This report summarizes and describes environmental levels of mercury in water, sediment, invertebrates, and fish from the Athabasca, Peace, and Slave river basins. Data were obtained from existing provincial and federal databases, the Northern Rivers Basins Study, and from government and private sector reports and publications.
Mercury has been measured in several hundred water samples from the Basins. Mercury was detected in only a few of these samples. However, appropriate field and laboratory protocols to sample mercury in water were not used in the past; thus most detections of this element in water may not be reliable. It is noteworthy however, that because of high detection limits (0.05 to 0.1 pg/kg) mercury was not detected in most municipal effluents, and only occasionally in industrial effluents.
Mercury is ubiquitous to all soils and sediments of the earth, and it is not surprising that it was found in sediment samples from the Basins at levels that range from 27 to 123 pg/kg (dry weight). Levels of mercury found in sediments were well below the current draft interim sediment guideline for mercury that was developed to protect aquatic life. The guideline is 170 pg/kg mercury (dry weight). There was no obvious increase in mercury in sediments downstream of industrial effluents compared with sediment at upstream sites. Sediment cores from Lake Athabasca indicate that mercury levels have not increased over at the past 50 years or more, and they also suggest that the Athabasca River basin is the principal source of mercury to Lake Athabasca.
Mercury was not detected (< 20 pg/kg) in nine invertebrate samples collected from the Athabasca River in the Hinton to Whitecourt reach (km 1244 to 1067). However, in 1983 in the reach from km 270 to 258 that spans the Suncor operation, mercury increased in aquatic invertebrates in the downstream direction, from 70 to 1400 pg/kg. This significant increase, and the unusually high level in aquatic invertebrates, suggests that the Suncor operation in the early 1980s was a significant source of mercury to the lower Athabasca River. However, mercury levels in a single sample of invertebrates from 1994 for this same reach suggests that the Suncor operation is no longer a major source of mercury.
Mercury was detected in all fish of every species taken from all lakes and rivers. In general, mercury levels in the Basins were highest in predatory fish species such as pike, walleye, burbot, and bull trout and the maximum levels were found in large specimens of these species. For the Athabasca River basin, the decreasing order for concentration of mercury in fish was walleye > goldeye > northern pike > longnose sucker > mountain whitefish. Because of high levels of mercury, consumption guidelines have been established for walleye and pike from two lakes in the Athabasca River basin, and for walleye caught from the Athabasca River. Consumption guidelines are reported by Alberta Environmental Protection in their "Annual Guide To Sport Fishing". In the reach of the Athabasca River from the town of Athabasca(km700)to the southern boundary of Wood Buffalo National Park(km 127),25%of all walleye had mercury concentrations that exceeded the Health Canada limit of 500 pg/kg. Detailed studies are required to determine the relative contribution ofnatural and industrial sources to the mercury
It is recommended that:
1. Mercury concentration in walleye from Lake Athabasca and at sites along the lower Athabasca River downstream from the town of Athabasca be measured at regular intervals, perhaps every two years.
2. A detailed study be conducted in the lower Athabasca River to evaluate and to identify mechanisms and pathways o f mercury uptake by aquatic biota. The tarsands, an organic rich substrate, forms a significant part of the banks of the Athabasca River and its tributaries in this reach. Tarsands may enhance mercury uptake into the food web. An evaluation of the contribution ofthe waste-water effluent from town ofFort McMurry and the contribution of the Suncor operation to mercury loading in the lower Athabasca River should be part of this study