LIGHT-INDUCED-CHANGES OF FE(II) FE(III) AND THEIR IMPLICATIONS FOR COLLOIDAL FORMS OF AL, MN, CU, ZN AND CD IN AN ACIDIC LAKE POLLUTED WITHMINE WASTE EFFLUENTS/

The photo induced reduction of ferric (hydr) oxides stabilises the fer rous state in acidic (pH 4) lake water, at light intensities higher th an 7 W/m2 and despite equilibrium with atmospheric oxygen. Precipitati on of ferric (hydr) oxides occurred at lower light intensities, partic ularly at water depths constantly below this light intensity and with contributions of Fe(II) from the bottom sediments. No specific reducin g agent could be identified, but the low concentrations of dissolved o rganic carbon and humic substances indicate that inorganic components could be involved in the reduction. A maximum of 20% of the copper and zinc concentrations and up to 50% of the cadmium were associated with colloidal matter. These distributions were observed at depths in the lake where the ferrous state was stable and with a fairly constant sol id/solution distribution of the trace metals.