Chronic toxicity of oil sands tailings pond sediments to early life stages of fathead minnow (Pimephales promelas)

Pre-treatment with extraction solvent yields higher recovery: Method optimization for efficient determination of polycyclic aromatic hydrocarbons in organic-rich fine-textured wastes

Fluid fine tailings (FFT) contain numerous organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Growing concerns of PAH toxicity warrants monitoring for environmental consequences and natural attenuation. Conventional Soxhlet extraction yields low (∼50%-60%) recovery of PAHs (naphthalene, phenanthrene, pyrene, dibenzofuran, fluorene, and dibenzothiophene) from FFT, which impedes accurate PAH determination. Therefore, an optimized method was developed in this study that included (1) selection of a suitable solvent, (2) enhancement of PAH recovery by pretreatment, (3) determination of optimal extraction time, and (4) optimization of sample cleanup procedure. Results showed that (1) dichloromethane (DCM) recovered significantly higher masses of PAHs from FFT than hexane (HEX), cyclohexane, or their mixtures with DCM; (2) pretreatment of FFT with DCM significantly improved PAHs recovery using either Soxhlet or mechanical shaking methods; (3) a 24-h Soxhlet extraction with pretreatment yielded the highest and the most consistent PAH recoveries; (4) DCM proved to be an efficient eluent for sample cleanup in silica gel column; and (5) consecutive cleanups with additional silica gel column removed excessive impurities without PAH losses. Therefore, this study developed an optimized method for PAH recoveries from FFT, achieving a pooled mean recovery of ∼94%. This method is applicable to other organic-rich fine-textured wastes such as sludge and clay sediments.

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.

Sources, spatial-distributions and fluxes of PAH-contaminated dusts in the Athabasca oil sands region

Atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) has increased in northern Alberta, Canada, due to industrial development in the Athabasca oil sands region (AOSR). However, the sources, summertime deposition fluxes and associated spatial patterns are poorly characterized, and the magnitude of contamination has not been directly contrasted with comparable measurements around large Canadian cities. PAHs were measured in Sphagnum moss collected from 30 bogs in the AOSR and compared with reference moss collected from various remote, rural and near-urban sites in Alberta and Ontario. At all 39 locations, strong correlations between depositional fluxes of PAHs and accumulation rates of ash (n = 117, r = 0.877, p < 0.001) implied that the main source of PAHs to moss was atmospheric deposition of particles. Average PAH concentrations at near-field AOSR sites (mean [SD], 62.4 [24.3] ng/g) were significantly higher than at far-field AOSR sites (44.9 [20.8] ng/g; p = 0.038) or the 7 reference sites in Alberta (20.6 [3.5] ng/g; p < 0.001). In fact, average PAH concentrations across the entire AOSR (7,850 km2) were approximately twice as high as in London, Ontario, or near petroleum upgrading and major traffic corridors in Edmonton, Alberta. A chemical mass balance model estimated that both delayed petcoke (33 % of PAHs) and fine tailings (38 % of PAHs) were the major sources of PAHs in the AOSR. Over the 2015 summer growing season, we estimate that 101-110 kg of PAHs (on 14,300-17,300 tonnes of PAH-containing dusts) were deposited to the AOSR within a 50 km radius of surface mining. Given that the highest PAH deposition was to the northern quadrant of the AOSR, which includes the First Nations community of Fort MacKay, further dust control measures should be considered to protect human and environmental health in the region.

Microbial community structural and functional differentiation in capped thickened oil sands tailings planted with native boreal species

The oil sands mining operations in Alberta have produced billions of m³ of tailings which must be reclaimed and integrated into various mine closure landforms, including terrestrial landforms. Microorganisms play a central role in nutrient cycling during the reclamation of disturbed landscapes, contributing to successful vegetation restoration and long-term sustainability. However, microbial community succession and response in reconstructed and revegetated tailings remain largely unexplored. This study aimed to monitor the structural and functional responses of microbial communities in tailings subjected to different capping and vegetation strategies over two growing seasons (GS). To achieve this, a column-based greenhouse experiment was conducted to investigate microbial communities in tailings that were capped with a layer (10 or 30 cm) of peat-mineral mix (PMM) and planted with either upland or wetland communities. DNA metabarcoding analysis of the bacterial 16S rRNA gene and fungal ITS2 region as well as shotgun metagenomics were used to asses the impact of treatments on microbial taxonomy and functions, respectively. Results showed that tailings microbial diversity and community composition changed considerably after two GS compared to baseline samples, while communities in the PMM capping layer were much more stable. Likewise, several microbial functions were significantly enriched in tailings after two GS. Interestingly, the impact of capping on bacterial communities in tailings varied depending on the plant community, leading to a higher number of differentially abundant taxa and to a decrease in Shannon diversity and evenness in the upland treatment but not in the wetland treatment. Moreover, while capping in the presence of wetland vegetation increased the energy-related metabolic functions (carbon, nitrogen, and sulfur), these functions were depleted by capping in the upland treatment. Fungi represented a small proportion of the microbial community in tailings, but the relative abundance of several taxa changed over time, while the capping treatments favored the growth of some beneficial taxa, notably the root endophyte Serendipita, in both upland and wetland columns. The results suggest that selecting the right combination of capping material and vegetation type may contribute to improve below-ground microbial processes and sustain plant growth in harsh environments such as oil sands tailings.

