Toxic contamination of freshwater fish – 5th edition
Status: Moderate
Trend: Deteriorating since 2016 for mercury
Unchanged for PCBs, penta-BDEs, and dioxins and furans
Unknown for PFOS
Prepared by: Denis Laliberté
Direction du suivi et de l’évaluation de l’état des milieux aquatiques Direction principale de la qualité des milieux aquatiques
Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs
Copyright information
Cat. No.: En78-5/2026E-PDF
ISBN: 978-0-660-99482-6
This publication may be reproduced for personal or internal use without permission, provided the source is fully acknowledged. However, reproduction of this publication in whole or in part for purposes of redistribution requires the prior written permission from the Canada Water Agency by contacting:
Canada Water Agency
510-234 Donald Street
Winnipeg, Manitoba
R3C 1M8
Canada
Email: water-eau@cwa-aec.gc.ca
© His Majesty the King in Right of Canada, as represented by the President of the Canada Water Agency and the Minister of the Environment, Climate Change and Nature, 2026
Published by authority of the Minister of l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs du Québec
© Gouvernement du Québec, 2026
Aussi disponible en français sous le titre : La contamination des poissons d’eau douce par les substances toxiques – 5e édition
Highlights
Between 2019 and 2024, for the species and sizes studied, mercury levels in fish tissues occasionally exceeded Health Canada’s guidelines,Footnote 1 while levels of perfluorooctane sulfonate (PFOS) frequently exceeded the criteria for the protection of fish-eating terrestrial wildlife established by the Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs (MELCCFP).Footnote 2 Levels of other toxic substances remained below the criteria and reference values for human consumption.
IssueFootnote 3
This indicator shows the level of contamination by mercury, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), dioxins and furans, and perfluoroalkyl substances (PFAS) in the tissues of walleye, northern pike, yellow perch and whole white sucker in Lake Saint-François, Lake Saint-Louis and Lake Saint-Pierre from 2014 to 2024 (Figure 1). Fish sampling is conducted every three to five years as part of the Réseau de suivi ichtyologique (RSI) [fish monitoring network]. The indicator helps provide recommendations on sport fish consumptionFootnote 3 and assess the risks posed to fish-eating wildlife by these bioaccumulative and environmentally persistent toxic substances.
Text description of Figure 1
Purpose of the Figure
- To show the locations of fish sampling stations along the St. Lawrence River and several tributaries, spanning from the Montréal area (west) to Québec City (east).
- Each numbered station is classified as sampled or not sampled between 2014 and 2024, according to the legend.
Geographical Extent
- Map covers the southern Quebec region, focusing on the St. Lawrence River corridor.
- Major municipalities visible: Montréal, Varennes, Sorel‑Tracy, Trois‑Rivières, Bécancour, Québec City.
- Key watercourses labelled in blue include the St. Lawrence River (main axis), Ottawa River (far southwest, marginal), Rivière des Prairies, Richelieu River, Saint‑Maurice River, Bécancour River, Nicolet River, Yamaska River, L’Assomption River, and additional tributaries.
Cartographic Elements and Layout
- North arrow in the upper left corner.
- Scale bar (0–25–50 km) in the lower left corner.
- Inset map (upper left) showing the study area within Quebec (outlined in red).
- Basemap features grey‑tone shaded relief and blue hydrographic network.
- Government of Quebec logo and credits in the lower right corner (“Environnement…” text partially visible but clearly indicating provincial authorship).
Legend – Symbol Meaning
- Legend title: “Fish Sampling Station”.
- Two symbols:
- Sampled (2014–2024): dark blue filled circles.
- Not sampled (2014–2024): light blue circles with outline.
- Stations numbered 1 to 20, distributed west to east along the river.
Distribution of Stations (West to East)
- Montréal region / immediate downstream: stations 1–11 positioned along the St. Lawrence, including sites near Montréal and Varennes.
