Culture experiments with the estuarine diatom Thalassiosira pseudonana (clone 3H) in highly chelated seawater media demonstrate that growth rate inhibition and copper content of cells are related to cupric ion activity, and not to total copper concentration. Cupric ion activity was altered independently of total copper concentration by varying the chelator concentration, and the pH....
Sunda, William, and Robert R. Guillard. 1976. "The relationship between cupric ion activity and the toxicity of copper to phytoplankton." Journal of Marine Research 34, (4). https://elischolar.library.yale.edu/journal_of_marine_research/1373