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PubMed2006

[Silica exposure index in gold mining].

OBJECTIVE: To develop a cumulative silica exposure index, including time period, duration and intensity of exposure, and to test this index as for occurrence and severity of silicosis. METHODS: A cross-sectional study was carried out comprising 140 former gold miners from two localities in Southeastern Brazil between November 1997 and December 1999. Complete data on occupational and medical histories, chest x-rays and spirometry were analyzed. Borderline cases on the x-rays were also submitted to high-resolution chest computed tomography. The exposure index was the sum of scores obtained by logarithmic transformation of respirable silica concentration related to job tasks, mines and work time. Parametric tests were used for comparing averages between the groups of interest. RESULTS: The silica exposure index was able to discriminate the main outcome (silicosis) as well as other outcomes (tuberculosis and lung emphysema) in the whole group at p-values of 0.008, 0.016 and <0.001 respectively. In regard to the four main categories of silicosis, the Tukey test showed differences in the averages of the exposure index in the categories 0 and 3 and 1 and 3. However, in the borderline cases subgroup, the exposure index was not satisfactory for cases submitted to x-rays and tomography and it could not differentiate other outcomes. CONCLUSIONS: The silica exposure index represents an advance in exposure evaluation of former miners. However, other information, such as clinical and lung functional data are needed for better understanding disease progress in silica exposed cases, especially among borderline cases.

Adult↗
PubMed1986

Evaluation of physical health effects due to volcanic hazards: crystalline silica in Mount St. Helens volcanic ash.

This investigation has shown that crystalline silica has been identified as being present in the Mount St. Helens volcanic ash at levels of 3 to 7 per cent by weight. This identification has been established using X-ray powder diffraction, infrared spectrophotometry, visible spectrophotometry, electron microscopy, and Laser Raman spectrophotometry. Quantitative analysis by IR, XRD, and visible spectrophotometry requires a preliminary phosphoric acid digestion of the ash sample to remove the plagioclase silicate material which interferes with the determination by these methods. Electron microscopic analysis as well as Laser Raman spectrophotometric analysis of the untreated ash confirms the presence of silica and at levels found by the XRD and IR analysis of the treated samples. An interlaboratory study of volcanic ash samples by 15 laboratories confirms the presence and levels of crystalline silica. Although several problems with applying the digestion procedure were observed in this hastily organized supply, all laboratories employing the digestion procedure reported the presence of crystalline silica. These results unequivocally put to rest the question of the presence of silica in the volcanic ash from eruptions of Mount St. Helens in 1980.

Disasters↗
PubMed2004

Preparation of a new type of fiber adsorbent attached with silica microparticles.

A new type of fiber adsorbent attached with silica microparticles was prepared. The silica microparticles were formed by the polymerization of silica oligomers on glass fibers, which were woven into a glass filter. The surface of the silica microparticles was chemically modified by bonding C18-ligands. SEM images indicated that the diameter of the uniform and spherical silica microparticles fixed on glass fibers was on the order of micrometers. It was confirmed that the glass filter adsorbent was effective for the adsorptive removal of toluene of low concentrations.

Journal Article↗
PubMed2004

A novel separation and preconcentration method for traces of manganese, cobalt, zinc and cadmium using coagulation of colloidal silica.

A separation and preconcentration method has been developed for traces of heavy metals using coagulation of colloidal silica. An appropriate amount of colloidal silica was added to a sample solution, the pH was adjusted to 11 with tetramethylammonium hydroxide solution and calcium chloride solution was then added to coagulate the silica. The coagulated silica and solution were separated by centrifugation, and the silica was then treated with hydrofluoric and perchloric acids. The residue was taken up in dilute nitric acid and subjected to ICP-AES to determine manganese, cobalt, zinc and cadmium. The proposed method was successfully applied to analysis of river-water.

Journal Article↗
PubMed2005

Bisphenol A analog-imprinted polymers prepared by an immobilized template on a modified silica microsphere matrix.

Bisphenol A (BPA)-recognizing imprinted polymers were synthesized using a template immobilized on silica where the template was grafted to aminopropyl silica. The silica-template conjugate was co-polymerized with a cross-linker (ethylene glycol dimethacrylate) and a functional monomer (4-vinylpyridine or methacrylic acid). The synthesized silica-polymer composites were treated with an aqueous NH4HF2 solution to dissolve the silica matrix. The 4-vinylpyridine-based imprinted polymer showed strong binding affinity to BPA and structurally related compounds having two hydroxyl groups at the 4,4'-position in the bisphenol structure.