Responses of Wild Finescale Dace (Phoxinus neogaeus) to Experimental Spills of Cold Lake Blend Diluted Bitumen at the International Institute for Sustainable Development-Experimental Lakes Area, Northwestern Ontario

Pipelines carrying diluted bitumen (dilbit) traverse North America and may result in dilbit release into sensitive freshwater ecosystems. To better understand the potential effects of a freshwater oil release, the Boreal-lake Oil Release Experiment by Additions to Limnocorrals project at the International Institute for Sustainable Development-Experimental Lakes Area (Ontario, Canada) modeled seven dilbit spills contained within a 10-m diameter of littoral limnocorrals in a boreal lake. Wild finescale dace (Phoxinus neogaeus) were released in the limnocorrals 21 days after oil addition and remained there for 70 days. Dilbit volumes covered a large range representing a regression of real spill sizes and total polycyclic aromatic compounds (TPAC) between 167 ng L^-1  day^-1 and 1989 ng L^-1  day^-1 . We report the effects of chronic exposure on reproductive potential as well as physiological responses in the gallbladder and liver. In exposures >1000 ng L^-1  day^-1 , there was a significant decrease in fish retrieval, culminating in zero recapture from the three highest treatments. Among the fish from the limnocorrals with lower levels of TPAC (<500 ng L^-1  day^-1 ), effects were inconsistent. Gallbladder bile fluorescence for a naphthalene metabolite was significantly different in fish from the oil-exposed limnocorrals when compared to the lake and reference corral, indicating that fish in these lower exposures were interacting with dilbit-derived polycyclic aromatic compounds. There were no significant differences in condition factor, somatic indices, or hepatocyte volume indices. There were also no significant changes in the development of testes or ovaries of exposed dace. The results from the present study may serve to orient policymakers and emergency responders to the range of TPAC exposures that may not significantly affect wild fish. Environ Toxicol Chem 2022;41:2745-2757. © 2022 SETAC.

Understanding Willow Transcriptional Response in the Context of Oil Sands Tailings Reclamation

One of the reclamation objectives for treated oil sands tailings (OST) is to establish boreal forest communities that can integrate with the surrounding area. Hence, selection of appropriate soil reclamation cover designs and plant species for revegetation are important aspects of tailings landform reclamation and closure. Research and monitoring of the long term and immediate impacts of capped OST on the growth and survival of native boreal plant species are currently underway. However, plant responses to OST-associated toxicity are not well known at the molecular level. Using RNA sequencing, we examined the effects of three types of OST on the willow transcriptome under different capping strategies. The transcriptomic data showed that some genes respond universally and others in a specific manner to different types of OST. Among the dominant and shared upregulated genes, we found some encoding protein detoxification (PD), Cytochrome P450 (CYPs), glutathione S-transferase regulatory process (GST), UDP-glycosyltransferase (UGT), and ABC transporter and regulatory process associated proteins. Moreover, genes encoding several stress-responsive transcription factors (bZIP, BHLH, ERF, MYB, NAC, WRKY) were upregulated with OST-exposure, while high numbers of transcripts related to photosynthetic activity and chloroplast structure and function were downregulated. Overall, the expression of 40 genes was found consistent across all tailings types and capping strategies. The qPCR analysis of a subset of these shared genes suggested that they could reliably distinguish plants exposed to different OST associated stress. Our results indicated that it is possible to develop OST stress exposure biosensors merely based on changes in the level of expression of a relatively small set of genes. The outcomes of this study will further guide optimization of OST capping and revegetation technology by using knowledge based plant stress adaptation strategies.

Extracts from Dated Lake Sediment Cores in the Athabasca Oil Sands Region Alter Ethoxyresorufin-O-deethylase Activity and Gene Expression in Avian Hepatocytes

Increases in oil sands mining operations in the Athabasca oil sands region have resulted in increased concentrations of polycyclic aromatic compounds (PACs) and heavy metals in aquatic systems located near surface mining operations. In the present study, sediment cores were collected from 3 lakes with varying proximity to surface mining operations to determine the differences in PAC concentrations. Sediment cores were separated into 2 sections-current mining (top; 2000-2017) and premining (bottom; pre-1945)-and extracts were prepared for in vitro screening using a well-established chicken embryonic hepatocyte (CEH) assay. Concentrations and composition of PACs varied between sites, with the highest ∑PACs in Saline Lake, 5 km from an active oil sands mine site. The proportion of alkylated PACs was greater than that of parent PACs in the top sediment sections compared with the bottom. Ethoxyresorufin-O-deethylase activity in CEH permitted the ranking of lake sites/core sections based on an aryl hydrocarbon receptor-mediated end point; mean median effect concentration values were lowest for the top cores from Saline Lake and another near-mining operations lake, referred to as WF1. A ToxChip polymerase chain reaction (PCR) array was used to evaluate gene expression changes across 43 target genes associated with numerous toxicological pathways following exposure to top and bottom sediment core extracts. The 2 study sites with the greatest ∑PAC concentrations (Saline Lake and WF1) had the highest gene expression alterations on the ToxChip PCR array (19 [top] and 17 [bottom]/43), compared with a reference site (13 [top] and 7 [bottom]/43). The avian in vitro bioassay was useful for identifying the toxicity of complex PAC extracts associated with variably contaminated sediment cores, supporting its potential use for hotspot identification and complex mixture screening. EnvironToxicol Chem 2021;40:1883-1893. © 2021 SETAC.

