Bioaccumulation and Toxicokinetics of Polycyclic Aromatic Compounds and Metals in Giant Floater Mussels (Pyganodon grandis) Exposed to a Simulated Diluted Bitumen Spill
Creators: name: Séguin, Jonathan Y.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2021
Subjects: Diluted Bitumen
Dilbit
IISD-ELA
Limnocorrals
Polycyclic Aromatic Compounds
PACs
Polycyclic aromatic hydrocarbons
PAHs
Metals
Bivalve
Mussels
Bioaccumulation
Bioconcentration
Toxicokinetics

description: Canadian bitumen is mainly transported in a diluted form via pipeline and train, all posing a risk as they can lead to the release of diluted bitumen (dilbit) in the environment. In the summer of 2018, a collaborative large-scale field experiment was conducted at the International Institute for Sustainable Development - Experimental Lakes Area (IISD-ELA), a world-renowned aquatic research facility. The research objectives of the Boreal lake Oil Release Experiment by Additions to Limnocorrals (BOREAL) project were to understand the fate, behaviour, and potential toxic effects of dilbit in a freshwater Boreal lake to inform evidence-based management strategies for the transport of dilbit. A range of controlled dilbit spills was performed in seven 10 m diameter limnocorrals (~100,000 L of water) resulting in environmentally realistic dilbit:water dilutions ranging from 1:69,200 to 1:504, representing the upper half of the distribution of oil spill sizes in North America in the last decade. Additionally, two limnocorrals not treated with dilbit were studied as controls. This thesis identifies the bioaccumulating compounds derived from naturally weathered dilbit in adult giant floater mussels (Pyganodon grandis), to determine the rates at which they were accumulated and excreted. More specifically, the bioaccumulation potential and toxicokinetic parameters of polycyclic aromatic compounds (PACs) and various metals were assessed in mussels exposed ex situ for 41 days (25 days of exposure and 16 days of depuration) to water from the limnocorrals. These compounds have shown to be toxic, carcinogenic, and mutagenic to aquatic organisms. Mussels exposed to dilbit-contaminated water experienced significantly greater TPACs concentrations (0.40 – 0.90 µg L-1, n=12) compared to mussels from the Control (0.017 µg L-1, n=4). Furthermore, dilbit-contaminated water had a higher proportion of alkylated PACs compared to their parent counterpart, demonstrating petrogenic PAC profiles. We detected significantly greater TPACs concentrations in mussels exposed to dilbit-contaminated water (25.92 – 27.79 µg g-1, ww Lipid, n=9, at day 25 of the uptake phase) compared to mussels from the Control (average of 2.62 ± 1.95 µg g-1, ww Lipid; ±SD, n=17). Alkylated PACs represented 96.4 ± 1.8%, ±SD, n=12 of TPACs in mussels from dilbit-contaminated treatments at day 25 of the uptake phase, indicating the importance of conducting a more inclusive assessment of petrochemical mixtures as most studies only focus on parent PACs. From first-order one-compartment models derived from nonlinear curve fitting of the accumulation phase or sequential modelling method, uptake (0.66 – 24.65 L g-1 day-1, n=87) and depuration (0.012 – 0.37 day-1, n=87) kinetic rate constants, as well as bioconcentration factors (log values from 3.85 – 6.12 L kg-1, n=87) for the 29 PACs that bioaccumulated in mussels suggested that alkylated PACs have greater bioaccumulation potential compared to their parent PAC counterpart. Results from this study also demonstrated that giant floater mussels could be used to biomonitor PAC contamination following oil spills as PACs accumulated in mussel tissue and were still present following the 16 day depuration phase. The results of this study are the largest, most comprehensive set of toxicokinetic and bioaccumulation information of PACs (44 analytes) in freshwater mussels obtained to date. Metal contamination following the controlled dilbit spill was minimal, but mussels exposed to water contaminated with naturally weathered dilbit experienced elevated concentrations of dissolved zinc (30.26 – 38.26 µg L-1, n=12) compared to the mussels in the uncontaminated water (6.75 ± 3.31 µg L-1, n=4), surpassing the Canadian water quality guidelines for the protection of aquatic life. However, it is not clear if dilbit contamination caused elevated zinc concentrations in the water as other factors, such as limnocorral building materials and/or galvanized minnow traps used in the limnocorrals, could have contributed to zinc contamination. Nonetheless, giant floater mussels did not accumulate zinc in their tissues.