EFFECT OF MICROWAVE-RADIATION ON SURFACE-CHARGE, SURFACE SITES AND IONIC STATE OF IRON, AND THE ACTIVITY OF CROCIDOLITE ASBESTOS FIBERS

Surface charge, surface sites, and the content of ferrous ions of croc idolite asbestos fibres are some of the properties which are considere d to play a role in determining their activity in biological systems. Any treatment which changes these properties may therefore change thei r activity and subsequently increase or decrease their toxicity in bio logical surroundings. Surfaces of crocidolite fibres are shown to be n egatively charged. In the present study, microwave radiation at 300 de grees C was able to increase the number of positive charges within the bulk of the crocidolite fibres. In the presence of atmospheric oxygen , this increase could simultaneously reduce the hydroxyl groups on the surface of the fibres. The increase in positive charge was monitored by: (i) Mossbauer spectroscopy, where a change in the oxidation state of iron from ferrous to ferric was observed, (ii) visual microscopic o bservations of the irradiated fibres where there was an increase in th eir aggregation, and (iii) the difficulty to suspend these radiated fi bres in solution. A decrease in the number of the surface hydroxyl gro ups on the other hand, was monitored by infrared spectroscopy. The red uction in the activity of the radiated crocidolite fibres was investig ated by studying their ability to peroxidize lipids. Results have show n that changes in their surface charge, surface site and a reduction o f the content of ferrous ions produce a concomitant decrease in their ability to initiate lipid peroxidation.