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Long-term changes in fish mercury levels in the historically impacted English-Wabigoon River system (Canada)

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Margaret R Neff
Margaret R Neff
Margaret R Neff
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Satyendra Bhavsar at Ontario Ministry of the Environment and Climate Change, Canada
Satyendra Bhavsar
  • Ontario Ministry of the Environment and Climate Change, Canada
George B Arhonditsis at University of Toronto
George B Arhonditsis
Rachael Fletcher
Rachael Fletcher
Rachael Fletcher
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Abstract and Figures

The English-Wabigoon River system in Northwestern Ontario, Canada, was one of the most heavily mercury-contaminated waterways in the world due to historical discharges in the 1960s from a chlor-alkali plant. This study examines long-term (1970-2010) monitoring data to assess temporal trends in mercury contamination in Walleye, Northern Pike and Lake Whitefish, three species important for sport and subsistence fishing in this region, using dynamic linear modeling and piecewise regression. For all lakes and species, there is a significant decline (36-94%) in mercury concentrations through time; however, there is evidence that this decline is either slowing down or levelling off. Concentrations in the English-Wabigoon fish are elevated, and may still present a potential health risk to humans consuming fish from this system. Various biotic and abiotic factors are examined as possible explanations to slowing rates of decline in mercury concentrations observed in the mid-1980s.
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... In Canada, between 1962 and 1975, a chloralkali plant discharged over 9 metric tons of inorganic Hg into a river that flowed into the traditional territories of Asubpeeschoseewagong Anishinaabek (also known as Grassy Narrows First Nation), located in Northern Ontario [16]. Hg, methylated in the aquatic system, was bio-accumulated and bio-magnified in fish [17], attaining concentrations 50 times the reference guidelines for fish consumption [18,19]. For the people of Grassy Narrows First Nation, fish was central to their culture and livelihood, as well as their dietary mainstay [20]. ...
... Levels stabilized around 1985 [19], but current levels remain high, possibly through ongoing erosion of high Hg particles by the river, as it meanders through contaminated floodplains [21]. Between 1970 and 1997, hair and blood samples were taken by governmental biomonitoring programs to assess Hg exposure of this First Nation community [22]. ...
... Walleye and Northern pike, taken from the river system downstream of the chloralkali plant, showed that MeHg made up 85-100% of total Hg concentration [32]. Studies have shown that Hg concentrations in Walleye, the fish most consumed by the people of Grassy Narrows, have remained stable since the mid-eighties to the early nineties, depending on location in this fluvial lake system [18,19]; the biomarkers of human exposure followed the same pattern [4]. ...
The evolution of symptoms of nervous system dysfunction in a First Nation community with a history of mercury exposure: a longitudinal study
Article
Full-text available
  • May 2024
  • ENVIRON HEALTH-GLOB
Background Since the 1960’s, mercury (Hg) contamination of the aquatic environment of Asubpeeschoseewagong Anishinabek (Grassy Narrows First Nation) territories has impacted the community members’ traditions, culture, livelihood, diet and health. Despite decreasing Hg exposure over time, a recent study suggested that long-term exposure contributed to later-life symptom clusters of nervous system dysfunction. Here, the objective was to evaluate, 5 years later, the prevalence and progression of these symptoms and examine the contribution of long-term, past Hg exposure. Methods The symptom questionnaire, applied in the 2016/17 Grassy Narrows Community Health Assessment (GN-CHA) (Time 1), was re-administered in the 2021/22 Niibin study (Time 2). A total of 85 adults (median age: 47y; range: 29-75y) responded at both times. Paired statistics were used to test the differences (Time 2 – Time 1) in self-reported symptom frequencies. The symptom clustering algorithm, derived from the entire study group of the GN-CHA (n = 391), which had yielded 6 clusters, was applied at Time 1 and 2. Equivalent hair Hg measurements (HHg) between 1970 and 1997 were used in Longitudinal Mixed Effects Models (LMEM), with a sub-group with ≥ 10 repeated HHg mesurements (age > 40y), to examine its associations with symptom cluster scores and their progression. Results For most symptoms, paired analyses (Time 2 – Time 1) showed a significant increase in persons reporting “ very often” or “all the time”, and in the mean Likert scores for younger and older participants (< and ≥ 50y). The increase in cluster scores was not associated with age or sex, except for sensory impairment where a greater increase in symptom frequency was observed for younger persons. LMEM showed that, for the sub-group, long-term past Hg exposure was associated with most cluster scores at both times, and importantly, for all clusters, with their rate of increase over time (Time 2 – Time 1). Conclusions The persistence of reported symptoms and their increase in frequency over the short 5-year period underline the need for adequate health care services. Results of the sub-group of persons > 40y, whose HHg reflects exposure over the 28-year sampling period, suggest that there may be a progressive impact of Hg on nervous system dysfunction.