- Sorel‑Tracy and Lake Saint‑Pierre region: stations 12–16 near Sorel‑Tracy, Lake Saint‑Pierre, and extending toward Trois‑Rivières.
- Bécancour area: station 17 near the south shore at Bécancour.
- Corridor toward Québec City: stations 18–20 located between major tributary confluences (e.g., Saint‑Maurice River) and the Québec City urban area (station 20 just upstream).
- Overall pattern: stations are concentrated along the main channel of the St. Lawrence, with a few near confluences or wider sections such as Lake Saint‑Pierre.
Readability and Contrast
- Station numbers (1–20) appear inside or adjacent to each circle.
- Good contrast between blue watercourses, grey relief, and blue station symbols helps distinguish features.
- Watercourse names appear in blue, while municipality names appear in black, using varied font sizes to indicate importance.
Key sources of contamination
Mercury
Mercury occurs naturally in rock, air and water and is also released into the environment by industrial sources. It is released into the environment through a wide range of consumer products and, in particular, via the burning of petroleum, oil and coal.Footnote 3 Footnote 4
PCBs
PCBs are a class of organic chemicals with multiple historical uses. These compounds have been banned in Canada since 1980, and their presence is solely due to human activity. PCBs were used in hydraulic and electrical equipment. Footnote 3 Footnote 5
PBDEs
PBDEs have been added to various plastic matrices, synthetic resins and textile fibres to reduce the flammability of a range of consumer products, furniture upholstery, electronics casings and automotive parts, among others. The use of PBDEs was gradually phased out between 2006 and 2012.Footnote 3 Footnote 6
Dioxins and furans
Dioxins and furans are formed in very small quantities as impurities during the production of certain pesticides or during chlorine bleaching in pulp and paper mills. They are also formed during the incineration of certain municipal and industrial waste and in fires involving electrical equipment containing chlorinated organics. Additionally, dioxins can result from natural causes, such as forest fires and volcanic eruptions.Footnote 3 Footnote 7
PFAS
PFAS are used as stain-resistant, non-stick and waterproofing agents, as well as for their flame-resistant properties.Footnote 3 Footnote 8
In Canada, the federal government has introduced regulations prohibiting the manufacture, use, sale and import of certain PFAS, such as PFOS, perfluorooctanoic acid (PFOA) and long-chain perfluorocarboxylic acids (PFCAs), as well as products containing them.
Factors affecting levels of contamination in fish
Mercury
Mercury accumulates in fish, shellfish and other edible freshwater organisms in a form that is potentially harmful to humans. The degree of contamination in fish varies depending on the species, age and location of capture. Fish-eating species—that is, those that feed on other fish, such as bass, pike, walleye and muskellunge—have the highest levels of contamination. Within the same species, larger specimens generally contain higher concentrations of mercury than smaller specimens.Footnote 3
PCBs, PBDEs, and dioxins and furans
PCBs, PBDEs, and dioxins and furans nearly always enter water bodies, where they largely bind to fine particles that remain suspended or settle to the bottom. They then enter aquatic organisms through the consumption of contaminated water or food, accumulating in fatty tissues.
Concentrations of these substances in fish depend on diet and tissue fat content. In lean fish, such as walleye, northern pike or yellow perch, these substances accumulate primarily in the liver or adipose tissue, whereas the white sucker, when analyzed whole with viscera, contains more fat and exhibits higher concentrations of contaminants than lean fish. In general, these contaminants accumulate in the viscera, fat and skin.Footnote 3
PFAS
In general, PFAS are extremely persistent in the environment, as fluorocarbon groups (primarily -CF2-) are highly stable and resistant to biodegradation, hydrolysis, photolysis and thermolysis. PFAS generally exhibit a combination of oleophobic, hydrophobic and hydrophilic properties across different parts of their chemical structure. It is important to note that, rather than accumulating in lipids, like PBDEs and organochlorines, some of these substances preferentially bind to proteins and are therefore found in protein-rich tissues, such as the flesh, liver and blood. For whole white sucker, a homogenate of all of these tissues is analyzed, instead of using flesh-only analysis.8
Key measurements
Categories for assessing contamination in fish flesh:
Good: All concentrations measured in fish flesh are below the reference values for human consumption or do not exceed them by more than 10% – not of concern.
