Integrated analysis of petroleum biomarkers and polycyclic aromatic compounds in lake sediment cores from an oil sands region

Paleolimnological evaluation of metal(loid) enrichment from oil sands and gold mining operations in northwestern Canada

Abundant reserves of metals and oil have spurred large-scale mining developments across northwestern Canada during the past 80 years. Historically, the associated emissions footprint of hazardous metal(loid)s has been difficult to identify, in part, because monitoring records are too short and sparse to have characterized their natural concentrations before mining began. Stratigraphic analysis of lake sediment cores has been employed where concerns of pollution exist to determine pre-disturbance metal(loid) concentrations and quantify the degree of enrichment since mining began. Here, we synthesize the current state of knowledge via systematic re-analysis of temporal variation in sediment metal(loid) concentrations from 51 lakes across four key regions spanning 670 km from bitumen mining in the Alberta Oil Sands Region (AOSR) to gold mining (Giant and Con mines) at Yellowknife in central Northwest Territories. Our compilation includes upland and floodplain lakes at varying distances from the mines to evaluate dispersal of pollution-indicator metal(loid)s from bitumen (vanadium and nickel) and gold mining (arsenic and antimony) via atmospheric and fluvial pathways. Results demonstrate 'severe' enrichment of vanadium and nickel at near-field sites (≤20 km) within the AOSR and 'severe' (near-field; ≤ 40 km) to 'considerable' (far-field; 40-80 km) enrichment of arsenic and antimony due to gold mining at Yellowknife via atmospheric pathways, but no evidence of enrichment of vanadium or nickel via atmospheric or fluvial pathways at the Peace-Athabasca Delta and Slave River Delta. Findings can be used by decision makers to evaluate risks associated with contaminant dispersal by the large-scale mining activities. In addition, we reflect upon methodological approaches to be considered when evaluating paleolimnological data for evidence of anthropogenic contributions to metal(loid) deposition and advocate for proactive inclusion of paleolimnology in the early design stage of environmental contaminant monitoring programs.

Tracking petrogenic hydrocarbons in lakes of the Peace-Athabasca Delta in Alberta, Canada using petroleum biomarkers

The Peace-Athabasca Delta (PAD) receives a mixture of hydrocarbons from biogenic, pyrogenic, and petrogenic processes. Source apportionment in the PAD has focussed on polycyclic aromatic compounds (PACs), which are ubiquitous in the environment and susceptible to weathering. In contrast, petroleum biomarkers of terpanes, hopanes, and steranes are degradation-resistant organic compounds found uniquely in petroleum products that can identify the input and origin of petrogenic hydrocarbons (PHCs). We provide an analysis of environmentally-relevant PHCs (including n-alkanes, PACs, and petroleum biomarkers) in surficial sediments of strategically selected lakes in the Athabasca and Peace deltas and adjacent boreal uplands. Alkanes were found to be predominately biogenic in all lakes. PAC sources were identified as wood combustion in the upland boreal lakes, a mixture of petrogenic and pyrogenic combustion in two closed-drainage lakes in the Peace Delta, and predominately petrogenic in two flood-prone Athabasca Delta lakes. Using multivariate analyses, raw Alberta oil sands were identified as a potential source of PHCs to the two flood-prone lakes in the Athabasca Delta. Biomarkers of terpanes and hopanes were identified in the Peace Delta and boreal uplands, likely from bitumen and transported atmospherically. These findings validate the use of petroleum biomarkers as tracers for bituminous sands in surficial lake sediments and their potential use in paleolimnological investigations at the PAD to improve understanding of relative roles of natural and industrial processes on far-field deposition of PHCs.

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.