https://hdl.handle.net/10388/14022

Cupe Flores, Beatriz Esther (2022) Delineating Effluent Exposure and Associated Risk to Aquatic Organisms Downstream of a Uranium Mine in Northern Saskatchewan, USASK Harvest - Theses and Dissertations, https://hdl.handle.net/10388/14022

Treated effluent from the McClean Lake uranium milling operation in northern Saskatchewan is released into the east basin of McClean Lake, which could potentially cause a variety of both chemical and physical disturbances to the aquatic ecosystem. This study aimed to delineate diluted effluent exposure focusing on combined metals and major ions using autonomous sensor technology, identify the associated risk to aquatic invertebrates, and determine the potential effect of that risk on macroinvertebrate communities within McClean Lake. Autonomous sensor units were deployed at ten locations in and upstream of McClean Lake. Water, sediment and benthic macroinvertebrates were also collected at the same monitoring locations. Complementary surface water was collected from selected sites to perform bioassays with larvae of the midge Chironomus dilutus. Results indicated temporal and spatial variations in effluent exposure based on sensor electrical conductivity (EC) measurements in the McClean Lake east basin. Individual Hazard Quotients (HQs) for water ranged from ‘moderate’ (0.40 – 0.69) to ‘very high’ (>1) for silver, cadmium, arsenic, selenium, mercury, iron and thallium. At all sites, major ions risk was <1. Individual HQs for sediment registered ‘moderate’ (0.40 – 0.69), ‘high’ (0.7 – 0.99) and ‘very high’ (>1) values for vanadium and cadmium. The cumulative risk in water and sediment for all metals combined was >1 at some sites in Vulture Lake (discharging into McClean Lake) and McClean Lake. More detailed estimation of aqueous selenium and arsenic risk, the only two metals with good correlation with sensor EC data, indicated that their 90th percentile HQ values were <1 in McClean Lake, suggesting that these contaminants of potential concern do not represent a significant direct risk to aquatic invertebrates. The metrics of macroinvertebrate communities (total abundance and Margalef index (MI)) did not follow the diluted effluent pattern. The final model from a Generalized Additive Modelling (GAM) exercise confirmed that EC, selenium, and chloride in water, and total organic carbon and cadmium in sediment are key elements that collectively may have influenced macroinvertebrate community composition as measured by MI at the study sites. Finally, across all test endpoints in the bioassays, exposure to lake water from Vulture Lake and McClean Lake had no statistically significant effects on C. dilutus.

https://harvest.usask.ca/bitstreams/ad702263-e72b-4342-9bb6-fed0fbf25854/download