Recent research suggests contaminants of emerging concern (CECs) are widespread and environmentally relevant concentrations can impact fishes. However, little is known about impacts of CECs to long-lived or rare species. The objective of this study was to characterize CEC concentrations in lake sturgeon (Acipenser fulvescens) serum and gametes. Blood serum was collected non-lethally from lake sturgeon at four lower Great Lakes basin sites: Detroit, upper Niagara, lower Niagara, and St. Lawrence rivers; additionally, gametes were collected from lake sturgeon in the St. Lawrence River. Samples were analyzed for pharmaceuticals and personal care products (PPCPs) and polybrominated diphenyl ethers (PBDEs). Overall, 44 different PPCPs were identified in serum and gamete samples across sites, with 22 PPCPs identified in at least 25% of serum samples and three PPCPs identified in 25% of gamete samples. PPCP concentrations in serum and gametes ranged from 0.00208 to 130 ppb and 0.00538–190 ppb, respectively. NMDS ordination revealed differences in the presence and concentrations of PPCPs in lake sturgeon serum across sites, however, N,N-diethyl-meta-toluamide (DEET), hydrocortisone, benztropine, and amitriptyline were detected in at least one serum sample at all sites. Additionally, DEET, 10-hydroxy-amitriptyline, and sertraline were detected in ≥25% of gamete samples collected from the St. Lawrence River. Twenty-six PBDE congeners were identified in 25% of serum samples and 24 were identified in 25% of gamete samples. PBDEs in serum were present across all sites and in gametes of St. Lawrence River lake sturgeon, and total PBDE concentrations in serum and gametes ranged from 0.184 to 12.7 ppb and 0.0826–0.44 ppb, respectively. Managers of lake sturgeon populations may need to consider the impacts of CECs if reproductive, developmental, behavioral, growth effects, or mortality are observed in the Great Lakes basin or other areas that are impacted by increased exposures to PPCPs and PBDEs.

Harbours, as strategic places in tourism and transportation, are exposed to many sources of contamination. Assessing the quality of harbours sediment by guidelines and regulations does not reflect the actual level of contamination and the risk posed to aquatic ecosystems. Selection of an appropriate management technique for contaminated sediments in those strategic locations is crucial for the aquatic environment. The purpose of this study is to show that insufficient information, provided by sediment quality guidelines (SQGs) to identify the actual contaminants, could lead to a destructive or potentially ineffective decision for risk reduction in contaminated harbours. A comprehensive evaluation on physicochemical characteristics of sediment and water samples of a shallow harbour in St. Lawrence River was performed. Results of trace metal fractionation and risk assessment indicated that Cd and Pb were the contaminants that could pose a threat to aquatic ecosystem, although the SQG outcomes implied that Cu and Zn may cause an adverse effect on the benthic organisms. The results of multivariate statistical analysis demonstrated that the locations in the vicinity of the maintenance area contained the most contaminated sediment samples and require appropriate management. Antifouling paint particles and probably the runoff entering the harbour were the main sources of pollution. Among the diverse range of management strategies, the resuspension technique is suggested as a viable alternative in this specific case for shallow locations with contaminated sediments. A suitable management strategy could reduce the cost of remediation process by identifying the actual contaminated spots and also reduce the risk of remobilization of trace metals.

We have developed a local mass balance model for the St. Lawrence River near Cornwall, Ontario that describes the fate and transport of mercury in three forms, elemental, divalent, and methylated, in a five compartment environment (air, water, sediments, periphyton, and benthos). Our objective was to construct a steady-state mass balance model to determine the dominant sources and sinks of mercury in this environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river to develop the model. The inflow of mercury was the major source to this system, accounting for 0.42 mol month−1, or 95.5% of all mercury inputs, whereas outflow was 0.28 mol month−1, or 63.6% of all losses, and sediment deposition was 0.12 mol month−1, or 27.3% of all losses. Uncertainty estimates were greatest for advective fluxes in surface water, porewater, periphyton, and benthic invertebrates.

Contaminated sediments in the St. Lawrence River remain a difficult problem despite decreases in emissions. Here, sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and diffusion from the sediment to the overlying water was 17.5 ± 10.6 SE ng cm−2 yr−1 for THg and 3.8 ± 1.7 SE ng cm−2 yr−1 for MeHg. These fluxes were very small when compared to the particle-bound mercury flux accumulating in the sediment (183 ± 30 SE ng cm−2 yr−1). Studies have reported that fish from the westernmost site have higher Hg concentrations than fish collected from the other two sites of the Cornwall Area of Concern, which could not be explained by differences in the Hg flux or THg concentrations in sediments, but the highest concentrations of sediment MeHg, and the greatest proportions of MeHg to THg in both sediment and pore water were observed where fish had highest MeHg concentrations.