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... 1 In 1970, very high Hg levels were reported in fish in the English-Wabigoon River system; inorganic Hg released by the chloralkali plant was being converted into methylmercury (MeHg), a highly toxic compound that bioaccumulates and biomagnifies in the aquatic food chain. 5,10 Hg concentrations in fish reached up to 24 lg=g, almost 50 times the upper limit considered safe for human consumption. 10 Communities received contradictory messages about whether or not they should continue to eat fish. ...
... 5,10 Hg concentrations in fish reached up to 24 lg=g, almost 50 times the upper limit considered safe for human consumption. 10 Communities received contradictory messages about whether or not they should continue to eat fish. Some lodge owners downplayed the importance of Hg contamination and continued the practice of shore meals, thereby placing fishing guides into the situation of choosing between their health and their livelihood. 1 In 1975, the main fishing lodge had shut down and the commercial fisheries were closed. 1 Over time, fish Hg concentrations declined, stabilizing by around 1985, 10,11 but they have remained to this day higher than in other Ontario lakes and rivers. ...
... 10 Communities received contradictory messages about whether or not they should continue to eat fish. Some lodge owners downplayed the importance of Hg contamination and continued the practice of shore meals, thereby placing fishing guides into the situation of choosing between their health and their livelihood. 1 In 1975, the main fishing lodge had shut down and the commercial fisheries were closed. 1 Over time, fish Hg concentrations declined, stabilizing by around 1985, 10,11 but they have remained to this day higher than in other Ontario lakes and rivers. 12 In the early 1970s, Canadian government biomonitoring programs for total Hg in hair, blood, and umbilical cord blood were initiated in the First Nation communities affected by the discharge into the English-Wabigoon River system. ...
The Contribution across Three Generations of Mercury Exposure to Attempted Suicide among Children and Youth in Grassy Narrows First Nation, Canada: An Intergenerational Analysis
Article
Full-text available
  • Jul 2023
  • ENVIRON HEALTH PERSP
Background: For 60 y, the people of Asubpeeschoseewagong Anishinabek (Grassy Narrows First Nation) have endured the effects of massive mercury (Hg) contamination of their river system, central to their traditions, culture, livelihood, and diet. In the years following the Hg discharge into the English-Wabigoon River system by a chloralkali plant in the early 1970s, there was a dramatic increase in youth suicides. Several authors attributed this increase solely to social disruption caused by the disaster. Objective: This research examined the possible contribution of Hg exposure across three generations on attempted suicides among today's children (5-11 y old) and youth (12-17 y old), using a matrilineal intergenerational paradigm. Methods: Information from the 2016-2017 Grassy Narrows Community Health Assessment (GN-CHA) survey was merged with Hg biomonitoring data from government surveillance programs (1970-1997). Data from 162 children/youth (5-17 years of age), whose mothers (n=80) had provided information on themselves, their parents, and children, were retained for analyses. Direct and indirect indicators of Hg exposure included a) grandfather had worked as a fishing guide, and b) mother's measured and estimated umbilical cord blood and childhood hair Hg and her fish consumption during pregnancy with this child. Structural equation modeling (SEM) was used to examine significant links from grandparents (G0) to mothers' exposure and mental health (G1) and children/youth (G2) risk for attempted suicide. Results: Mothers' (G1) median age was 33 y, 86.3% of grandmothers (G0) had lived in Grassy Narrows territory during their pregnancy, and 52.5% of grandfathers (G0) had worked as fishing guides. Sixty percent of children (G2) were <12 years of age. Mothers reported that among teenagers (G2: 12-17 years of age), 41.2% of girls and 10.7% of boys had ever attempted suicide. The SEM suggested two pathways that significantly linked grandparents (G0) to children's (G2) attempted suicides: a) through mothers' (G1) prenatal and childhood Hg exposure and psychological distress, and b) through maternal fish consumption during pregnancy (G1/G2), which is an important contributor to children's emotional state and behavior. Discussion: Despite minimal individual information on G0 and G1 past life experiences, the findings support the hypothesis that Hg exposure over three generations contributes to the mental health of today's children and youth. The prevalence of Grassy Narrows youth ever having attempted suicide is three times that of other First Nations in Canada. https://doi.org/10.1289/EHP11301.