Moderate: Concentrations measured in fish flesh are near the reference values for human consumption, but one species may exceed these values locally by more than 10% – monitoring is needed.
Poor: Several species have flesh concentrations exceeding the reference values for human consumption by more than 10%, or a single species exhibits concentrations exceeding these values throughout the entire fluvial corridor – of concern.
Status and trends
Mercury
Over the 2019–2024 period, average mercury concentrations were below Health Canada’s guideline of 0.5 mg/kgFootnote 1 for the sale of walleye, with the exception of levels on the north shore of Lake Saint-Louis in 2019, and for yellow perch and white sucker. However, northern pike had an average mercury concentration exceeding this guideline on the north shore of Lake Saint-François in 2022 (0.59 mg/kg) and the south shore of Lake Saint‑Louis in 2024 (0.58 mg/kg), as well as on the north shore of Lake Saint-Pierre in 2021 (0.69 mg/kg) and the south shore of Lake Saint-Pierre in 2019 (0.54 mg/kg) and 2021 (0.53 mg/kg) (Figure 2).
An upward trend for mercury
When comparing the average mercury concentrations measured during the 2019–2024 period with those of the 2014–2016 period measured in walleye (425 mm), northern pike (600 mm), yellow perch (215 mm) and white sucker (425 mm), the following trends were observed:
- Lake Saint-François: On the south shore in 2022, walleye (0.31 mg/kg) showed a significant increase of 41% in average mercury concentrations. On the north shore in 2022, yellow perch (0.31 mg/kg) and whole white sucker (0.26 mg/kg) showed significant increases of 24% and 86%, respectively, in average mercury concentrations compared with 2014.
- Lake Saint-Louis: On the south shore in 2024, northern pike (0.58 mg/kg) and yellow perch (0.30 mg/kg) showed significant decreases of 28% and 25%, respectively, in mercury concentrations compared with 2016.
- Lake Saint-Pierre: On the south shore in 2021, walleye (0.50 mg/kg), northern pike (0.53 mg/kg), yellow perch (0.23 mg/kg) and whole white sucker (0.21 mg/kg) showed significant increases of 35%, 56%, 21% and 62%, respectively, in mercury concentrations compared with 2016. On the north shore in 2021, walleye (0.47 mg/kg), northern pike (0.69 mg/kg), yellow perch (0.27 mg/kg) and whole white sucker (0.20 mg/kg) also showed significant increases of 42%, 57%, 17% and 54%, respectively, in mercury concentrations compared with 2016.
Figure 2: Trends in average mercury concentrations in the flesh of walleye (425 mm),
northern pike (600 mm), yellow perch (215 mm) and white sucker (425 mm) in the
St. Lawrence River for the 2014–2024 period.
Text description of Figure 2
Graph Type
- Comparative vertical bar chart.
- Multiple bar clusters representing different sampling stations and years.
Vertical Axis
- Indicates mercury concentration in milligrams per kilogram (mg/kg).
- Scale ranges from 0 to 1.0 mg/kg.
- A black dashed horizontal line marks the human consumption standard: 0.5 mg/kg.
Horizontal Axis
- Shows station groups by lake:
- Lake Saint‑François – south shore (stations 1 and 2)
- Lake Saint‑François – north shore (station 3)
- Lake Saint‑Louis – south shore (stations 5 and 6)
- Lake Saint‑Louis – north shore (station 7)
- Lake Saint‑Pierre – north shore (stations 13 and 14)
- Lake Saint‑Pierre – south shore (stations 15 and 16)
- Each group includes sampling years (e.g., 2014, 2016, 2019, 2021, 2022, 2024 depending on the site).
