Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SILICA”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed2001

Chemical characteristics and leachability of organically contaminated heavy metal sludge solidified by silica fume and cement.

This paper discusses the development of mixtures with silica fume as a stabilization/solidification agent and binder for industrial wastewater residue containing organic and heavy metal contaminants. The UCS (Unconfined Compressive Strength) gradually increased to 66.7% as the silica fume content increased to 15%. The leaching of TOC and chromium decreased as more OPC was substituted with silica fume. When the mix had 5% silica fume, it retained about 85% TOC, and chromium leached out 0.76 mg-Cr/g-Cr in acidic solution. Also, microstructural studies on the solidified wastes through the scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction analysis showed that the silica fume caused an inhibition to the ettringite formation which did not contribute to setting, but coated the cement particles and retarded the setting reactions. The results indicated that the incorporation of silica fume into the cement matrix minimized the detrimental effects of organic materials on the cement hydration reaction and contaminant leachability.

Adsorption↗
PubMed2001

Inhaled amorphous silica particulates: what do we know about their toxicological profiles?

The International Agency for Research on Cancer (IARC) recently published a monograph on the evaluation of carcinogenic risks to humans of exposure to crystalline and amorphous silica particles. The IARC Working Group concluded that crystalline silica, in the form of quartz or cristobalite, from occupational sources posed a carcinogenic risk to humans (Category 1). IARC also determined that amorphous silica particles were not classifiable as to its carcinogenicity to humans (Category 3). With regard to amorphous silica, the evaluation was based primarily on the lack of toxicological and epidemiological data for these materials and this was noted in the IARC document. This manuscript is designed to provide a brief summary of the limited inhalation toxicity database related to amorphous silica particulates and to cite a few studies wherein the pulmonary toxicological effects of inhaled crystalline and amorphous silica particles were compared.

Air Pollutants, Occupational↗
PubMed2001

Reactive oxygen species and molecular mechanism of silica-induced lung injury.

Silica particles are considered to be fibrogenic and carcinogenic agents, but the mechanisms of disease initiation and progression are not fully understood. This article summarizes the literature on the generation of reactive oxygen species (ROS) directly from interaction of silica with aqueous medium and from silica-stimulated cells. This article also discusses the role of ROS in silica-induced lung injury, with particular focus on the silica-induced NF-kappaB activation, including the molecular mechanisms of its regulation, its possible attenuation, and its relationship to silica-induced generation of cyclooxygenase II and TNF-alpha.

Air Pollutants, Occupational↗
PubMed2001

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

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

Air Pollutants, Occupational↗
PubMed2001

[Free crystalline silica: possibilities and limitations of its detection and determination in dust using infrared spectrometry].

The effect of the commonly occurring industrial dust components on the detection of crystalline silica and crystobalite by means of infrared spectrometry was investigated. The influence of minerals interfering in infrared with quartz and crystobalite: kaolinite, microcline, albite, mullite, and amorphous silica, as well as of the mixture of SiO2 crystalline forms was analyzed. The study was based on the computer-aided summing up of crystalline silica spectra with spectra of interfering components and spectra resulting from further transformation: deconvolved spectra, the second and fourth orders derivative spectra. It was found that the smallest amount of silica, possible to be detected in mixtures with interfering components amounted to 1-5% and crystobalite to 2-10%. The limit of detection, using the pellet technique in the adopted conditions of spectra registration, accounted for 0.5 microgram for silica and 1 microgram for crystobalite, whereas using PVC filters, 1 microgram of silica and 4 micrograms of crystobalite could be detected.

Dust↗
PubMedDate not supplied

Effect of inhaled crystalline silica in a rat model: time course of pulmonary reactions.

