Temporal and spatial trends of mercury in fish collected in the English–Wabigoon river system in Ontario, Canada☆
Introduction
Between 1962 and 1970, an alkaline chlorine plant located near Dryden, Ontario, Canada, dumped approximately 10 metric tonnes of inorganic mercury into the English–Wabigoon river system. This mercury was converted to the toxic methylated form by sulfide-reducing bacteria in the water, and was subsequently incorporated into the river ecosystem. By March of 1970, the Ontario Ministry of Energy and Resource Management had ordered all companies in the province to stop dumping effluent containing mercury (Conway, 1986, Shkilnyk, 1985). In May 1970, the Ontario government banned commercial fishing on all lakes and tributaries of the English–Wabigoon river system (Shkilnyk, 1985). All fish species from the river system were considered to be so contaminated as to be unfit for human consumption. Research conducted to determine the levels of contamination in the aquatic ecosystem in the area found elevated mercury levels in fish, particularly from Clay Lake, in which Walleye were recorded with values as high as 16 mg/kg (Armstrong and Scott, 1979, Fimreite and Reynolds, 1973, Scott, 1974, Scott and Armstrong, 1972).
The town of Dryden is located on Wabigoon Lake, which is the headwater of the Wabigoon River. The Wabigoon River is joined by the English River at Ball Lake. The combined river systems then flow west into the Winnipeg River and eventually into Lake Winnipeg. Two First Nation communities, Wabaseemong and Grassy Narrows reserves (Anishanaabe First Nations, Northwestern Ontario) are located on the River, with Grassy Narrows located several hundred kilometres upstream of Wabaseemong (Fig. 1). These communities are under the administration of the Grand Council Treaty #3, which governs 28 First Nation communities and all of the lands and headwaters of the Winnipeg River ecosystem in Canada.
The Grassy Narrows and Wabaseemong First Nations communities traditionally depend on the plants and animals of the river system for food and other subsistence activities. The perception that the river system was polluted affected the community members' confidence in the value of their traditional foods and lifestyle. Fewer people went out fishing and hunting, and an increased reliance on market foods was seen (Shkilnyk, 1985). The closure of the fisheries and the failure of several sport-fishing lodges in the area had considerable economic effects on the band members, many of whom relied on guiding and commercial fishing for employment (Kneen, 2002).
There have been no records of methylmercury levels in the English–Wabigoon fish in published literature since the 1970s. This project was initiated by the Grand Council Treaty #3 office and conducted in collaboration with the researchers from the Centre for Indigenous Peoples' Nutrition and Environment (CINE) at McGill University, Montréal. The objective was to study the current levels of methylmercury in fish in the English–Wabigoon river system; this will allow members of the Grassy Narrows and Wabaseemong First Nations communities to make informed choices on fish consumption.
Section snippets
Sample collection
Consultation with the Band Councils and key band members from both communities determined which fish species are most frequently consumed by community members, and the local lakes that are commonly harvested. Four species were selected for the analysis: Walleye (Stizostedion vitreum vitreum), Northern Pike (Esox lucuis), Large-mouth Bass (Micropterus salmoides), and Whitefish (Coregonus clupeaformis). The fish were harvested from the following seven lakes in the Grassy Narrows territory: Ball
Results
Mean total mercury concentrations and associated standard deviation values were calculated for each species from each lake, as well as the mean length and length range (Table 1).
The factors Lake, Length and the interaction Lake ⁎ Length are significant for all the four species of fish. The Q–Q plots based on the output of GLM for each species show that they are a good fit and the ANOVA model is robust.
Pairwise comparisons show that all 4 species of fish in Clay Lake had higher Hg concentrations
Discussion
A well-established relationship exists between fish age, length and mercury level (Gerstenberger and Dellinger, 2002). In this study, length was used as a proxy measurement for age, as it is fast and easy to determine in the field. In addition, length is more likely to be used by anglers when determining contamination risk (Gerstenberger and Dellinger, 2002). All of the fish harvested from the lakes in the Grassy Narrows Territory exhibit a significant relationship between length and mercury
Conclusion
The examination of historic studies in the English–Wabigoon river system reveals that the mercury levels have decreased since the introduction of controls on dumping in 1970. Despite this, fish samples of Bass, Northern Pike, and Walleye from some common harvest lakes, are seen to still have mercury concentrations above what is considered safe for frequent consumption. This finding has important implications for the Anishanaabe communities that rely on these species as part of a traditional
Acknowledgements
We thank all the participants of the study and the support of the Chief and Council of the Grassy Narrow and Wabaseemong First Nations. Special thanks to Betsy Mandamin and Steve Fobister Jr. for their help throughout the project. Funding was provided by Health Canada.
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Hg levels in fish in the English–Wabigoon river system have declined since the 1970s, indicating that nearby First Nations communities can consume the fish in this river as part of a traditional diet, without undue health concerns.