Oil sands process-affected water impairs the olfactory system of rainbow trout (Oncorhynchus mykiss)

A Light Touch: Solar Photocatalysis Detoxifies Oil Sands Process-Affected Waters Prior to Significant Treatment of Naphthenic Acids

Environmental reclamation of Canada's oil sands tailings ponds is among the single largest water treatment challenges globally. The toxicity of oil sands process-affected water (OSPW) has been associated with its dissolved organics, a complex mixture of naphthenic acid fraction components (NAFCs). Here, we evaluated solar treatment with buoyant photocatalysts (BPCs) as a passive advanced oxidation process (P-AOP) for OSPW remediation. Photocatalysis fully degraded naphthenic acids (NAs) and acid extractable organics (AEO) in 3 different OSPW samples. However, classical NAs and AEO, traditionally considered among the principal toxicants in OSPW, were not correlated with OSPW toxicity herein. Instead, nontarget petroleomic analysis revealed that low-polarity organosulfur compounds, composing <10% of the total AEO, apparently accounted for the majority of waters' toxicity to fish, as described by a model of tissue partitioning. These findings have implications for OSPW release, for which a less extensive but more selective treatment may be required than previously expected.

Examining the immunotoxicity of oil sands process affected waters using a human macrophage cell line

Oil sands process affected water (OSPW) is produced during the surface mining of the oil sands bitumen deposits in Northern Alberta. OSPW contains variable quantities of organic and inorganic components causing toxic effects on living organisms. Advanced Oxidation Processes (AOPs) are widely used to degrade toxic organic components from OSPW including naphthenic acids (NAs). However, there is no established biological procedure to assess the effectiveness of the remediation processes. Our previous study showed that human macrophage cells (THP-1) can be used as a bioindicator system to evaluate the effectiveness of OSPW treatments through examining the proinflammatory gene transcription levels. In the present study, we investigated the immunotoxicological changes in THP-1 cells following exposure to untreated and AOP-treated OSPW. Specifically, using proinflammatory cytokine protein secretion assays we showed that AOP treatment significantly abrogates the ability of OSPW to induce the secretion of IL-1β, IL-6, IL-8, TNF-α, IL-1Ra and MCP-1. By measuring transcriptional activity as well as surface protein expression levels, we also showed that two select immune cell surface markers, CD40 and CD54, were significantly elevated following OSPW exposure. However, AOP treatments abolished the immunostimulatory properties of OSPW to enhance the surface expression of these immune proteins. Finally, a transcriptome-based approach was used to examine the proinflammatory effects of OSPW as well as the abrogation of immunotoxicity following AOP treatments. Overall, this research shows how a human macrophage cell-based biomonitoring system serves as an effective in vitro tool to study the immunotoxicity of OSPW samples before and after targeted remediation strategies.

Interaction of the Olfactory System of Rainbow Trout (Oncorhynchus mykiss) with Diltiazem

Diltiazem is ubiquitously prescribed and has been reported in many effluents and freshwater bodies. Being a calcium channel blocker, diltiazem could disrupt the function of the sensory and central nervous systems. In the present study, using electro-olfactography (EOG), we investigated the interaction of diltiazem with the olfactory sensory neurons (OSNs) of rainbow trout by looking into the detection threshold and effects of immediate (~5 min) and acute (24 h) exposure to diltiazem at 6.6, 66, and 660 µg/L. We also studied the accumulation of the drug in fish plasma and whole body. Brief exposure to diltiazem impaired the OSN response to a chemosensory stimulus in a concentration-dependent manner at 6.6 µg/L and higher, whereas OSNs exposed for 24 h only displayed an impairment at 660 µg/L. Chemical analysis showed that the accumulation of diltiazem in fish plasma and body correlated with the EOG response because it was 10 times higher in the group that displayed a significant impairment (660 µg/L) compared to the other 2 groups (6.6, 66 µg/L). This correlation suggests that the impact of diltiazem on OSNs might partially be through the accumulated molecules in the fish bloodstream. Fish did not detect diltiazem as a sensory stimulus even at concentrations as high as 660 µg/L; thus, fish could potentially swim toward or fail to escape harmful concentrations of diltiazem. Environ Toxicol Chem 2022;41:554-550. © 2020 SETAC.

Physiological Responses of Fish to Oil Spills

Millions of tons of oil are spilled in aquatic environments every decade, and this oil has the potential to greatly impact fish populations. Here, we review available information on the physiological effects of oil and polycyclic aromatic hydrocarbons on fish. Oil toxicity affects multiple biological systems, including cardiac function, cholesterol biosynthesis, peripheral and central nervous system function, the stress response, and osmoregulatory and acid-base balance processes. We propose that cholesterol depletion may be a significant contributor to impacts on cardiac, neuronal, and synaptic function as well as reduced cortisol production and release. Furthermore, it is possible that intracellular calcium homeostasis-a part of cardiotoxic and neuronal function that is affected by oil exposure-may be related to cholesterol depletion. A detailed understanding of oil impacts and affected physiological processes is emerging, but knowledge of their combined effects on fish in natural habitats is largely lacking. We identify key areas deserving attention in future research.

