Challenges and Potential Solutions in Analyzing Trace Element Concentrations and Size Distributions in Boreal Rivers and Peat Bog Waters
Creators: Yu, Wang
Publisher: name: University of Alberta Library
Year: 2024

<p>Trace elements (TEs) can exist in water in various forms including hydrolyzed ions, simple inorganic molecules, organic complexes, adsorbed onto inorganic and organic particles, or incorporated into suspended particles. These forms of TEs establish limits on their bioaccessibility. Size becomes critical in studying the fate, transport, and potential bioavailability of TEs in natural waters. However, some TEs may undergo loss due to adsorption, while contamination and carryover can also arise. These effects become critical during the analysis of elements at low or ultra-low concentrations (e.g., ng L-1) during filtration and AF4-ICP-MS analysis procedures. These inconsistencies are thereafter regarded as artefacts in this thesis. Currently, there is limited understanding of these artefacts concerning the size species of dissolved TEs in aquatic environments. The following studies primarily focus on the artefacts associated with 1) the measurements of colloidal TEs in Canadian boreal waters using AF4-ICP-MS, 2) filtration through filters with a pore size of 0.45 µm to measure the size distribution of TEs in diverse types of surface waters, 3) the analysis of colloidal TEs in acidic peat bog waters. <br>
Chapter 1 serves as an introduction to the overall project background, including natural waters, aquatic colloidal systems, colloid-TE interactions, and relevant analytical techniques. Problem statements and research objectives are also included in this chapter. <br>
Chapter 2 provides a comprehensive review of the diverse applications of AF4 in investigating colloids and their associations with TEs in aquatic systems. This chapter also includes a detailed description of the theoretical background and challenges involved in these applications. <br>
Chapter 3 focuses on potential artefacts caused by filtration through filters with a pore size of 0.45 µm. The results indicated that neutral and weakly alkaline waters, such as boreal rivers, exhibited more substantial variations in the measurements of primarily ionic, and colloid-associated TEs in filtrates compared to acidic waters like bog waters. Cartridge filtration demonstrated a higher efficiency in retaining ions and excluding colloids within boreal river waters than membrane filtration. Despite similar dissolved concentrations obtained, filtration methods with consistent pore sizes can yield different results in terms of the concentration and size distribution of TEs. <br>
Chapter 4 investigates potential artefacts associated with measuring the concentration of the size species of dissolved TEs within DOM-rich waters using AF4-UV-ICP-MS. The results indicate that some TEs (e.g., Co, Ni, Cu, and Pb) can be lost through adsorption, and that contamination and carryover may occur during the fractionation process. The measurement of colloidal TE is susceptible to analytical bias, significantly impeding the precise quantification of TEs in AF4-UV-ICP-MS analysis. The presence of sample colloids, specifically DOM, plays a crucial role in the occurrence of these artefacts. Detailed strategies for addressing these issues are presented and discussed.<br>
Chapter 5 focuses on the potential artefacts in analyzing the size distribution of dissolved TEs in acidic and DOM-rich bog waters. Waters extracted from Sphagnum moss and porewaters from peat were examined. The adsorption of DOM onto a polyethersulfone (PES) membrane poses a challenge, potentially causing membrane clogging and leading to a shift in the elution of TEs towards a shorter retention time. Selecting a membrane with an appropriate pore size is crucial to minimize the risk of clogging. Notably, despite the abundance of DOM in both types of bog waters, a substantial number of micronutrients (e.g., Mn, Co, Ni, Zn, and Mo) predominantly existed as primarily ionic species. Our findings revealed a notably higher proportion of primarily inorganic colloids observed in moss waters compared to peat porewaters: this may be indicative of dissolution of atmospheric dusts as porewaters migrate through the moss layer into the underlying peat layer.<br>
This thesis is intended to help improve the precision and accuracy of the size-based analysis of TEs in the dissolved fraction of natural waters. The findings and strategies presented here will be of great interest to scientists seeking to develop routine methods to separate primarily ionic and colloidal forms of TEs, and quantify their size distribution  in the dissolved fraction of natural waters.</p>