Saturated with 6 different cations (Li, Na, K, Ca, Mg, Ba) its swelling in ethylene glycol, glycerol and water and its homogeneous hydration extents according to the relative humidity have been studied. Our results were compared with those found for montmorillonites, beidellites and vermiculites in order to estimate the respective influence of the surface charge density and the charge localization on the swelling properties. The three-dimensional organization of the saponite is more or less affected by random stacking faults and by multiple b/3 translations according to the exchangeable cation, the swelling state and the nature of the solvation liquid. Our experimental results indicate that the three-dimensional order met in the hydrated saponites can be explained by an anchoring of the layers towards each other by chains made up of cation -dipole interactions and of hydrogen bonds between negatively charged surface oxygens and the interlayer water. This type of interlayer link is relatively weak. It is therefore easy to introduce stacking faults in these edifices in particular by grinding of the samples.

. Can. J. Chem. 65, 2338 (1987).Formation of hydroxyl radicals, in relatively large quantities, by oxygen reduction due to the surface activity of asbestos in a cell-free system is demonstrated, using electron spin resonance and a spin trapping agent. The quantity of OH' produced (in general, above l o i 4 mg-I for a Canadian chrysotile) is a function of activation or passivation of the electron donor surface sites of the minerals. The role of these radicals in oxidative stress in relation to the toxic properties of these minerals is discussed.ROGER ZALMA, LIONEL BONNEAU, JOELLE GUIGNARD, HENRI PEZERAT et MARIE-CLAUDE JAURAND. Can. J. Chem. 65, 2338 (1987).En utilisant la technique des pikgeurs de radicaux et la spectroscopie en rksonance paramagnetique Clectronique on peut montrer que la rkactivitC de surface des amiantes permet, en milieu tampon, la rkduction de I'oxygbne en radicaux hydroxyles (OH'). La quantitC de radicaux formts (en gtntral supkrieure ? I lOI4 mg-I pour le chrysotile canadien) est fonction de l'activation ou de la passivation des sites de surface i caractgre Clectro-donneur. Le r61e de ces radicaux dans les phknombnes de ccstress oxydant* est discutk en relation avec les propriktts toxiques des amiantes.It is known that asbestos fibres induce chromosome damage, which might be implicated in the sequential steps of carcinogenesis. This phenomenon might be related to the formation of oxy radicals in the presence of asbestos, this formation being postulated from biochemical data concerning asbestos-induced damage to cells and lipid peroxidation (1-4), and in relation to redox properties as shown up by electron spin resonance (esr) ( 5 , 6).Weitzman and Graceffa (7) and Eberhart and RomanoFranco (8) demonstrated that asbestos catalyzes the generation of hydroxyl (OH') and superoxide (02:) radicals from hydrogen peroxide (H202) in a cell-free system. But all ironcontaining minerals (with Fe2+ or Fe3+) have approximately the same activity in such a system (9, lo), and the bioavailability of H202 is low. In our model system, with techniques similar to that of Weitzman and Graceffa (7) (esr and spin trapping agent), but taking into account the phenomenon of activation or passivation of the surface active sites of asbestos, we are able to demonstrate the formation of a high level of OH' from the reduction of oxygen, which is completely bioavailable. Our model system differs from the one employing H202 in that only part of the iron-containing minerals is active in the reduction of 02, according to the following reactions:

Twenty eight moderately water-soluble to insoluble chromium (VI) compounds, such as zinc and lead chromate, industrial and laboratory synthesized pigments, and the analytical reagents strontium, barium and calcium chromate, were physicochemically characterized and studied for cytotoxicity and morphological transformation in cultured Syrian hamster embryo (SHE) cells. In vivo validation of malignancy of transformed SHE cells was performed. A high physicochemical diversity among the complex chromium pigments was revealed. The solubility of the compounds was greatly increased after incubation in a complete medium and even higher under cell culture conditions. The cytotoxic effects appeared to be due principally to extracellular solubilized chromium because the most solubilized compounds. Zn, Ca and Sr chromates, were equitoxic at about the same Cr concentration treatment and 8-fold more cytotoxic than less soluble compounds such as some Pb chromates and Ba chromate. However, certain physicochemical properties of lead chromate pigments could also influence their cytotoxic activity. All test compounds were, in a dose-dependent manner, efficient in inducing morphological transformation of SHE cells. Many of the Cr pigments, although physicochemically different, were similarly effective in transformation induction. Nevertheless, compounds among Zn and Pb chromates had various transforming potencies. Ba chromate was the least active in inducing transformation. Certain physicochemical properties could mediate the transforming activity but no particular relationship could be established between any one of the physicochemical parameters and the transforming potency. Cloned morphologically-transformed colonies of SHE cells were grown in soft agar medium and showed true neoplastic behaviour by tumour formation in syngeneic animals. These results show that various chromate pigments containing either Zn or Pb, of medium to very low aqueous solubility, induced neoplastic transformation of SHE cells.

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