Benzhydryl Compounds↗
PubMed2006

Properties of monolithic silica columns for HPLC.

Monolithic silica columns and their use in high peak-capacity HPLC separations are reviewed. Monolithic silica columns can potentially provide higher overall performance than particle-packed columns based on the variable external porosity and variable through-pore size/skeleton size ratios. The high permeability of monolithic silica columns resulting from the high porosity is shown to be advantageous to generate large numbers of theoretical plates with long capillary columns. High permeability together with the high stability of the network structures of silica allows their use in high-speed separations required for a second-dimension column in two dimensional HPLC. Disadvantages of monolithic silica columns are also described.

Benzene Derivatives↗
PubMed1986

Pulmonary deposition and effects of inhaled silica particles after short-term exposures in the rat.

The present study was designed to evaluate the pulmonary deposition and the effects of inhaled silica particles in the rat model. Wistar (W/M strain) rats were exposed to silica aerosols generated from a fluidized bed dust generator for 1 hr a day, intermittently for 6 days, using a "nose-only" inhalation chamber. After the cessation of the exposures, analysis of lavaged bronchoalveolar cells (BAC) and histological examinations of lungs and tracheobronchial lymph nodes (TBLN) were performed during a period of 6 months. Total cell yields and the proportions of alveolar macrophages (AM) in BAC were not altered, whereas the proportions of lymphocytes in BAC were significantly increased in the exposed animals. Although the proportions of silica-laden AM in BAC were gradually decreased during the 6 months, particle-laden AM were predominantly and persistently observed in the alveoli under light microscopy. Silica particles were also identified in macrophages of granulomatous nodules in pulmonary peribronchial lymphoid tissues(PBLT) and TBLN, indicating the translocation of particles via the lymph. Associated with pulmonary particle deposition, some characteristic histopathological features were evident, including thickening of alveolar duct bifurcations and lymphocyte infiltrations both in the alveolar sacs and around the interstitial blood vessels. At later months after the exposures, the alveolar interstitium was thickened with the increase of fibroblasts and collagen. These results implicate that short-term exposures of silica particles in the rat can evoke histopathologic changes in the lungs and lymphatic tissues, associated with their deposition and translocation.

Animals↗
PubMed2002

Level of silica in the respirable dust inhaled by dental technicians with demonstration of respirable symptoms.

Dental technicians are exposed to various dusts in working laboratories. This study was conducted to measure level of silica in the respirable dust generated from dental fixed prosthodontics manufacturing processes using Fourier Transform Infrared Spectroscopy (FTIR), and to compare their occurrence of respiratory symptoms with that of non-dental hospital workers (control group). Respirable dusts were personally sampled from dental technicians working at dental laboratories in Seoul Korea according to NIOSH Method 0600. Fifty personal samples were obtained during porcelain or polishing process and weighed by a gravimetric method. Concentration of respirable dust was 651 +/- 548 microg/m3 (Mean +/- SD) with highest concentration of 2,874 microg/m3 during the porcelain process and 725 +/- 414 microg/m3 with highest concentration of 1,764 microg/m3 during the polishing process. Concentration of silica was 6.51 +/- 6.07 microg/m3 with 18.85 microg/m3 highest and 14.88 +/- 11.21 microg/m3 with 50.98 microg/m3 highest for the porcelain and polishing process, respectively. Level of silica contents in the dust was 0.81% and 1.66% for the porcelain and polishing process, respectively. The level of silica contents and silica concentration were significantly different between the two processes. Comparing prevalence of respiratory symptoms between non-smoking seventeen dental technicians and thirty-five control workers, wheezing and rhinorrhea were significantly more manifested in the dental technicians than the controls. Total frequency of respiratory symptoms was also significantly higher in the dental technicians than the controls.

Adult↗
PubMed1990

High dietary calcium to phosphorus ratio and alkali-forming potential as factors promoting silica urolithiasis in sheep.

