Metal, PCB, Dioxin and Furan Concentrations in Fish and Sediments from Four Lakes in Nord-du-Québec in 2001
This environmental study pertains to lakes Chibougamau, Aux Dorés, Obatogamau, and Waconichi. These lakes are used in particular by the Cree communities for sustenance fishing and by the residents of the Baie-James Region and other Québec regions for sport fishing.
The lacustrine sediments of Lac Chibougamau and Lac aux Dorés were analysed for their heavy metal and PCB levels. Samples from two mining effluents and from four waste sites located on the periphery of these lakes were also analysed for their metal levels. In addition, three fish species from these two lakes were sampled with the aim of assessing the influence of mining on mercury levels in fish. These levels were also compared to those of fish coming from the Obatogamau lakes and the control lake Lac Waconichi. Finally, five fish species from these four lakes were measured for heavy metals, PCBs, and dioxins and furans.
During the 2001 sampling campaign, concentrations in mining effluents of the metals included in the directive for the mining industry were below the authorized limits. However, a bioassay carried out in 2002 from the final effluent of the Copper Rand mine drainage basin, showed toxicity and did not meet the directive’s standards for this parameter.
Sediments contained high levels of some metals, namely arsenic, cadmium, copper, nickel, and zinc. Sites near the Copper Rand mine, located south of the Principale mine and at the foot of Principale tailings site, show the highest concentrations for these metals. However, given the different types of mineralization that occur at these sites, it was not possible to precisely distinguish the proportion of metals natural in origin from the proportion of metals anthropic in origin.
No PCB was detected in sediments of Lac Chibougamau and Lac Aux Dorés.
The elevated arsenic, cadmium, copper, nickel, and zinc levels in sediments near tailings sites had no perceivable effect on the levels measured in fish flesh, which were similar to those measured at the control site (Lac Waconichi).
In fish, levels for toxic metals such as arsenic, cadmium, chromium, and lead were weak or below the detection limit.
Currently available data does not prove that mining activity near Lac Chibougamau and Lac aux Dorés has caused an increase in mercury levels in fish.
For the four studied lakes, the average mercury levels for walleye, northern pike, and small, medium, and large lake trout were generally lower or equal to the Québec average.
Mercury levels in walleye, northern pike, and lake trout caught in lakes Chibougamau, Aux Dorés, and Obatogamau were higher than those measured at the Lac Waconichi (control lake). The highest levels were observed at Lac Obatogamau. The differences among the lakes still remain to be explained; it is likely that these relate to the different natural characteristics of the lakes.
At Lac Chibougamau, mercury levels for lake trout caught in 2001 were lower than those of specimens caught in 1999.
Lac Waconichi (control lake) showed mercury concentrations below the 0.5 mg/kg directive (Health Canada directive for the sale of fishery products) for all of the five species of fish analyzed.
At Lac Chibougamau, only the mercury levels for medium-size and large lake trout, along with northern pike and large burbot exceeded the Health Canada directive for mercury.
At Lac aux Dorés, the Health Canada directive for mercury was exceeded only by medium-size and large lake trout and large burbot.
At Lac Obatogamau, aside from lake trout that was not caught for this study, only whitefish (all sizes), small northern pike, and small walleye showed mercury levels below the Health Canada directive. The directive was exceeded by medium and large northern pike and walleye, as well as for burbot of all sizes.
Mercury levels in all fish analysed exceeded the 0.033 mg/kg limit for the protection of fish-eating terrestrial wildlife.
The Health Canada directive and the standard for fish-eating terrestrial wildlife is frequently exceeded in Québec’s natural environment, in particular for fish-eating species such as walleye, northern pike, and lake trout. Atmospheric deposition of mercury and its biomagnification in the food chain (subsequent to its transformation in methylmercury by aquatic bacteria) are the main causes of the exceeding of these limits.
All PCB and dioxin and furan levels remained below the Health Canada standards of 2000 µg/kg and 15 ng/kg respectively. Lake trout were the only fish species exceeding the limit of 160 µg/kg for PCBs and 0.66 ng/kg for dioxins and furans in 2,3,7,8-TCDD toxic equivalents for the protection of fish-eating terrestrial wildlife.
The entirety of this study’s results shows that metal contamination in fish flesh is limited to mercury. Nevertheless, the level of contamination is not unusual and is comparable to levels measured at many other locations in Québec. PCB levels in lake trout of Lac aux Dorés and Lac Chibougamau should be monitored.
The toxins in one mining effluent and the elevated levels of certain metals in sediments near tailings sites at Lac aux Dorés and Lac Chibougamau are likely to cause toxicity for aquatic organisms and thus constitute a concern.
Reference: LALIBERTÉ, D. and G. TREMBLAY. 2002. Metal, PCB, Dioxin and Furan Concentrations in Fish and Sediments from Four Lakes in Northern Québec in 2001. Québec. Ministère de l’Environnement. Direction du suivi de l’état de l’environnement. Envirodoq no ENV/2002/0203. Report no. QE-129. 38 pp. and 4 appendices.Report, PDF format, 1,3 Mo