Metal, PCB, Dioxin and Furan Concentrations in Fish and Sediments from Four Lakes in Nord-du-Québec in 2002
Since 1998, in order to assess the quality of the fishery resource in the Chibougamau region, the ministère de l’Environnement du Québec and the Société de la faune et des parcs du Québec of the ministère des Ressources naturelles et de la Faune et des Parcs du Québec have been conducting analyses of metals and organic compounds in fish flesh. Four lakes have been under study: lakes Chibougamau, aux Dorés, Waconichi and Obatogamau.
These lakes are used in particular by Cree communities for sustenance fishing and by the residents of the Baie-James Region and other Québec regions for sport fishing.
The shores of Lac Chibougamau and Lac aux Dorés are the location of significant surface-level mineralized zones, some of which have been mined. The Obatogamau lakes, for their part, are influenced by the presence of a mine located in the Rivière Nemenjiche basin while Lac Waconichi is considered as the control lake since there is no mining activity or significant mineralization in the immediate vicinity.
The results of the 2001 study demonstrated that metal contamination in fish flesh was limited to mercury. Certain species showed levels that exceeded the 0.5 mg/kg standard (Health Canada standard for the sale of fishery products). The highest levels were observed in the Obatogamau lakes. Nonetheless, the latter concentration levels were not unusual and were comparable to levels measured at many other locations in Québec. In addition, the data do not prove that mining activities near Lac Chibougamau and Lac aux Dorés have caused an increase in mercury or other metal levels in fish.
It was pointed out however that the PCB levels in lake trout from Lac aux Dorés and Lac Chibougamau should be monitored. The origin of the PCBs remains to be explained, and no PCBs were detected in sediments from Lac Chibougamau or Lac aux Dorés.
Sediments taken near tailing sites 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 the Principale tailing site, showed the highest concentrations of these metals. However, given the different types of mineralization at these sites, it was not possible to precisely distinguish the proportion of metals occurring naturally from the proportion of anthropic origin.
The toxins in one mining effluent and the high levels of certain metals in sediments near tailing sites at Lac aux Dorés and Lac Chibougamau are likely to cause toxicity in aquatic organisms and thus remain a cause for concern.
In light of these results, the objective of the 2002 study has been to identify the extent of the zone of contaminated sediments located downstream from mining industries (for Lac aux Dorés) and to confirm the metal levels contained in sediments in sectors located both close to and far from mines (for Lac Chibougamau). It also aims to describe the impacts of the mining industry, if any, as evidenced in sediments from Lac Waconichi (control lake) and the Obatogamau lakes. In addition, the study has attempted to determine whether fish from the Obatogamau lakes show mercury levels that vary according to distance from mining activities.
Highlights: 2002 study
In 2002, the levels of 13 metals were measured in 39 sediment samples from lakes Chibougamau, aux Dorés, Waconichi and Obatogamau. Mercury analyses were also conducted on the flesh of 293 fish belonging to 6 species from Lac Chibougamau and the Obatogamau lakes. Composite flesh and liver samples, based on the size classifications of the different species, will soon be analysed with the aim of detecting a number of metals and PCBs, as well as dioxins and furans. Metal levels in certain small whole fish will also be measured.
Sediments from Lac Waconichi (control lake) show very low metal levels, in particular copper (9 mg/kg) and arsenic (4 mg/kg), pointing both to the absence of mining influence on this lake and of significant nearby mineralization.
For Lac aux Dorés, in the sector downstream from the Principale tailing site, only copper (400 mg/kg) and nickel (63 mg/kg) show concentrations that exceed the guidelines of probable effect (197 mg/kg and 61 mg/kg respectively). This contamination, especially with respect to copper, is noted on the western shore as far as over 3.5 km downstream from the aforementioned tailing site. The concentration levels are however lower than those observed in 2001 near the mines (upstream sector).
For Lac Chibougamau, a sediment sample taken in a ditch near the Eaton Bay tailing site shows a very high concentration of copper (1,300 mg/kg), i.e. 6.6 times the guidelines of probable effect. Levels of arsenic (41 mg/kg) and nickel (89 mg/kg) also exceed their respective guidelines at this site. These levels confirm the 2001 observations for this sector and the potential toxicity for aquatic organisms.
