Differences in phytotoxicity and dissipation between ionized and nonionized oil sands naphthenic acids in wetland plants

Abstract

Naphthenic acids (NAs) are composed of alkyl-substituted acyclic and cycloaliphatic carboxylic acids and, because they are acutely toxic to fish, are of toxicological concern. During the caustic hot-water extraction of oil from the bitumen in oil sands deposits, NAs become concentrated in the resulting tailings pond water. The present study investigated if dissipation of NAs occurs in the presence of hydroponically grown emergent macrophytes (Typha latifolia, Phragmites australis, and Scirpus acutus) to determine the potential for phytoremediation of these compounds. Plants were grown with oil sands NAs (pKa approximately 5-6) in medium at pH 7.8 (predominantly ionized NAs) and pH 5.0 (predominantly nonionized NAs) to determine if, by altering their chemical form, NAs may be more accessible to plants and, thus, undergo increased dissipation. Whereas the oil sands NA mixture in its nonionized form was more toxic to wetland plants than its ionized form, neither form appeared to be sequestered by wetland plants. The present study demonstrated that plants may selectively enhance the dissipation of individual nonionized NA compounds, which contributes to toxicity reduction but does not translate into detectable total NA dissipation within experimental error and natural variation. Plants were able to reduce the toxicity of a NA system over 30 d, increasing the median lethal concentration (LC50; % of hydroponic solution) of the medium for Daphnia magna by 23.3% +/- 8.1% (mean +/- standard error; nonionized NAs) and 37.0% +/- 2.7% (ionized NAs) as determined by acute toxicity bioassays. This reduction in toxicity was 7.3% +/- 2.6% (nonionized NAs) and 45.0% +/- 6.8% (ionized NAs) greater than that in unplanted systems.

Characterization of oil sands acids in plant tissue using Orbitrap ultra‐high resolution mass spectrometry with electrospray ionization

“…[5,6] Earlier investigations into the bioremediation of naphthenic acids used low-, medium-and ultra-high-resolution electrospray ionization mass spectrometry (ESI-MS) to determine if wetland plants selectively dissipate individual naphthenic acid compounds from Athabasca oil sands naphthenic acid mixtures. [7][8][9][10] For hydroponic systems investigated by Armstrong et al, [7,8] the characterization of oil sands components was limited to water samples with no determination of components directly in the plant tissue itself. Ultrahigh resolution using Fourier transform ion cyclotron resonance (FTICR)-MS analysis was likewise based on the detailed characterization of water systems.…”

Ultrahigh-resolution mass spectrometry of simulated runoff from treated oil sands mature fine tailings

“…Armstrong et al 7, 8. employed low‐resolution electrospray ionization mass spectrometry (ESI‐MS) to characterize the runoff from treated MFT and to determine if the emergent native macrophyte common reed ( Phragmites australis subsp.…”

“…The relative abundance of each naphthenic acid was determined by arranging the mass spectral data according to carbon number and –Z family, as per Holowenko et al 2. For the hydroponic systems investigated by Armstrong et al .,7, 8 all runoff samples were phytotoxic, and O 2 species alone (indicative of classical naphthenic acids) were implicated as the toxicant, along with elevated salts and high pH levels. However, given our recent findings9, 10 that low‐resolution ESI‐MS can mask the presence of other principal toxic components, we have extended the investigation to the characterization of the runoff water by the use of ultrahigh mass resolution.…”

Chitosan Biopolymers for Analysis of Organic Acids in Aquatic Environments of Treatment Wetlands

“…Various methods have been proposed for the remediation of OSPW [4]. One of them includes the use of wetland plants to metabolize NAFCs to form by-products that are less toxic [5] [6]. However, the limitation of this method is in the quantification of NAFCs after the wetland treatment where fatty acids and humic-like materials that are produced may yield false positive NAFC concentration levels, based on conventional extraction methods such as liquid-liquid extraction.…”

“…The improvements in solid-phase extraction (SPE) are anticipated to occur via preconcentration of naphthenic acids and minimization of other background interferents. We anticipate the use of such sorbent materials will contribute to further efforts in remediation of waterborne contaminants such as phytoremediation technology [5] [6].…”