Species Represented (Legend)
- Walleye (Doré jaune): blue bar.
- Northern pike (Grand brochet): dark grey bar.
- Yellow perch (Perchaude): red outlined bar.
- Whole-body white sucker (Meunier noir entier): orange bar.
- Human consumption standard (0.5 mg/kg): black dashed line.
Main Visual Observations
- Northern pike (dark grey bars) consistently shows the highest mercury concentrations across most stations and years.
- Several measurements exceed the 0.5 mg/kg standard, including:
- Lake Saint‑François north shore (2014 and 2022)
- Lake Saint‑Louis south shore (2016)
- Lake Saint‑Pierre north shore (2019 and 2021)
- Several measurements exceed the 0.5 mg/kg standard, including:
- Walleye (blue bars) shows moderate concentrations, with some values approaching or slightly exceeding the standard, for example:
- Lake Saint‑Louis north shore (2019)
- Yellow perch (red outlined bars) displays low to moderate mercury levels, always below the human consumption guideline.
- Whole-body white sucker (orange bars) consistently presents the lowest mercury concentrations, all well below the guideline.
- Mercury levels vary substantially among lakes, stations, and sampling years.
General Trends
- The highest concentrations for several species occur:
- At Lake Saint‑François, especially on the north shore (station 3).
- At Lake Saint‑Pierre, particularly on the north shore (stations 13 and 14).
- Predatory species (e.g., northern pike and walleye) show higher mercury levels compared to species at lower trophic levels such as perch and white sucker.
Polychlorinated biphenyls (PCBs)
Average PCB concentrations measured in fish flesh from 2019 to 2024 were all below the European Union standard of 125 µg/kg.Footnote 9 In addition, for whole white sucker, the average PCB concentrations were all below the MELCCFPFootnote 2 protection criterion of 160 µg/kg for fish-eating terrestrial wildlife, with the exception of the north shore of Lake Saint-Pierre in 2021, which slightly exceeds the criterion (Figure 3).
Average PCB concentrations in fish flesh show few differences across the studied areas, with the exception of walleye on the north (60 µg/kg) and south (93 µg/kg) shores of Lake Saint-François in 2022 and whole white sucker on the north shore (176 µg/kg) of Lake Saint-Pierre in 2021 (Figure 3).
The average PCB concentrations measured during the 2019–2024 period remain relatively comparable to those of the 2014–2016 period, with the exception of the average concentrations in walleye captured on the south shore of Lake Saint-François in 2022 (93 µg/kg) when compared with the value for 2014 (49 µg/kg).
Figure 3: Trends in average PCB concentrations in the flesh of walleye, northern pike,
yellow perch and whole white sucker in the St. Lawrence River for the 2014–2024 period.
Text description of Figure 3
Chart Type
- Comparative vertical bar chart.
- Bar clusters represent different stations and sampling years.
Vertical Axis (Y‑axis)
- Displays PCB concentrations in micrograms per kilogram (µg/kg).
- Scale ranges from 0 to 250 µg/kg.
- Two horizontal reference lines:
- Solid black line: European Union standard – 125 µg/kg.
- Black dashed line: Wildlife protection criterion for piscivorous terrestrial species – 160 µg/kg.
Horizontal Axis
- Shows sampling stations grouped by lake:
- Lake Saint‑François – south shore (stations 1 and 2)
- Lake Saint‑François – north shore (station 3)
- Lake Saint‑Louis – south shore (stations 5 and 6)
- Lake Saint‑Louis – north shore (station 7)
- Lake Saint‑Pierre – north shore (stations 13 and 14)
- Lake Saint‑Pierre – south shore (stations 15 and 16)
- Below each station: sampling years (2014, 2016, 2019, 2021, 2022, 2024 depending on location).
Species Represented (Legend)
- Walleye: blue bars.
- Yellow perch: red outlined bars.
