Investigation of the competitive effects of copper and zinc on fulvic acid complexation: Modeling and analytical approaches

Cu and Zn are physiologically vital metals facilitating the proper functioning of many enzymes. However, a flux in anthropogenic activities have elevated the concentrations of these metals in natural waters causing the biological requirements to be exceeded and raising concern in how these metals will affect aquatic organisms. When multiple metals exist in natural waters, a non-additive toxicological effect can occur, where the sum of the metal concentrations becomes more or less harmful than that of the individual metals themselves. The most bioavailable, and thus the most toxic solution species, of both Cu and Zn are the divalent metal cations (Cu2+ and Zn2+ ). Metal speciation in natural waters is controlled by many water chemistry parameters, most importantly pH and the presence of organic and inorganic ligands. The use of both modeling and analytical techniques can help quantify the chemical species and examine their role in aquatic toxicity.;This thesis gives insight into the competition of trace metals in natural waters for complexation to organic and inorganic ligands. The purpose of this work was to help explain the observed synergistic toxicological effects on the tested specimen, D. magna, occurring when Cu and Zn are together in solution. A series of geochemical models were generated in Visual MINTEQ to identify the major complexes and ions resulting from the toxicity testing conditions. These modeled results were a basis for setting up a series of experiments and were also used for explaining the resulting analytical data. The two analytical approaches were the Cu2+-ISE and Fl FFF-ICP-MS. Modeling and ISE results provide support for the hypothesis that Cu and Zn compete for complexation with organic ligands. Although Fl FFF-ICPMS did not provide quantitative support for this, it did prove to be useful for characterizing metal-DOC complexes.