dust, and no dust. All were interrogated about their smoking habits. In 1954 there was found to be a significant reduction in expiratory flow rate of workers in dusty jobs in soda ash compared with the group not exposed to dust but this result was nullified in a random sample group in 1955 and in full groups in 1956. Respiratory sickness absence was found to be slightly greater in workers in dusty occupations, particularly in lime dust. No pneumoconiosis was detected on miniature films. The survey of smoking habits revealed that smoking was associated with a definite decrease in the expiratory flow rate, particularly after the age of 40 in heavy smokers. It was concluded that smoking habits played a more important part than alkaline dusts in the reduction of respiratory efficiency as measured by a study of sickness absence and performance of a simple spirometric test.
PMCID: PMC1037861  PMID: 13618520
24.  Role of computed tomography in evaluating asbestos related lung disease. 
To find how computed tomography (CT) may be effectively used in individuals with suspected asbestos related lung disease 30 men with a history of exposure to asbestos were studied. All subjects underwent high kilovoltage posteroanterior and left lateral chest radiographs and chest CT. Eighteen were randomly selected asbestos workers referred for routine surveillance. The remaining 12 were patients who had been referred for investigation of respiratory symptoms or abnormal routine chest radiograph, or both, and found to have chest radiographic changes compatible with asbestos related lung disease. In the group referred for routine surveillance both pleural shadowing and pulmonary shadowing were shown on CT but not chest radiographs in only one case. Five were thought to have pleural shadowing on chest radiographs but this was confirmed on CT in only one case. All 12 patients referred for investigation showed pleural shadowing on chest radiographs; this was confirmed in all cases on CT which also showed unsuspected pulmonary shadowing in five cases. These findings suggest that it is not appropriate to use chest CT routinely in all asbestos workers referred for routine surveillance. When CT is used selectively in those with pleural shadowing on plain chest radiography, however, it is helpful in refuting or confirming the presence of pleural disease and may show unsuspected pulmonary shadowing.
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PMCID: PMC1009867  PMID: 2590642
25.  The biology of talc. 
Data are presented on the effects on health of talc dusts from exposure in industry and use of talc-containing health products. The mineralogy of talc and the composition of cosmetic and industrial grade talc dusts are described. Studies in animals are reviewed, and epidemiological data are considered in relation to exposures that occur during industrial and consumer uses of talc dusts. Hamsters exposed to 8 mg/m3 of respirable cosmetic grade talc dust for up to 150 minutes a day for 300 consecutive days showed no difference in incidence or nature of pathological lesions from those observed in a group of untreated animals. A retrospective study of the causes of death of 227 talc mine millers exposed to cosmetic grade talc at the threshold limit value for talc (20 million parts per cubic foot) for an average of 15-8 years showed that the causes of death were no different from those in a control cohort not exposed to talc dust. The available data indicate that talc dust exposure in the modern mining of cosmetic grade talc does not appear to be injurious to health. The significantly lower dust exposure in the normal use of cosmetic grade talc dusts in talc-containing health and cosmetic products confirms that their use is not a hazard to health.
PMCID: PMC1008143  PMID: 793610

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