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... Between 1962 and 1969 the Dryden Chemical Company located in Dryden, northwestern Ontario, discharged approximately 10 tonnes of mercury from a chlor-alkali plant into the Wabigoon River ( Fig. 1; Armstrong and Hamilton 1973). In 1974, mercury contamination of this river and lake system was found in fish as far as Tetu Lake, 250 km downstream of Dryden (Neff et al. 2012). During 1972 in the east basin of Clay Lake, which is the first lake (86 km) downstream of Dryden, surface sediment and water mercury concentrations were >6000 ng/g and 120 ng/L, respectively (Armstrong and Hamilton 1973). ...
... More recent studies of sediment and fish mercury concentrations in Clay Lake (Lockhart et al. 2000;Kinghorn et al. 2007;Neff et al. 2012) found that recovery was initially rapid for both sediments and fish. However, since the early 1980s, sediments have declined much more slowly and walleye mercury concentrations in muscle have plateaued at about 2 μg/g, wet weight, 4-and 10-fold higher than commercial and subsistence consumption guidelines, respectively. ...
... Some natural recovery in the sediments has occurred during the intervening decades, with the rate being rapid at first and then slowing to a very low rate. Fish also recovered rapidly at first but have not decreased since the mid 1980s (Fig. 8b, Neff et al. 2012). The divergence of fish recovery from sediment recovery is likely linked to the continuing inputs of MeHg to Clay Lake from upstream. ...
Why the English–Wabigoon river system is still polluted by mercury 57 years after its contamination
Article
Full-text available
  • Dec 2021
Between 1962 and 1969, 10 tonnes of mercury were discharged from a chlor-alkali plant in Dryden, Ontario, to the English–Wabigoon River. Present-day fish mercury concentrations are amongst the highest recorded in Canada. In 2017, the Grassy Narrows Science Team found no evidence of ongoing discharges from the plant site to the river water, even though large quantities of mercury remain at the site. Instead, our data suggest that ongoing erosion of high mercury particles by the river, as it meanders through contaminated floodplains, is responsible for present-day transport of mercury to Clay Lake and to Ball Lake, located 154 km downstream. In Clay Lake, surface sediment total mercury concentrations and inflow water concentrations are still about 15 times above background (86 km downstream), and in Ball Lake mercury concentrations in sediments appeared to be still increasing. The remobilization of legacy inorganic mercury from riverbank erosion between Dryden and Clay Lake stimulates methyl mercury production there, in Clay Lake, and in Ball Lake. The large quantities of methyl mercury produced between Dryden and Clay Lake are mostly dissolved in water and are swept downstream, elevating concentrations in water and biota throughout the system. Several options for remediating the ongoing contamination are discussed.
