Master of Science (MSc)
Biological and Chemical Sciences
Faculty of Science
Ian Hamilton, Lilian DeBruin
Natural Organic Matter (NOM) is known to reduce metal, such as copper, toxicity in aquatic environments. Copper is essential for organisms, but elevated concentrations of dissolved copper can potentially be toxic. The toxicity of copper is related to its bioavailability, which is influenced by toxicity modifying factors, such as NOM (quantified as Dissolved Organic Carbon (DOC) in mg C/L), alkalinity, pH and major cation and anion concentrations. The principles are the same for fresh and saltwater, but the influence of high salt concentrations, such as in estuaries, and associated activity corrections, can modify NOM complexation of metals (i.e., modify logK values). The magnitude of such corrections has not been systematically studied in the context of risk assessment tools such as the Biotic Ligand Model (BLM), and the mathematical tools currently used to correct logK values for salt effects have not been fully tested experimentally. The purpose of this study is to address these gaps by determining logK values across a range of salinities for copper association with salicylic acid as a proxy to NOM. This study used varying concentrations of salt, either as artificial seawater (10 to 100%) or simply as sodium sulfate salt ( ). In these salt solutions, logK values for copper binding to salicylic acid were determined using fluorescence quenching titrations and nonlinear regression (the so-called Ryan-Weber method). Salicylic acid is a well-defined compound, so these logK values were compared to certified values from the National Institute of Standards and Technology (NIST) measured at different ionic strengths. In addition, comparisons of logK values were made between measured values, NIST interpolations, and calculations using the extended Debye-Huckel (DH) equation. The results show that the extended DH calculation has a great agreement with the certified NIST values. However, the fluorescence quenching method has disagreement compared to other methods. It was off by an order magnitude. As a future study, it is better to test different methods such as Ion Selective Electrode and how the results match others.
Barnawi, Fatimah, "Influence of Salinity on Copper-Ligand Formation Constants" (2020). Theses and Dissertations (Comprehensive). 2262.