Master of Science (MSc)
Faculty of Science
Dr. Scott Smith
Dr. James McGeer
The speciation of copper plays a strong role in determining bioavailability and toxicity upon copper exposure in marine environments. Specifically, natural organic matter (NOM) can complex with copper, influencing speciation and decreasing bioavailability. The aim of this research was to determine accurate copper speciation values using literature and new techniques and applying the techniques that reflect the most accurate speciation values to investigate the influence of NOM quantity and quality on copper speciation and toxicity. The results from this study will have implications on the development of a marine Biotic Ligand Model (BLM). Free copper was measured using a flow-through ion selective electrode (ISE) system. A published external calibration Cu ISE method showed a wide variability in measured free copper values and so method improvements were investigated. This resulted in the development of an internal calibration flow-through ISE method. This new method showed an increase in sample reproducibility and agreed well with modeled free copper values for well defined systems. This method was then applied to measure free copper at the LC50 for toxicity assays performed for nine sample locations using the rotifer, Brachionus plicatilis. NOM was characterized for each site through dissolved organic carbon (DOC) concentrations, fluorescence excitation-emission matrices (FEEM) and fluorescence quenching, combined with spectral resolution techniques to quantify humic-, fulvic-, tryptophan- and tyrosine-like fractions. The toxicity results showed two trends with DOC. In the first case, DOC was protective against copper toxicity (r2 = 0.72, p-value = 0.016), however a plateau in protective effect was observed above DOC concentrations above approximately 2 mg C L-1. This suggests salt- induced colloid formation could be occurring resulting in a decrease of binding sites available to complex free copper. The second relationship between LC50 and DOC can be described by the equation LC50 (µg L-1) = 25.15DOC0.47 (r2 = 0.61, p-value = 0.008) including two outlier sites in statistical analysis or LC50 (µg L-1) = 22.86DOC0.45 (r2 = 0.71, p-value = 0.009) excluding the outlier sites. Humic- and fulvic-like fractions showed a linear correlation with toxicity however tryptophan and tyrosine showed no correlation. Overall, only fulvic-like fractions were significant. Free copper at the LC50 for each site remained constant (average pCu = 10.14), within the Biotic Ligand Model (BLM) prediction factor of two, while the LC50 values ranged from 333 to 980 nM. This suggests that differences in water chemistries alter the total amount of copper that needs to be added to a system to reach a critical free copper concentration required to cause toxicity. This was supported by fluorescence quenching data that was used to determine binding capacities and stability constants for the different fluorescent fractions within DOC. Binding capacities at multiple fluorophores ranged from 4 to 1614 nmole mg C-1. The sum of the binding capacities were linearly correlated with LC50 (r2 = 0.67, p-value = 0.008) which supports the observed toxicity data that more total copper was required to reach the same free copper. Binding sites ranged from one to three ligands per sample. Binding was relatively strong for all sites, with logK values ranging from 9.33 to 11.22. In addition, free copper was calculated using this data and the results agreed with the ISE data within ± 0.3 pCu. This supports the theory that a critical free copper concentration is required to cause toxicity. As well these results confirm the applicability of fluorescence quenching techniques in marine water.
Tait, Tara N., "Determination of Copper Speciation, Bioavailability and Toxicity in Saltwater Environments" (2013). Theses and Dissertations (Comprehensive). 1615.