Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Chemistry

Program Name/Specialization

Environmental Science

Faculty/School

Faculty of Science

First Advisor

Scott Smith

Advisor Role

Supervisor

Abstract

Natural organic matter (NOM) is considered an important factor in the protection of the aquatic environments; organic ligands can complex with metals, to decrease their toxicity and bioavailability. NOM is measured as dissolved organic carbon (DOC) in mg C/L. Silver metal can enter into the aquatic environment from natural and anthropogenic sources, and is found in different chemical forms. Free silver ion (Ag+) is considered as the most toxic form of the metal. However, it can form complexes with both inorganic and organic ligands, such as ammonia, chloride, hydroxyl, carbonato, phosphato, and thiol groups. Thiol is the most important ligand because it forms very strong complexes with Ag. To date, the behavior of silver in the aquatic environment, is still not well understood. The aim of this research is divided to three steps. First, the experimental objective of this study was to determine free silver ion binding to NOM in three different commercially available sources. Also, samples were tested under different pH (4.0, 6.0, 8.0 and 10.0) conditions. In the laboratory tests, the technique that was used was a flow through ion selective electrode (ISE) system utilizing an Ag2S electrode. In the second step, Windermere Humic Aqueous Model (WHAM), which is a very important risk assessment tool, was validated by comparison WHAM and ISE silver speciation results. Silver binding to NOM depends on the specific ligands in each samples. For example, the sample with the most sulphur content was also strongest in binding to silver. Also, pH plays an important role in silver bioavailability. When pH increases, NOM has more sites available to bind to silver ions. In contrast, proton concentration increases at low pH and competes with free silver cations to bind with NOM. Finally, optical characterization of NOM was performed using absorbance (SAC340) and fluorescence indices (FI) in order to distinguish among NOM samples. It found that optical characteristics have similar value for all NOM samples.

Convocation Year

2017

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