Non-metallic toxicological hazards: some of the newer compounds in industry.
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Fluorine↗
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Retention of carbon and alteration of expected 13C-tracer enrichments by silylated derivatives using continuous-flow combustion-isotope ratio mass spectrometry.
Continuous-flow inlets from oxidation reactors are commonly used systems for biological sample introduction into isotope ratio mass spectrometers (IRMS) to measure 13C enrichment above natural abundance. Because the samples must be volatile enough to pass through a gas chromatograph, silylated derivatization reactions are commonly used to modify biological molecules to add the necessary volatility. Addition of a tert-butyldimethylsilyl (TBDMS) group is a common derivatization approach. However, we have found that samples do not produce the expected increment in measured 13C abundance as the TBDMS derivatives. We have made measurements of 13C enrichment of leucine and glutamate standards of known 13C enrichment using derivatives without silicon (N-acetyl n-propyl ester), with silicon (TBDMS), and an intermediate case. The measurements of 13C in amino acids derivatized without silicon were as expected. The 13C enrichment measurements using the TBDMS derivative were higher than expected but could be corrected to produce the expected 13C enrichment measurement by IRMS if one carbon was removed per silicon. We postulate that the silicon in the derivative forms silicon carbide compounds in the heated cupric oxide reactor, rather than forming silicon dioxide. Doing so reduces the amount of CO2 formed from the carbon in the sample. Silylated derivatives retain carbon with the silicon and must be used carefully and with correction factors to measure 13C enrichments by continuous-flow IRMS.
Carbon↗
Gelation of sodium silicate; effect of sulfuric acid, hydrochloric acid, ammonium sulfate, and sodium aluminate.
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Aluminum Compounds↗
[Favorable physical action exerted on the growth of plant tissue cultures by the contact of gelose medium or silicon gel].
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Agar↗
A stable compound containing a silicon-silicon triple bond.
The reaction of 2,2,3,3-tetrabromo-1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasilane with four equivalents of potassium graphite (KC8) in tetrahydrofuran produces 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyl-2-tetrasilyne, a stable compound with a silicon-silicon triple bond, which can be isolated as emerald green crystals stable up to 100 degrees C in the absence of air. The SiSi triple-bond length (and its estimated standard deviation) is 2.0622(9) angstroms, which shows half the magnitude of the bond shortening of alkynes compared with that of alkenes. Unlike alkynes, the substituents at the SiSi group are not arranged in a linear fashion, but are trans-bent with a bond angle of 137.44(4) degrees.
Journal Article↗
Silicon and silicone levels in patients with silicone implants.
Although a potential link between silicone gel breast implants and autoimmune connective tissue disease has been suggested, none has been proven. The potential role of silicone as an immune adjuvant remains very controversial. Currently available techniques do not easily allow precise measurements of silicone in tissues. However, all compounds containing silicon (which would include silicone) can be measured accurately. The present study was designed to measure silicon levels in the fibrous capsules of patients with silicone-gel breast implants, saline breast implants and silicone inflatable penile prostheses. Baseline control silicon levels were obtained from the breast tissue of patients undergoing breast reduction, who had no exposure to breast implants. All silicon measurements were carried out using atomic absorption spectrometry with a graphite furnace. The mean silicon levels in 16 breast tissue control samples from 8 patients undergoing breast reduction varied from 0.046 to 0.742 micrograms/g dry weight, with the median mean being 0.0927. The median silicon level in capsules from 6 patients with saline implants was 7.7 micrograms/g (range 36.6). The median silicon level in capsules from 5 patients with silicone inflatable penile prostheses was 19.5 micrograms/g (range 34.8). Although the levels of silicon in capsules of patients with saline breast prostheses and penile implants were higher than in control samples, they were much lower than those from the capsules of the 58 gel implants (median 9979 micrograms/g). Of the 58 silicone gel breast implants (from 20 patients with bilateral implant removal and 18 patients with unilateral removal) which had been inserted from 1974 to 1990, 28 were intact, 8 had pinhole leaks, and 22 were ruptured. Median capsule silicon levels and ranges for all 58 implants, for intact only, for leaking, and for ruptured were: 9979 (152,000), 10,477 (88,703), 6592 (65,396), and 9922 (152,387) micrograms/g respectively. There were no significant differences in silicon levels associated with implant status, duration in situ, or year of implantation. Capsule contracture was not associated with higher levels of capsule silicon. Capsule silicon levels were about 10(6) times higher than previously assayed blood silicon levels. This may be because silicone released from implants remains localized in capsular tissue, or because blood-borne silicone is quickly excreted. Using 29Si nuclear magnetic resonance spectroscopy, no detectable silicone was found in the blood of 7 control women and 7 women with silicone-gel implants (5 with known implant rupture).
