Baseline studies in the Slave River, NWT, 1990–1994: Part I. Evaluation of the chemical quality of water and suspended sediment from the Slave River (NWT)

Abstract

The Slave River watershed at the Alberta-Northwest Territories border drains a large area and is the recipient of chemical compounds from a variety of aquatic sources, including the Athabasca and Peace Rivers. The potential for contamination from industrial and agricultural processes upstream is very real. Thus, the Slave River Environmental Quality Monitoring Program was established in 1990 to assess the water and suspended sediment quality in the territorial portion of the river. A baseline data set with which to determine present and future effects from upstream activities and long-range transport of contaminants was created. The number of ‘above detect’ data points from measurements of polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and chlorinated phenolics (CPs) in water was small and those concentrations of compounds that were above analytical detection limits were very low and unlikely to have adverse effects on the ecosystem. No pesticide levels were ever detected in the water during the 5-year monitoring period, even though long-range transport of these contaminants to the Arctic have been well-documented. Levels of metals were often observed in measurable concentrations in the Slave River water, and frequently exceeded water quality guidelines, although not by any substantial amount. It was concluded that although the concentrations were relatively high, the metals are probably occurring naturally, and not from upstream industrial sources. It was speculated that aquatic biota had probably adapted to these levels. Although PAH concentrations in suspended sediment from the Slave River at Fort Smith often exceeded the ‘Lowest Effect Level’ guideline established in bottom sediment by the Ontario Ministry of the Environment, values remained well below the ‘Severe Effect Level’. Conclusions were reached that PAH concentrations in Slave River suspended sediment were not substantial enough to cause a threat to the ecosystem. Metal levels in suspended sediment remained variable over the 5-year monitoring period and no trends could be seen regarding an overall increase or decrease in concentrations. The low number of ‘above detect’ data points for pesticides and chlorinated phenolics observed in the suspended sediment during the program suggested that adverse impacts would not be occurring from these contaminants in the watershed. Lastly, although certain concentrations of dioxins and furans were measured and were often higher than levels observed in the Wapiti/Smoky River system and the Athabasca River, the values were very small and the contributing homologues had a minimal toxic potential. Detectable levels of 2,3,7,8-TCDD were never observed in the suspended sediment in the Slave River at Fort Smith. Sediment elutriate tests over a 48 h period using Dophnia magna and Photobacterium phosphoreum (Microtox) indicated little acute toxicity. These results seem plausible, given that chemical concentrations of contaminants in the suspended sediment were generally very low or below analytical detection. It can be concluded from the extensive data set collected during the 5-year program that impact from upstream industrial and agricultural sources is, at the present time, negligible, and that the environmental quality of the Slave River at Fort Smith is pristine. Also, the extensive data set has established a baseline, which can be used for future comparative purposes.