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

Abstract

Oil sand operations in Alberta, Canada will eventually include returning treated process-affected waters to the environment. Organic constituents in oil sand process-affected water (OSPW) represent complex mixtures of nonionic and ionic (e.g., naphthenic acids) compounds, and compositions can vary spatially and temporally, which has impeded development of water quality benchmarks. To address this challenge, it was hypothesized that solid phase microextraction fibers coated with polydimethylsiloxane (PDMS) could be used as a biomimetic extraction (BE) to measure bioavailable organics in OSPW. Organic constituents of OSPW were assumed to contribute additively to toxicity, and partitioning to PDMS was assumed to be predictive of accumulation in target lipids, which were the presumed site of action. This method was tested using toxicity data for individual model compounds, defined mixtures, and organic mixtures extracted from OSPW. Toxicity was correlated with BE data, which supports the use of this method in hazard assessments of acute lethality to aquatic organisms. A species sensitivity distribution (SSD), based on target lipid model and BE values, was similar to SSDs based on residues in tissues for both nonionic and ionic organics. BE was shown to be an analytical tool that accounts for bioaccumulation of organic compound mixtures from which toxicity can be predicted, with the potential to aid in the development of water quality guidelines.

Recommendations for Improving Methods and Models for Aquatic Hazard Assessment of Ionizable Organic Chemicals

“…Individual CTLBBs were also calculated for each individual chemical (Supplemental Data, Table S1), and a summary of the range of individual CTLBBs is shown in the Supplemental Data. The CTLBB analysis demonstrates that IOCs that are not assigned as specifically acting gave consistent results with other TLM applications for polar and nonpolar chemicals (Kipka and Di Toro ), although the IOCs investigated in the present study all lay at the lower limits of the species–CTLBB distribution of earlier studies (Kipka and Di Toro ; Redman et al ). The lower CTLBBs derived in the present study may be attributable to differences in how K lip/w (neutral) was estimated in earlier work.…”

“…This critical body burden model can be applied to large sets of chemicals with only physicochemical properties and measured ECs as input parameters. In the following analysis we build on prior work (Redman et al ) to show that the TLM may also be applied to IOCs but only if there is less than a pH unit gradient between the external medium and the inside of the organisms. If this is not the case, the ion‐trapping model for baseline toxicity derived below (see section Ion‐trapping model to explain the pH dependence of toxicity ) should be used.…”

“…Prior application of the TLM to IOCs (Redman et al ) assumed that neutral and charged species are equipotent in contributing to baseline toxicity and therefore act in a concentration addition manner, as described by Equation . For IOCs, Equation is converted from Equation simply by replacing K lip/w of the neutral species by D lip/w (pH).…”

Challenges and Benefits of Approaches Used to Integrate Regional Monitoring Programs

“…Another objective of reconfiguring the regional monitoring in the OSR was increasing the quality of the work through external peer-review. While many papers have been published by researchers funded by this program (e.g., Summers et al, 2016;Makar et al, 2018;Landis et al, 2019), additional work also occurs in the region outside of the OSM funding envelope, including industry-funded research, compliance monitoring, provincial monitoring, and independent research (e.g., Shotyk et al, 2017;Redman et al, 2018;Fennell and Arciszewski, 2019). Since 2012 these research efforts have collectively produced hundreds of research papers.…”

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

“…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 ).…”