Thesis (doctoral)--Turku, 1983.

Thesis (M.S.P.H.)--University of Michigan, 1941.

Thesis (M.S.P.H.)--University of Michigan, 1941.

Thesis (M.S.P.H.)--University of Michigan, 1942.

Thesis (M.S.P.H.)--University of Michigan, 1942.

Thesis (Ph.D.(Public Health))--University of the Witwatersrand, Faculty of Health Sciences, 2012 / Introduction Personal exposure to respirable crystalline silica (commonly in the form of quartz) causes serious adverse health effects and has been well documented in industries formally known as the ‘dusty trades’. Very little information exists on personal quartz exposure in agricultural settings. Silica exposure is an important public health issue particularly in settings of high tuberculosis (TB) and Human Immunodeficiency Virus (HIV) rates. The mineral has contributed to serious epidemics of TB in southern Africa and other low and middle - income regions of the world because of the increased risk of pulmonary tuberculosis in silica exposed workers. It is well known that HIV infection increases the incidence of TB and the risk of tuberculosis in individuals with both HIV and silicosis is larger than the sum of each factor. Globally (especially in resource poor countries), agriculture employs a very large population that may be affected. Objectives The objectives of the PhD were to review the published literature on respirable quartz exposure and associated disease in agricultural related settings systematically; to measure personal time weighted average respirable dust and quartz on sandy, sandy loam and clay soil farms in the Free State and North - West provinces of South Africa; to ascertain whether soil type is a determinant of exposure to respirable quartz; to identify additional determinants of quartz exposure in farming; to estimate annual cumulative respirable quartz exposure; and to discuss some occupational health implications and research needs. Methodology Published studies on exposure to silica and quartz in agriculture and related settings as well as silica - associated disease in farming were searched systematically through “PubMed”; and, critiqued. Three farms, located in the Free State and North West provinces of South Africa, had their soil type confirmed as sandy, sandy loam and clay; and, from these, a total of 298 respirable dust and respirable quartz measurements were collected between July 2006 - November 2009 during periods of major farming operations. These measurements were collected using standard international measurement and analytical methods. Quartz determinations were done using X - ray diffraction by a quality - assured, accredited laboratory, and were verified by a leading external agency. Respirable quartz values below the limit of detection (22 μg.m-3) were estimated using multiple imputation. Non - parametric tests were used to compare quartz exposure from the three different soil types. Variables such as soil type, commodity farmed, activity (nature of work done), process (manual vs mechanical), quartz % and weather variables (e.g. wind and humidity during the week prior of and during sampling) were used in bivariate and multiple regression modeling to identify determinants of respirable quartz exposure. Logistic regression was done aiming to identify determinants of respirable quartz greater than 50 μg.m-3 and to deal with data points below the detection limit without including multiple imputation methods. The annual cumulative exposure was estimated for a typical farm worker on the sandy soil farm using activity - specific measurements and duration of each activity in a year. Particle sizes of respirable dust fraction were determined using laser light scattering. Results Literature review In total, 17 studies were identified: 11 investigated respirable dust and quartz exposure on farms and six quartz related disease in agricultural settings. They provided convincing evidence of a respirable quartz risk on sandy soil farms but scant evidence of associated disease. Exposure to respirable dust and quartz Respirable quartz measurements from the three South African farms ranged from not detectable to 626 μg.m-3 and confirmed the quartz hazard: some concentrations exceeded generally accepted occupational exposure limits in all activities evaluated, even though 278 (93.3 %) of the respirable dust concentrations were well below a commonly used occupational exposure limit of 2 mg.m-3. Fifty seven percent, 59% and 81% of the respirable quartz measurements on the sandy soil, sandy loam soil and clay soil farm respectively exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) of 25 μg.m-3. Twelve percent and 13% of respirable quartz concentrations exceeded 100 μg.m-3 on the sandy soil and sandy loam soil farms respectively, but none exceeded this level on the clay soil farm. Determinants of exposure The proportions of measurements greater than 100 μg.m-3 were not significantly different between the sandy and sandy loam soil farms (prop.test; p = 0.65), but both were significantly larger than for the clay soil farm (prop.test; p= 0.001). The percentage of quartz in respirable dust was determined for all three farms using samples of a size such that all measurements were well above the analytical detection limit. Percentages ranged from 0.5 - 94.4% with no significant difference in the median quartz percentages across the three farms (Kruskal - Wallis test; p = 0.91). Bivariate analyses showed that commodity (Kruskal - Wallis test; p = 0.001), activity (Kruskal-Wallis test; p = 0.001) and process (Wilcoxon test; p = 0.003) were associated with respirable quartz concentrations. Multiple linear regression showed that soil type, season, commodity, activity, process, quartz