Research on per- and polyfluoroalkyl substances (PFAS) in freshwater ecosystems has focused primarily on legacy compounds and little is still known on the presence of emerging PFAS. Here, we investigated the occurrence of 60 anionic, zwitterionic, and cationic PFAS in a food web of the St. Lawrence River (Quebec, Canada) near a major metropolitan area. Water, sediments, aquatic vegetation, invertebrates, and 14 fish species were targeted for analysis. Levels of perfluorobutanoic acid (PFBA) in river water exceeded those of perfluorooctanoic acid (PFOA) or perfluorooctane sulfonate (PFOS), and a zwitterionic betaine was observed for the first time in the St. Lawrence River. The highest mean PFAS concentrations were observed for the benthopelagic top predator Smallmouth bass (Micropterus dolomieu, Σ₆₀PFAS ∼ 92 ± 34 ng/g wet weight whole-body) and the lowest for aquatic plants (0.52–2.3 ng/g). Up to 33 PFAS were detected in biotic samples, with frequent occurrences of emerging PFAS such as perfluorobutane sulfonamide (FBSA) and perfluoroethyl cyclohexane sulfonate (PFECHS), while targeted ether-PFAS all remained undetected. PFOS and long-chain perfluorocarboxylates (C10–C13 PFCAs) dominated the contamination profiles in biota except for insects where PFBA was predominant. Gammarids, molluscs, and insects also had frequent detections of PFOA and fluorotelomer sulfonates, an important distinction with fish and presumably due to different metabolism. Based on bioaccumulation factors >5000 and trophic magnification factors >1, long-chain (C10–C13) PFCAs, PFOS, perfluorodecane sulfonate, and perfluorooctane sulfonamide qualified as very bioaccumulative and biomagnifying. Newly monitored PFAS such as FBSA and PFECHS were biomagnified but moderately bioaccumulative, while PFOA was biodiluted.

The occurrence and spatial distribution of selected pesticides were investigated along a 200-km reach of the St. Lawrence River (SLR) and tributaries in Quebec, Canada. Surface water samples (n = 68) were collected in the summer 2017 and analyzed for glyphosate, atrazine (ATZ), 8 systemic insecticides (acetamiprid, clothianidin, dinotefuran, fipronil, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam) and some metabolites. Overall, 99% of the surface water samples were positive to at least one of the targeted pesticides. The most recurrent compounds were glyphosate (detection frequency: 84%), ATZ (82%), thiamethoxam (59%), desethylatrazine (DEA: 47%), and clothianidin (46%). Glyphosate displayed variable levels (4–3,000 ng L−1), with higher concentrations in south tributaries (e.g., Nicolet and Yamaska). In positive samples, the sum of ATZ and DEA varied between 5 and 860 ng L−1, and the sum of 6 priority neonicotinoids between 1.5 and 115 ng L−1. From Repentigny to the Sorel Islands, the spatial distribution of pesticides within the St. Lawrence River was governed by the different upstream sources (i.e., Great Lakes vs. Ottawa River) due to the limited mixing of the different water masses. Cross-sectional patterns revealed higher concentrations of glyphosate and neonicotinoids in the north portions of transects, while the middle and south portions showed higher levels of atrazine. In Lake St. Pierre and further downstream, cross-sections revealed higher levels of the targeted pesticides near the southern portions of the SLR. This may be due to the higher contributions from south shore tributaries impacted by major agricultural areas, compared to north shore tributaries with forest land and less cropland use. Surface water samples were compliant with guidelines for the protection of aquatic life (chronic effects) for glyphosate and atrazine. However, 31% of the samples were found to surpass the guideline value of 8.3 ng L−1 for the sum of six priority neonicotinoids.

