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PubMed1999

Pulmonary dysfunction in silica-exposed workers: a relationship to radiographic signs of silicosis and emphysema.

BACKGROUND: It has been established that occupational exposure to silica dust may cause significant impairment of pulmonary function. To compare the contribution of silicosis and emphysema to pulmonary dysfunction, radiographic signs of silicosis and emphysema in silica exposed workers were analyzed. METHODS: Two hundred and twenty workers exposed to silica working in a Chinese refractory plant were selected as study subjects. Their findings of silicosis and emphysematous changes on radiograph were classified and evaluated. A questionnaire on respiratory symptoms, smoking, and occupational history was administered. All the workers performed measurements of spirometry and CO single-breath diffusing capacity. RESULTS: Radiographic hyperinflation was detected in 9% of the workers without silicosis and in 33% of the workers with silicosis. Silicosis was significantly associated with hyperinflation after adjusting for exposure duration, age, and smoking. Respiratory symptoms were more frequent in the more severe cases of silicosis. Regression analysis showed that silicosis was significantly associated with decreases in the parameters of pulmonary function, but the significance disappeared when the hyperinflation term was added to the models. Radiographic hyperinflation was strongly associated with decreases in FEV1 and FEV1/FVC while relevant factors were controlled. Comparison between workers with and without hyperinflation showed that the former had significantly lower pulmonary function values. CONCLUSIONS: The results suggest that emphysema associated with silicosis is likely to be responsible for pulmonary obstruction and decreased diffusing capacity occurring in silica-exposed workers.

Adult↗
PubMed2000

Is silicosis required for silica-associated lung cancer?

BACKGROUND: Abundant epidemiologic and experimental evidence supports the 1997 International Agency for Research on Cancer classification of crystalline silica as a human lung carcinogen. Nonetheless, there remains uncertainty about whether excessive lung cancer occurs exclusively among workers with silicosis. METHODS: A review was performed of published occupational epidemiologic literature directly pertinent to the interrelations among silica exposure, silicosis, and lung cancer. RESULTS: The association between silica and lung cancer is generally, but not uniformly, stronger among silicotics than nonsilicotics. However, the existing literature is ambiguous due to incomplete or biased ascertainment of silicosis, inadequate exposure assessment, and the inherently strong correlation between silica exposure and silicosis which hinders efforts to disentangle unique contributions to lung cancer risk. CONCLUSIONS: Until more conclusive epidemiologic findings become available, population-based or individually-based risk assessments should treat silicosis and lung cancer as distinct entities whose cause/effect relations are not necessarily linked.

Environmental Exposure↗
PubMed2000

Apatite growth on calcium adsorbed surface of wet flocculated silica particles immersed in a modified simulated body fluid.

An alternative method for the calcium phosphate apatite formation onto the surface of flocculated pure silica particles is reported, in an attempt to understand the possible mechanism for the apatite formation. A stable silica sol was flocculated by adding calcium ions in aqueous solution. The wet flocks were resuspended in a basic aqueous solution containing a calcium salt, trying to allow the absorption of calcium ions onto the silica surface through a hydrogen ion exchange. The as-prepared materials were immersed in a modified simulated body fluid at different temperatures (37 and 90 degrees C) and silica concentrations. It was found that these factors have a strong influence on the apatite formation. The apatite formation was confirmed by (31)P MAS-NMR, FT-Raman, XRD, and TEM.

Adsorption↗
PubMed1978

Silica reaction simulating fibrous histiocytoma.

An unusual foreign body reaction to silica (quartz), resembling fibrous histiocytoma, is described in 7 patients (age range 22 to 71 years). These lesions occurred in the inguinal region (4 cases) or the abdominal wall (3 cases), and in 5 instances were associated with a history of injection at the same site 10 to 41 years previously. Most commonly the injection consisted of the administration of a sclerosing agent for the repair of a hernia. Microscopically these lesions contained broad sheets of histiocytes separated by bands or concentrically lamellated nodules of collagen. Intra- and extra-cellular birefringent crystals, identified by x-ray diffraction as silica (quartz), were present in all cases and served to distinguish this process from a true neoplasm. Although the injection therapy for hernia is now obsolete, it was formerly practiced in the United States with a variety of sclerosing agents including silica (quartz). Since these lesions are often confused with a benign or malignant fibrous histiocytoma it is recommended that fibro-histiocytic lesions associated with a previous hernia or injection at the same site be examined for the presence of silica.