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... Another program assessed Hg concentrations in umbilical cord blood collected at the local hospital [3,4]. Biomarker Hg concentrations from Grassy Narrows First Nation followed a similar pattern to Hg levels in local fish from the contaminated river system, with extremely high concentrations in the early 1970's, a sharp decline until 1977 and a less pronounced decline until 1987, after which, mean concentrations remained relatively stable [5,6]. ...
... In this community, fish, especially walleye, is the source of Hg exposure [4,5]. Table 2 contains the responses to the GN-CHA questions on past and current fish consumption frequency. ...
Past mercury exposure and current symptoms of nervous system dysfunction in adults of a First Nation community (Canada)
Article
Full-text available
  • Mar 2022
  • ENVIRON HEALTH-GLOB
Background The watershed in Asubpeeschoseewagong Netum Anishinabek (Grassy Narrows First Nation) territory has been contaminated by mercury (Hg) since 1962, resulting in very high Hg concentrations in fish, central to the community’s culture, traditions, economy and diet. Biomarkers of Hg exposure (umbilical cord blood and hair/blood samples), monitored between 1970 and 1997, decreased over time. A recent Grassy Narrows Community Health Assessment (GN-CHA) survey included current symptoms of nervous system dysfunction. The present study aimed to cluster self-reported symptoms and examine their associations with past Hg exposure. Methods The GN-CHA included 391 adults. Symptom clustering used a two-step segmentation approach. Umbilical cord Hg and/or yearly measurements of equivalent hair Hg were available for 242 participants. Structural Equation Models (SEM) displayed the associations between Hg exposure and clusters, with Hg exposure modelled as a latent variable or in separate variables (prenatal, childhood and having had hair Hg ≥ 5 μg/g at least once over the sampling period). Longitudinal Mixed Effects Models (LMEM) served to examine past hair Hg with respect to clusters. Results A total of 37 symptoms bonded into 6 clusters, representing Extrapyramidal impairment, Sensory impairment, Cranial nerve disturbances, Gross motor impairment, Neuro-cognitive deficits and Affect/Mood disorders. Median Hg concentrations were 5 μg/L (1–78.5) and 1.1 μg/g (0.2–16) for umbilical cord and childhood hair, respectively. More than one-third (36.6%) had hair Hg ≥ 5 μg/g at least once. In SEM, latent Hg was directly associated with Extrapyramidal and Sensory impairment, Cranial nerve disturbances and Affect/Mood disorders. Direct associations were observed for prenatal exposure with Affect/Mood disorders, for childhood exposure with Extrapyramidal impairment and Cranial nerve disturbances, and for hair Hg ≥ 5 μg/g with Extrapyramidal and Sensory impairment. For all clusters, a further association between past Hg exposure and symptom clusters was mediated by diagnosed nervous system disorders. LMEM showed higher past hair Hg among those with higher scores for all clusters, except Affect/Mood disorders. Conclusion Our findings provide evidence that in this First Nation community, past Hg exposure from fish consumption was associated with later-life clusters of coexisting symptoms of nervous system dysfunction.
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... Fish Hg concentrations generally exceeded 2 µg/g and reached levels as high as 17 µg/g [3]. In the years following the control of the discharge, fish Hg declined; the trend transitioned in the mid 1980s and since the early nineties, concentrations have remained relatively stable [4,5]. They are still among the highest in Canada [6]. ...
