Phillip M. Fedorak

The Athabasca oil sands in northeastern Alberta, Canada represent the second largest petroleum reserve in the world. The process of extracting bitumen from the oil sands uses huge volumes of water, drawn from sources in the Athabasca River basin, and numerous mining companies operate adjacent to the river. Oil sands process-affected water (OSPW) from open pit mining is placed in large settling basins or tailings ponds that have the potential to leak. The goal is to eventually reclaim the tailings ponds to become functional ecosystems. Natural outcrops of oil sands in contact with surface waters also occur, and there are anecdotal reports in the media that fish caught near the Athabasca oil sands have an unusual flavor or odor. Several analytical and sensory studies have been undertaken to address this issue. Two major questions related to fish tainting arise: (1) Do the current oil sands mining, extraction and upgrading processes cause fish tainting in surrounding waters? (2) What is the tainting potential for fish that become established in reclaimed waters in the future? This review examines the types of compounds in OSPW that might contribute to tainting and the sensory science literature available related to fish tainting and the oil sands.

The oil sands industry is rapidly expanding surface mining and bitumen extraction operations near the Athabasca River in northeastern Alberta, Canada. There are anecdotal comments that the fish from the Athabasca River have an off-taste, implying that the oil sands operations are the cause. This study was done to determine if the taste of wild fishes caught near the Athabasca oil sands was less preferred than the taste of fishes collected from two other river basins in Alberta. In blinded experiments, consumer sensory panels, of 40 to 44 participants, tasted steamed samples of each of three fish species (walleye (Sander vitreus), northern pike (Esox lucius), and lake whitefish (Coregonus clupeaformis)) from three different sources in Alberta (the Athabasca River, Buck Lake, and McGregor Lake). Data analyses showed that there was no evidence from the consumer preference rankings that the taste of the fish from the Athabasca River was preferred less than the taste of fish from two other water bodies in Alberta.

Naphthenic acids (general formula C_nH_2n+ZO₂) are found in petroleum and oil sands deposits. Release of these acids to aquatic environments is a concern because of their potential toxicity. Naphthenic acids consist of a complex mixture of carboxylic acids, and estimating their concentrations in environmental samples is a challenge. Two recent reports have described gas chromatography-mass spectrometry (GC-MS) methods to selectively detect these acids in fish flesh and water samples. The methods use N-methyl-N-(t-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA) with 1% t-butyldimethylchlorosilane (t-BDMCS) to derivatize naphthenic acids to their t-butyldimethylsilyl derivatives. Single ion monitoring (SIM) was used to detect the fragment m/z 267, which corresponds to the derivatives of one isomer class (n = 13 and Z = −4) of naphthenic acids. The SIM chromatograms give a characteristic naphthenic acids hump between retention times 15 and 20 min and a sharp peak for the t-butyldimethylsilyl derivatized surrogate standard, 9-fluorenecarboxylic acid. Integration of this hump and the peak from the surrogate standard allows quantification of the naphthenic acids. Using newly purchased MTBSTFA containing 1% t-BDMCS (from three different suppliers) yielded SIM chromatograms with one or two large contaminating peaks (eluting at 16.7 and 18.8 min) that interfered with integration of the hump, rendering the method unreliable. The contaminants were traced to the presence of t-BDMCS. Each of the three suppliers sells MTBSTFA devoid of t-BDMCS, and using MTBSTFA without 1% t-BDMCS was found to be suitable for the GC-MS method.

Many oil fields are in remote locations, and the time required for shipment of produced water samples for microbiological examination may be lengthy. No studies have reported on how storage of oil field waters can change their characteristics. Produced water samples from three Alberta oil fields were collected in sterile, industry-approved 4-l epoxy-lined steel cans, sealed with minimal headspace and stored under anoxic conditions for 14 days at either 4°C or room temperature (ca. 21°C). Storage resulted in significant changes in water chemistry, microbial number estimates and/or community response to amendment with nitrate. During room-temperature storage, activity and growth of sulfate-reducing bacteria (and, to a lesser extent, fermenters and methanogens) in the samples led to significant changes in sulfide, acetate and propionate concentrations as well as a significant increase in most probable number estimates, particularly of sulfate-reducing bacteria. Sulfide production during room-temperature storage was likely to be responsible for the altered response to nitrate amendment observed in microcosms containing sulfidogenic samples. Refrigerated storage suppressed sulfate reduction and growth of sulfate-reducing bacteria. However, declines in sulfide concentrations were observed in two of the three samples stored at 4°C, suggesting abiotic losses of sulfide. In one of the samples stored at room temperature, nitrate amendment led to ammonification. These results demonstrate that storage of oil field water samples for 14 days, such as might occur because of lengthy transport times or delays before analysis in the laboratory, can affect microbial numbers and activity as well as water sample chemistry.

Nitrate amendment is normally an effective method for sulfide control in oil field-produced waters. However, this approach has occasionally failed to prevent sulfide accumulation, despite the presence of active nitrate-reducing bacterial populations. Here, we report our study of bulk chemical transformations in microcosms of oil field waters containing nitrate-reducing, sulfide-oxidizing bacteria, but lacking denitrifying heterotrophs. Amendment with combinations of nitrate, acetate, and phosphate altered the microbial sulfur and nitrogen transformations. Elemental sulfur produced by chemotrophic nitrate-reducing bacteria was re-reduced heterotrophically to sulfide. Ammonification, rather than denitrification, was the predominant pathway for nitrate reduction. The application of nitrite led to transient sulfide depletion, possibly due to higher rates of nitrite reduction. The addition of molybdate suppressed both the accumulation of sulfide and the heterotrophic reduction of nitrate. Therefore, sulfidogenesis was likely due to elemental sulfur-reducing heterotrophic bacteria, and the nitrate-reducing microbial community consisted mainly of facultatively chemotrophic microbes. This study describes one set of conditions for continued sulfidogenesis during nitrate reduction, with important implications for nitrate control of sulfide production in oil fields.