Numerous investigations have been conducted to elucidate mechanisms involved in the initiation and progression of silicosis. However, most of these studies involved bolus exposure of rats to silica, i.e. intratracheal instillation or a short duration inhalation exposure to a high dose of silica. Therefore, the question of pulmonary overload has been an issue in these studies. The objective of the current investigation was to monitor the time course of pulmonary reactions of rats exposed by inhalation to a non-overload level of crystalline silica. To accomplish this, rats were exposed to 15 mg/m3 silica, 6 h/day, 5 days/week for up to 116 days of exposure. At various times (5-116 days exposure), animals were sacrificed and silica lung burden, lung damage, inflammation, NF-KB activation, reactive oxygen species and nitric oxide production, cytokine production, alveolar type II epithelial cell activity, and fibrosis were monitored. Activation of NF-KB/DNA binding in BAL cells was evident after 5 days of silica inhalation and increased linearly with continued exposure. Parameters of pulmonary damage, inflammation and alveolar type II epithelial cell activity rapidly increased to a significantly elevated but stable new level through the first 41 days of exposure and increased at a steep rate thereafter. Pulmonary fibrosis was measurable only after this explosive rise in lung damage and inflammation, as was the steep increase in TNF-alpha and IL-1 production from BAL cells and the dramatic rise in lavageable alveolar macrophages. Indicators of oxidant stress and pulmonary production of nitric oxide exhibited a time course which was similar to that for lung damage and inflammation with the steep rise correlating with initiation of pulmonary fibrosis. Staining for iNOS and nitrotyrosine was localized in granulomatous regions of the lung and bronchial associated lymphoid tissue. Therefore, these data demonstrate that the generation of oxidants and nitric oxide, in particular, is temporally and anatomically associated with the development of lung damage, inflammation, granulomas and fibrosis. This suggests an important role for nitric oxide in the initiation of silicosis.

Administration, Inhalation↗
PubMed2002

Silica induced early fibrogenic reaction in lung of mice ameliorated by Nyctanthes arbortristis extract.

OBJECTIVE: To investigate the pharmacological effect of Nyctanthes arbortristis (NAT) leaf extract in the prevention of lung injury induced by silica particles. METHOD: Lung injury was induced in Swiss mice through inhalation exposure to silica particles (< 5 mu) using a Flow Past Nose Only Inhalation Chamber at the rate of -10 mg/m3 respirable mass for 5 h. Lung bronchoalveolar lavage (BAL) fluid collected between 48 and 72 h was subjected to protein profiling by electrophoresis and cytokine evaluation by solid phase sandwich ELISA. Lung histopathology was performed to evaluate lung injury. RESULTS: Inhalation of silica increased the level of tumor necrosis factor-alpha (TNF-alpha), and of the 66 and 63 kDa peptides in the BAL fluid in comparison to sham-treated control. Pre-treatment of silica exposed mice with NAT leaf extract significantly prevented the accumulation of TNF-alpha in the BAL fluid, but the 66 and 63 kDa peptides remained unchanged. The extract was also effective in the prevention of silica-induced early fibrogenic reactions like congestion, edema and infiltration of nucleated cells in the interstitial alveolar spaces, and thickening of alveolar septa in mouse lung. CONCLUSION: NAT leaf extract helps in bypassing silica induced initial lung injury in mice.

Administration, Oral↗
PubMedDate not supplied

Early events of experimental exposure to amorphous and crystalline silica in the rat: time course of surfactant protein D.

Pneumoconioses determined by chronic inhalation of different kinds of silica present with peculiar clinical and histopathological features. Silicosis, caused by crystalline silica, is characterized by typical fibrous parenchymal nodules. Less defined are pneumoconioses due to amorphous silica. Aim of current experimental research on silicosis is to investigate the early events that lead to nodular fibrosis of the lung. A secretory component of the pulmonary environment, surfactant, seems to be involved in silica toxicity; surfactant protein D is a protein constituent, apparently involved in the homeostasis of the phospholipid component. We studied the behaviour of SP-D 2, 12 and 24 hours after treatment with 200 mg/kg crystalline silica or pumice powder suspended in 400 microl/kg saline solution and instiled intratracheally to rats. Both immunohistochemical localization and immunoblotting quantification demonstrated a sensible increase in intracellular SP-D, localized in alveolar type II cells and some bronchiolar epithelial cells, 2 hours after treatment. Increment appears less marked 12 hours after administration, reaching again levels comparable to control at 24 hours. The behaviour of SP-D after pumice instilation is similar, but with a significantly minor increment at 2 hours. These results indicate crystalline silica as responsible for a stronger acute injury of pulmonary tissue.

