monitoring-uptake-localization-organic-compounds-plant-tissues-using

Monitoring the Uptake and Localization of Organic Compounds in Plant Tissues Using a Hydroponic <sup>14</sup>C-radiolabelling Assay and Phosphor Imaging

Phytoremediation, the use of plants to mitigate environmental contaminants, offers a sustainable and cost-effective approach to cleaning contaminated ...

University of Calgary

Oil sands surface mining generates vast quantities of oil sands process-affected water (OSPW) as a by-product of bitumen extraction. The acid extractable organic (AEO) fraction of OSPW contains several contaminants, including naphthenic acids (NAs). While responses of living organisms to NA and AEO exposure have been described at the developmental, physiological, metabolic and gene expression levels, the effects of these compounds at the cellular and subcellular level are limited. Using live cell fluorescence microscopy and a suite of fluorescent marker proteins, we studied the intracellular responses of the plant cell cytoskeleton and several membrane-bound organelles to NA and AEO treatments. A rapid disassembly of cortical microtubules and a decrease in dynamics associated with actin filaments was observed in response to these treatments. Concomitantly, the integrity and dynamics of mitochondria, peroxisomes, Golgi stacks, and endoplasmic reticulum were also altered. AEO treatments were the most toxic to cells and resulted in the accumulation reactive oxygen species. This study provides foundational evidence for intracellular responses to NA and AEO exposure using two evolutionarily diverse model plant cell types. This cellular assay could be used to identify the most toxic components of AEO sub-fractions, and assist in determining the effectiveness of OSPW remediation efforts.

Exposure to naphthenic acids and the acid extractable organic fraction from oil sands process-affected water alters the subcellular structure and dynamics of plant cells.

Bitumen extraction from surface-mined oil sands deposits results in the accumulation of large volumes of oil sands process-affected water (OSPW). Naphthenic acids (NAs) are primary contributors to OSPW toxicity and have been a focal point for the development of OSPW remediation strategies. Phytoremediation is an approach that utilizes plants and their associated microbes to remediate contaminants from soil and groundwater. While previous evidence has indicated a role for phytoremediation in OSPW treatment through the transformation and degradation of NAs, there are no reports that demonstrate the direct uptake of NAs into plant tissue. Using NAs labelled with C radioisotopes (C-NAs) paired with whole-plant autoradiography, we show that NAs representing aliphatic (linear), single-ring, and diamondoid compounds were effectively removed from hydroponic solution and OSPW-treated soil by sandbar willow (Salix interior) and slender wheatgrass (Elymus trachycaulus) and their associated microbiomes. The NA-derived C label accumulated in root and shoot tissues of both plant species and was concentrated in vascular tissue and rapidly growing sink tissues, indicating that C-NAs or their metabolic derivatives were incorporated into physiological processes within the plants. Slender wheatgrass seedlings grown under axenic (sterile) hydroponic and soil conditions also effectively removed all C-NAs, including a highly stable diamondoid NA, demonstrating that plants can directly take up simple and complex NAs without the assistance of microbes. Furthermore, root and shoot tissue fractionation into major biomolecule groups suggests that NA-derived carbon is allocated toward biomolecule synthesis rapidly after NA treatment. These findings provide evidence of plant-mediated uptake of NAs and support a direct role for plants and their associated microbes in the development of future large-scale OSPW phytoremediation strategies.

Detection of naphthenic acid uptake into root and shoot tissues indicates a direct role for plants in the remediation of oil sands process-affected water.