Breast Implants↗
Analysis of silicon levels in capsules of gel and saline breast implants and of penile prostheses.
Although a potential link between silicone-gel breast implants and autoimmune connective tissue disease has been suggested, none has been proven. The potential role of silicone as an immune adjuvant remains very controversial. Currently available techniques do not allow precise measurements of silicone in tissues. However, all compounds containing silicon (including silicone) can be measured accurately. The present study was designed to measure silicon levels in the fibrous capsules of patients with silicone-gel breast implants, saline breast implants, and silicone inflatable penile prostheses. Baseline control silicon levels were obtained from the breast tissue of patients undergoing breast reduction, who had no exposure to breast implants. All silicon measurements were carried out using atomic absorption spectrometry with a graphite furnace. Silicon was measured in a normal heptane extract of silicone from dried tissue. The mean silicon levels in 16 breast tissue control samples from 8 patients undergoing breast reduction varied from 0.025 to 0.742 micrograms/gm with the median mean being 0.0927. The median silicon level in capsules from six patients with saline implants was 7.7 micrograms/gm (range, 1.9-36.6 micrograms/gm). The median silicon level in capsules from five patients with silicone inflatable penile prostheses was 19.5 micrograms/gm (range, 1.9-34.8 micrograms/gm). Although the levels of silicon in capsules of patients with saline breast prostheses and penile implants were higher than in control samples, they were much lower than those from the capsules of the 58 gel implants (median, 9,979 micrograms/gm; range, 371-152,000 micrograms/gm).(ABSTRACT TRUNCATED AT 250 WORDS)
Breast↗
Evaluation of MEMS materials of construction for implantable medical devices.
Medical devices based on microelectro-mechanical systems (MEMS) platforms are currently being proposed for a wide variety of implantable applications. However, biocompatibility data for typical MEMS materials of construction and processing, obtained from standard tests currently recognized by regulatory agencies, has not been published. Likewise, the effects of common sterilization techniques on MEMS material properties have not been reported. Medical device regulatory requirements dictate that materials that are biocompatibility tested be processed and sterilized in a manner equivalent to the final production device. Material, processing, and sterilization method can impact the final result. Six candidate materials for implantable MEMS devices, and one encapsulating material, were fabricated using typical MEMS processing techniques and sterilized. All seven materials were evaluated using a baseline battery of ISO 10993 physicochemical and biocompatibility tests. In addition, samples of these materials were evaluated using a scanning electron microscope (SEM) pre- and post-sterilization. While not addressing all facets of ISO 10993 testing, the biocompatibility and SEM data indicate few concerns about use of these materials in implant applications.
Biocompatible Materials↗
Cytotoxicity of respirable dusts from industrial minerals: comparison of two naturally occurring and two man-made silicates.
The membranolytic and cytotoxic properties of two naturally occurring (chrysotile asbestos; attapulgite clay) and two man-made (Fiberfrax, an aluminium-silicate, and xonotlite, a calcium silicate) industrial minerals were compared. "Short" fiber fractions of chrysotile and Fiberfrax were obtained by sedimentation in demineralized water, while the attapulgite and xonotlite samples were used as obtained. The aluminium silicate fibers were found to be non- hemolytic, while for the other three silicates, chrysotile had the strongest hemolysis potential, followed very closely by xonotlite; attapulgite was less hemolytic than the former two silicates, but was nevertheless highly hemolytic to the rat erythrocytes. Using rat pulmonary alveolar macrophages, the in vitro cytotoxicity assays showed that with fresh cell monolayers, all four silicates were equivalent in causing cell damages at a dose of 250 micrograms; at a lower dose (50 micrograms), the intensity of the cytotoxic effect was in the decreasing order: Fiberfrax greater than attapulgite greater than chrysotile greater than xonotlite. With one day-old cultured cell monolayers, a dose of 250 micrograms of the silicates fibers was less cytotoxic, with the exception of the attapulgite fibers which remained essentially as cytotoxic as with the fresh cell monolayers. The reduced cytotoxic response was especially noticeable with the chrysotile fibers. At 50 micrograms, the cytotoxicity scale of the mineral dusts with one day-old cell monolayers was essentially the same as the one obtained with the fresh cell monolayers, that is: Fiberfrax approximately equal to attapulgite greater than chrysotile greater than or equal to xonotlite. Overall, these in vitro tests imply: 1) that all four industrial silicates tested can be considered to be "biologically active"; 2) that on the basis of their different reactivities with the two types of cell culture conditions used, their biological reactivity in vivo might be quite distinct. This might be especially true for at least the chrysotile, attapulgite and xonotlite short fibers, considering that these three types of silicate dusts have very similar dimensions. Moreover, for the chrysotile and attapulgite samples, fiber numbers is probably not an important factor, since the density of the two silicates is roughly the same. The unaltered cytotoxic responses of the American attapulgite fibers in the two macrophage assays correlate well with the fact that short attapulgite fibers seems to have a stronger in vivo reactivity than short chrysotile fibers. In fact, it might be the strongest of the four industrial silicates tested.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Anti-(human immunodeficiency virus) activity of polyoxotungstates and their inhibition of human immunodeficiency virus reverse transcriptase.
Heteropolyoxotungstates of the Keggin class containing different heteroatoms were tested for inhibition of two strains of human immunodeficiency virus 1 (HIV-1); they exhibited varying antiviral activity. Compounds containing boron were inactive, only one of those containing phosphorus showed selective anti-viral activity, whereas all silicon-containing compounds exhibited significant anti-viral activity in C8166 cells infected with the IIIB strain. Their effectiveness was some 10-fold higher in JM cells with selectivity indices of about 2000. The silicotungstates were effective inhibitors of HIV reverse transcriptase, showing greater inhibition with RNA/DNA template primers than with DNA/DNA template.primer. Kinetic analysis demonstrated that they inhibit the enzyme by different mechanisms, as, of the four compounds examined, two competed with template.primer and two competed with deoxynucleoside triphosphate. Inhibition of DNA polymerase activity by these compounds was compared using polymerases from different sources, including human; although not necessarily most specific for HIV-1 reverse transcriptase, they did not inhibit all DNA polymerases to a similar degree.
Antiviral Agents↗
Exhaustive soxhlet extraction for the complete removal of residual compounds to provide a nonleaching silicone elastomer.
All commercially available silicone devices contain freely diffusible silicone oils, uncured oligomers, and other impurities (such as catalysts). These residuals have been found in quantities as high as 20% by weight in commercially available silicone medical devices. The fate and effects of these residuals have been the topic of much debate recently. In this study, a method for complete removal of these residual compounds was investigated. The total amount of extractable residuals was determined through exhaustive Soxhlet extraction of 5 silicone elastomers. LIM 6030 had 6.29%, LIM 6070 had 5.74%, Q7-4750 had 3.02%, Q7-4780 had 3.22%, and SE1935 had 0.13% extractables by weight. The amount of silicon containing residuals leaching from both the extracted and nonextracted samples was also evaluated for 3 and 18 days by inductively coiled plasma (ICP) analysis. A significant amount of leachable compounds, reported as microg Si/mg solid sample, was found in all nonextracted elastomers with the exception of SE1935 compared to blanks. The amount of leachable compounds found in the extracted elastomers was not found to be significantly higher than the amount found in the blanks. The residual compounds in silicone elastomers may be completely removed by exhaustive Soxhlet extraction and the resulting polymer does not leach silicon-containing compounds in vitro.
Biocompatible Materials↗
Rat lung reactivity to natural and man-made fibrous silicates following short-term exposure.
The inflammatory and fibrogenic potential of three naturally occurring and two man-made industrial minerals were compared. Groups of five rats each received respectively a single intratracheal instillation of saline (control), UICC chrysotile B asbestos, short chrysotile 4T30, attapulgite, xonotlite (a calcium silicate), and Fiberfrax (an aluminum silicate) at doses of 1, 5, and 10 mg. One month after the treatment, assessment of lung morphology and bronchoalveolar lavage were performed on each animal. Under these conditions, UICC chrysotile B at all doses tested (1, 5, and 10 mg) induced fibrotic lesions in bronchiolar tissues while short chrysotile 4T30 (1, 5, and 10 mg) caused focal accumulation of inflammatory cells in the alveolar structures but no apparent fibrosis. Compared to these positive reactions with different fibrogenicity, xonotlite caused minimal inflammatory reactions detectable only at high dose (10 mg) and by bronchoalveolar analysis. By contrast, the rat lung reacted more significantly to attapulgite and Fiberfrax although the tissue reaction differed considerably for these two materials. While attapulgite, at doses up to 10 mg caused minimal reactions characterized by mononuclear cell infiltration mainly in the alveolar structures, Fiberfrax at 1 mg and higher caused significant granulomatous reactions and the appearance of early fibrosis. Overall the order of lung biological reactivity observed for the various silicates was xonotlite much less than attapulgite less than short chrysotile 4T30 less than Fiberfrax less than UICC chrysotile B. These observations indicate that Fiberfrax, attapulgite, and, to a lesser extent, xonotlite are biologically active within the time span studied and potentially deleterious for lung tissue.
Animals↗
Adsorption studies on clays. I. The adsorption of two alkaloids by activated attapulgite, halloysite, and kaolin.
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Adsorption↗
Adsorption studies on clays. II. The adsorption of bacteria by activated attapulgite, halloysite, and kaolin.
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Adsorption↗
Background urinary 1-hydroxypyrene levels in non-occupationally exposed individuals in the Province of Québec, Canada, and comparison with its excretion in workers exposed to PAH mixtures.
The urinary excretion of 1-hydroxypyrene (1-OHP) was measured in two reference groups of non-occupationally exposed individuals and in four groups of workers. Two of these groups were exposed to what were considered to be low levels of polycyclic aromatic hydrocarbons (PAH) on the basis that even post-shift 1-OHP excretion values were low (< 2 mumol/mol creatinine). Therefore, urine samples were collected from these workers after a period of > 60 h without occupational exposure which should yield values approaching background levels. Pooling these results with those of the reference groups yielded a total of 140 individuals having a mean (geometric) excretion of 0.08 mumol/mol creatinine and 5th, 50th and 95th percentiles of 0.02, 0.09 and 0.32 mumol/mol creatinine. The mean (geometric) excretion in the 95 nonsmokers and 45 smokers of this pool was 0.07 and 0.12 mumol/mol creatinine, respectively (one-tailed Student t-test, P < 0.001). Both this background excretion and the contribution of smoking appeared small in comparison with the excretion levels observed in some groups of exposed workers. Indeed, creosote workers described in this report had a geometric mean (range) excretion of 1.63 (0.18-10.47) mumol/mol creatinine during their working week. It is concluded that, for the biological monitoring of workers exposed to PAH, urinary 1-OHP appears to be a useful bioindicator for which background environmental contamination or smoking habits can be neglected in most cases.
Air Pollutants↗
Sorption-desorption of cadmium in aqueous palygorskite, sepiolite, and calcite suspensions: isotherm hysteresis.
