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Demand for unconventional crude oils continues to drive the production of diluted bitumen (dilbit) within Western Canada, promoting increased transport volumes across the extensive 700,000 km pipeline system of Canada and the USA. Despite this vast extent of terrestrial transport, the current understanding of the behavior and fate of spilled dilbit within shallow groundwater systems is limited. To this end, oil spill experiments with a dilbit (Cold Lake Blend) and a physicochemically similar conventional heavy crude oil (Conventional Heavy Blend) were conducted for 104 days in large soil columns (1 m height × 0.6 m diameter) engineered to model contaminant transport in the unsaturated (vadose) zone. Around two-fold greater concentrations and 6-41 % faster rates of vadose zone transport of benzene, toluene, ethylbenzene and xylenes (BTEX) and polycyclic aromatic compounds (PACs) were observed in the dilbit- compared to conventional heavy crude-contaminated columns. As determined by Orbitrap mass spectrometry, the O x S x species abundances in the acid extractable organics (AEOs) fraction of column leachate from both oil types increased over time, ostensibly due to microbial degradation of petroleum. Bioaccumulation of petroleum constituents in fathead minnow (Pimephales promelas) larvae exposed to contaminated leachate was confirmed through the induction of developmental malformations lasting up to 34 days and increased abundance of cyp1a mRNA observed throughout the experiment. Toxicity was comparable between the two oils but could not be fully attributed to metals, BTEX, PACs or AEOs, implying the presence of uncharacterized teratogens capable of being transported within the vadose zone following terrestrial dilbit and conventional heavy crude oil surface spills., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2024. Published by Elsevier Ltd. All rights reserved.)

Increasing global demands for oils are fueling the production of diluted bitumen (DB) from Canada's oil sands region. More weathered than conventional crude (CC) oils, Alberta bitumen is often diluted with lighter petroleum oils to reduce density and viscosity to meet pipeline specifications for transportation. Being a heavy oil product that is transported in large volumes across Canada and the USA, there has been interest to compare its behavior and toxicity characteristics when spilled to those of CC. To determine the influence of environmental weathering upon DB following a freshwater spill, we conducted separate controlled spills of Cold Lake Blend DB and Mixed Sweet Blend light CC oil in a mesocosm spill-tank system at 24 °C with wave-action for 56 days. DB-contaminated waters remained acutely lethal for a period of 14 days to early life stage fathead minnows (Pimephales promelas) exposed during embryologic development, while CC was lethal for 1 day. However, concentrations of mono- and polycyclic aromatic compounds, often claimed to be principally responsible for the acute and chronic toxicity of crude oils, were consistently higher in CC water compared to DB. Elevated aromatic concentrations in CC water correlated with higher prevalences of developmental malformations, reduced heart and growth rates, and impacts on the aryl hydrocarbon receptor pathway. Organic acids were measured over the course of the studies and O 2 containing naphthenic acids were present at greater relative abundances in DB- compared to CC-contaminated water, with their attenuation correlating with reduced acute and sublethal toxicity. Furthermore, organic acid degradation products accumulated with time and likely contributed to the consistently sublethal toxicity of the weathered oils throughout the experiment. Improved characterization of the fractions including organic acids and those organic compounds found within the unresolved complex mixture of fresh and weathered crude oils is necessary to adequately understand and prepare for the risks that accidental petroleum spills pose to aquatic resources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