The zebra mussel, Dreissena polymorpha constitutes an extensively used sentinel species for biomonitoring in European and North American freshwater systems. However, this invasive species is gradually replaced in freshwater ecosystem by Dreissena bugensis, a closely related dreissenid species that shares common morphological characteristics but possess some physiological differences. However, few are known about differences on more integrated physiological processes that are generally used as biomarkers in biological monitoring studies. Declining of zebra mussel populations raises the question of the sustainability of using one or both species indifferently to maintain the quality of environmental pollution monitoring data. In our study, we performed a field comparative study measuring immune-related markers and bioaccumulation of PCBs, PAHs and PBDEs in sympatrically occurring mussel populations from three sites of the St. Lawrence River. For tested organisms, species were identified using RFLP analysis. Measurement of bioaccumulated organic compounds indicated a higher accumulation of PCBs and PBDEs in D. bugensis soft tissues compared to D. polymorpha while no differences were noticed for PAHs. Results of hemocytic parameters highlighted that differences of hemocyte distributions were associated to modulations of phagocytic activities. Moreover, marked differences occurred in measurement of hemocytic oxidative activity, indicating divergences between the two species for ROS regulation strategies. This physiological characteristic may deeply influence species responses facing environmental or pollution related stress and induce bias if the two species are not differentiated in further biomarker or bioaccumulation measurement-based studies.

Environmental contaminant monitoring traditionally relies on targeted analysis, and very few tools are currently available to monitor “unexpected” or “unknown” compounds. In the present study, a non-targeted workflow (suspect screening) was developed to investigate plastic-related chemicals and other environmental contaminants in a top predator freshwater fish species, the northern pike, from the St. Lawrence River, Canada. Samples were extracted using sonication-assisted liquid extraction and analyzed by high performance liquid chromatography coupled with quadrupole time of flight mass spectrometry (HPLC-QTOF-MS). Ten bisphenol compounds were used to test the analytical performances of the method, and satisfactory results were obtained in terms of instrumental linearity (r2 > 0.97), recoveries, (86.53–119.32%), inter-day precision and method detection limits. The non-targeted workflow data processing parameters were studied, and the peak height filters (peak filtering step) were found to influence significantly the capacity to detect and identify trace chemicals in pike muscle extracts. None of the ten bisphenol analogues were detected in pike extracts suggesting the absence of accumulation for these chemicals in pike muscle. However, the non-targeted workflow enabled the identification of diethyl phthalate (DEP) and perfluorooctanesulfonic acid (PFOS) in pike extracts. This approach thus can be also applied to various contaminants in other biological matrices and environmental samples.

Within wetlands, epiphytes and macrophytes play an important role in storage and transfer of metals, through the food web. However, there is a lack of information about spatial and temporal changes in their metal levels, including those of mercury (Hg), a key priority contaminant of aquatic systems. We assessed total mercury (THg) and methylmercury (MeHg) concentrations of epiphyte/macrophyte complexes in Lake St. Pierre, a large fluvial lake of the St. Lawrence River (Québec, Canada). THg and MeHg concentrations were ten fold higher in epiphytes than in macrophytes. THg concentrations in epiphytes linearly decreased as a function of the autotrophic index, suggesting a role of algae in epiphyte Hg accumulation, and % of MeHg in epiphytes reached values as high as 74%. Spatio-temporal variability in THg and MeHg concentrations in epiphytes and macrophytes were influenced by water temperature, available light, host species, water level, dissolved organic carbon and dissolved oxygen.

Lake St. Pierre (LSP), constituted of a 120 km² stretching of the St. Lawrence River (Southern Québec), hosts the largest freshwater fishery industry in Canada. The lake drains, through its main tributaries, an important area of agrarian land and was subjected to intense industrial activities in the past century. In this paper, we present (1) an estimation of the seasonal aquatic mercury (Hg) inputs to LSP from the St-Lawrence River and two major tributaries; (2) a reconstruction, by the analysis of sediment cores, of the historic inputs of Hg into LSP and in a large riparian wetland, Bay St. François. Our results indicate that the aquatic Hg inputs to LSP (290 kg Hg between April 2003 and April 2004) are moderately elevated with most of the inputs occurring from the St. Lawrence River, either in spring or early winter, during high flow episodes. The sediment profiles suggest a recent decrease in Hg inputs, likely attributable to improvements of industrial practices. The observed perturbation of the surface sediments give evidence of an active hydrodynamic regime, suggesting that LSP could only act as a transitory system for suspended sediment and Hg, with seasonal accumulation and recurrent re-suspension resulting from changes in the hydrodynamic regime. Finally, we observed positive MeHg fluxes from the sediment to the water at different seasons in Bay St. François. However, Hg levels in fish like walleyes of LSP are reported to be low, which could be explained by faster fish growth rates following in part intense fishing pressure in LSP.