mechanisms of metal toxicity are similar in many phyla, this framework should 

 be useful for toxicity studies with many aquatic organisms, and can serve as the 

 general basis for design and interpretation of such studies. 



Although the importance of both organic complexing agents and trace 

 metals in phytoplankton cultures has been recognized for some time, the 

 critical role played by the speciation of trace metals in controlUng their 

 toxicity and availabiUty to algae has just begun to be understood. It has now 

 been estabUshed that it is the activity of the free ions, rather than the total 

 metal concentrations, which determine the toxicity of metals to 

 phytoplankton (46, 2). The study of the chemical processes which govern the 

 activity of a given trace metal in culture media becomes then a prime area of 

 concern to phycologists interested in metal toxicity experiments. An 

 enumeration of these processes includes inorganic complexation, chelation, 

 precipitation and adsorption. In addition, indirect chemical effects involving 

 several interacting chemical species in the medium can influence trace metal 

 activities in unobvious ways. In this study, these basic principles of Aquatic 

 Chemistry (43) that apply to metals in phytoplankton cultures will be 

 discussed systematically. 



There are but a few free metal activities that can be experimentally mea- 

 sured in the range and under the conditions of interest. There are also few 

 metallic complexes which can be analytically determined in chemical 

 systems as complex as culturing media. Therefore, theoretical equilibrium 

 calculations will be used throughout this paper to assess metal speciation 

 and activities. The assumption of equilibrium is a reasonable one when the 

 proper precautions are taken during medium preparation. Thermodynamic 

 calculations provide, then, a convenient means of illustrating the critical 

 chemical principles, even if they have inherent uncertainties. Complications 

 introduced in the chemistry of the system by kinetic phenomena, or by the 

 influence of the algae, will be discussed for each of the examined processes. 



Copper has been the metal of choice in studies of metal toxicity of 

 phytoplankton because it has been postulated that cupric ion toxicity might 

 play a role in the ecology of phytoplankton in some natural waters (6, 37, 7, 

 10). In keeping with this situation, this paper will focus, albeit not exclusively, 

 on copper which provides a rather good example for metal speciation and 

 toxicity in phytoplankton cultures. 



EQUILIBRIUM SPECIATION OF METALS IN CULTURING 

 MEDIA 



Before studying in detail the role of chemical processes in controlling metal 

 speciation, it seems useful to examine what metal species are expected to be 

 important in typical culturing media. 



39 



