Degradation and aquatic toxicity of naphthenic acids in oil sands process-affected waters using simulated wetlands Navdeep S. Toor a,⇑ , Eric D. Franz a , Phillip M. Fedorak b , Michael D. MacKinnon c , Karsten Liber a a Toxicology Centre, 44 Campus Drive, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5B3 b Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9 c Syncrude Canada Ltd., Edmonton Research Centre, 9421-17 Avenue, Edmonton, Alberta, Canada T6N 1H4 highlights " Toxicity of oil sands process-affected waters associated with naphthenic acids (NAs). " Examined NAs degradation and aquatic toxicity using simulated wetland microcosms. " Microcosms successfully reduced total NAs concentrations, but process was incomplete. " Persistent Microtox Ò toxicity is likely associated with the residual NAs components. " Acute toxicity of oil sands process-affected waters to rainbow trout was completely removed. article info Article history: Received 13 January 2012 Received in revised form 25 July 2012 Accepted 27 July 2012 Available online 20 September 2012 Keywords: Oil sands process water Naphthenic acids Microcosms Microtox Ò abstract Oil sands process-affected waters (OSPWs) produced during the extraction of bitumen at the Athabasca Oil Sands (AOS) located in northeastern Alberta, Canada, are toxic to many aquatic organisms. Much of this toxicity is related to a group of dissolved organic acids known as naphthenic acids (NAs). Naphthenic acids are a natural component of bitumen and are released into process water during the separation of bitumen from the oil sand ore by a caustic hot water extraction process. Using laboratory microcosms as an analogue of a proposed constructed wetland reclamation strategy for OSPW, we evaluated the effec- tiveness of these microcosms in degrading NAs and reducing the aquatic toxicity of OSPW over a 52-week test period. Experimental manipulations included two sources of OSPW (one from Syncrude Canada Ltd. and one from Suncor Energy Inc.), two different hydraulic retention times (HRTs; 40 and 400 d), and increased nutrient availability (added nitrate and phosphate). Microcosms with a longer HRT (for both OSPWs) showed higher reductions in total NAs concentrations (64–74% NAs reduction, p < 0.05) over the test period, while nutrient enrichment appeared to have little effect. A 96 h static acute rainbow trout (Oncorhynchus mykiss) bioassay showed that the initial acute toxicity of Syncrude OSPW (LC50 = 67% v/v) was reduced (LC50 > 100% v/v) independent of HRT. However, EC20s from separate Microtox Ò bioassays were relatively unchanged when comparing the input and microcosm waters at both HRTs over the 52- week study period (p > 0.05), indicating that some sub-lethal toxicity persisted under these experimental conditions. The present study demonstrated that given sufficiently long HRTs, simulated wetland micro- cosms containing OSPW significantly reduced total NAs concentrations and acute toxicity, but left behind a persistent component of the NAs mixture that appeared to be associated with residual chronic toxicity. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction At the Athabasca Oil Sands (AOS) in northeastern Alberta, Can- ada, the caustic hot water extraction process described by Clark in 1932 is still used by some companies with surface mining opera- tions to separate bitumen from oil sand ore (Clark and Pasternack, 1932). In current integrated surface mining operations at the AOS, approximately 2–2.5 m 3 of fresh water is required to produce 1 m 3 of synthetic crude oil (W. Zubot, Syncrude Canada Ltd., Edmonton, AB, Canada, personal communication). At production rates that are approaching one million barrels of oil per day, this results in the build-up of large inventories of liquid tailings, of which oil sands process-affected waters (OSPWs) is a major component and a sig- nificant stakeholder concern (MacKinnon, 1989; Holroyd and Sim- ieritsch, 2009). Previous toxicological investigations have shown that freshly produced OSPW, and OSPW contained within the active tailings system, are toxic to various aquatic organisms 0045-6535/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2012.07.059 ⇑ Corresponding author. Tel.: +1 306 966 7441; fax: +1 306 931 1664. E-mail address: nav.toor@usask.ca (N.S. Toor). Chemosphere 90 (2013) 449–458 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere