Crystalline Silica Particles Research Articles

Effect of particle size and modulation frequency on the photoacoustic spectra of silica powders

Investigations of the infrared spectra of crystalline and amorphous silica particles of different sizes (0.05, 5, 10, 15, 30, 45, and 260 μm) in the range of 400-4000 cm -1 using Fourier transform infrared/photoacoustic spectroscopy are reported. The change in the intensity I of the signal with porosity ∈ of powders follows the ∈/(1-∈) dependence for strong bands and ∈ dependence for weaker bands are predicted by the theory of McGovern et al. For strong bands, I also follows the empirical relation I∼D -n , where D is the particle diameter in cm and n=0.34-0.42

Surface and Bulk Infrared Modes of Crystalline and Amorphous Silica Particles: A Study of the Relation of Surface Structure to Cytotoxicity of Respirable Silica

Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity.

Surface and bulk infrared modes of crystalline and amorphous silica particles: a study of the relation of surface structure to cytotoxicity of respirable silica.

Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity.

Adhesive formulations manipulated by the addition of fumed colloidal silica

3 HEALTH AND SAFETY DATA Silicosis is associated with the inhalation of microscopic particles of crystalline silica. However, fumed silica is amorphous and below the particle sizes associated with lung damage [4]. But it is reported that breathing air contaminated with a high concentration of hydrophobic fumed silica can cause nausea, dizziness and eye irritation. The manufacturer recommends that a dust mask be worn while using hydrophobic silica. It is a good practice to wear a dust mask and polyethylene gloves when using either grade of fumed silica. Both grades are capable of removing oils from the skin. 0.014 1.76 amorphous 8.0-10.0 0.2%* none 0.007 1.46 amorphous 3.5-4.2 none 3.0%t Hydrophilic ES. Hydrophobic RS. Particle size (diameter in !-tm) Refractive index X-ray form pRin water Surface ammonia Moisture content

Enhancement by BCG of macrophage-like suppressor cells that inhibit the expression of cytotoxic T-cell effector function

The expression of alloimmune splenic T-cell-mediated cytotoxicity, as determined by the 51Cr release assay, in animals undergoing allograft rejection, was observed to be inhibited by a cell present in the plastic-adherent fractions of the spleens. The activity of the suppressor cell, induced by the presence of the allograft, was enhanced if the animals were treated with BCG: The latter also potentiated the rejection response. The suppressor cell acted at the cytolytic phase of the effector function so that there was a measurable increase in the response if the suppressor cells were removed from the immune spleens prior to the assay. The cell responsible for the suppressor activity was macrophage-like in its characteristics, being of light density, adherent to glass surfaces, Thy-1-negative and sensitive to the toxic effects of crystalline silica particles.

The Effect of Silica Injections on the Rejection of Eimeria from Nonspecific Hosts

Parasites of the genus Eimeria are characteristically host specific. Peritoneal macrophages obtained from nonspecific hosts (guinea fowl and turkeys) were found to greatly reduce the viability of sporozoites of E. tenella from the chicken in vitro (Long and Millard, 1979, Parasitology 78: 239-247). We have demonstrated here that the in vivo inhibition of macrophage activity enabled infection with Eimeria to occur in a nonspecific host. It has been shown that crystalline silica particles are selectively toxic to macrophages in vivo and in vitro without altering the viability of lymphocytes (Lotzova and Cudkowicz, 1974, J. Immunol. 13: 343-345; Kessel et al., 1963, Brit. J. Exptl. Pathol. 44: 351364; Vigliani and Pernis, 1963, Adv. Tuberc. Res. 12: 230-282). After phagocytosis, silica has a cytotoxic effect on the macrophage probably by interacting with the macrophage lysosomal membrane releasing hydrolytic enzymes into the cytoplasm (Allison et al., 1966, J. Exp. Med. 124: 141-154). For the present study, silica particles were used to investigate the possible role of macrophages in the host specificity of Eimeria. Two-week-old male, White Leghorn chickens were inoculated per os with a mixture of 500,000 sporulated oocysts of turkey coccidia (a mixture of E. dispersa, E. meleagrimitis and E. adenoeides). Silica particles of an average size of 5 /im were obtained from Dr. K. Roback, Steinkoklenbergbauverein, Germany. Doses of 3 mg/0.5 ml buffered saline were injected i.v. twice daily into the wing vein. Chickens were given the silica injections by group on days 1 through 4 PI. All the feces discharged were collected and examined for oocysts daily, starting on the 5th day PI, and terminating on the 15th day PI. The combined results of two identical experiments are given in Table I. Oocysts were produced in all groups that were treated with silica; the predominant oocysts produced were identified morphologically as E. dispersa. In one of the two experiments, untreated, infected chickens discharged oocysts on only one day (5th day). Silica-treated chickens produced 17 to 126 times more oocysts over periods ranging from 5 to 15 days after oocyst inoculation. The greatest number of oocysts was discharged in all groups between 5 and 9 days PI. This corresponded with the minimum prepatent periods of Eimeria dispersa species used in this study. More oocysts were produced in those birds given the silica injections 3 to 4 days PI than those birds given the injections on days 0 through 3 PI. The treatment given 3 to 4 days PI coincided with the termination of schizogony and the start of gametogony. Thus, macrophages may play some role, either directly or indirectly, in the host specificity of coccidia by affecting the asexual cycle and perhaps the sexual cycle as well. The treatment inhibited host specific mechanism(s) of those chickens given silica on days 0 to 2 PI, but the effect was greater when silica was given 3 to 4 days PI. Thus, the mechanisms involved in the innate resistance of nonspecific hosts to Eimeria may be effective against early gametocytes. After 2 to 4 days in the chickens' circulation, most of the silica may have been sequestered in lymphoid tissue (Pearsal and Weiser, 1968, J. Reticuloendothel. Soc. 5: 107-120). The increase in the number of oocysts produced on days 13 to 15 PI may reflect the delayed effects of the silica treatment. However, more evidence is needed to adequately explain this finding. The oocysts collected from these birds completed their life cycle when inoculated into turkeys, confirming that the oocysts produced by chickens given the silica treatment were indeed turkey coccidia. Doran (1978, J. Parasitol. 64: 882-885) was able to produce a light

CYTOTOXICITY IN GRAFT-VERSUS-HOST REACTION

Graft-versus-host (GVH) reactions were induced in adult F1 hybrid mice with the i.p. injection of parental strain spleen cells. Peritoneal exudate and spleen cells of the F1 hybrids taken 8 days after the induction of GVH reaction had a nonspecific in vitro cytotoxic effect which was measured by using 51Cr-labeled target cells of parental genotype. The cytotoxic cells in the peritoneal exudates were shown to be macrophages which adhered to plastic surfaces and were sensitive to the toxic action of crystalline silica particles. Moreover, the injection of partially purified syngeneic macrophages into the F1 hybrids undergoing GVH reactions increased the cytotoxic activity of the peritoneal exudate cells obtained from these animals. These results suggest that during GVH reaction host macrophages are activated into a state of nonspecific cytotoxicity.