Sheep were used to study factors previously found to promote silica urolithiasis in a rat model. In addition to high silica, these dietary factors included elevated calcium, a high calcium to phosphorus ratio and alkali-forming effects. Wether lambs had ad libitum access to a diet of 50% of grass hay and 50% ground oats plus supplement. Diet analysis was 3.4% total SiO2, .29% calcium, .25% phosphorus, 11.3% CP and 28% ADF. Treatments (40 lambs/treatment) consisted of a control (C), limestone to increase dietary calcium to .6% (L), L + 1% sodium bicarbonate (LS) and L + 1% ammonium chloride (LA). After a 91-d experimental period followed by a 56-d postexperimental finishing period, silica kidney deposits were found in all treatments, and SiO2 made up 74% to 97% of the urolithic ash. Kidney urolith incidences in the four treatments were C, 7/40; L, 12/40; LS, 20/40; and LA, 9/40. A higher urolith incidence in LS (LS vs C, P less than .05) and a trend toward a higher incidence in L (L vs C, P less than .2), accompanied by elevated urine pH (L = LS greater than C greater than LA, P less than .01), lend support to the concept that high-silica diets having high calcium to phosphorus ratios and alkali-forming potentials contribute to silica urolithiasis.

Alkalies↗
PubMed1994

A method for isolating and preparing silica bodies in grasses for scanning electron microscopy.

Silica bodies are discrete deposits of dehydrated silica within epidermal cells. To describe these bodies completely, surrounding organic and unsilicified material must be removed. Methods generally used for isolating and preparing silica bodies were unsuitable for most grass species. An effective method for studying grasses is described here. After ashing the plant tissue, the ash was repeatedly rinsed with HCl in a specialized multiple funnel manifold and collected on Nuclepore filters. In addition, the silica bodies were sonicated for a few minutes to remove any remaining mineral impurities. Compared to conventional procedures, this method has a number of advantages: unsilicified material and mineral impurities were removed effectively, smaller quantities of plant tissue could be used, and the loss of silica bodies was minimized.

Microscopy, Electron, Scanning↗
PubMed2007

[Effects of Gymnadenia conopsea alcohol extract on collagen synthesis in rat lungs exposed to silica and its mechanism of antioxidative stress].

OBJECTIVE: To explore the effects of Gymnadenia conopsea alcohol extract (GcAE) on the collagen synthesis in rat lungs exposed to silica and the influence on antioxidase activities, level of lipid peroxidation (LPO). METHODS: One hundred and twenty rats were randomly divided into control group, silica group, and GcAE-treated group. Silicotic animal models were established by direct tracheal instillation of silica into rat lungs surgically. From the second day of model establishment, rats in GcAE-treated group were orally given GcAE [8 g/(kg x d) corresponding to raw herb]. At 7, 14, 21, 28 and 60 days after establishment of the animal model, eight rats in each group were sacrificed, and samples were collected. The malondialdehyde (MDA) content, superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in plasma were assayed by a spectrophotometer. Types I and III collagen were detected by Sirius red polarization and microscopy, and measuered by Image-Pro Plus Version 4.5 for Windows software. RESULTS: GcAE could reduce the lung/body weight ratio of rats exposed to silica, the synthesis of types I and III collagen of the lungs and the level of lipid peroxidation, increase the activities of SOD and GPx. CONCLUSION: GcAE can ameliorate the silica-induced pulmonary fibrosis by increasing the activities of antioxidase and alleviating the damage of lipid peroxidation to the lungs.

Administration, Oral↗
PubMed1999

Effects of non-mining occupational silica exposure on proportional mortality from silicosis and systemic sclerosis.

OBJECTIVE: Studies report an association between mining related silica exposure and systemic sclerosis (SSc). This study evaluated associations between non-mining occupational silica exposure, silicosis, and SSc. METHODS: The US National Institute for Occupational Safety and Health (NIOSH) recently identified 36 non-mining occupations in which workers face the "potential for substantial silica exposure." Data from death certificates in 25 US states during 1985-92 were analyzed to determine whether excess proportional mortality from silicosis or SSc occurred among those who worked in these occupations. RESULTS: Proportional mortality from silicosis in the occupations identified by NIOSH was significantly elevated among men [proportional mortality ratio (PMR) = 1.4; p < 0.0001] and women (PMR = 7.1; p = 0.002). The proportional mortality from SSc was not elevated among men (PMR = 1.0; p = 0.90) and was lower than expected among women (PMR = 0.8; p = 0.39). CONCLUSION: When cited on death certificates, the non-mining occupational categories identified by NIOSH reflect prior silica exposure; however, no evidence of excess mortality from SSc was observed in these occupations. The reported increased frequency of SSc among miners may depend on a level or mode of silica exposure unique to the mining industry.

