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 de pendent on a copper-resistant algal species [Taub, 1989. Aquatic Ecotoxicol ogy: 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, Oocy stis pusilla, was able to bloom in microcosms that had been devoid of organ ismal activity for several weeks due to the addition of copper at a high co ncentration (31.5 mu M). In the present study, experiments were performed t o characterize the range in tolerance of O. pusilla to copper, determine it s growth under low and high pH regimes as a function of copper exposure, an d to examine its ability to alter pH and ionic-copper activity (ICu) over t ime. Total-copper (TCu) concentrations up to 78.7 mu M and ICu values as hi gh 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 hermeti c effect (enhanced response at intermediate concentrations). Even though it s abundance was severely depressed in a TCu solution of 157.5 mu M, this sp ecies was able to increase fourfold in 14 days. O. pusilla increased its nu mbers 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 co pper-stressed environments that would characteristically have a low pH. Fro m this work, and related studies, we concluded that the primary mechanism a llowing O. pusilla to reduce ionic-copper activity in culture solutions and microcosms was the release of organic copper-complexing ligands and that b iomass sorption may have been important only at very high cell densities. ( C) 1998 Elsevier Science B.V. All rights reserved.