Characterizing visual field loss from past mercury exposure in an Indigenous riverine community (Grassy Narrows First Nation, Canada): a cluster-based approach
Article
Full-text available
  • Oct 2024
  • ENVIRON HEALTH-GLOB
Background Between 1962 and 1975, a chlor-alkali plant in Canada discharged approximately 9 metric tons of mercury (Hg) into the Wabigoon River. Over the following decades, biomarkers of Hg exposure of persons from Grassy Narrows First Nation (Asubpeeschoseewagong Anishinabek), located downriver from the discharge, reflected Hg concentrations in fish. Hg exposure is known to target the calcarine fissure, resulting in visual field (VF) loss. Most studies and clinical reports focus solely on peripheral VF loss; little is known about the impact of Hg on the central and paracentral portions. The present study sought to characterize the patterns of VF loss with respect to past and current Hg. Methods A 28-year hair-Hg (HHg) database, created from a 1970–97 government biomonitoring program, served to select study participants with ≥ 4 year-based HHg measurements (n = 81). Blood-Hg was assessed for current exposure. Light sensitivity thresholds across the VF were analyzed monocularly, using a Humphrey Field Analyzer (HFA). Following post-hoc exclusions, based on HFA interpretation indices, 65 participants were retained. Both eyes were combined for analyses (n = 130 eyes). Unsupervised hierarchical clustering of HFA plot data was used to identify patterns of VF loss. A series of mixed effects models (MEM) were performed to test the associations for current Hg exposure with respect to HFA interpretation indices and clusters, as well as for longitudinal past Hg exposure. Results The clustering approach decomposed the light sensitivity deficits into 5 concentric clusters, with greatest loss in the peripheral clusters. No relation was observed between any of the cluster scores and current blood-Hg. VF deficits increased with past Hg exposure. Longitudinal MEM showed that HHg was significantly (p < 0.05) associated with all peripheral, paracentral, and central cluster scores, as well as with HFA interpretation indices. Conclusions Past Hg exposure in Grassy Narrows First Nation was associated with present day VF loss. The cluster-based location-specific approach identified patterns of VF loss associated with long-term Hg exposure, in both the peripheral and the central areas. The functional implications of this type of visual loss should be investigated.
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... Although fish Hg concentrations from the Wabigoon River system have declined since the 1970s (Kinghorn et al., 2007;Neff et al., 2012), as of 2018 (McGovarin, 2020) Hg concentrations in walleye sampled at Wabigoon Rapids and Clay Lake still exceeded the Canadian guideline for commercially-sold fish (0.5 μg/g) (Health Canada, 2007), suggesting active MMHg production in the system. Consequently, further research is crucial to understand the continued methylation of legacy Hg into MMHg that makes it available for bioaccumulation. ...
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... In 1970, fish was a dietary mainstay [12] and blood Hg concentrations were the highest in Canada [13]. Hg exposure decreased over time and stabilized in the mid 1980s [14], paralleling the decline in fish Hg concentrations [15]. Fish Hg levels remain high due primarily to the remobilization of inorganic Hg from riverbank erosion [16]. ...
Visual Characteristics of Adults with Long-Standing History of Dietary Exposure to Mercury in Grassy Narrows First Nation, Canada
Article
Full-text available
Since the 1960s, Grassy Narrows First Nation (Ontario, Canada) has been exposed to methyl mercury (Hg) through fish consumption, resulting from industrial pollution of their territorial waters. This cross-sectional study describes the visual characteristics of adults with documented Hg exposure between 1970 and 1997. Oculo-visual examinations of 80 community members included visual acuity, automated visual fields, optical coherence tomography [OCT], color vision and contrast sensitivity. Median age was 57 years (IQR 51–63) and 55% of participants were women. Median visual acuity was 0.1 logMAR (Snellen 6/6.4; IQR 0–0.2). A total of 26% of participants presented a Visual Field Index inferior to 62%, and qualitative losses assessment showed concentric constriction (18%), end-stage concentric loss (18%), and complex defects (24%). On OCT, retinal nerve fiber layer scans showed 74% of participants within normal/green range. For color testing with the Hardy, Rand, and Rittler test, 40% presented at least one type of color defect, and with the Lanthony D-15 test, median color confusion index was 1.59 (IQR 1.33–1.96). Contrast sensitivity showed moderate loss for 83% of participants. These findings demonstrate important loss of visual field, color vision, and contrast sensitivity in older adults in a context of long-term exposure to Hg in Grassy Narrows First Nation.
