Document Type


Degree Name

Master of Science (MSc)



Program Name/Specialization

Integrative Biology


Faculty of Science

First Advisor

James McGeer

Advisor Role



This study focuses on the effect of Ca and dissolved organic matter (DOM) on Ni toxicity to Hyalella azteca in soft waters (interpreted in the context of the biotic ligand model (BLM)) and is linked to a larger project directed at understanding the recovery of aquatic systems from long term smelter damage. Amphipods (source: Hannah Lake, Sudbury ON) were cultured and tested in soft waters (12 mg CaCO3/L, pH 7.0, 21ºC) following Environment Canada standard method EPS 1/RM/33 (Environment Canada, 1997). Effects of Ca, but not Mg, were observed where a 5-fold increase in protection was a result of an increase of Ca concentrations from 0.1 to 2.0 mM. DOM was collected from sites previously impacted and recovering from long term smelter emissions and also from reference sites in central Ontario. Dissolved organic carbon (DOC) concentrations at 6 mg/L and higher offered protection against Ni toxicity. Acute toxicity tests with different DOM sources (at 6 mg DOC/L) showed variation in protective capacity but no clear links to measured optical characteristics were observed. DOM sources also reduced short term (6h) whole body accumulation of Ni but there was no correlation between the capacity of DOM to reduce accumulation and its ability to mitigate toxicity. Application of the BLM illustrated that acute toxicity could be modelled reasonably well except for some effects of Ca (2.0mM). Chronic (28d) effects on Hyalella occurred at much lower Ni concentrations (acute to chronic ratio of approximately 50) and the protective effects of Ca and DOM were proportionally similar. For example, 1mM Ca increased the chronic LC50 by 3-fold. Growth (assessed as dry weight) was generally a more sensitive indicator of impacts than survival. In exposures without modifying factors, the EC20 and EC50 for growth were 1.4 and 12.7 µg Ni/L, respectively, while the LC50 was 13.8 (CI: 11.5 - 16.7) µg Ni/L. Contrary to other studies, this research did not show relationships between DOM quality and toxicity mitigation and this demonstrates the need for an improved understanding of DOM characteristics in relation to the potential impact of Ni.

Convocation Year