The oil sands region in Western Canada is one of the world's largest proven oil reserves. To facilitate pipeline transport, highly viscous oil sands bitumen is blended with lighter hydrocarbon fractions to produce diluted bitumen (dilbit). Anticipated increases in dilbit production and transport raise the risk of inland spills. To understand the behaviour of dilbit in the unsaturated or vadose zone following a surface spill, we ran parallel dilbit and conventional heavy crude exposures, along with an untreated control, using large soil-filled columns over 104 days. Phospholipid fatty acids (PLFAs), biomarkers for the active microbial population, were extracted from column soil cores. Stable carbon isotope contents (δ 13 C) of individual PLFAs and radiocarbon contents (Δ 14 C) of bulk PLFAs were characterized over the course of the experiment. The Δ 14 C PLFA values in soils impacted by dilbit (-221.1 to -54.7‰) and conventional heavy crude (-259.4 to -97.9‰) indicated similar levels of microbial uptake of fossil carbon. In contrast, Δ 14 C PLFA values in the control column (-46.1 to +53.7‰) reflected assimilation of more recently fixed organic carbon. Sequencing of 16S ribosomal RNA genes extracted from soil cores revealed a significant increase in the relative abundance of Polaromonas, a known hydrocarbon-degrader, following exposure to both types of oil. This study demonstrates that in the first several months following a surface spill, dilbit has a similar potential for biodegradation by a native shallow subsurface microbial community as conventional heavy crude oil., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2023. Published by Elsevier Ltd. All rights reserved.)

The pesticide 3-trifluoromethyl-4-nitrophenol (TFM) is applied to rivers and streams draining into the Laurentian Great Lakes to control populations of invasive sea lamprey ( Petromyzon marinus ), which are ongoing threats to fisheries during the lamprey's hematophagous, parasitic juvenile life stage. While TFM targets larval sea lamprey during treatments, threatened populations of juvenile lake sturgeon ( Acipenser fulvescens ), particularly young-of-the-year (<100 mm in length), may be adversely affected by TFM when their habitats overlap with larval sea lamprey. Exposure to TFM causes marked reductions in tissue glycogen and high energy phosphagens in lamprey and rainbow trout ( Oncorhynchus mykiss ) by interfering with oxidative ATP production in the mitochondria. To test that environmentally relevant concentrations of TFM would similarly affect juvenile lake sturgeon, we exposed them to the larval sea lamprey minimum lethal concentration (9-h LC 99.9 ), which mimicked concentrations of a typical lampricide application and quantified energy stores and metabolites in the carcass, liver and brain. Exposure to TFM reduced brain ATP, PCr and glycogen by 50-60%, while lactate increased by 45-50% at 6 and 9 h. A rapid and sustained depletion of liver glucose and glycogen of more than 50% was also observed, whereas the respective concentrations of ATP and glycogen were reduced by 60% and 80% after 9 h, along with higher lactate and a slight metabolic acidosis (~0.1 pH unit). We conclude that exposure to environmentally relevant concentrations of TFM causes metabolic disturbances in lake sturgeon that can lead to impaired physiological performance and, in some cases, mortality. Our observations support practices such as delaying TFM treatments to late summer/fall or using alternative TFM application strategies to mitigate non-target effects in waters where lake sturgeon are present. These actions would help to conserve this historically and culturally significant species in the Great Lakes., (© The Author(s) 2021. Published by Oxford University Press and the Society for Experimental Biology.)

The toxic unit and additive index approaches were used to understand how 2 pesticides, 3-trifluoromethyl-4-nitrophenol (TFM) and 2,5-dichloro-4-nitrosalicylanilide (niclosamide; Nic), interact in mixtures. Our first objective was to determine whether the interaction was strictly additive or greater than additive at doses comparable to those used to control invasive sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes, and our second was to compare the utility of the toxic unit and additive index models for determining how TFM and Nic interacted. Typically, TFM is mixed with Nic (1-2%, w/v) to increase its potency and reduce TFM use. However, there is little information on how the 2 chemicals interact. Using a well-studied, resident nontarget fish, the rainbow trout (Oncorhynchus mykiss), we conducted toxicity tests with TFM, Nic, and TFM:Nic (100:1, w/v; TFM/1% Nic) mixtures over 12 h to determine if the interaction was strictly additive, less than additive (antagonistic), or greater than additive (synergistic). The toxic unit and additive index approaches indicated synergistic interactions at environmentally relevant concentrations, suggesting that both are valid approaches for predicting how TFM and Nic interact. The toxic unit approach was simpler to conceptualize and to calculate, and we recommend that it be used when describing how TFM and Nic, and other similar organic compounds, interact with each other in aquatic ecosystems. Environ Toxicol Chem 2021;40:1419-1430. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC., (© 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.)

Ecological risk assessments (ERAs) of polycyclic aromatic compounds (PACs), as single congeners or in mixtures, present technical challenges that raise concerns about their accuracy and validity for Canadian environments. Of more than 100,000 possible PAC structures, the toxicity of fewer than 1% have been tested as individual compounds, limiting the assessment of complex mixtures. Because of the diversity in modes of PAC action, the additivity of mixtures cannot be assumed, and mixture compositions change rapidly with weathering. In vertebrates, PACs are rapidly oxygenated by cytochrome P450 enzymes, often to metabolites that are more toxic than the parent compound. The ability to predict the ecological fate, distribution and effects of PACs is limited by toxicity data derived from tests of a few responses with a limited array of test species, under optimal laboratory conditions. Although several models are available to predict PAC toxicity and rank species sensitivity, they were developed with data biased by test methods, and the reported toxicities of many PACs exceed their solubility limits. As a result, Canadian Environmental Quality Guidelines for a few individual PACs provide little support for ERAs of complex mixtures in emissions and at contaminated sites. These issues are illustrated by reviews of three case studies of PAC-contaminated sites relevant to Canadian ecosystems. Interactions among ecosystem characteristics, the behaviour, fate and distribution of PACs, and non-chemical stresses on PAC-exposed species prevented clear associations between cause and effect. The uncertainties of ERAs can only be reduced by estimating the toxicity of a wider array of PACs to species typical of Canada's diverse geography and environmental conditions. Improvements are needed to models that predict toxicity, and more field studies of contaminated sites in Canada are needed to understand the ecological effects of PAC mixtures., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The pesticide, 3-trifluoromethyl-4-nitrophenol (TFM), is used to control invasive sea lamprey ( Petromyzon marinus ) populations in the Laurentian Great Lakes. Applied to infested tributaries, it is most toxic to larval sea lamprey, which have a low capacity to detoxify TFM. However, TFM can be toxic to lake sturgeon ( Acipenser fulvescens ), whose populations are at risk throughout the basin. They are most vulnerable to TFM in early life stages, with the greatest risk of non-target mortality occurring in waters with high alkalinity. We quantified TFM toxicity and used radio-labelled TFM ( 14 C-TFM) to measure TFM uptake rates in lake sturgeon in waters of different pH and alkalinity. Regardless of pH or alkalinity, TFM uptake was 2-3-fold higher in young-of-the-year (YOY) than in age 1-year-plus (1+) sturgeon, likely due to higher mass-specific metabolic rates in the smaller YOY fish. As expected, TFM uptake was highest at lower (pH 6.5) versus higher (pH 9.0) pH, indicating that it is taken up across the gills by diffusion in its unionized form. Uptake decreased as alkalinity increased from low (~50 mg L -1 as CaCO 3 ) to moderate alkalinity (~150 mg L -1 as CaCO 3 ), before plateauing at high alkalinity (~250 mg L -1 as CaCO 3 ). Toxicity curves revealed that the 12-h LC 50 and 12-h LC 99.9 of TFM to lake sturgeon were in fact higher (less toxic) than in sea lamprey, regardless of alkalinity. However, in actual treatments, 1.3-1.5 times the minimum lethal TFM concentration (MLC = LC 99.9 ) to lamprey is applied to maximize mortality, disproportionately amplifying TFM toxicity to sturgeon at higher alkalinities. We conclude that limiting TFM treatments to late summer/early fall in waters of moderate-high alkalinity, when lake sturgeon are larger with lower rates of TFM uptake, would mitigate non-target TFM effects and help conserve populations of these ancient, culturally important fishes., (© The Author(s) 2019. Published by Oxford University Press and the Society for Experimental Biology.)