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Retrospective mercury exposure and current symptoms of nervous system dysfunction in adults of a First Nation community (Canada)
Preprint
Full-text available
  • Oct 2021
Background: The watershed in Asubpeeschoseewagong Netum Anishinabek (Grassy Narrows First Nation) territory has been contaminated by mercury (Hg) since 1962, resulting in very high Hg concentrations in fish, central to the community’s culture, traditions, economy and diet. Biomarkers of Hg (umbilical cord blood and hair/blood samples), monitored between 1970 and 1997, decreased over time. A recent Grassy Narrows Community Health Assessment (GN-CHA) survey included current symptoms of nervous system dysfunction. The present study aimed to cluster self-reported symptoms and examine their relation to past Hg exposure. Methods: The GN-CHA included 391 Registered adult Band members. Symptom clustering used a two-step segmentation approach. Umbilical cord Hg and yearly measurements of hair Hg were available for 242 participants. Longitudinal Mixed Effects Models (LMEM) served to examine past hair Hg with respect to clusters. Structural Equation Models (SEM) displayed direct and indirect pathways between Hg exposure and clusters, with Hg exposure modelled as a latent variable or in separate time periods (prenatal, childhood and having had hair Hg ≥ 5µg/g at least once). Results: A total of 37 symptoms bonded into 6 clusters, representing Extrapyramidal impairment, Sensory impairment, Cranial nerve disturbances, Gross motor impairment, Neuro-cognitive deficits and Affect/Mood disorders. Median Hg concentrations were 5µg/L (1-78.5) and 1.1µg/g (0.2-16) for umbilical cord and childhood hair, respectively. More than one-third (36.6%) had hair Hg ≥ 5 µg/g at least once. LMEM shows higher long-term hair Hg among those with higher scores for most clusters. In SEM, latent Hg is directly and indirectly associated with all clusters. The contribution of prenatal exposure is mediated by childhood exposure, except for Affect/Mood disorders, where the association is direct. Hair Hg ≥ 5 µg/g is directly related to Extrapyramidal and Sensory impairment. Conclusion: Our findings provide evidence that in this First Nation community, past Hg exposure from fish consumption was associated with later-life clusters of coexisting symptoms of nervous system dysfunction. Given the complexity of the interrelations between the various determinants of chronic health problems in this and other First Nation communities, LMEM and SEM methods provide the opportunity to trace direct and/or indirect effect routes of potential “causal impact”.
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Forecasting PCB Concentrations in Lake Michigan Salmonids: A Dynamic Linear Model Approach
Article
Full-text available
  • Aug 1998
Ecological time-series data often consist of highly variable observations collected from ecosystems whose structure and function are changing, making trend assessment and forecasting difficult. Dynamic linear models (DLMs) were used to study time trends in annual average PCB concentrations in five species of Lake Michigan salmonids, using data collected from 1972 to 1994 by both the Michigan and Wisconsin Departments of Natural Resources. DLMs use an adaptive fitting procedure to track trends in the rate of decline over time, in contrast to other approaches that fit fixed parameters. We used this method to make forecasts of PCB concentrations in these fishes, along with Bayesian credible-interval estimates associated with these forecasts. Point estimates of PCB concentrations in all five species show a decline through a 10-yr forecast horizon. However, upper bounds on the 90% credible-interval uncertainty estimates for chinook salmon and lake trout indicate that steady or slightly increasing annual average PCB concentrations are within the 90% credible interval for the 10-yr forecast horizon. DLM forecasts corroborate other modeling results for Lake Michigan salmonids that suggest that PCBs will decline very slowly over the next decade.