Animals↗
PubMed1992

[Wound healing by homeopathic silica dilutions in mice].

Highly diluted solutions of silica are widely used in homeopathic medicine to treat lesions such as chronic wounds, ulcers, and abscesses. We tested the therapeutic effects of homeopathic dilutions of silica on induced chronic wounds. Holes were made in the ears of mice by dental wire, which then remained hanging from the ear to cause persistent mechanical irritation. In each experiment 3 or 4 groups of 10 mice each were treated by adding homeopathic dilutions of silica (10(-10), 10(-60), 10(-400)) and of saline (10(-10), respectively, to the drinking water of the mice for 4-20 days. The size of the wound holes was measured every second day (grades 0-4) and/or by an objective image analysis system. The results showed that in 7/11 experiments the ear holes of the silica-treated animals were significantly smaller (p less than 0.05-0.001) and healed faster than in those treated with saline. Also the therapeutic effect increased progressively with increase in dilution of the silica (10(-10) less than 10(-60) less than 10(-400)). These results show that homeopathic dilutions of silica (even well beyond Avogadro's number) clearly have a therapeutic effect on wound healing and that our experimental model for studying wound healing is a very useful tool for such studies.

Animals↗
PubMed2002

[Spirometrically controlled quantitative CT for detection of pulmonary function in silica-exposed workers].

OBJECTIVE: To evaluate the diagnostic value of spirometrically controlled quantitative CT in silica-exposed workers. METHODS: Whole lung spiral scans at 50% vital capacity (VC) and image with high resolution CT(HRCT) at 10% VC and 90% VC level and 5 cm above/below carina were performed in 62 silica-exposed workers and 54 healthy adults. Automatic evaluation software, Pulmo, was used to evaluate the quantitative parameters and compared with clinical pulmonary function tests. RESULTS: 9 workers with emphysema were detected by CT scans from 62 silica-exposed workers. The quantitative parameters of 10% VC and 90% VC were significantly different between the silica-exposed workers and the controls (P < 0.05). With the increasing of length of exposure to silica dust, the difference showed a ladder-like rising. CONCLUSION: Spirometrically controlled quantitative CT is a sensitive, accurate and objective method. It is superior to conventional CT and pulmonary function tests for the early detection in silica-exposed workers, espicially for detecting early stage of small airway disease.

Humans↗
PubMed2003

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

OBJECTIVE: To investigate the gene 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 group. 0.2 g/kg body weight of silica was injected intratracheally in silica group. Samples of lung tissue were collected 1, 3, 5, 7, 14 and 28 d after injection. RT-PCR method was used to analyze the gene expression of TGF-beta(1) in lung tissue of silica-treated mice. RESULTS: The expression of TGF-beta(1) gene in lung tissue elevated from the 3rd day (1.20 +/- 0.15) and the peak value was on the 7th day (1.74 +/- 0.19). Then the expression decreased from the 14th to 28th day. But there was still higher than control until the 28th day. CONCLUSION: TGF-beta(1) may play an important role in silica-induced pulmonary fibrosis.

Animals↗
PubMedDate not supplied

Microemulsion processing of silica-polymer nanocomposites.

Silica-polymer nanocomposites have been synthesized via polymerizable bicontinuous microemulsions to disperse functionalized/nonfunctionalized SiO2 nanoparticles uniformly in a polymerized microemulsion system as revealed by transmission electron microscopy. The effect of both types of SiO2 nanoparticles in the polymerized microemulsion increased its glass transition temperature (Tg) from 90 to 128 degrees C. TgS of functionalized silica nanocomposites were about 15 degrees C higher than those of nonfunctionalized samples. As expected, both hardness and modulus of the nanocomposites increased with the loading of both types of silica from 2 to 6 wt%. In the case of nonfunctionalized silica, the improvement of properties may be simply exerted by the conventional filler effect due to the better dispersion of nanoparticles of silica in fluid microemulsion prior to the polymerization. The additional effect for the functionalized silica containing a terminal vinyl group is that It could be grafted to the polymer matrix through cross-polymerization with microemulsion-formed polymer to establish strong nanocomposite networks.

