BIOLOGICALLY MEDIATED DISSOLUTION OF GLASS

Microbes play an important role in the dissolution of natural and synt hetic glasses. The frequent technical use of glass and the abundance o f glass at the earth's surface make this process one of the most impor tant weathering reactions. In particular the alteration of volcanic gl ass provides a direct pathway for mantle-derived materials into the hy drosphere. To begin understanding the kinetics of these processes, we carried out three experiments exposing to seawater polished surfaces o f nuclear-waste glass. The durations of experiments were: 410 days wit h continuously flowing sand-filtered, unsterilized seawater (approx. 2 X 10(6) 1; Exp. 1), 126 days with a marine cyanobacterium culture (50 ml, Exp. 2), and for 225 days under sterile conditions (250 ml, Exp. 3). The sterile experiment (Exp. 3) did not show significant signs of alteration. Exp. 1 resulted in development of a several mu m thick bio film and surface corrosion with grooves exceeding 10 mu m in length an d 0.5 mu m in width. Cyanobacterial cultures also developed a biofilm on the glass surfaces, thinner than in Exp. 1. The glass surfaces them selves were corroded with approximately 0.5-mu m-sized pits clustering in 5 mu m broad zones parallel to the polishing direction. These expe riments show that biofilms develop within months and the corrosion of glass is enhanced by the presence of bacteria, The time scales of biol ogically mediated glass corrosion are fast when compared to most geolo gical processes. We expect that volcanic ash is rapidly colonized in t he oceanic water column, in deep-sea sediments, and in soils. The biol ogical degradation of basaltic glass may contribute significantly to t he oceanic nutrient cycle, the chemical exchange between bottom waters and marine sediments, and the fertility of volcanic soils.