percentage, humidity on the morning of measurement and interactions between activity, respirable dust exposure and quartz percentage were significantly related to respitable quartz exposure. Logistic regression showed that, during univariate analyses, cereal planter operator, increased quartz % in respirable dust, decreased humidity on the day of measurement and increased respirable dust concentration were all significantly associated with quartz levels above 50 μg.m-3. Multivariate analyses showed that cereal planter operator remained a strong determinant of higher level of exposure relative to other activity (OR 3.76 95% CI 1.64 - 8.63). Increased levels of quartz % in respirable dust increased the ORs for exposure above 50 μg.m-3. Annual cumulative exposure The estimated annual cumulative exposure of a farm worker exposed at the highest concentration measured for each task exceeded the cumulative exposure had the worker been exposed at 100 μg.m-3 by 1.46 times. At median quartz exposures measured for each of the activities done during the year, the chances of exceeding the cumulative exposure if exposed at the South African OEL are small: the ratio of the estimated cumulative exposure indices to occupational exposure limit cumulative exposure = 0.29. Particle size The median D50 particle size of the 30 respirable dust samples measured in this study was 5.53 μm with the smallest D50 value reported by the laboratory being 3.39 μm. Conclusion Despite its ubiquity, little is known about quartz exposure in the agricultural industry. This thesis not only demonstrates significant potential for overexposure in some settings, it also may be the biggest study of its kind: it is the first study to have measured a large number (298) of personal respirable quartz concentrations across various activities on three farms known to have different soil types. It is also the first study in farming that attempted to relate personal respirable quartz exposures to possible determinants, to consider potential modifiers of quartz exposure and to estimate annual cumulative quartz exposure. The study adds considerably to the evidence that over - exposure to quartz may be a risk in farming and has identified the need for practical interventions and research gaps. In addition, this study makes it possible to use the detailed analyses of silica exposure determinants in farming in other settings with similar conditions. Soil type may determine whether exposure is greater than 100 μg.m-3, but the job type and the manner in which the task is performed (e.g. mechanical or manual) may be important determinants of exposure. Identifying quartz exposure determinants (e.g. type of job) and modifiers will be of value to focus implementation of controls, which is of particular importance in developing countries. The nature of farming and weather variables may add information about exposure risk and should be included with soil type in future farming exposure assessment studies. Given the large numbers of farm workers possibly exposed to silica and the seriousness of silica - associated diseases, some dust - related occupational health interventions should be considered in South African farming, particularly because during the course of the studies none of the South African farms had medical surveillance programmes in place and few, if any, dust control measures were observed. Practitioners working in farming areas should be aware that silica - associated diseases may occur in farm workers; therefore despite limited evidence for silica associated disease, occupational health interventions appear justified. No study previously has defined the burden of silica – associated diseases in farming. A starting point may be to perform radiological surveys on long service farm workers (possibly more than 20 years service and performing dusty activities) on a sandy soil farm, as sandy soils are likely to produce the highest silica levels. An effort should also be made to define the duration and intensity of silica exposure in farming over the annual cycle. Lastly, cost - effective methods to reduce respirable dust and silica exposure in farming should be identified.

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A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. / The prevalence of tuberculosis in South African miners is substantially higher than that of in the general population. Through exposure to dust which leads to different degrees of silicosis, and by working in enclosed spaces where coughed out bacilli can survive in droplet nuclei and be inhaled by other workers, miners are especially prone to to become infected with M. tuberculosis and develop the disease. It is not only the working conditions which promote transmission of M. tuberculosis, but the living conditions as well. Most miners live and sleep in rooms shared by up to eight other men, which increases the opportunity for transmission, leading to both primary and reinfection tuberculosis. / IT2018

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains vii, 94 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 86-87).

Se ha desarrollado y aplicado un método espectrofotométrico modificado de análisis cuantitativo de sílice libre en mezclas con silicatos, por espectroscopía infrarroja. Las muestras fueron sumamente pequeñas, inferiores a 5 micrones. Este es un método eficaz en contaminación del aire con polvo mineral, especialmente en tareas de perforación minera, por cuanto a partir del mismo espectro obtenido de la muestra, se determina el tamaño promedio de las partículas de sílice libre, factor al que se debe, entre otros, la toxicidad de este compuesto, dando origen a la enfermedad conocida como "silicosis".