The extraction and processing of bitumen from the oil sands in northern Alberta, Canada generates large volumes of oil sands process-affected water (OSPW). OSPW contains a complex mixture of inorganic and organic compounds, including naphthenic acid fraction compounds (NAFCs) that are of particular concern due to their toxicity to aquatic organisms. Phytoremediation is a cost-effective, scalable approach that has the potential to remove NAFCs from OSPW and reduce OSPW toxicity. Environmental pH influences the chemical form and bioavailability of NAFCs. However, little is known about the influence of pH on the uptake of NAFCs in plant systems. This study sought to elucidate the impact of rhizosphere pH on the uptake of NAFCs using a sandbar willow (Salix interior) hydroponic system. To mimic and maintain the naturally low pH conditions of the root, OSPW solutions in these systems were adjusted to a low pH level (pH 5.0) and their NAFC uptake from solution was compared to that of OSPW at native pH (pH 8.0). Our findings revealed that the lower pH hydroponic systems demonstrated enhanced NAFC removal from solution as determined by LC-MS analysis, where up to 26% of NAFCs were removed from OSPW over 72 h at pH 5.0 compared to 8% removed at pH 8.0. Similarly, analysis of spike-in C-labeled NAs demonstrated that the OSPW hydroponic system rapidly removed a relatively labile NA (C-cyclohexane carboxylic acid) from solution at both pH levels, whereas near complete removal of a recalcitrant NA (C-1-adamantane carboxylic acid) was observed in pH 5.0 solutions only. These results provide insight into the importance of rhizosphere pH on efficient NAFC uptake by plant root systems. Further research will determine whether OSPW phytoremediation efficiency can be enhanced using field treatment conditions that promote low rhizosphere pH levels.

The effect of rhizosphere pH on removal of naphthenic acid fraction compounds from oil sands process-affected water in a willow hydroponic system.

The Athabasca oil sands region of Alberta, Canada contains one of the world's largest unconventional petroleum deposits. There is concern about residual contaminants where tailings are integrated during reclamation and the related adverse effects this may have. Some of the primary toxic organic contaminants in oilsands tailings are naphthenic acid fraction compounds (NAFCs). To plan for successful reclamation, it is imperative to understand the behaviour and fate of tailings-derived NAFCs over time where these are re-integrated into landforms. In this companion article to Degenhardt et al. (2023), we examine different reclamation integration scenarios using oil sands process-affected materials (OSPMs) at laboratory scale using wetland plants and minimal amounts of caps to explore how cap materials and thickness will affect the of NAFCs in the systems. Specifically, we examine how capping materials and thicknesses affect NAFCs adsorbed to two treated fluid fine tailings, centrifuged (CF) and co-mixed (CM) tailings over three years. Both CF and CM were placed in columns capped with peat mineral mix (PMM) and/or glacial till and planted with graminoid or woody wetland plants. Both CF and CM had considerable NAFC concentrations (CF 3717 mg/kg, CM 321 mg/kg). The O NAFC class was >90 % of the total adsorbed to CF and CM throughout. Relatively thin PMM caps reduced NAFC burdens in CF columns, where 10 cm of PMM resulted in the greatest reduction. Expressed water from substrate self-weight consolidation had significantly lower NAFC concentrations when capping material was present. However, NAFC oxidation (i.e., O to O, O to O, etc.) was limited in capped CF and CM. These results indicate that capping CF and CM with a thin (5-10 cm) layer of PMM may help reduce NAFC concentrations and limit their mobility into the cap, potentially lowering plant mortality and improving tailings reclamation success rates.

Chemical succession of naphthenic acid fraction compounds in reclamation landscape mesocosms established on centrifuged and co-mixed fluid fine tailings from the Athabasca oil sands.

Article	Year
Exposure to naphthenic acids and the acid extractable organic fraction from oil sands process-affected water alters the subcellular structure and dynamics of plant cells. The Science of the total environment\| PubMed ID: 30463136	2019
Detection of naphthenic acid uptake into root and shoot tissues indicates a direct role for plants in the remediation of oil sands process-affected water. The Science of the total environment\| PubMed ID: 34328940	2021
The effect of rhizosphere pH on removal of naphthenic acid fraction compounds from oil sands process-affected water in a willow hydroponic system. The Science of the total environment\| PubMed ID: 38997021	2024
Chemical succession of naphthenic acid fraction compounds in reclamation landscape mesocosms established on centrifuged and co-mixed fluid fine tailings from the Athabasca oil sands. The Science of the total environment\| PubMed ID: 39637536	2024

Mitchell E. Alberts

Biography

JoVE Journal Publications

Other Publications