- Northern pike: dark grey bars.
- Whole‑body white sucker: orange bars.
- EU standard (125 µg/kg): solid black line.
- Wildlife protection criterion (160 µg/kg): dashed black line.
Main Visual Observations
- Whole‑body white sucker (orange bars) consistently shows the highest PCB concentrations across most stations.
- Several values exceed the wildlife protection criterion (160 µg/kg), including:
- Lake Saint‑Pierre – north shore (2016, 2019, 2021, with very high peaks)
- Lake Saint‑François – south shore (2014)
- Several values exceed the wildlife protection criterion (160 µg/kg), including:
- Many values also exceed the EU guideline of 125 µg/kg.
- Walleye (blue bars) exhibits moderate concentrations, with some values approaching the 125 µg/kg threshold:
- Lake Saint‑François – south shore (2014)
- Lake Saint‑François – north shore (2014 and 2022)
- Northern pike (dark grey bars) shows low to moderate concentrations, all below both the 125 µg/kg and 160 µg/kg thresholds.
- Yellow perch (red outlined bars) consistently presents the lowest PCB concentrations, well below both regulatory thresholds.
- PCB concentrations vary significantly across lakes, stations, and years.
General Trends
- The stations with the highest concentrations are:
- Lake Saint‑Pierre, especially the north shore (stations 13 and 14).
- Lake Saint‑François, particularly the south shore in certain years.
- Lower‑trophic‑level species such as whole‑body white sucker show marked PCB bioaccumulation at several stations.
- Predatory species (walleye, northern pike) exhibit intermediate concentrations but generally lower than those observed in white sucker.
Polybrominated diphenyl ethers (PBDEs)
There is no reference value for the amount of PBDEs in fish flesh that is considered acceptable for human consumption. From 2019 to 2024, the average concentrations for the three main congener groups normally detected in fish (tetra‑BDEs, penta‑BDEs and hexa‑BDEs) were all below the respective criteria of 44 µg/kg, 3 µg/kg and 4 µg/kg.Footnote 2 Footnote 10
The average concentrations of total PBDEs in fish flesh show little variation across the studied areas. However, in whole white sucker from the north (20.8 µg/kg) and south (11.2 µg/kg) shores of Lake Saint-Pierre in 2021, these levels were relatively lower than those observed in 2016 (Figure 4).
In contrast, the average concentrations of total PBDEs measured during the 2019–2024 period show a downward trend compared with the 2014–2016 period, particularly in whole white sucker on the north shore of Lake Saint-Pierre in 2021 (20.8 µg/kg) relative to 2016 (27.7 µg/kg), and on the south shore in 2021 (11.2 µg/kg) relative to 2016 (22 µg/kg).
Figure 4: Trends in average total PBDE concentrations in the flesh of walleye, northern
pike, yellow perch and whole white sucker in the St. Lawrence River for the 2014–2024
period.
Text description of Figure 4
Chart Type
- Vertical bar chart.
- Bar clusters represent individual monitoring stations, each including multiple sampling years.
Vertical Axis
- Measures total PBDE concentrations in micrograms per kilogram (µg/kg).
- Scale ranges from 0 to 40 µg/kg.
Horizontal Axis
- Displays sampling stations grouped by lake:
- Lake Saint‑François – south shore (stations 1 and 2)
- Lake Saint‑François – north shore (station 3)
- Lake Saint‑Louis – south shore (stations 5 and 6)
- Lake Saint‑Louis – north shore (station 7)
- Lake Saint‑Pierre – north shore (stations 13 and 14)
- Lake Saint‑Pierre – south shore (stations 15 and 16)
- Below each station are the sampling years (2014, 2016, 2019, 2021, 2022, or 2024 depending on the site).
Species Represented (Legend)
- Walleye: blue bars.
- Northern pike: dark grey bars.
- Yellow perch: red outlined bars.
- Whole‑body white sucker: orange bars.
