INFLUENCE OF SALINITY AND MINERALIZATION ON TRACE-METAL SORPTION TO CYANOBACTERIA IN NATURAL-WATERS

The equilibrium distribution of Cd, Cu and Pb between the cyanobacteri um Anabaena spp. and natural lake water as a function of salinity and degree of algal decomposition, was studied using batch experiments. Ad sorption isotherms could be described with the Freundlich equation. Di stribution coefficients (Kd) for Anabaena spp. were largest for Pb, fo llowed by Cd and Cu. The variation in Kd values for Cd was explained b y a model accounting for metal complexation to the algal surface and c omplexation by dissolved ligands of variable concentration. The phytop lankton/water distribution of Cd in waters of different salinity appea rs to be regulated by the free Cd2+ activity in solution. Mineralizati on of Anabaena spp. for 42 d resulted in a decrease of the solid to wa ter ratio by a factor of 12, and an increase in K-d for Cd (factor fou r), Cu (factor eight) and Pb (factor 10-20). The increase in K-d is at tributed to a higher affinity of the metals for the adsorbent. The use of constant K-d values for mineralizing phytoplankton and detritus in trace metal fate models, may result in underestimations of bound frac tions. The extent to which this fraction is underestimated, depends on the time course of the distribution coefficient and the solid to wate r ratio during the mineralization process.