Effect of thermal treatment on the surface characteristics and hemolytic activity of respirable size silica particles.
Razzaboni-BL; Bolsaitis-P; Wallace-WE Jr.; Keane-MJ
NIOSH 1990 Sep; :215-230
The effect of thermal treatment on the surface properties and hemolytic activity of respirable silica particles was examined. Min- u-sil (14808607), Cab-o-sil (7631869), and cristobalite (14464461) were tested for their ability to hemolyze sheep blood erythrocyte suspensions before or after calcining by heating to 100 to 1095 degrees-C for 48 or 72 hours. Changes induced in surface structure were examined by photo acoustic infrared spectroscopic analysis and zeta potential measurements. The hemolytic activity of untreated Cab-o-sil was approximately 1 order of magnitude greater than that of untreated Min-u-sil when expressed on a per unit mass basis. Both dusts were significantly more hemolytic than cristobalite. When expressed on a per unit surface area basis the hemolytic potential of untreated Min-u-sil was approximately 3 to 4 times that of Cab-o-sil. The hemolytic potentials of untreated Cab-o-sil and cristobalite were comparable on this basis. Calcination decreased the hemolytic activity of Min-u-sil and Cab-o-sil. The lo of hemolytic activity was paralleled by a loss of infrared absorption bands characteristic of surface silanol groups. The calcined Min-u- sil and Cab-o-sil dusts gradually recovered their hemolytic potential when stored in desiccators. Recovery occurred within 10 to 30 days in the case of Cab-o-sil, but required at least 180 days in the case of Min-u-sil. The recovery of hemolytic activity was accompanied by an increase in infrared spectral bands characteristic of the hydroxylated surface. Calcination was accompanied by the zeta potentials becoming more negative. Min-u-sil samples that had lost 50% of their hemolytic activity after being heated to 800 degrees for 48 hours were treated with 5% sodium-hydroxide or 10% hydrochloric-acid. Min-u-sil recovered its full hemolytic potential after treatment with sodium-hydroxide, but not hydrochloric-acid. The authors conclude that the hemolytic activity of respirable silica particles can be correlated with the concentration of silanol groups on the surface.
NIOSH-Author; In-vitro-studies; Silica-dusts; Surface-properties; Thermal-effects; Chemical-structure; Cytotoxicity; Respirable-dust; Hemolysis
14808-60-7; 7631-86-9; 14464-46-1
Proceedings of the VIIth International Pneumoconioses Conference