Chronic Toxicity of Surface Water from a Canadian Oil Sands End Pit Lake to the Freshwater Invertebrates Chironomus dilutus and Ceriodaphnia dubia

Permanent reclamation of tailings generated by surface mining in the Canadian oil sands may be achieved through the creation of end pit lakes (EPLs) in which tailings are stored in mined-out pits and capped with water. However, these tailings contain high concentrations of dissolved organics, metals, and salts, and thus surface water quality of EPLs is a significant concern. This is the first study to investigate the chronic toxicity of surface water from Base Mine Lake (BML), the Canadian oil sands first large-scale EPL, to aquatic invertebrates that play a vital role in the early development of aquatic ecosystems (Chironomus dilutus and Ceriodaphnia dubia). After exposure of C. dilutus larvae for 23 days and C. dubia neonates for 8 days, no mortality was observed in any treatment with whole BML surface water. However, the emergence of C. dilutus adults was delayed by nearly 1 week, and their survival was significantly reduced (36%) compared with the controls. Reproduction (fecundity) of C. dubia was reduced by 20% after exposure to 2014 BML surface water; however, the effect was not observed after exposure to BML surface water collected a year later in 2015. Despite some adverse effects, the results of this study indicate that BML surface water quality is improving over time and is able to support certain salt-tolerant aquatic organisms. Because salinity within BML will persist for decades without manual intervention, the ecological development of the lake will likely resemble that of a brackish or estuarine ecosystem with reduced diversity.

Exposure to Crude Oil from the Deepwater Horizon Oil Spill Impairs Oil Avoidance Behavior without Affecting Olfactory Physiology in Juvenile Mahi-Mahi (Coryphaena hippurus)

The understanding of the detection threshold and behavioral response of fishes in response to crude oil is critical to predicting the effects of oil spills on wild fish populations. The Deepwater Horizon oil spill released approximately 4.9 million barrels of crude oil into the northern Gulf of Mexico in 2010, overlapping spatially and temporally with the habitat of many pelagic fish species. Yet, it is unknown whether highly migratory species, such as mahi-mahi (Coryphaena hippurus), might detect and avoid oil contaminated waters. We tested the ability of control and oil-exposed juvenile mahi-mahi (15-45 mm) to avoid two dilutions of crude oil in a two-channel flume. Control fish avoided the higher concentration (27.1 μg/L Σ₅₀PAH), while oil-exposed (24 h, 18.0 μg/L Σ₅₀PAH) conspecifics did not. Electro-olfactogram (EOG) data demonstrated that both control and oil-exposed (24 h, 14.5 μg/L Σ₅₀PAH) juvenile mahi-mahi (27-85 mm) could detect crude oil as an olfactory cue and that oil-exposure did not affect the EOG amplitude or duration in response to oil or other cues. These results show that a brief oil exposure impairs the ability of mahi-mahi to avoid oil and suggests that this alteration likely results from injury to higher order central nervous system processing rather than impaired olfactory physiology.

Damsels in Distress: Oil Exposure Modifies Behavior and Olfaction in Bicolor Damselfish (Stegastes partitus)

In fishes, olfactory cues evoke behavioral responses that are crucial to survival; however, the receptors, olfactory sensory neurons, are directly exposed to the environment and are susceptible to damage from aquatic contaminants. In 2010, 4.9 million barrels of crude oil were released into the northern Gulf of Mexico from the Deepwater Horizon disaster, exposing marine organisms to this environmental contaminant. We examined the ability of bicolor damselfish (Stegastes partitus), exposed to the water accommodated fraction (WAF) of crude oil, to respond to chemical alarm cue (CAC) using a two-channel flume. Control bicolor damselfish avoided CAC in the flume choice test, whereas WAF-exposed conspecifics did not. This lack of avoidance persisted following 8 days of control water conditions. We then examined the physiological response to CAC, brine shrimp rinse, bile salt, and amino acid cues using the electro-olfactogram (EOG) technique and found that WAF-exposed bicolor damselfish were less likely to detect CAC as an olfactory cue but showed no difference in EOG amplitude or duration compared to controls. These data indicate that a sublethal WAF exposure directly modifies detection and avoidance of CAC beyond the exposure period and may suggest reduced predator avoidance behavior in oil-exposed fish in the wild.