M2 AM Aquatic Ecotoxicology (Part 1)
Monday, 14 November 2005: 8:00 AM - 11:40 AM in Ballroom 2

(ROB-1117-816577) Identifying the cause of benthic invertebrate community impairment at a uranium operation.

Robertson, E.¹, Liber, K.¹, ¹ Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

ABSTRACT- Past monitoring has noted benthic invertebrate community impairment downstream of the Key Lake uranium operation in northern Saskatchewan, Canada. This research was aimed at identifying the cause(s) of this impact using a weight of evidence approach. Preliminary work in 2003 used a Sediment Quality Triad approach to verify the presence and extent of benthic community impairment at a series of downstream sites, as well as develop hypotheses on what stressor(s) could be responsible for the observed effects. Results confirmed the presence of an effect on benthic community structure, in addition to significant differences in surface water, pore water and whole-sediment chemistry. However, results from the whole-sediment toxicity test using Hyalella azteca indicated that whole-sediment may not be the primary cause of benthic community impairment. Therefore, in the summer of 2004, in-situ and laboratory bioassays using H. azteca were conducted in addition to the Sediment Quality Triad as part of a more broad investigation. This expanded approach was used to determine which environmental compartment(s) could be responsible for the benthic impairment observed in-situ. The in-situ bioassay used caged H. azteca in both surface water exposure chambers and surface water-sediment exposure chambers in order to determine if surface water was playing a role in benthic impairment. The laboratory bioassays using H. azteca were conducted to determine the isolated toxicity of surface water, pore water and whole-sediment. The results of the in-situ and laboratory bioassays both demonstrated that surface water was the primary cause of acute H. azteca toxicity and hence benthic impairment. In the summer of 2005, selected Toxicity Identification Evaluations (TIEs) will be conducted on the surface water to characterize and/or identify the specific cause(s) of H. azteca toxicity and consequently benthic impairment. Results of the TIEs will be presented on the relationships between H. azteca mortality and contaminant concentrations.

Key words: causal investigation, weight of evidence, Hyalella azteca, uranium industry