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Relationships among Fat Weight, Body Weight, Water Weight, and Condition Factors in Wild Atlantic Salmon Parr
Article
Full-text available
  • Mar 2000
We investigated the relationship between fat content and condition indices in Atlantic salmon Salmo salar parr sampled from a wild population on a seasonal basis. Condition of individual fish was indexed by residuals from the least-squares regressions of fat weight, dry weight, wet weight, and water weight (separately on fork length) as well as by relative condition factor, Fulton's condition factor, percent fat, and percent water. For all fish analyzed in the study (n = 284), residualized fat weight accounted for 81% of the variation in percent fat, for 58% of the variation in residualized dry weight, for 46% of the variation in residualized wet weight and relative condition factor, for 41% of the variation in Fulton's condition factor, for 35% of the variation in residualized water weight, and for 28% of the variation in percent water. All indices except Fulton's condition factor, residualized water weight, and percent water were significantly correlated with fat weight for all combinations of sex and season. The indices based on fat weight provided the most information about seasonal and gender differences in terms of nutritional status, followed by the index based on dry weight, the indices based on wet weight, and the indices based on water weight. Residual indices are useful for testing the relationship between physiological and morphometric condition indices, and they provide an alternative to more traditional condition indices when the assumptions underlying the use of traditional indices are not valid.
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Mercury in sediment and fish communities of Lake Vanern, Sweden: Recovery from contamination
Article
  • Dec 2001
The past effluents of mercury (Hg) into Lake Vanern were considerable. The consequences of, and recovery from these have been monitored through continuous measurements of mercury in sediment and fish. Mercury levels in lake sediments in the vicinity of the main source of mercury, a chloralkali plant on the northern shore, have only decreased by slightly more than a half since the mid-1970s, despite a radical decrease in effluents from the source, already during the 1960s. The mercury levels in pike (Esox lucius) have decreased to a similar extent during this time period. They are now about 30% higher in the worst affected parts of the lake compared to the least affected parts. Lower levels have been measured in perch (Perca fluviatilis) and salmonoid fish in the lake. Despite the increased presence of mercury in the sediment of Lake Vanern, the mercury levels in the fish of the lake are relatively low compared to fish in lakes situated in the same region, but not affected by any local mercury effluents. As calculated, the total fish biomass of L. Vanern holds less than 1000th of the amount of mercury contained in the upper, biologically active layers of the bottom sediment of the lake. This demonstrates the potential influence of various environmental factors and motivates continued monitoring of mercury levels in the lake in the future.
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Mercury Contamination of Fish in Northwestern Ontario
Article
  • Jan 1973
Mercury levels were determined in lateral musculature of fish from Northwestern Ontario in specimens taken upstream and downstream from a chlorine plant, and from a number of lakes not contaminated from any known source. The maximum mercury levels in northern pike (Esox lucius), burbot (Lota lota), and walleye (Stizostedion vitreum) were 27.8, 24.8, and 19.6 ppm respectively, measured in specimens taken 50-60 miles downstream from the plant. They decreased proportionally to the distance from the plant but were clearly elevated even 200 miles downstream. The levels in specimens from suspected uncontaminated lakes were generally below 1 ppm but frequently above the 0.2 ppm often considered as the maximum background concentrations. The latter finding may possibly be explained on the basis of the oligotrophic conditions characteristic for these lakes.
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Range Extension, Present and Potential Distribution, and Possible Effects of Rainbow Smelt in Hudson Bay Drainage Waters of Northwestern Ontario, Manitoba, and Minnesota
Article
  • Feb 1994
Rainbow smelt Osmerus mordax introduced into the Great Lakes watershed (Crystal Lake, Michigan) in about 1912, began colonizing the Great Lakes in the 1920s. The species now is found throughout much of the Great Lakes watershed of Ontario and in the Mississippi–Missouri drainage as a result of inadvertent or intentional introductions. Gill-net and trawling surveys in 1989 and 1990 of 79 lakes (92 separate times or sites) in the Winnipeg River system of the Hudson Bay drainage in northwestern Ontario, southeastern Manitoba, and northeastern Minnesota revealed or confirmed the presence of rainbow smelt in 19 lakes and extended the species' known range in the Rainy, English, and Wabigoon river systems. Rainbow smelt also were discovered in Lake Winnipeg late in 1990 and in Lake of the Woods in early 1991. Elsewhere, the establishment of rainbow smelt in new water bodies often has been associated with changes in native fish populations. The potential now exists for further spread of rainbow smelt in this watershed as far as Hudson Bay.
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