Main Visual Observations
- Whole‑body white sucker (orange bars) shows the highest PBDE concentrations at nearly all stations.
- Very elevated values occur in:
- Lake Saint‑Pierre – north shore (stations 13 and 14) in 2016, 2019, and 2021, with concentrations often above 20 µg/kg and reaching close to 30 µg/kg in 2016.
- Lake Saint‑Pierre – south shore (stations 15 and 16) in 2016, 2019, and 2021, with concentrations mostly between 10 and 20 µg/kg.
- Lake Saint‑François – north shore (station 3) in 2014, with a peak near 8 µg/kg.
- Very elevated values occur in:
- Walleye (blue bars) shows low concentrations, generally between 1 and 4 µg/kg across stations and years.
- Northern pike (dark grey bars) presents low to moderate concentrations, mostly below 5 µg/kg.
- Yellow perch (red outlined bars) consistently exhibits the lowest PBDE concentrations, often ranging from 0 to 1 µg/kg and always far below the levels observed in white sucker.
- Concentrations vary substantially by lake, station, and year, with a strong contrast between white sucker and the other species.
General Trends
- The highest PBDE concentrations occur in Lake Saint‑Pierre, particularly at north‑shore stations.
- Whole‑body white sucker — a benthic species — shows much higher PBDE accumulation than the predatory species (walleye and northern pike).
- Predatory species display low to moderate concentrations, substantially lower than those observed for white sucker.
- Yellow perch consistently records the lowest PBDE levels across all stations.
Dioxins and furans
During the 2019–2024 period, the average concentrations of dioxins and furans in fish flesh, expressed as 2,3,7,8-TCDD toxic equivalents, remained below the European Union standard of 3.5 ng/kgFootnote 9 in all species across all areas. Values ranged from 0 to 0.044 ng/kg, except for an average value of 0.28 ng/kg in walleye on the north shore of Lake Saint‑François (Figure 5).
During the 2019–2024 period, the average concentrations of 2,3,7,8‑TCDD toxic equivalents in whole white sucker were all below the 0.66 ng/kgFootnote 5 criterion for the protection of fish-eating terrestrial wildlife, except on the north shore of Lake Saint-Pierre in 2021, where a concentration of 0.716 ng/kg was measured. The highest values were measured in whole white sucker on the north shore of Lake Saint-Pierre in 2019 and 2021 (0.525 ng/kg and 0.716 ng/kg) and on the north and south shores of Lake Saint-François in 2022 (0.5 ng/kg and 0.4 ng/kg; Figure 5).
Figure 5: Trends in average concentrations of total 2,3,7,8-TCDD toxic equivalents in the
flesh of walleye, northern pike, yellow perch and whole white sucker in the St. Lawrence
River for the 2014–2024 period.
Text description of Figure 5
Chart Type
- Comparative vertical bar chart.
- Bar clusters correspond to monitoring stations and include several sampling years.
Vertical Axis
- Displays toxic equivalents (TEQ) of dioxins in nanograms per kilogram (ng/kg).
- Scale ranges from 0 to 4.0 ng/kg.
Horizontal Axis
- Shows sampling stations grouped by lake:
- Lake Saint‑François – south shore (stations 1 and 2)
- Lake Saint‑François – north shore (station 3)
- Lake Saint‑Louis – south shore (stations 5 and 6)
- Lake Saint‑Louis – north shore (station 7)
- Lake Saint‑Pierre – north shore (stations 13 and 14)
- Lake Saint‑Pierre – south shore (stations 15 and 16)
- Sampling years shown beneath each station vary by site (2014, 2016, 2019, 2021, 2022, 2024).
Legend
- Walleye: blue bars
- Northern pike: dark grey bars
- Yellow perch: red outlined bars
- Whole‑body white sucker: orange bars
- Solid black line: European Union standard – 3.5 ng/kg
- Black dashed line: Wildlife protection criterion for piscivorous terrestrial species – 0.66 ng/kg TEQ
Main Visual Observations
- Whole‑body white sucker (orange bars) consistently exhibits the highest TEQ values across stations.
