SEARCH · Search PubMed
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.
Explore the source record for details and available documents.
The role of free intracellular calcium [Ca2+]i was studied in the production of reactive oxygen metabolites (ROM) by human polymorphonuclear leukocytes (PMNL) after a single or two repeated doses of quartz. The significance of [Ca2+]i in the production of ROM was also studied after a dose of quartz prior to, or after, a dose of formylmethionylleucylphenylalanine (fMLP). When the production of ROM and changes in [Ca2+]i were measured after repeated stimulations of cells, the cells were always washed between stimulations. A dose of quartz elevated [Ca2+]i in untreated and washed cells, whereas a second dose of quartz did not induce any further increase in [Ca2+]i. On the contrary, quartz stimulated ROM production after both one and two consecutive doses. fMLP alone elevated [Ca2+]i and increased the production of ROM. Quartz before fMLP did not modify fMLP-induced [Ca2+]i increase, but attenuated fMLP-induced ROM production. Quartz-induced elevation of [Ca2+]i was not affected by a prior dose of fMLP, but the production of ROM by quartz was greatly amplified by prior exposure of PMNL to fMLP. Thus, both quartz and fMLP increase the production of ROM by mechanisms in which [Ca2+]i may have a key role. Priming of PMNL with fMLP prior to quartz seems to amplify quartz-induced ROM production but not to affect [Ca2+]i. It is plausible that both [Ca2+]i-dependent and -independent mechanisms may account for quartz-induced ROM production in PMNL.
Following the classification of quartz as a human carcinogen by the IARC, many standard-setting committees are currently trying to convert this hazard into their national or EU standards. Since human data to set a safe exposure limit for quartz are limited, we hypothesized that lung burden data on quartz in coal miners' lungs after lifetime exposure could be used to set a non-carcinogenic lung burden of quartz, and that this might be valid for other groups occupationally exposed to quartz. A review of data shows that lungs of coal miners with simple coal workers' pneumoconiosis (sCWP) typically contain up to 30 g of dust, and in one specific study lung burdens between 0.7 and 1.7 g of quartz were associated with macules only, and no sCWP. Assuming independent actions of coal and quartz and no clearance of quartz, and sCWP as a prerequisite for lung cancer due to quartz exposure in coal mine dust, a simple kinetic approach was applied. A no observed adverse effect level (NOAEL) for quartz of between 0.03 and 0.13 mg/m3 (40 yr exposure) is derived, but it is concluded that more refined physiologically based pharmacokinetic modelling is needed for a better estimate, also including interindividual differences in lung clearance. Considering the independent effects of, and the well-known interaction between coal and quartz, these data could be important to other workplaces with usual mixed-dust exposure.
In 1997, the IARC (International Agency for Research on Cancer) reevaluated its quartz classification from a class 2 carcinogen, to that of a class 1, stating sufficient evidence for carcinogenicity in both humans and experimental animals. However, tumor development did not occur across all occupational settings. It is probable that this is due to the considerable differences in toxicity between workplace quartz in comparison to quartz used in experimental studies. We therefore hypothesized that workplace quartz samples differ in toxicity from standard experimental quartz samples at equal mass. To test this hypothesis we compared 2 workplace quartz samples (RH1 and OM) with standard experimental quartz (DQ12) in several assays commonly used in particle toxicology. The sizes of the quartz samples were as closely matched as possible. The endpoints of this study were inflammation in the rat lung following intratracheal instillation (1000 microg or 250 microg for 3 or 14 days), release of soluble iron, cytotoxicity to cells in culture, and surface reactivity as assessed by hemolysis and ESR. The workplace samples did not cause inflammation at any dose or time point. DQ12 quartz caused marked inflammatory responses, as measured by an increased number of neutrophils in the lungs of instilled animals for both time points and doses. Protein in the bronchoalveolar lavage also increased in animals exposed to DQ12 but not the workplace samples. In vitro, DQ12 had the greatest hemolytic activity but only RH1 released substantial amounts of soluble iron. The increased inflammogenicity of DQ12 was not wholly explained by a greater surface area, by diameter, or by releasable iron. The hemolytic activity of DQ12, while not being informative in terms of understanding the mechanism of carcinogenicity, was the best in vitro predictor for in vivo activity. Therefore the surface reactivity of DQ12 appears to drive its inflammogenicity.
Fibrogenic effects of siliceous ceramic raw materials (quartz and quartz sand), heated at 1200 degrees C for 72 hours (conditions of ceramic products burning) have been investigated. The evaluation of fibrogenic effects has been based on wet lungs weight and hydroxyproline content in rats' lungs after an intratracheal administration of 50 mg of the test dust, during 3 and 6 months' experiment. The obtained results indicate that high temperature affects the polymorphous transformation of silica. The transformation varies, e.g. crystabillite has been found in quartz, whereas in quartz sands, quartz has been found apart from crystaballite. In the Isere quartz from Nowosolna crystalline silica content has been decreased, as compared to unheated samples. Heating does not reduce fibrogenic effects of some samples e.g. quartz sand from Biała Góra), or the activity may be increased (e.g. quartz sand from Winiary), or is not changed (quartz from Austria). The tendency of changes in biological aggressiveness of siliceous dusts subjected to high temperature cannot be foreseen, as those changes depend on different factos, among others on the content of various impurities.