Sorption isotherms have been widely used to assess the heavy metal retention characteristics of soil particles. Desorption behavior of the retained metals, however, usually differ from that of sorption, leading to a lack of coincidence in the experimentally obtained sorption and desorption isotherms. In this study, we examine the nonsingularity of cadmium (Cd) sorption-desorption isotherms, to check the possible hysteresis and reversibility phenomena, in aqueous palygorskite, sepiolite and calcite systems. Sorption of Cd was carried out using a 24-h batch equilibration experiment with eight different Cd solution concentrations, equivalent to 20-100% of maximum sorption capacity of each mineral. Immediately after sorption, desorption took place using successive dilution method with five consecutive desorption steps. Both Cd sorption and desorption data were adequately described by Freundlich equation (0.81<r(2)<0.99). The sorption and desorption reactions, however, did not provide the same isotherms, indicating that hysteresis occurred in Cd sorption-desorption processes. The extent of hysteresis was quantified based on the differences obtained from sorption and desorption isotherms regarding the amount of Cd sorbed, the Freundlich exponent, and the Cd distribution coefficient. The results revealed that, sepiolite possessed the most hysteretic behavior among the minerals studied. Calcite showed much smaller hysteresis compared to the other two silicate clays at low Cd surface load, but its hysteresis indices significantly increased, and exceeded that of palygorskite, as the amount of Cd in the systems increased. The average amount of Cd released after five desorption steps, was 13.8%, 2.2% and 3.6% for the palygorskite, sepiolite and calcite, respectively, indicating that a large portion of Cd was irreversibly retained by the minerals.
Cadmium↗
The crystallization of an aluminosilicate glass in the K2O-Al2O3-SiO2 system.
OBJECTIVES: The aims of the study were to explore the nucleation and crystallization kinetics of an aluminosilicate glass in K2O-Al2O3-SiO2 system and to characterize it. OBJECTIVES: A starting glass composition of wt%; 64.2% SiO2, 16.1% Al2O3, 10.9% K2O, 4.3% Na2O, 1.7% CaO, 0.5% LiO and 0.4% TiO2 was heated in an electric furnace and later quenched to produce glasses. The glass powders were heat treated using differing heat treatment schedules and quenched. Dta, Xrd, Eds and Sem analyses were used to characterize and explore the crystallization kinetics of the glasses. RESULTS: Phase separation of the glasses was identified and characterized in the glasses. Tetragonal leucite, cubic leucite and sanadine glass-ceramics were produced. Fine leucite crystals (1 microm2) were crystallized with minimal matrix microcracking. SIGNIFICANCE: Amorphous phase separation appeared to be an important precursor to nucleation and crystal growth in the alkali aluminosilicate glasses explored. It was possible to control the crystallization of tetragonal leucite and sanidine phases by selected heat treatment of glass powders and monoliths, resulting in the production of fine grained tetragonal leucite glass-ceramics.
Aluminum Oxide↗
Use of laterite for the removal of fluoride from contaminated drinking water.
The effects of different operational variables on the mechanistic function of laterite in removal of fluoride have been investigated. Thermodynamic parameters such as free energy change, enthalpy, and entropy of the process, as well as the sorption isotherm, were evaluated. The extent of solute removal is determined by initial solute concentration, operational conditions, laterite dose, and solution pH. For a fixed set of experimental conditions, a model equation is developed from which the percent removal corresponding to each load of fluoride is determined. The mechanism of fluoride adsorption is governed by the zero point charge of laterite and follows a first-order rate equation. pH has a vital role influencing the surface characteristics of laterite. To simulate the flow dynamics, fluoride solution was run through a fixed bed column. The pattern of breakthrough curves for different influent fluoride concentration, pH, and column bed height was characterized. The column efficiency was tested from the bed depth-service time model. The elution of the retained fluoride was studied and the effectiveness of column operation was determined by the retention-elution cycles.
Adsorption↗