- Several values exceed the wildlife protection criterion of 0.66 ng/kg TEQ, including:
- Lake Saint‑Pierre – north shore (stations 13 and 14) in 2016, 2019, and 2021.
- Lake Saint‑Pierre – south shore (stations 15 and 16) in 2016 and 2019.
- Lake Saint‑François – north shore (station 3) in 2014.
- Some values approach or slightly exceed 1 ng/kg.
- Several values exceed the wildlife protection criterion of 0.66 ng/kg TEQ, including:
- Walleye (blue bars) shows low TEQ concentrations, typically between 0 and 0.5 ng/kg depending on the station and year.
- Northern pike (dark grey bars) shows very low concentrations at all stations, generally below 0.2 ng/kg.
- Yellow perch (red outlined bars) consistently displays the lowest TEQ concentrations, often near zero.
- No fish species exceeds the European Union standard of 3.5 ng/kg.
General Trends
- The highest TEQ concentrations occur in Lake Saint‑Pierre, particularly at the north‑shore stations.
- Whole‑body white sucker, a benthic species, shows the greatest accumulation of dioxin toxic equivalents.
- Predatory species such as walleye and northern pike show low to very low TEQ levels.
- Yellow perch maintains the lowest concentrations across all lakes and stations.
PFAS
Of the 37 PFAS analyzed in fish, only 4 were frequently detected. Perfluorooctane sulfonate (PFOS) alone accounted for an average of 85% of total PFAS concentrations. The other three main PFAS detected were perfluorodecane sulfonate (PFDS), perfluorodecanoic acid (PFDA) and perfluoroundecanoic acid (PFUnDA) (Figure 6). Currently, criteria exist only for PFOS, and there are no guidelines yet in Canada for the human consumption of fish; European Union standardsFootnote 9 vary by species and are difficult to apply to species in Quebec. However, preventive recommendations have been issued advising women planning a pregnancy, pregnant women and breastfeeding women to reduce their monthly consumption of freshwater fish from the St. Lawrence River by half.Footnote 3
From 2019 to 2024, 89% of the average PFOS concentrations, with the exception of three fish flesh samples from Lake Saint-Pierre, exceeded the MELCCFP criterion of 4.6 µg/kg for the protection of fish-eating terrestrial wildlife (mammals).Footnote 2 In the flesh of walleye, northern pike and yellow perch, the extent of exceedances ranged from 1.1 to 2.8 times the criterion, while in whole white sucker, exceedances ranged from 6 to 10 times the criterion. The criterion of 8.2 µg/kg for the protection of avian fauna was exceeded in the flesh of walleye, northern pike and yellow perch on nine occasions (33.3%), all located in Lake Saint-François and Lake Saint-Louis. For whole white sucker, 100% of concentrations exceeded the criterion of 8.2 µg/kg; however, no white sucker were captured in Lake Saint-Louis.
In fish flesh, average concentrations ranged from 5.2 to 13 µg/kg for walleye, 3.5 to 7.3 µg/kg for northern pike, and 1.4 to 12.8 µg/kg for yellow perch. The lowest concentration was measured in yellow perch on the north shore of Lake Saint-Pierre in 2021. For whole white sucker, concentrations ranged from 28 to 47.6 µg/kg, with the highest values measured on the south shore of Lake Saint-Pierre in 2019 (46.6 µg/kg) and 2021 (47.6 µg/kg). The next highest values were observed on the north shore of Lake Saint-Pierre in 2019 (37 µg/kg) and 2021 (31 µg/kg), as well as on the south shore (30 µg/kg) and north shore (28 µg/kg) of Lake Saint-François in 2022.
Figure 6: Trends in average PFOS, PFDS, PFDA and PFUnDA concentrations in the flesh
of walleye, northern pike, yellow perch and whole white sucker in the St. Lawrence River
for the 2019–2024 period.
