Characterizing Dissolved Organic Matter and Cu2+, Zn2+, Ni2+, and Pb2+ Binding in Salt Water and Implications for Toxicity

The binding of metal to dissolved organic matter in aquatic environments is important in controlling the bioavailability and potential toxicity of metals such as Zn2+, Pb2+, Ni2+ and Cu2+. The purpose of this research is to: (i) quantify binding capacity to different sources of marine organic matter at environmentally relevant concentrations; (ii) test fluorescence quenching and voltammetric method for use in seawater conditions and; (iii) compare predicted speciation parameters with toxicological observations in the same samples. Information regarding the solubility of copper and copper compounds is important for risk assessment and can be used to set site specific criteria. Transformation/dissolution tests were completed to determine solubility of copper and cuprous oxide powder. The measured solution copper concentration values were compared to a copper solubility model which isolated the precipitate formation tenorite, malachite and copper hydroxide to be able to identify which precipitate would best describe the results obtained from the experiment. Tenorite underestimated solubility at 22 ppb while malachite and copper hydroxide overestimated copper solubility, 150 ppb and 600 ppb respectively. The experimental data point, 47.9 ppb was placed between the tenorite precipitation model and the malachite precipitation model still leaving questions about how to optimize the modeling of copper solubility. Fluorescence spectroscopy was used to determine stability of natural organic matter (NOM) during storage and variability in the molecular nature of the NOM from different sources. The molecular differences in NOM will allow for the determination of a source dependence on toxicity and whether or not it should be a factor considered in the BLM. Fluorescence Index (FI) was determined for all the NOM samples and had a range of 1.12 to 1.54 indicating that the fulvic acid within the samples was terrestrially derived. PARAFAC was used to determine the relative concentration of three components within the organic material determined to be tryptophan-like, humic and fulvic-like and tyrosine-like material. The comparison of the relative percents of each of these components showed a significant increase within the tryptophan-like material from 10% to 72% and a decrease in humic and fulvic-like material from 85% to 16% after storage, for a specific sample. The NOM did not remain stable and the quality of the sample changed during the storage procedure. This potentially was caused by the fractionation method used to collect the NOM samples. Copper fluorescence quenching has been validated for marine systems. Experimental results agree with a tryptophan model and copper ion selective electrode results. The fluorescence quenching model did not agree with tryptophan model for lead, nickel and zinc and disagreed with lead toxicity data. The interaction of lead with a dissolved organic carbon (DOC) concentration of 2 mg C/L provided an EC50 of 738 (680-796) nM while a concentration of 12 mg C/L had an EC50 of 757 (680-830) nM for early lifestage development tests with blue mussel larvae. Binding capacity determined by fluorescence quenching suggested a dose dependence. Voltammetric methods demonstrated that a 2 and 12 mg C/L had similar binding capacity with an increase in by binding capacity by a factor of 1.1 consistent with the EC50 data. Voltammetric methods agree with lead toxicity data. Information on lack of dose dependence in seawater can be implemented in a marine Biotic ligand model (BLM). More work is necessary to determine exact relationships. Knowledge regarding salinity dependence and source dependence are important to implement a BLM. Binding capacities were determined for two different organic matter concentrations and three different salinities. Four different NOM sources were tested Nordic Reservoir, Pachena, Inshore Brazil and Bamfield. No significant differences were found within the NOM sources comparing salinities and concentrations. A statistically significant difference was found when comparing the four different sources of NOM to each other. The NOM with a lower humic and fulvic acid-like fraction was found to be significantly different from the NOM with a higher concentration of humic and fulvic-acid like component. The percent of fluorophore fraction was compared to the binding capacity to determine any potential trends. A strong trend was found for the humic and fulvic acid like fraction (R2=0.9327), a slight trend for the tryptophan like fraction (R2=0.7811) and no trend for the tyrosine like fraction (R2=0.4436)