Physicochemical studies on the adsorption properties of asbestos - 2. An EPR and fluorescence study on the adsorption of pyrene

Toxic asbestos fibers are known to be carriers of carcinogenic polyaromatic hydrocarbons (PAM) when ingested by human lungs. To clarify the asbestos-P AM interactions, the adsorption properties of four different asbestos, name ly amosite, anthofillite, crocidolite, and chrysotile (termed AMOS, ANTHO, CROX, and CHRYS, respectively), toward pyrene (py) were investigated by ele ctron paramagnetic resonance (EPR) and fluorescence spectroscopy, both stea dy state and time resolved. Pyrene was labeled with a nitroxide TEMPO radic al (py-T) for the EPR study. EPR provided information on the adsorption abi lity of the surface toward py-T and on the interactions between py-T and su rface sites, mainly cooperative in nature. Pyrene molecules organize on AMO S samples in a packed layer; the radical works as a separator and prevents the attaching of the py-T molecules at the surface, but the N-O groups of t he few adsorbed molecules directly interact with the surface. The interacti ng sites at the ANTHO surface are quite far from each other; therefore py-T instead of py may form a monolayer at the asbestos surface. The surface of CROX strongly adsorbs both excimers of py and monomers of py-T, orienting the nitroxide groups toward the polar sites at the surface. The surface of CHRYS is the most adsorbing toward py and py-T, but the nitroxide group doe s not directly interact with the surface. By increasing concentration, py-T saturates the CROX and the CHRYS surface interacting sites, and then forms a disordered liquid-like multilayer. The close average distance calculated for py-T adsorbed at the CROX surface (12 Angstrom) suggests that the py-T molecules intercalate in an "up-and-down" conformation. The chemical compo sition of the different asbestos and their different structural properties affect the distribution of the polar sites at the external surface, modifyi ng the adsorption properties. This study confirms the synergetic effect bet ween the toxicity of the asbestos fibers and the adsorption of polyaromatic hydrocarbons at their surface, which mainly depends on the surface propert ies of the asbestos. (C) 2001 Academic Press.