Adult↗
PubMed2001

A case-control study of the relationships among silica exposure, gastric cancer, and esophageal cancer.

BACKGROUND: We examined the effect of silica exposure on gastric and esophageal cancer mortality using a cancer control series in a population setting. METHODS: Cases and controls were restricted to male subjects and were drawn from death certificates in the Tobi area of Japan. A control group was selected from a series of deaths due to colon cancer, and cancers of other organs. The Japanese death certificate system is comprehensive because all deaths must be reported to the local office and death certificates are written by medical doctors. Age and smoking habits adjusted the Mantel-Haenszel odds ratios were estimated. RESULTS: For gastric cancer, the age-, smoking-adjusted odds ratios were 1.22 (95% CI 0.74-2.01) for colon cancer and the other cancer control for silica exposure work, and 1. 36 (95% CI 0.76-2.43) for silicosis. For esophageal cancer, the age- and smoking-adjusted odds ratios were 1.53 (95% CI 0.59-3.96) for the cancer control for silica exposure, and 2.33 (95% CI 0.87-6.23) for silicosis, respectively. CONCLUSIONS: The results suggest that gastric and esophageal cancer were related to silica exposure and silicosis in the study area, although they did not reach a statistically significant level because of the small sample size. The estimated odds ratios were higher for esophageal cancer and silicotic patients.

Adult↗
PubMed2001

In vitro bioactivity and structural features of mildly heat-treated sol-gel-derived silica fibers.

The ability of sol-gel-derived silica fibers heat treated at a low temperature to induce formation of bone-like calcium phosphate (HCA) on their surfaces provides alternatives for the design of novel biomaterials, for example as implants used in tissue guiding or bone repairs. In this study, dry spinning was used to prepare the sol-gel fibers, which were heat-treated at 175 degrees and 250 degrees C. In addition, the differences in the surface topography (in a nanometer scale) of different fibers with respect to their in vitro bioactivity were studied. The structure of the fibers was varied using three different factors: (1) spinnable sols having varying structures and sizes of silica polymers to establish varying viscosity levels; (2) aging of green-state fibers; and (3) heat treatment of fibers. The in vitro bioactivity and solubility tests were done in simulated body fluid (SBF). To monitor surface topography and roughness of the heat-treated silica fibers, a scanning probe microscopy (SPM) with tapping mode AFM was used. Different fibers obtained clearly different properties. The fibers spun at about eta > 3.0 Pas had the best properties with respect to bioactivity, especially when they were heat-treated at 175 degrees C. It was found that surface structure in a nanometer scale was the most important factor controlling the in vitro bioactivity of heat-treated silica fibers. The correct proportions between the peaks and peak distances at the surfaces are suggested to be important with respect to in vitro bioactivity. The results indicate that peak distance distribution between 5-50 nm, especially between 5-20 nm, together with a peak height > or = 1 nm is most favorable for calcium phosphate formation.

Absorbable Implants↗
PubMed2001

Apatite nucleation on silica surface: a zeta potential approach.

Zeta potential measurements on pure silica, prepared by the sol-gel method from tetraethoxysilane under acidic conditions, are reported in different suspensions. Water suspensions and suspensions containing calcium or phosphate ions with and without NaCl were tested. zeta potential measurements were carried out as a function of the pH and ion concentration. Also, calcium and phosphate adsorption on silica was determined experimentally. The results of zeta potential and adsorption measurements suggest that both calcium and phosphate ions can be adsorbed on the silica surface; however, calcium adsorption is stronger than phosphate adsorption. When calcium and sodium ions are present in the suspension, calcium adsorption decreases. It seems that certain sites on the silica surface are specific for calcium adsorption.

Apatites↗
PubMed2002

Surface organometallic chemistry of main group elements: selective synthesis of silica supported [triple bond Si-OB(C(6)F(5))(3)](-)[HNEt(2)Ph](+).