Ammonia and chromate interaction explains unresolved Hyalella azteca mortality in Flanders' sediment bioassays

Agricultural, industrial and household chemicals are emitted in large rivers along populated areas, transported by water and deposited in sediments, posing (eco)toxicological risks. Sediments have received less attention than surface waters, likely because of the intrinsic complexity of interactions between sediment constituents complicating correct framing of exposures. Sadly, thorough assessment of the in situ behavior of sediment constituents in bioassays is often not practical. Alternatively, we related physicochemical properties of sediments from field testing to results from bioassays. The case study covers Flemish sediment (incl. Scheldt and Meuse) and mortality of Hyalella azteca, a sensitive bio-indicator. Though variable across Flanders' main water bodies, heavy metals and ammoniacal nitrogen dominate the observed toxicity according to toxic unit (TU) assessments. Depending on the water body we explain between 50 and 90% of the variance in the observed H. azteca mortality, substantially more than previous ecotoxicity studies. We attribute the remaining variance to potential incoherently documented biophysicochemical sediment properties and concentrations of non-target biocides, testing conditions/set-ups and/or species variabilities. We discuss the relative influence of heavy metals/metaloxides, nitrogen (e.g. fertilizer), polycyclic aromatics and organochlorides. We highlight both direct and indirect mortality mechanisms. We note potential synergetic mixture effects between ammoniacal nitrogen and chromium. Such synergy may be phenomenological of 'standard' aerobic bioassays, and prove a complementary method alongside the 'acid-volatile sulfide test' to more effectively link concentration to toxicity. Future study ought to include variation in biophysicochemical properties between sampling locations and batch bioassays. Our approach enables water managers to interpret their monitoring data by converting sediment concentrations to H. azteca mortality and prioritize substances that contribute most.

Bioconcentration of Organotin Cations during Molting Inhibits Heterocypris incongruens Growth

The densely populated North Sea region encompasses catchments of rivers such as Scheldt and Meuse. Herein, agricultural, industrial, and household chemicals are emitted, transported by water, and deposited in sediments, posing ecological risks. Though sediment monitoring is often costly and time-intensive, modeling its toxicity to biota has received little attention. Due to high complexity of interacting variables that induce overall toxicity, monitoring data only sporadically validates current models. Via a range of concepts, we related bio-physicochemical constituents of sediment in Flanders to results from toxicity bioassays performed on the ostracod Heterocypris incongruens. Depending on the water body, we explain up to 90% of the variance in H. incongruens growth. Though variable across Flanders' main water bodies, organotin cations and ammonia dominate the observed toxicity according to toxic unit (TU) assessments. Approximately 10% relates to testing conditions/setups, species variabilities, incoherently documented pollutant concentrations, and/or bio-physicochemical sediment properties. We elucidated the influence of organotin cations and ammonia relative to other metal(oxides) and biocides. Surprisingly, the tributylin cation appeared ∼1000 times more toxic to H. incongruens as compared to "single-substance" bioassays for similar species. We inferred indirect mixture effects between organotin, ammonia, and phosphate. Via chemical speciation calculations, we observed strong physicochemical and biological interactions between phosphate and organotin cations. These interactions enhance bioconcentration and explain the elevated toxicity of organotin cations. Our study aids water managers and policy makers to interpret monitoring data on a mechanistic basis. As sampled sediments differ, future modeling requires more emphasis on characterizing and parametrizing the interactions between bioassay constituents. We envision that this will aid in bridging the gap between testing in the laboratory and field observations.

Effects of Environmentally Relevant Residual Levels of Diluted Bitumen on Wild Fathead Minnows (Pimephales promelas)

Transportation of crude oil across North America's boreal ecozone creates the potential for spills in freshwater where less is known about the sensitivity of resident fish than for marine systems. The sensitivity of wild fathead minnows (FHM) to residual concentrations (ppb range) of the water accommodated fraction (WAF) of diluted bitumen (dilbit) was assessed by exposing them for 21 days followed by a 14 days depuration. Target concentrations were well below detection limits for GC-MS, but were estimated by dilution factor (1:100,000 and 1:1,000,000 WAF:water) to contain less than 0.0003 μg/L of polycyclic aromatic compounds. Confinement and handling stress caused by transfer of wild fish into tanks much smaller than their natural range resulted in mortality and lower body condition among all groups, but interactive effects of oil exposures still resulted in females with smaller cortical alveolar oocytes, and males with larger testicular lobe lumen sizes. Additional studies examining the compounded effects of stress and environmentally relevant oil exposures in wild fishes are needed.