Assessment of mercury enrichment in lake sediment records from Alberta Oil Sands development via fluvial and atmospheric pathways

Abstract

Exploitation of bitumen-rich deposits in the Alberta Oil Sands Region (AOSR) by large-scale mining and processing activities has generated widespread concern about the potential for dispersal of harmful contaminants to aquatic ecosystems via fluvial and atmospheric pathways. The release of mercury has received attention because it is a potent neurotoxin for wildlife and humans. However, knowledge of baseline mercury concentration prior to disturbance is required to evaluate the extent to which oil sands development has contributed mercury to aquatic ecosystems. Here, we use stratigraphic analysis of total mercury concentration ([THg]) in radiometrically dated sediment cores from nine floodplain lakes in the AOSR and downstream Peace-Athabasca Delta (PAD) and two upland lakes in the PAD region to establish pre-1900 baseline [THg] and evaluate if [THg] has become enriched via fluvial and atmospheric pathways since oil sands mining and processing began in 1967. Concentrations of THg in sediment cores from the study lakes range from 0.022–0.096 mg/kg (dry wt.) and are below the Canadian interim sediment quality guidelines for freshwater (0.17 mg/kg). Results demonstrate no enrichment of [THg] above pre-1900 baseline via fluvial pathways at floodplain lakes in the AOSR or PAD. Enrichment of [THg] was detected via atmospheric pathways at upland lakes in the PAD region, but this occurred prior to oil sands development and aligns with long-range transport of emissions from coal combustion and other anthropogenic sources across the northern hemisphere recognized in many other lake sediment records. The inventory of anthropogenic [THg] in the upland lakes in the AOSR is less than at the Experimental Lakes Area of northwestern Ontario (Canada), widely regarded as a “pristine” area. The absence of enrichment of [THg] in lake sediment via fluvial pathways is a critical finding for stakeholders, and we recommend that monitoring at the floodplain lakes be used to inform stewardship as oil sands operators prepare to discharge treated oil sands process waters directly into the Athabasca River upstream of the PAD.

A framework for integrated monitoring of status and trends in water balance, water chemistry and contamination of shallow lakes across a remote dynamic freshwater delta

“…The status and range of environmental conditions, as defined here for each lake during 2015-2019, can serve as benchmark references for comparison to future monitoring data to quantify the extent of aquatic ecosystem degradation caused by hydrological change and contamination, and associated shifts in water chemistry. The knowledge gained may also be used to select a subset of lakes with specific characteristics that enable quantification of trends in contaminant deposition via atmospheric versus fluvial pathways to lakes of the PAD (e.g., [90,91]). Knowledge gained from the results displayed in summary maps can be used to identify lakes that are most vulnerable to aquatic ecosystem degradation caused by changes in hydrological processes and contaminant deposition.…”

“…upland lakes and floodplain lakes in the PAD to establish pre-development baseline concentrations for substances of concern, and to quantify the degree of enrichment since oil sands development via atmospheric and fluvial pathways, respectively[86][87][88][89][90][91][92][93]. These studies analysed concentrations of polycyclic aromatic compounds (PACs), trace elements, and total mercury, and established pre-development baselines from sediment deposited before 1920 to characterize the range of variation before industrial development in the Lower Athabasca River watershed.…”

Spatial distribution of trace elements and potential contamination sources for surface sediments of the North-Western Black Sea, Romania

“…Although fluvial inputs are relevant, direct discharges of wastewater/groundwater/rainwater/polluting products, coastal erosion, atmospheric deposition of particulate matter derived from natural and anthropogenic processes should not be neglected (Mülayim and Balkıs, 2015;Kay et al, 2022;Romano et al, 2022). Accumulation of TEs in marine sediments depends on various factors, e.g., water depth, water physicochemical properties (pH, salinity, temperature, dissolved oxygen and organic matter content), sediment composition and texture, intensity/direction of winds, waves, and currents, fluvial, atmospheric, and other natural or anthropogenic inputs (Oros, 2019;Constantinescu et al, 2023).…”