Identifying the causes of oil sands coke leachate toxicity to aquatic invertebrates

Abstract

A previous study found that coke leachates (CL) collected from oil sands field sites were acutely toxic to Ceriodaphnia dubia; however, the cause of toxicity was not known. Therefore, the purpose of this study was to generate CL in the laboratory to evaluate the toxicity response of C. dubia and perform chronic toxicity identification evaluation (TIE) tests to identify the causes of CL toxicity. Coke was subjected to a 15-d batch leaching process at pH 5.5 and 9.5. Leachates were filtered on day 15 and used for chemical and toxicological characterization. The 7-d median lethal concentration (LC50) was 6.3 and 28.7% (v/v) for pH 5.5 and 9.5 CLs, respectively. Trace element characterization of the CLs showed Ni and V levels to be well above their respective 7-d LC50s for C. dubia. Addition of ethylenediaminetetraacetic acid significantly (p ≤ 0.05) improved survival and reproduction in pH 5.5 CL, but not in pH 9.5 CL. Cationic and anionic resins removed toxicity of pH 5.5 CL only. Conversely, the toxicity of pH 9.5 CL was completely removed with an anion resin alone, suggesting that the pH 9.5 CL contained metals that formed oxyanions. Toxicity reappeared when Ni and V were added back to anion resin-treated CLs. The TIE results combined with the trace element chemistry suggest that both Ni and V are the cause of toxicity in pH 5.5 CL, whereas V appears to be the primary cause of toxicity in pH 9.5 CL. Environmental monitoring and risk assessments should therefore focus on the fate and toxicity of metals, especially Ni and V, in coke-amended oil sands reclamation landscapes.

Removal of organic acids from water using biochar and petroleum coke

“…PC has a higher content of N and S; 1.74% and 7.1%, respectively, whereas, BC contains only a trace amount of S (0.07%). The high content of sulfur in PC matches with the previous analyses of Alberta oil sand PC (Puttaswamy and Liber, 2011;Puttaswamy and Liber, 2012).…”

Estimation of vanadium water quality benchmarks for the protection of aquatic life with relevance to the Athabasca Oil Sands region using species sensitivity distributions

“…Previous studies have found coke to leach high concentrations of V into solution upon exposure to water, including process‐affected waters . An 18‐mo lysimeter study found V to leach from coke into solution at concentrations >1000 μg/L, orders of magnitude greater than background concentrations .…”

Assessment of seven Canadian rivers in relation to stages in oil sands industrial development, 1972–2010

“…Both As and Se are also on the US Environmental Protection Agency's list of priority pollutants (www.epa.gov). Vanadium is a toxic component of the coke leachate produced during the upgrading of bitumen to synthetic crude oil (7 day median lethal concentration, LC 50 < 30% v/v Ceriodaphnia dubia) (Puttaswamy and Liber 2011). Collectively, these elements may help to distinguish natural versus oil sands mining inputs to surface waters.…”