Copper Tolerance By The Freshwater Algal Species Oocystis Pusilla And Its Ability To Alter Free-Ion Copper

Previous studies with copper-stressed microcosms found that recovery was dependent on a copper-resistant algal species [Taub, 1989. Aquatic Ecotoxicology: Fundamental Concepts and Methodologies, pp. 47-92. Meader, J.P., Taub, F.B., Sibley, T.H., 1993. Ecol. Appl. 3, 139-155]. One algal species, Oocystis pusilla, was able to bloom in microcosms that had been devoid of organismal activity for several weeks due to the addition of copper at a high concentration (31.5 mu M). In the present study, experiments were performed to characterize the range in tolerance of O. pusilla to copper, determine its growth under low and high pH regimes as a function of copper exposure, and to examine its ability to alter pH and ionic-copper activity (ICu) over time. Total-copper (TCu) concentrations up to 78.7 mu M and ICu values as high as 0.9 mu M had no negative effects on O. pusilla, indicating that it is highly copper-tolerant. The best growth for O. pusilla generally occurred in the range of 8-20 mu M (total or dissolved copper), indicating a hermetic effect (enhanced response at intermediate concentrations). Even though its abundance was severely depressed in a TCu solution of 157.5 mu M, this species was able to increase fourfold in 14 days. O. pusilla increased its numbers at a faster rate in high pH (approximate to 9) solutions; however, it was able to propagate when pH was lower ( approximate to 7) and copper was high. These characteristics would allow this species to bloom in highly copper-stressed environments that would characteristically have a low pH. From this work, and related studies, we concluded that the primary mechanism allowing O. pusilla to reduce ionic-copper activity in culture solutions and microcosms was the release of organic copper-complexing ligands and that biomass sorption may have been important only at very high cell densities. (C) 1998 Elsevier Science B.V. All rights reserved.