Studies on surface properties of asbestos. III. Interactions between asbestos and polynuclear aromatic hydrocarbons

The purpose of this study is to reveal the nature of the physicochemical interactions between asbestos and polynuclear aromatic hydrocarbons (PAH) in an organic liquid medium, and to assist in the understanding of synergistic effects between asbestos and PAH in bronchopulmonary cancers. The adsorption curves of three PAH (phenanthrene, fluorene, dimethyl-7,12-benzanthracene) on chrysotile and crocidolite are multistep isotherms and show the formation of bidimensional condensed layers (2D) of PAH. This phenomenon is observed with solids having a dominant basic character (asbestos, magnesia) but is not detected with acidic solids (alumina, silica-alumina). The elimination of water and dissolved gases (O2, CO2) in the liquid medium increased the affinity of asbestos for PAH. The coadsorption CO2-phenanthrene on the substrate decreased the adsorbed quantities of solute but did not inhibit the formation of layers (2D). The adsorption is weaker on leached chrysotile, than on original chrysotile; the amorphous silica coating the fibers has no affinity for PAH; the adsorption is only due to some active sites present on the surface of residual chrysotile which is accessible to phenanthrene. The formation of layers (2D) is due to strong interactions between PAH having an induced or permanent dipole moment and the active electron donor sites present on the mineral surface. The equilibrium equation between the adsorbed layer and the PAH in solution is established by reference to theoretical studies, and the results allowed us to classify the charge density of the mineral surface. The interactions between PAH and asbestos allowed us to explain the differences introduced in the kinetics of PAH uptake toward the cells when PAH is preadsorbed on asbestos. This fact could, in part, explain the synergistic effects observed in carcinogenesis.