Evaluation Studies as Topic↗
PubMed2000

[Cytoimmunologic changes in material obtained from bronchoalveolar lavage (BAL) in asymptomatic individuals chronically exposed to silica dust].

The aim of this study was to determine and to evaluate silica induced lung cell reactivity--if any--in bronchoalveolar space, before clinical changes develop. Bronchoalveolar lavage (BAL) was carried out in 15 nonsmoking individuals with chronic professional silica exposure, free of lung signs and symptoms. Controls were healthy nonsmokers. Routine BAL cytology (HE, MGG) was completed by mast cell staining (toluidine blue). BAL lymphocyte subsets were phenotyped by direct two- and three-color immunofluorescence (applied DAKO A/S monoclonal antibodies: anti-CD3, CD4, CD8, CD11b, CD14, CD15, CD16 + 56, CD19, CD25, CD45, HLA-DR). Parallel staining was performed in peripheral blood. In individuals with chronic silica exposure we found: significant increase in alveolar macrophage (362 +/- 45 vs 160 +/- 33 x 10(3) cells/ml, p < 0.05), lymphocyte (61 +/- 9 vs 24 +/- 5 x 10(3) cells/ml, p < 0.05) and BAL total cell (415 +/- 76 vs 187 +/- 34 x 10(3) cells/ml, p < 0.05) numbers; significant increase in mast cell (0.4 +/- 0.1 vs 0.2 +/- 0.1, p < 0.05), NK cell (7.0 +/- 1.8 vs 3.6 +/- 1.0, p < 0.05) and Th early activated lymphocyte percent (CD4 + CD25+ calculated as percentage of CD4+ cells: 15.1 +/- 1.5 vs 7.8 +/- 1.6, p < 0.01). All results were presented as median +/- SEM. Bronchoalveolar space of people with chronic silica exposure usually shows pathological reaction (especially macrophagic alveolitis), although they are free of manifested pulmonary disease. Th early activated lymphocytes, NK cells and mast cells seem to play important role in the early interstitial lung tissue reaction to silica.

Adolescent↗
PubMed2001

Cellular and molecular mechanisms regulating silica-induced adhesion molecule expression in mice.

Exposure of mice to silica particles generates an intense inflammatory response characterized by the influx of neutrophils and monocytes into the alveoli with resulting cell activation. These cell trafficking and effector functions are, in part, mediated by different families of adhesion molecules. One such adhesion protein, intercellular adhesion molecule-1 (ICAM-1), is expressed on a variety of cells including vascular endothelial cells, fibroblasts, types I and II alveolar epithelial cells, some lymphocytes, and monocytes/macrophages. Over the last several years, our laboratory has focused on silica-induced ICAM-1 expression in exposed mice (in vivo) and cells (in vitro) by examining the role and regulation of this adhesion protein on pulmonary cells. We have determined that intratracheal exposure of mice to silica (2 mg per mouse) elicits increased expression of ICAM-1 on pulmonary macrophages and type II epithelial cells within the lung parenchyma, on bronchoalveolar lavage macrophages, and as a soluble protein in lavage fluid. We hypothesize that increased ICAM-1 expression mayparticipate in silica-induced neutrophil influx into the alveoli, as well as in macrophage-derived phlogistic signals responsible for migration of neutrophils. ICAM-1 expression on silica-exposed mouse macrophages is enhanced by reactive oxygen species (ROS) and tumor necrosis factor-alpha (TNF-alpha) and appears to be regulated through specific sequence elements within the ICAM-1 promoter.

Air Pollutants, Occupational↗
PubMed2000

[Recent advances of silica packing in high performance liquid chromatography].

Developments of silica packings in high performance liquid chromatography are reviewed with 65 references. Preparative and modification methods of silica packings are introduced. The physical characterization on silica surface is elucidated. The applications of silica packings in HPLC are outlined and the trends of silica packings in China are described.

Chemical Phenomena↗
PubMed1992

Increased manganese superoxide dismutase protein in type II epithelial cells of rat lungs after inhalation of crocidolite asbestos or cristobalite silica.

