Effect of Lipid Partitioning on Predictions of Acute Toxicity of Oil Sands Process Affected Water to Embryos of Fathead Minnow (Pimephales promelas)

Abstract

Dissolved organic compounds in oil sands process affected water (OSPW) are known to be responsible for most of its toxicity to aquatic organisms, but the complexity of this mixture prevents use of traditional bottom-up approaches for predicting toxicities of mixtures. Therefore, a top-down approach to predict toxicity of the dissolved organic fraction of OSPW was developed and tested. Accurate masses (i.e., m/z) determined by ultrahigh resolution mass spectrometry in negative and positive ionization modes were used to assign empirical chemical formulas to each chemical species in the mixture. For each chemical species, a predictive measure of lipid accumulation was estimated by stir-bar sorptive extraction (SBSE) to poly(dimethyl)siloxane, or by partitioning to solid-supported lipid membranes (SSLM). A narcosis mode of action was assumed and the target-lipid model was used to estimate potencies of mixtures by assuming strict additivity. A model developed using a combination of the SBSE and SSLM lipid partitioning estimates, whereby the accumulation of chemicals to neutral and polar lipids was explicitly considered, was best for predicting empirical values of LC50 in 96-h acute toxicity tests with embryos of fathead minnow (Pimephales promelas). Model predictions were within 4-fold of observed toxicity for 75% of OSPW samples, and within 8.5-fold for all samples tested, which is comparable to the range of interlaboratory variability for in vivo toxicity testing.

Application of the Target Lipid Model and Passive Samplers to Characterize the Toxicity of Bioavailable Organics in Oil Sands Process-Affected Water

“…Passive samplers have been commonly applied to measure freely dissolved concentrations of individual organic chemicals, including recent applications to OSPW − and NAs . Solid phase microextraction (SPME) has been adapted to measure the bioavailability of aqueous exposures petroleum hydrocarbon mixtures. ,− When relatively small volumes of SPME polymers are used in aqueous exposures, the freely dissolved oil concentrations in solution that dictate toxicity are not depleted, and the chromatographic area under the curve for all constituents absorbed onto the SPME fiber can be used as a surrogate measure for quantifying the bioavailability of petroleum contaminated samples.…”

Overview of Existing Science to Inform Oil Sands Process Water Release: A Technical Workshop Summary

“…However, the complexity of the organics in OSPW creates a practical challenge for determining treatment methods (Headley et al ; Pereira et al 2013; Goff et al ; Brown and Ulrich ; Quinlan and Tam ; Wilde et al ; Ajaero et al ), in addition to estimating potential risks (West et al ; Huang et al ). The estimation of potential risk is further supported through an existing understanding of chemical properties such as the propensity for bioaccumulation (Zhang et al ; Morandi et al ).…”

“…As noted in the Oil sands process water chemistry section, the composition is broader than the classic naphthenic acids and includes a variety of charged and polar structures, and some molecules with integrated N and S. Work continues to identify the toxic fractions of bioavailable mixtures of chemicals in OSPW using effects‐directed analyses (Yue et al 2014; Zhang et al ; Morandi et al ; Hughes, Mahaffey et al ; McQueen, Kinley et al ; Bauer ) coupled with conventional and high‐resolution analytical techniques, as well as novel passive sampling methods to measure the bioavailable organics in OSPW (Redman et al ).…”

Mechanisms of pH-Dependent Uptake of Ionizable Organic Chemicals by Fish from Oil Sands Process-Affected Water (OSPW)

“…Acute toxicity, however, is thought to be mostly associated with NAs present in the acidic fraction of some OSPWs. , Hence, it is reasonable to expect a strong influence of environmental pH on bioavailabilities and toxic potencies of constituents of OSPW. While the differential partitioning of IOCs from OSPW to neutral and polar lipids on toxicity has been comprehensively studied previously by employing the target lipid model, , effects of pH on bioavailabilities of these chemicals have not been systematically addressed to date …”

“…27,28 Hence, it is reasonable to expect a strong influence of environmental pH on bioavailabilities and toxic potencies of constituents of OSPW. While the differential partitioning of IOCs from OSPW to neutral and polar lipids on toxicity has been comprehensively studied previously by employing the target lipid model, 29,30 effects of pH on bioavailabilities of these chemicals have not been systematically addressed to date. 5 To overcome the limitations of assessments of bioaccumulation of IOCs in general, and dissolved organics present in OSPW specifically, in the research presented here, a rapid, in vitro screening method using the rainbow trout gill cell line RTgill-W1 was applied to study pH-dependent permeation of IOCs across epithelia of gills of fish.…”