Simulating a Spill of Diluted Bitumen: Environmental Weathering and Submergence in a Model Freshwater System

Abstract

The main petroleum product transported through pipelines in Canada is diluted bitumen (dilbit), a semiliquid form of heavy crude oil mixed with natural gas condensates to facilitate transport. The weathering, fate, behavior, and environmental effects of dilbit are crucial to consider when responding to a spill; however, few environmental studies on dilbit have been completed. We report on 11‐d‐long experimental spills of dilbit (Cold Lake Winter Blend) in outdoor microcosms meant to simulate a low‐energy aquatic system containing natural lake water and sediments treated with low (1:8000 oil:water) and high (1:800 oil:water) volumes of dilbit. In the first 24 h of the experiment, volatile hydrocarbons quickly evaporated from the dilbit, resulting in increased dilbit density and viscosity. These changes in dilbit's physical and chemical properties ultimately led to its submergence after 8 d. We also detected rapid accumulation of polycyclic aromatic compounds in the water column of the treated microcosms following the spills. The present study provides new information on the environmental fate and behavior of dilbit in a freshwater environment that will be critical to environmental risk assessments of proposed pipeline projects. In particular, the study demonstrates the propensity for dilbit to sink under ambient environmental conditions in freshwaters typical of many boreal lakes. Environ Toxicol Chem 2019;38:2621–2628. © 2019 SETAC

RNA Sequencing of Lake Charr Epidermal Mucus to Assess Molecular Effects of Diluted Bitumen Exposure in a Boreal Lake

“…As dilbit was exposed to weathering in the field, it is likely that lighter molecular weight compounds volatilized, leaving an increased proportion of higher molecular weight 3-and 4-ring PACs. Chemistry results are supported by previous studies simulating dilbit spills in outdoor tanks containing lake water and sediments where rapid desorption of PACs into the water column was observed, most notably phenanthrenes, dibenzothiophenes, and fluorenes (Stoyanovich et al, 2019).…”

“…Due to its complex chemical composition and multiple factors affecting its chemical properties, it may be difficult to understand the fate and behavior of spilled dilbit in freshwater environments. In order to better understand dilbit's behavior in low-energy lake systems, Stoyanovich et al, 2019 conducted experimental releases of dilbit in outdoor microcosms containing natural lake water and sediments (Stoyanovich et al, 2019). As volatile hydrocarbons evaporated, dilbit increased in density and viscosity, resulting in its submergence after 8 days.…”

Direct mass spectrometric analysis of naphthenic acids and polycyclic aromatic hydrocarbons in waters impacted by diluted bitumen and conventional crude oil

“…However, with time, weathering of DB allows a 112 portion of its lighter diluent content to evaporate. Evaporative loss of light oil components 113 increases the density of the bulk oil, potentially allowing a portion to submerge or sink, 114 particularly in turbulent waters with high concentrations of suspended mineral fines which 115 adhere to dispersed oil droplets and form dense oil-mineral aggregates (Hua et al, 2018;King et 116 al., 2014;Stoyanovich et al, 2019). Because DB is much more viscous than CC, it is much less 117 responsive to chemical dispersant application, particularly after weathering has occurred to any 118 appreciable extent (Yang et al, 2018).…”

Bioaccumulation and toxicokinetics of polycyclic aromatic compounds and metals in giant floater mussels (Pyganodon grandis) exposed to a simulated diluted bitumen spill

“…Since PAC contamination in the sediment was not a factor in this experiment, any PAC accumulation in mussel tissue was a result of exposure to contaminated water only. However, dilbit can sink in freshwater, as seen in the Kalamazoo River spill (U.S. Fish and Wildlife Service et al, 2015), as well as in a study involving outdoor microcosms containing natural lake water (Stoyanovich et al, 2019), making dilbit-contaminated sediment a potential source of PACs for freshwater mussels.…”