Table 4-3. Calculation of Total Metal Concentrations Needed 

 to Change the Cupric Ion Activity in Aquil While Maintaining 

 the Other Metal Activities Constant 

 (log (concentration) or [activity] , M) 



activities vary with total copper in modified Aquil medium containing "Tris", a 

 ligand known to chelate mostly copper (44). Upon variations in copper 

 concentration, the other metals are seen to have a much more constant activity 

 in Aquil with Tris than in Aquil with only EDTA. » 



One of the principal ways by which indirect chemical effects can be initiated 

 is through pH variations. For example, pH has an indirect effect on metal 

 complexation due to the acid-base properties of the coordinating ligands. 

 Figure 4-9 illustrates this effect for Mn, Cu and Zn in Aquil, with EDTA and 

 Aquil with Tris. In this case, Tris mediates a much greater indirect effect than 

 EDTA: zinc and especially cupric ion activities are markedly depressed by 

 increasing pH in the Tris medium, while the activities of all three ions remain 

 essentially constant in the EDTA medium. Increases in pH, which can be 

 brought about by photosynthetic carbon uptake if the aeration of the culture 

 is insufficient, can also result in precipitation as illustrated in Figure 4-6. 

 Adsorption on the fresh precipitate will follow, resulting in an unquantified 

 decrease in the soluble concentration of trace metals. It is apparent that pH is a 

 major factor in determining directly and indirectly the activity and toxicity of 

 trace metals, and should be monitored regularly in metal toxicity experiments. 



CONCLUSION 



The chemistry of metals in the external milieu of algal cells is only one of 

 the determinants of their toxicity. The literature on bacteria and higher cells 

 abounds with examples of how the sensitivity of a particular strain or clone to 

 a particular toxicant, depends markedly on the physiological status of the cells 

 (9, 4). Ahhough it is often recognized that the same situation should apply to 

 phytoplankton, this concept has received scant attention in recent algal 

 literature. It stands to reason that the previous history of an algal cell, its 



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