Still for Lac Chibougamau, sediments taken far from mining activities show concentrations of arsenic, chromium, nickel, lead and zinc that are significantly higher in the north than in the south. Different mineralizations may explain these discrepancies. For arsenic, chromium and nickel, the levels in the north (McKenzie Bay) are, respectively, 1.6, 1.3 and 2.3 times higher than the guidelines of probable effect.
Lac Chibougamau and Lac aux Dorés are influenced by the ultramafic rocks of the Cummings Complex located near the shore of Lac Chibougamau. This complex harbours abnormal contents of copper, chromium, nickel and cobalt, in part explaining the higher metal concentrations in this sector.
Concerning the Obatogamau lakes, Rivière Nemenjiche, a tributary draining a mining site, contains sediments with high concentrations of arsenic (85 mg/kg), copper (680 mg/kg), and mercury (0.77 mg/kg). These levels exceed the guideline of probable effect and represent a potential risk for aquatic organisms. The high mercury levels in the sediments could be attributed to the use of mercury on the Joe Mann mining site from 1956 to 1958.
On Rivière Nemenjiche, the differences observed downstream and upstream sediments from the mining site suggest that this industry could be responsible for increases in metal levels. High levels may be observed in the Obatogamau lakes as far as Lac Le Royer, located downstream. However, the proximity of Grenvillian faults in this sector is likely to increase the natural metal levels in the sediments, particularly concentrations of mercury. Other sediment samplings will have to be taken in order to identify the scope and origin of the contamination.
Concerning the Obatogamau lakes once again, mercury emissions originating from the mining site may have caused an increase in adjusted average mercury levels near the mouth of Rivière Nemenjiche varying from 0.07 mg/kg to 0.3 mg/kg according to the species in question. In percentages, these increases are » 41% for northern pike, » 22% for walleye, » 100% for lake whitefish and » 94% for burbot. However, part of this increase may be attributed to the presence of older fish, particularly walleye, in the Rivière Nemenjiche sector as compared to the western sector (Lac Fancamp) of the Obatogamau lakes.
In spite of the differences observed, the mercury contamination measured is not unusual and is comparable to levels at a number of Québec sites. As such, the average mercury levels for all species remain below or similar to the average levels measured across Québec. This situation is nevertheless far from ideal since Québec’s waterways are subject to airborne pollution and levels frequently exceed the Health Canada standard (0.5 mg/kg).
In the Obatogamau lakes, the standard is exceeded in walleye and medium-sized and large northern pike as well as in burbot of all sizes, with the exception of those caught in the western sector (Lac Fancamp), an area not influenced by mining activity. Large whitefish and white suckers of all sizes show levels below the standard at all sites.
For Lac Chibougamau, the average mercury levels exceed the standard for large and medium‑sized lake trout as well as for northern pike, walleye and large burbot.
Among the three metals (arsenic, mercury and selenium) analysed in the fish, only mercury levels exceed the Health Canada standards for the sale of fishery products.
The results show that for Lac aux Dorés high levels of copper in sediments extend over 3.5 km downstream from mining activities. The copper levels measured are likely to cause toxicity in aquatic organisms.
For the Obatogamau lakes, a mining site may have contributed to increased metal levels in sediments (copper, arsenic and mercury). The levels measured are high enough to present toxicity for aquatic organisms. The high mercury levels in sediments may have caused increased mercury concentrations in fish, ranging from 22% to 100% according to the species in question. In spite of these increases, the mercury contamination measured is not unusual and is comparable to levels observed in a number of Québec locations.
Reference: Laliberté, Denis, 2004. Metal Concentrations in Fish and Sediments from Lakes aux Dorés, Chibougamau, Obatogamau and Waconichi in 2002, Québec, ministère de l’Environnement, Direction du suivi de l’état de l’environnement, envirodoq no ENV/2004/0137/A, collection no QE/142/A, 28 pp. and 3 appendices.
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