Crystallization↗
PubMedDate not supplied

Cutaneous silica granuloma: a lesion that might be clinically underdiagnosed.

Cutaneous silica granuloma is a poorly understood, uncommon condition. There have been relatively few reports of cutaneous silica granuloma despite the well-known ubiquitous nature of silica in the environment. The characteristic latency period between the time of silica exposure to the time of clinical onset of granuloma, lack of clear-cut histories of exposure in most cases and likelihood of spontaneous resolution, may challenge the diagnosis. Thus, cutaneous silica granuloma might be a lesion that is often underdiagnosed. Here we describe a patient with characteristic findings of cutaneous silica granuloma.

Adult↗
PubMed2005

[Free crystalline silica: a comparison of methods for its determination in total dust].

BACKGROUND: The major objective of the study was to compare and investigate the usefulness of quantitative analyses of free crystalline silica (FCS) in the assessment of dust exposure in samples of total dust of varied composition, using three methods: chemical method in common use in Poland; infrared spectrometry; and x-ray powder diffraction. MATERIALS AND METHODS: Mineral composition and FCS contents were investigated in 9 laboratory samples of raw materials, materials, and industrial wastes, containing from about 2 to over 80% of crystalline silica and reduced to particles of size corresponding with that of total dust. Sample components were identified using XRD and FT-IR methods. Ten independent determinations of FCS with each of the three study methods were performed in dust samples. An analysis of linear correlation was applied to investigate interrelationship between mean FCS determinations. RESULTS: In analyzed dust samples, along with silica dust there were numerous minerals interfering with silica during the quantitative analysis. Comparison of mean results of FCS determinations showed that the results obtained using the FT-IR method were by 12-13% lower than those obtained with two other methods. However, the differences observed were within the limits of changeability of results associated with their precision and dependence on reference materials used. CONCLUSIONS: Assessment of occupational exposure to dusts containing crystalline silica can be performed on the basis of quantitative analysis of FCS in total dusts using each of the compared methods. The FT-IR method is most appropriate for the FCS determination in samples of small amount of silica or collected at low dust concentrations; the XRD method for the analysis of multicomponent samples; and the chemical method in the case of medium and high FCS contents in samples or high concentrations of dusts in the work environment.

Air Pollutants, Occupational↗
PubMed2005

Role of cyclinD1 and CDK4 in the carcinogenesis induced by silica.

OBJECTIVE: To study the role of cyclinD1 and CDK4 in malignant transformation of human fetal lung diploid fibroblast cell line (2BS) induced by silica. METHODS: Recombination vectors with sense and antisense pXJ41-cyclinD1 and pXJ41-CDK4 were constructed, and then transfected into the malignant transformed cells induced by silica, respectively. At the same time, pXJ41-neo was used as the control. RESULTS: During the progress of the malignant transformation of 2BS cells induced by silica, cyclinD1 and CDK4 were overexpressed. Antisense RNA suppressed cyclinD1 and CDK4 gene expression in the antisense pXJ41-cyclinD1 and pXJ41-CDK4 transfected cells. Antisense RNA led to cell cycle arrest, resulting in lengthened G1 phase (the percentages of cells in the G1 phase changed from 45.1% to 52.7% and 58.0% for cyclinD1 and CDK4 transfected cells, respectively), and eventually attenuated the increase of the proliferation of malignant transformed cells induced by silica. Compared with malignant transformed cells induced by silica, cells transfected with antisense pXJ41-cyclinD1 and pXJ41-CDK4 showed obviously reduced growth rates. On the 8th day, the suppression rates were 58.69 and 77.43% (the growth rate of malignant transformed cells induced by silica was 100%), doubling time changed from 21.0 h to 31.4 h and 21.0 h to 42.7 h, respectively, the growth capacities on soft agar of cells transfected by antisense pXJ41-cyclinD1 and pXJ41-CDK4 decreased obviously. CONCLUSION: CyclinD1 and CDK4 play an important role in maintaining transformed phenotype of the cancer cells.