The reaction of the Lewis acid B(C(6)F(5))(3) with silanol groups of silica surfaces, dehydroxylated at different temperatures (300, 500, 700, and 800 degrees C), has been investigated in presence of the Brønsted base NEt(2)Ph. The structure of the resulting modified silica supports [triple bond Si-OB(C(6)F(5))(3)](-)[HNEt(2)Ph](+) (1) has been carefully identified by IR and multinuclear solid-state NMR spectroscopies, isotopic (2)H and (18)O labeling, elemental analysis, molecular modeling, and comparison with synthesized molecular models. Highly dehydroxylated silica surfaces were required to transform selectively each silanol group into unique [triple bond Si-OB(C(6)F(5))(3)](-)[HNEt(2)Ph](+) fragments. For lower dehydroxylation temperatures, two sorts of surface sites were coexisting on silica: the free silanol groups [triple bond SiOH] and the ionic species 1.

Journal Article↗
PubMed2001

Use of vancomycin silica stationary phase in packed capillary electrochromatography I. Enantiomer separation of basic compounds.

Chiral separation of basic compounds was achieved by using 75 or 100 microm ID fused-silica capillaries packed with a vanoomycin-modified diol silica stationary phase. The capillary was firstly packed for about 12 cm with a slurry mixture composed of diolsilica (3:1) then with the vancomycin modified diol-silica (3:1) (23 cm), and finally with diol-silica (3:1) for about 2 cm. Frits were prepared by a heating wire at the two ends of the capillary; the detector window was prepared at 8.5 cm from the end of the capillary where vancomycin was not present. The influence of the mobile phase composition (pH and concentration, organic modifier type and concentration) on the velocity of the electroosmotic flow, chiral resolution and enantioselectivity was studied. Good enantiomeric resolution was achieved for atenolol, oxprenolol, propranolol, and venlafaxine using a mobile phase composition of 100 mM ammonium acetate solution (pH 6)/water/acetonitrile (5:5:90 v/v/v) while for terbutaline a mixture of 5:15:80 v/v/v provided the best separations. The use of methanol instead of acetonitrile caused a general increase of enantiomer resolution of the studied compounds together with a reduction of efficiency and detector response. However, the combination of acetonitrile and methanol in the mobile phase (as, e.g., 10% methanol and 80% acetonitrile) allowed to improve the enantiomer resolution with satisfactory detector response.

Acetates↗
PubMed1982

Does occupational exposure to silica cause lung cancer?

Silica is not generally considered to be a carcinogen, however, occupations characterized by high exposure to crystalline silica have excessive rates of lung cancer mortality. Respiratory cancer excesses have been reported from North America and from Europe for the following dusty trades in which exposure to silica is a common factor: iron and steel foundry workers, steel casting workers, sand blasters, metal molders, non-uranium miners, and ceramic workers. These findings have been reinforced by two reports from the Swedish Pneumoconiosis Register and the Ontario Ministry of Labor indicating that silicotics have statistically significant risks of lung cancer mortality. Animal studies suggest that silica can be an initiating carcinogen or can act as a cocarcinogen or promoter when combined with benzo(a)pyrene. We propose three candidate hypotheses and two pathways for silicocarcinogenesis.

Animals↗
PubMed1986

Case-control study of silicosis, silica exposure, and lung cancer in white South African gold miners.

A case-control study was undertaken to assess the association between lung cancer and silicosis or silica dust exposure in white South African gold miners. Cases and controls were identified from deaths reported to the Gold Miners Provident Fund for the period January, 1979-October, 1983. Two controls were matched to each case by year of birth (+/- 2 years) and by smoking (+/- 5 cigarettes or equivalents per day) assessed 10 years (+/- 2 years) prior to death. One hundred thirty-three matched triplets were identified. The results showed no overall association between lung cancer and radiological silicosis (OR = 1.08, p = 0.92). Autopsy data indicated no overall associations between lung cancer and silicosis of the lung parenchyma (OR = 1.49, p = 0.11), the pleura (OR = 0.72, p = 0.30), or the hilar glands (OR = 0.85, p = 0.72). A trend toward increased severity of silicosis of the parenchyma was evident; however, this was not statistically significant (p = 0.08). Odds ratios for lung cancer and silicosis were higher at lower levels of cumulative silica dust exposure (ORs = 2.43, 1.72, 1.35 and 0.62 for lung cancer and autopsy silicosis of the parenchyma for the lowest, second, third, and highest quartiles of dust exposure, respectively; all p greater than 0.05). Cases did not differ from controls for total silica dust exposure, length of exposure, weighted average intensity of exposure, or number of shifts at high dust (all p greater than 0.20). The data do not support the hypothesis of a carcinogenic role for silica dust and no statistically significant associations were found between lung cancer and silicosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Gold↗
PubMed1989

Silica exposure and silicosis among Ontario hardrock miners: II. Exposure estimates.