Fibrogenic effects of amorphous quartz dusts are discussed more and more during recent years. In order to study alterations due to amorphous silica (quartz glass VP 203-006) in comparison with crystalline quartz (DQ-12), an inhalation experiment in rats was carried out. Male Wistar rats were separated in two dust exposed groups (n = 35) and one control group (n = 30). The experiment was carried out in inhalation chambers with a slowly rotating animal cage for 12 months, 7 h per day, and 5 days per week. The dust concentration was 10 mg/m3. After 4 and after 8 months of inhalation, 5 animals of each group were sacrificed. After 12 months 15 rats of the dust exposed groups and 10 controls were euthanized. The remaining animals were kept for another 12 months post-inhalation period. Regarding the macroscopical appearance of the lungs, the relative organ weights and the histomorphological reaction pattern, marked dust depending differences are obvious. In the lungs of DQ-12-exposed animals diffuse structural changes occur, including fibrosis and severe reaction of macrophages. Histology of lungs from quartz glass exposed animals reveals only a slight and focally arranged cellular reaction with a few collagenous fibers. However, in both dust exposed groups the mediastinal lymph nodes are extremely enlarged with severe fibroses. Additionally, the following blood parameters were determined: lysozyme, ACE, GOT, GPT, and AP. The most pronounced changes are detectable in lysozyme and GOT after DQ-12 exposure. After quartz glass exposure, the levels of these parameters are similar to the controls. These results show that the amorphous quartz tested in this experiment (quartz-glass VP 203-006) has to be considered as a compound with certain biological effects. The establishing of occupational standards seems to be justified. But, assessing the effects, the different physical and/or chemical properties of various amorphous quartz dusts have to be considered.
The aim of this study was to compare the X-ray diffraction and infrared spectrophotometric patterns of two samples of alpha quartz (QUIN1 and QUIN2) with that of NIST SRM 1878a alpha quartz certified 100% crystalline. As it is known that the intensity diffracted and the absorbance per mass unit for a given type of alpha quartz depend on its particle size, this factor was taken into account. To do this, different types of alpha quartz were sampled on filters using a Dorr-Oliver cyclone to select particle size. Variation in the flow rate of the cyclone in the range 1.2-2.8 l/min allowed the volume median diameter of the sampled particles to be varied. For the four strongest diffraction lines it was observed that the intensity per mass unit increased with the volume median diameter of the particles. For infrared spectrophotometry for analytical band wavelengths close to 12.5 micro m, it was observed that the absorbance per mass unit decreased as particle size increased. The opposite effect was noted for analytical band wavelengths >14.4 micro m. Compared with SRM 1878a alpha quartz, certified 100% crystalline, the purity of QUIN1 alpha quartz was 93.1% (confidence interval 92.4-93.8%) when measured by X-ray diffraction and 91.5% (confidence interval 90.1-92.9%) when measured by infrared spectrophotometry. In the case of QUIN2 alpha quartz the purity was globally lower.
PURPOSE: The purpose of the investigation was to compare the performances of teeth restored with quartz fiber, carbon-quartz fiber, and zirconium-dioxide posts covered with all-ceramic crowns when subjected to a cyclic loading test performed in a wet environment. MATERIALS AND METHODS: Forty single-rooted human lower premolars having similar dimensions were endodontically treated and mounted in acrylic resin blocks with a simulated periodontal ligament. The teeth were divided into three experimental groups and one control group. Post holes 8 mm long were prepared in the roots of the experimental groups in which quartz fiber, carbon-quartz fiber, and zirconium dioxide posts were cemented. In the control group, no posts were used. The crown buildup was made with composite resin. The teeth were covered with all-ceramic crowns and intermittently loaded at an angle of 45 degrees to the long axis of the tooth at a frequency of two loads per second. RESULTS: Only one failure (root fracture + post fracture) was observed in each of the fiber post groups, while in the zirconium dioxide post group, six failures were observed (one crown fracture and 5 root fractures + post fractures). The Kaplan-Meier analysis of the three experimental groups showed that the survival rate of zirconium dioxide posts was significantly lower than that of both types of fiber post. All the experimental groups showed a survival rate higher than that of the control group. CONCLUSION: Fiber posts reduced to a minimum the risk of root fractures of teeth restored with composite cores and Empress crowns under the present experimental conditions (intermittent loading in a wet environment).
The experimental frost weathering of a quartz sandstone is being carried out as part of a series of laboratory simulations to investigate geomorphic mechanisms capable of producing loess-sized quartz silt. The preliminary results are reported in this paper. Frost weathering simulations involved two different temperature regimes: (a) -5 degrees C-+15 degrees C, and (b) -12 degrees C-+15 degrees C. Debris production was observed for both temperature regimes with the blocks subjected to the more intense freezing regime experiencing the most disintegration. Scanning electron microscopic (SEM) examination and particle size analysis revealed that the debris produced by both these experiments included a significant silt sized fraction. Further SEM examinations of this debris demonstrated the presence of silt sized fragments of quartz overgrowths among the debris. It is suggested that overgrowth detachment occurs during frost weathering by either the penetration into and subsequent freezing of water in the gaps between overgrowths and host grains, or pressures applied to the outer surfaces of overgrowths during frost cycles causes them to collapse onto the underlying grain.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.