Text description of Figure 6
Chart Type
- Stacked vertical bar chart.
- Each bar represents one fish species sampled at a specific station and year.
- Colored segments within each bar correspond to individual PFAS compounds.
Vertical Axis
- Total PFAS concentration in micrograms per kilogram (µg/kg).
- Scale from 0 to 60 µg/kg.
Horizontal Axis
- Stations grouped by lake:
- Lake Saint‑François – south shore (stations 1 and 2)
- Lake Saint‑François – north shore (station 3)
- Lake Saint‑Louis – south shore (stations 5 and 6)
- Lake Saint‑Louis – north shore (station 7)
- Lake Saint‑Pierre – north shore (stations 13 and 14)
- Lake Saint‑Pierre – south shore (stations 15 and 16)
- Beneath each station, the sampling years are shown (2014, 2016, 2019, 2021, 2022, or 2024 depending on the site).
- Species codes displayed under each bar:
- D: walleye
- B: northern pike
- P: yellow perch
- M: whole‑body white sucker
Legend
- PFOS: blue.
- PFDS: grey.
- PFDA: yellow.
- PFUnDA: orange.
- Dashed black line: Wildlife protection criterion for piscivorous terrestrial fauna – 8.2 µg/kg (avian).
- Dash‑dot black line: Wildlife protection criterion for piscivorous terrestrial fauna – 4.6 µg/kg (mammal).
Main Visual Observations
- PFOS (blue) overwhelmingly dominates total PFAS concentrations across all stations and species.
- Multiple bars exceed wildlife protection criteria, especially at:
- Lake Saint‑Pierre – north shore (stations 13 and 14) in 2019 and 2021, with totals reaching roughly 50 µg/kg.
- Lake Saint‑Pierre – south shore (stations 15 and 16) in 2016, 2019, and 2021, with totals around 30–40 µg/kg.
- Lake Saint‑François – north shore (station 3) in 2014, with a high value near 30 µg/kg.
- Multiple bars exceed wildlife protection criteria, especially at:
- Whole‑body white sucker (M) shows the highest PFAS totals for most stations and years.
- Other compounds (PFDS, PFDA, PFUnDA) contribute relatively small fractions to the totals:
- PFDS (grey) and PFDA (yellow) occur at low levels.
- PFUnDA (orange) appears at modest levels and contributes more noticeably at some Lake Saint‑Pierre stations.
- Predatory species (walleye and northern pike) generally have lower totals than white sucker.
- Yellow perch (P) consistently shows the lowest totals among the species sampled.
General Trends
- The highest PFAS totals are observed in:
- Lake Saint‑Pierre, particularly at north‑shore stations (13 and 14).
- Certain years at Lake Saint‑François, notably station 3.
- PFOS is the predominant contaminant across nearly all samples.
- Wildlife protection criteria for piscivorous fauna are frequently exceeded, most notably for white sucker.
Outlook
Stricter regulations and several government programs have significantly reduced the discharge of contaminants into the St. Lawrence–Great Lakes system. The available data indicate that concentrations of toxic substances are low enough to permit moderate or occasional consumption of fish from the St. Lawrence, allowing humans to reap the associated health benefits.
State of the St. Lawrence Monitoring Program
Environment and Climate Change Canada; Fisheries and Oceans Canada; Parks Canada
and the Ministère de l’Environnement, de la Lutte contre les changements climatiques, de
la Faune et des Parcs du Québec—and Stratégies Saint-Laurent, a non-governmental
organization that works actively with riverside communities, are pooling their expertise
and efforts to provide Canadians with information on the state of the St. Lawrence and the
long-term trends affecting it.
For more information about the State of the St. Lawrence Monitoring Program, please
consult our website: https://www.planstlaurent.qc.ca/en/developing-knowledge/state-st-lawrence-monitoring-program.