Manganese-containing superoxide dismutase (Mn-SOD) is a mitochondrial enzyme implicated in cellular defense from oxidative damage. We investigated the immunocytochemical distribution and protein concentration of Mn-SOD in rat lungs in response to aerosolized crocidolite asbestos or cristobalite silica, fibrogenic minerals eliciting generation of oxidants by cellular and acellular pathways. Rats were exposed to 7-10 mg/m3 dust for 6 hours a day for 10 days. Experimental and sham control rats were euthanized 10 days after cessation of exposure, and lungs prepared for immunocytochemistry and determination of amounts of Mn-SOD protein. Quantitation of Western blots showed that the amount of immunodetectable Mn-SOD increased in lungs exposed to asbestos or silica by approximately 1.3- and 2.4-fold, respectively, when compared with sham controls. Immunoelectron microscopy using the protein A-gold technique showed that Mn-SOD was located predominantly in mitochondria of type II epithelial cells. Fibroblasts contained little immunodetectable Mn-SOD, whereas type I epithelial cells, polymorphonuclear leukocytes (PMNs), and endothelial cells contained no detectable protein. Some alveolar macrophages (AMs) were found with labeled mitochondria, whereas most interstitial macrophages had no detectable protein. Quantitative analysis of type II cells showed that the number of immunogold particles per unit of mitochondrial area increased in the terminal airways of lungs exposed to asbestos or silica by 2.2-fold and 3.6-fold, respectively, over controls. Morphometric analyses indicated that the size of type II cells, as well as the number of interstitial macrophages and PMNs, increased in the terminal respiratory tissue of silica-exposed lungs. Less pronounced histopathologic changes were evident in asbestos-exposed lungs. These results indicate that the relative concentration of Mn-SOD increases preferentially in type II epithelial cells subsequent to inhalation of silica or asbestos. The magnitude of induction of Mn-SOD protein in these cells and whole lung correlated with the inflammatory potential of these minerals.

Administration, Inhalation↗
PubMed2002

[Study on silica induced DNA damage and its influence factor].

OBJECTIVE: To detect DNA damage in Chinese Hamster Lung Fibroblast(CHLF) exposed to low doses of silica particles(7.5 - 120.0 micrograms/ml). METHODS: Comet assay was used to detect DNA damage. The cells were divided into various groups by doses and incubation time of silica particles to observe silica-induced DNA damage; and the influence of hydroxyl radicals and calcium ion in DNA damage by using deferoxamine and verapamil was also studied. The tail lengths of comet were used to measure DNA damage. RESULTS: The tail lengths were significantly longer in exposed cells, compared to matched controls(P < 0.01), and were increased in a dose-dependent manner from 7.5-120.0 micrograms/ml. The tail lengths of two-hour group were longer than one-hour group. When exposed to 90 micrograms/ml silica particles, 0.5-2.0 mmol/L deferoxamine and 2.5-20.0 micrograms/ml verapamil could attenuate silica-induced DNA damage effectively, their protective effects were increased in a concentration-dependent manner. CONCLUSION: Small dose of SiO2 could induce CHLF DNA damage. Calcium ion and hydroxyl radical may take part in this process, antioxidant and calcium antagonate may protect SiO2 induced DNA damage.

Animals↗
PubMed2003

[Immunohistochemical method for the detecting expression of transforming growth factor-beta1 in lung tissues of silica-treated mice].

OBJECTIVE: To investigate the protein expression of transforming growth factor-beta(1) (TGF-beta(1)) in lung tissues of silica-treated mice. METHODS: The experimental mice were divided into control and silica groups. 0.2 g/kg body weight of silica was injected intratracheally in mice of silica group. Samples of lung tissue were collected 1, 3, 5, 7, 14 and 28 d after injection. The immunohistochemical method was used to analyze the protein expression of TGF-beta(1). RESULTS: In control mice, the expression of TGF-beta(1) in lung tissue was slightly positive while it was markedly increased in silica-treated mice. The expression was significantly elevated from the 7th day to 14th day. The expression in alveolar macrophages reached the peak on the 5th day [(93.4% +/- 2.8%) vs (42.2% +/- 12.0%), P < 0.01]. CONCLUSION: TGF-beta(1) may play an important role in early development of silicosis.

Animals↗