Towards an Understanding of Dissolved Organic Matter Molecular Composition and Reactivity in the Environment

• Main Author: Cottrell, Barbara
• Other Authors: Simpson, Andre
• Language: en_ca
• Published: 2013
• Subjects: Dissolved organic matter; Photochemistry; NMR; FT-ICR-MS; GCxGC-TOFMS; 0425
• Online Access: http://hdl.handle.net/1807/43501

Dissolved organic matter (DOM), one of the most complex naturally occurring mixtures, plays a central role in the biogeochemistry and the photochemistry of natural waters. A complete understanding of the environmental role of DOM will come only from the elucidation of the relationship between its structure and function. This thesis presents new work on the separation, characterization, and reactivity of DOM in rainwater, freshwater, and seawater. A new separation technique based on counterbalance capillary electrophoresis was developed for the separation of Suwannee River NOM. A comparative study of the organic content of rainwater was accomplished using nuclear magnetic resonance (NMR) with spectral database matching ,Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS), and comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOFMS). Three complementary, non-overlapping datasets identified of over 400 compounds. Analysis of the FT-ICR-MS data using van Krevelen diagrams and the carbon oxidation state showed variation in the elemental composition and molecular size. Over 50% of the compounds identified in this study were known components of secondary organic aerosol (SOA) and volatile organic carbon (VOCs). Dissolved organic matter (DOM) plays a central role in the photochemistry of natural waters through the production of reactive oxygen species and the triplet excited state of DOM (3DOM*). These reactive species are central to the reactivity, transport, and fate of both natural and anthropogenic chemicals in the environment. Laser flash photolysis (LFP) was used to demonstrate that particulate organic matter (POM) generates a triplet excited state species (3POM*). LFP of seawater from the Pacific Ocean and the Bermuda Atlantic Time Series Station detected similar excited state species from surface to 4535m. Metal speciation has been implicated in the photochemistry of natural waters. Copper immobilized metal affinity chromatography (IMAC) of seawater and freshwater isolated a low and a high affinity fraction that generated excited state transients. Excitation-emission matrix spectroscopy showed that while the seawater fractions were autochthonous, freshwater fractions enriched in chromophoric DOM (CDOM), were allochthonous. The discovery of these different classes of compounds in freshwater and seawater has important implications both for the mineralization of DOM and the removal of xenobiotics in the aquatic environment.