EFFECTS OF FREE CU2-WATER ALGAE( AND ZN2+ IONS ON GROWTH AND METAL ACCUMULATION IN FRESH)

Five species of unicellular green algae were exposed to a broad range of Cu2+ and Zn2+ concentrations to examine the relationship between th e free Cu2+ and Zn2+ ion concentrations and algal growth at metal conc entrations relevant for freshwater phytoplankton. We estimated extra- and intracellular metal concentrations and characterized the adsorptio n of copper and zinc on algal surfaces. The optimal growth rate of Sce nedesmus subspicatus occurred in a broad range of Cu2+ and Zn2+ concen trations (from 10(-15) to 10(-7) and from 10(-12) to 10(-55) M, respec tively). Chlamydomonas reinhardtii reacted more sensitively toward cop per, optimal growth was achieved only at a pCu (= -log[Cu2+]) around 1 1, whereas growth was optimal over a broad range of free Zn2+ concentr ations (from 10(-12) to 10(-6) M). The optimal range for growth of Chl orella fusca occurred over about three orders of magnitude of the free Cu2+ concentration (from 10(-13) to 10(-10) M). Chlamydomonas culture s isolated from Lake Constance tolerated Cu2+ concentrations over seve n orders of magnitude (pCu = 7 to 14). The growth of algae showed a hi gh tolerance toward high intracellular copper and zinc concentrations. This suggests that the cells may immobilize the metals intracellularl y. The affinity of copper for algal surfaces is higher than that of zi nc in the experimental concentration range: adsorption constants log K -Ca (11.06) > log K-Zn (6.49) (pH = 7.9). These freshwater algae toler ate higher Cu2+ and Zn2+ concentrations than marine algal species. In comparison to our lake data, the results obtained from the culture alg ae indicate a possible role for copper as a limiting factor for certai n algal species in eutrophic lakes.