An epidemiological investigation was carried out to determine the relationship between silicosis in hardrock miners in Ontario and cumulative exposure to silica (free crystalline silica--alpha quartz) dust. This second report describes a side-by-side air-sampling program used to derive a konimeter/gravimetric silica conversion curve. A total of 2,360 filter samples and 90,000 konimeter samples were taken over 2 years in two mines representing the ore types gold and uranium, both in existing conditions as well as in an experimental stope in which dry drilling was used to simulate the high dust conditions of the past. The method of calculating cumulative respirable silica exposure indices for each miner is reported.

Environmental Exposure↗
PubMed1995

Mortality study of gold miners exposed to silica and nonasbestiform amphibole minerals: an update with 14 more years of follow-up.

We have updated a study of 3,328 gold miners who worked underground for at least 1 year between 1940-1965 in South Dakota, extending the follow-up from 1977 to 1990. The exposures of concern were silica and nonasbestiform amphibole minerals. The lung cancer standardized mortality ratio (SMR) was 1.13 (95% confidence interval [CI] 0.94-1.36, 115 observed) when the U.S. population was used as the referent group, increasing to 1.25 (95% CI 1.03-1.51) when the county was used as the referent, and to 1.27 (1.02-1.55) for person-time with more than 30 years potential latency. However, lung cancer mortality did not show a positive exposure-response trend with estimated cumulative dust exposure. Data on smoking habits suggested that the miners smoked slightly more than the U.S. population in a 1960 cross-sectional survey. In contrast to lung cancer, other diseases known to be associated with silica exposure (tuberculosis and silicosis) were significantly increased (SMR = 3.44 and 2.61) and exhibited clear exposure-response trends. Nonmalignant renal disease, also associated with silica exposure, was elevated for those hired in early years and showed a significant positive exposure-response trend. Multiple-cause analysis revealed significant excesses of arthritis, musculoskeletal diseases (including systemic lupus and sclerosis), and skin conditions (including scleroderma and lupus), diseases of autoimmune origin which have been associated with silica exposure in other studies. Multiple cause analysis also showed a significant excess of diseases of the blood and blood-forming organs.

Case-Control Studies↗
PubMed2005

Mesoporous silica nanoreactors for highly efficient proteolysis.

Protein digestion inside the nanoreactor channels of mesoporous silica (SBA-15) is reported, and evaluated by using peptide-mass mapping. Both proteases and substrates were efficiently captured within these biocompatible nanoreactors. After 10 minutes, the mass spectrum of the protein digests released from the mesoporous-silica-based nanoreactors revealed the presence of eight peptides covering 58% of the protein sequence with an intense signal (signal/noise ratio > 70). In comparison, the conventional overnight in-solution digestion of proteins under otherwise identical conditions generated only three peptides (27% sequence coverage). We propose that this order-of-magnitude increase in the proteolytic reaction rate is mainly attributed to two factors: substrate enrichment within mesoporous silica channels and enzyme immobilization. The surface properties and macrostructure of the mesoporous silica were studied to reveal their significant influence on proteolytic reactions.

Hydrolysis↗
PubMed2005

Structural preferences of single-walled silica nanostructures: nanospheres and chemically stable nanotubes.

Structural preferences of single-walled and coordinatively saturated spherical and tubular nanostructures of silica have been determined by ab initio calculations. Two families of spherical (SiO2)n clusters derived from Platonic solids and Archimedean polyhedra are depicted, with n ranging from 4-120. The analogue of a truncated icosidodecahedron, Ih-symmetric Si120O240, is favored in energy, closely followed by the Ih-symmetric Si60O120-truncated icosahedron. The silica nanotubes derived from spherical clusters are capped by Si2O2 rings, whereas the tubular section consists of single oxygen bridges. Periodic studies performed with open-ended silica nanotubes and the alpha-quartz polymorph of silica, along with a comparisons to fullerenes and carbon nanotubes, suggest that tubes with diameters of approximately 1 nm should be chemically stable.

