Document Type


Degree Name

Master of Science (MSc)



Program Name/Specialization

Integrative Biology


Faculty of Science

First Advisor

Dr. Jim McGeer

Advisor Role



Technology critical elements (TCEs) are increasingly used in high and green technologies but there is little aquatic toxicity data for TCEs, particularly in fresh water. The objective of this study was to investigate the toxicity of two TCEs, Ge and Y, to Daphnia magna and Hyalella azteca and to understand the role of natural organic matter and cations on toxicity modification. Testing followed standard methods. The 48 h EC50 for D. magna was 11.6 (95% CI of 9.64-13.8) mg Ge/L based on measured dissolved concentrations at test end. The addition of NOM at 10 mg DOC/L resulted in a significant three-fold increase in EC50 value but not all sources produced this protective effect. For H. azteca, the 96 h EC50 was 8.65 (7.24-10.4) mg Ge/L and tests with NOM showed no protective effect. The 14-d chronic EC20s for H. azteca were 0.17 (-0.34-0.68) and 1.83 (0.15-3.51) mg Ge/L for survival and growth. NOM did not show a protective effect. Tests with Y on D. magna were done in a medium with hardness of 50 mg CaCO3/L at pH 6.8. Yttrium did not precipitate in acute exposures however, in chronic tests adsorption to food occurred. Dissolved Y concentrations in the NOM added tests were higher than the corresponding concentrations in medium without NOM. The 48 h EC50 was 217 (182-262) mg Y/L (based on dissolved Y at test end). NOM at 10 mg DOC/L, 1.5 mM CaCl2, and 3 mM NaCl) resulted in significant protection against acute Y toxicity to D. magna. In the unmodified medium, the 21-d chronic EC20s were 0.39 (0.10-1.52), mg Y/L, 9.59 (5.78-15.9), and 17.7 (95% CI na) mg Y/L for reproduction, wet weight, and dry weight. Additions of NOM and CaCl2 did not produce a clear protective effect for survival, reproduction, nor growth but in general, the results suggest a protective influence for NOM and Ca2+. The study contributes data towards understanding the toxicity of Ge and Y and the importance of toxicity modifying factors for improved ecological risk assessment of Ge and Y.

Convocation Year


Convocation Season


Available for download on Saturday, September 30, 2023