Carcinogens, Environmental↗
PubMed2006

An in vitro investigation of the effect of the addition of untreated and surface treated silica on the transverse and impact strength of poly(methyl methacrylate) acrylic resin.

Silica is a commonly used filler in dental materials and as a reinforcing agent in industry. The aim of this study was to further investigate the effect of the addition of untreated and a novel surface treated silica on the transverse bend and impact strength of acrylic resin denture base material. It was hypothesized that the silica/resin composite materials would have an improved flexural and impact strength than the conventional heat-cured acrylic resin. Three types of untreated and two of treated silica powder were used in this study. The range of percentages used were 1%, 0.5%, 0.2%, 0.1%. The treated particles were coated with hexamethyldisilazane or dimethyldichloridesilazane. Conventional heat cured acrylic resin was used as a control. The modulus of rupture for all groups of acrylic resin containing silica was significantly lower than for the control. The modulus of elasticity was not significantly greater than the control group. For the impact strength statistical analysis revealed a significant difference between the groups. There was a nonsignificant increase in the impact strength for specimens compared to the control. In conclusion the addition of silica to poly(methyl methacrylate) denture base materials did not produce a significant improvement in the transverse bend or impact strength compared to conventional heat-cured acrylic resin. The incorporation of untreated and surface treated silica cannot be recommended as a method of reinforcement.

Acrylic Resins↗
PubMedDate not supplied

[Effect of silica on the anti-tumour activity of "Corynebacterium parvum" (author's transl)].

Silica, a specifically toxic substance for macrophages, has been used to study the role of these cells in the Corynebacterium parvum-induced anti-tumour protection. In the two experimental tumours studied, silica, C. parvum and tumour cells were injected by the same route: the intravenous route in the case of lymphosarcoma in XVII mice and the intraperitoneal in that of mammary carcinoma in C3H mice. The inhibition of the anti-tumour effect of C. parvum by the administration of silica was more pronounced in C3H than in XVII mice. Silica administration has only a weak and transient depressive effect on the stimulation of macrophage phagocytic activity induced by C. parvum. In addition, silica injection increased the adjuvant effect of C. parvum on the sheep red blood cell antibody response. These results suggest that the silica induced abrogation of the anti-tumour effect of C. parvum could be due to a local inhibition of macrophage stimulation at the tumour inoculation site.

Animals↗
PubMed1986

Silica-induced hypertrophy of type II cells in the lungs of rats.

Several investigators have reported the appearance of hypertrophic type II cells in the lungs of silica-treated rats. The purpose of this study was to isolate and characterize these hypertrophic type II cells. Lungs were digested with trypsin and the released cells were separated by using a flow gradient during centrifugal elutriation. Type II cells from control lungs were distributed in the flow gradient as a single population, whereas type II cells from the lungs of silica-treated rats had a bimodal distribution suggesting the presence of two distinct populations of type II cells; one of these populations appeared hypertrophic (type IIB) and the other appeared normal (type II cells; one of these populations appeared hypertrophic (type IIB) and the other appeared normal (type IIA). These two populations of type II cells from silica-treated rats differed significantly in cell size and their lamellar body content. The mean volume of type IIA and type IIB cells was 350 +/- 38 micron 3 and 523 +/- 29 micron 3, respectively. The mean number of lamellar bodies in type IIA and type IIB cells was 77 +/- 53 and 131 +/- 84 per cell, respectively. The mean volume of lamellar bodies was 0.39 +/- 0.09 micron 3 in type IIA cells and 0.66 +/- 0.10 micron 3 in type IIB cells. Type IIA cells were not significantly different from type II cells from the lungs of untreated rats. The distribution of type II cells from silica-treated lungs was such that 2 weeks after a single intratracheal injection of silica (10 mg/rat) type IIB cells accounted for 39.2 +/- 6.4% of the total type II cells recovered after centrifugal elutriation. The general morphological appearance of the isolated type IIA and type IIB cells was similar to that observed in type II cells isolated from untreated rats. These data indicate that hypertrophic type II cells may be isolated from the lungs of silica-treated rats and separated from normal type II cells thus allowing the role of these unusual type II cells in lung injury and repair to be investigated.

Alkaline Phosphatase↗