Master of Science (MSc)
Faculty of Science
The industrial demand for rare earth elements (REEs) is growing and as a result, environmental exposure is a concern. Very little is understood about the toxicity of REEs in aquatic environments. The objective of this research is to evaluate the acute and chronic toxicity of Tm and to also understand the toxicity modifying influence of dissolved organic matter (DOM) and cationic competition (Ca2+, Mg2+ and Na+). Furthermore, the aim of this study was to determine linkages between Tm bioaccumulation, growth and survival during chronic exposures. Standard methods (Environment Canada) were followed for both 96h acute and 14d chronic tests, in media with a hardness of 60 mg CaCO3/L, a pH of 7.6 at 23°C. Hyalella azteca neonates (2-9 d for acute and 0-3 d old for chronic) were used and mortality (acute and chronic) as well as dry weight and accumulation of Tm for survivors were the endpoints. For acute tests, the potential protective effect of cationic competition was tested with Ca (0.25-1.50 mM), Na (0.25-1.55 mM) and Mg (0.06-0.38 mM). The effect of Luther Marsh and Kouchibouguac DOM complexation (at dissolved organic carbon (DOC) concentrations of 2, 7 and 12 mg C/L) were also evaluated. For chronic tests, the potential protective effect of competition was tested with Ca (0.25 – 1.5 mM) and Luther Marsh DOM (7 mg C/L). Surviving Hyalella were dried, weighed, tissues dissolved and measured for Tm accumulation. Dissolved Tm concentrations were lower than total (unfiltered) Tm concentrations indicating that precipitation occurred and this was particularly the case at higher concentrations. No protective effect was seen for Na or Mg in acute tests, nor was a protective effect for Ca observed in both acute and chronic tests. However, dissolved organic matter was protective (both of the sources) at dissolved organic carbon (DOC) concentrations of 7 and 12 mg DOC/L for acute tests as well as at 7 mg DOC/L in the chronic test. ii Bioaccumulation at 14 d of exposure was also shown to be reduced at higher concentrations of Ca even though survival was not. This study contributes data towards the understanding of Tm toxicity in aquatic environments and REEs in general.
Loveridge, Alexandria H., "Do Toxicity Modifying Factors Influence Acute or Chronic Toxicity of Thulium to Hyalella azteca?" (2016). Theses and Dissertations (Comprehensive). 1836.
Available for download on Friday, June 23, 2017