Journal Article↗
PubMed2006

Silica-coated Ln3+-Doped LaF3 nanoparticles as robust down- and upconverting biolabels.

The preparation of nearly monodisperse (40 nm), silica-coated LaF(3):Ln(3+) nanoparticles and their bioconjugation to FITC-avidin (FITC=fluorescein isothiocyanate) is described in this report. Doping of the LaF(3) core with selected luminescent Ln(3+) ions allows the particles to display a range of emission lines from the visible to the near-infrared region (lambda=450-1650 nm). First, the use of Tb(3+) and Eu(3+) ions resulted in green (lambda=541 nm) and red (lambda=591 and 612 nm) emissions, respectively, by energy downconversion processes. Second, the use of Nd(3+) gave emission lines at lambda=870, 1070 and 1350 nm and Er(3+) gave an emission line at lambda=1540 nm by energy downconversion processes. Additionally, the Er(3+) ions gave green and red emissions and Tm(3+) ions gave an emission at lambda=800 nm by upconversion processes when codoped with Yb(3+) (lambda(ex)=980 nm). Bioconjugation of avidin, which has a bound fluorophore (FITC) as the reporter, was carried out by means of surface modification of the silica particles with 3-aminopropyltrimethoxysilane, followed by reaction with the biotin-N-hydroxysuccinimide activated ester to form an amide bond, imparting biological activity to the particles. A 25-fold or better increase in the FITC signal relative to the non-biotinylated silica particles indicated that there is minimal nonspecific binding of FITC-avidin to the silica particles.

Avidin↗
PubMed2006

Does silica surface catalyse peptide bond formation? New insights from first-principles calculations.

The role that silica surface could have played in prebiotic chemistry as a catalyst for peptide bond formation has been addressed at the B3LYP/6-31+G(d,p) level for a model reaction involving glycine and ammonia on a silica cluster mimicking an isolated terminal silanol group present at the silica surface. Hydrogen-bond complexation between glycine and the silanol is followed by the formation of the mixed surface anhydride Si(surf)-O-C(=O)-R, which has been suggested in the literature to activate the C=O bond towards nucleophilic attack by a second glycine molecule, here simulated by the simpler NH3 molecule. However, B3LYP/6-31+G(d,p) calculations show that formation of the surface mixed anhydride Si(surf)-O-C(=O)-R is disfavoured (delta(r)G298 approximately 6 kcal mol(-1)), and that the surface bond only moderately lowers the free-energy barrier of the nucleophilic attack responsible for peptide bond formation (deltaG298(double dagger) approximately 48 kcal mol(-1)) in comparison with the uncatalysed reaction (deltaG298(double dagger) approximately 52 kcal mol(-1)). A further decrease of the free-energy barrier of peptide bond formation (deltaG298(double dagger) approximately 41 kcal mol(-1)) is achieved by a single water molecule close to the reaction centre acting as a proton-transfer helper in the activated complex. A possible role of strained silica surface defects on the formation of the surface mixed anhydride Si(surf)-O-C(=O)-R has also been addressed.

Catalysis↗
PubMed2004

Nanowires for surface enlargement of narrow-bore fused-silica tubing.

A method for preparation of silica nanowires with dimensions of d = 10-100 nm, l = 5-500 nm, is described. The nanostructured material is an integral part of the inner surface of narrow bore fused-silica capillary tubing. The wire preparation method is based on a decomposition of 2-chloro-1,1,2-trifluoroethyl methyl ether at elevated temperature and pressure. The silica bulk material is rearranged via a sustained silica-hydrogen fluoride chemistry, and reaction mechanisms for this process are proposed. The method is suitable for preparing long lengths of tubing with the modified surface. It is our belief that the texture of the capillary wall with its increased surface area is useful for applications such as microreactions, catalysis, and high-resolution pressure and/or electrodriven open-tubular liquid chromatography.

Chromatography, Liquid↗