Skip to main content

Currently Skimming:

3 Environmental Processes, Behavior, and Toxicity of Diluted Bitumen
Pages 35-72

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 35...
... The discussion further distinguishes ways in which the behavior of diluted bitumen is similar to or distinct from that of the light and medium crude oils that are commonly transported in U.S. pipelines.
From page 36...
... Notably, one potential outcome of photooxidation of crude oils is the production of persistent molecules in the environment32 containing carboxylic acids and alcohols, which may be soluble in water. Thus, these photoproducts may be transported in surface waters or groundwater.35 Photochemical enhancement of toxicity has been demonstrated for some polycyclic aromatic hydrocarbons (PAHs)
From page 37...
... ENVIRONMENTAL PROCESSES, BEHAVIOR, AND TOXICITY 37 Figure 3-1  Processes affecting the composition, amount, and behavior of diluted bitumen.
From page 38...
... studied shortterm biodegradation in the laboratory using residual oil in sediment from the Kalamazoo River that was collected 19-20 months after a diluted bitumen spill.41 Over 28 days of aerobic incubation of sediment slurries with inorganic nutrients added, about 25% of the total petroleum hydrocarbons degraded, mostly in the first 14 days. The decreasing rate of biodegradation over the 28-day period suggested that the majority of the spilled oil would not degrade over time scales of at least a few months in spite of the experiment's favorable conditions for bacterial activity.
From page 39...
... The relatively light natural-gas condensates often used as the diluent in diluted bitumen are particularly volatile. The loss of volatiles thus leads to a residue strongly resembling the original bitumen, and this is a key behavior that distinguishes diluted bitumen from other commonly transported crude oils.
From page 40...
... The time difference could be important when responding to an oil spill, where a difference of 12 hours could result in submergence of the oil. Dissolution If the spilled oil is in contact with water, components that are at least slightly soluble in water will be lost by dissolution.
From page 41...
... Spreading On land, spreading of spilled oil is often limited, but when oil reaches a water surface it starts to spread immediately.45 Unless constrained, the oil will continue to spread out into a thin film, or slick, due mostly to interfacial tension.45 Spreading rapidly increases the footprint of oil in the environment and can make recovery efforts more difficult, but it also makes the oil more exposed to photooxidation and evaporation. Small amounts of crude oil can spread into a very thin layer, or "sheen," that is readily visible.
From page 42...
... rose almost vertically and reached the surface within hours,44c,48 while small droplets rose more slowly or became permanently entrained.49 Studies of surface oil slicks50 predicted rapid transport of large oil droplets and slow transport of smaller droplets, causing the formation of a comet-shaped oil slick on the water surface. The DSD affects not only the transport but also the fate and toxicity of spilled oil.
From page 43...
... A his topathological study of fishes conducted shortly after the spill showed evidence for toxic effects, whereas short-term bioassays with invertebrates conducted in later years were less conclusive. Sampling of fishes and benthic invertebrates indicated that communities returned to normal after the first year, although the apparent decline in the first year was clearest for invertebrates, and it is difficult to distinguish the relative roles of direct toxicity of the spilled oil from the effects of cleanup activities (particularly sediment disturbance)
From page 44...
... with time as a function of the oil viscosity, based on model simulations.53 High-viscosity oils would require hours to disperse into an equilibrium droplet size distribution. rate (ε, W/kg)
From page 45...
... The viscosities of mesostable emulsions are 20-80 times higher than that of the starting oil. These emulsions generally break down within a few days into oil and water or sometimes into water, oil, and emulsion remnants.51 Mesostable emulsions are viscous liquids that are reddish brown in color.
From page 46...
... The dissolution of soluble components from oil may also cease once emulsification has occurred. Adhesion Adhesion was considered in Chapter 2 as a physical property of oil, and diluted bitumen tends to be more adhesive than other commonly transported crude oils.
From page 47...
... of sufficient density to submerge. This section focuses on OPAs, although the high density of weathered diluted bitumen is expected to increase sedimentation by all three routes, relative to commonly transported crude oils.
From page 48...
... The formation of aggregates depends on the viscosity of the oil droplet, the surface areas and mineralogy of the particles, and the salinity of the water.58 Salinity enhances the formation of OPAs, but the onset of aggregation is very steep, becoming important at salinities as low as 1/200 that of seawater.54b, 58b The extent of adsorption also depends on the surface properties of the sediment particles and other particles such as algal cells. The relative quantity of residual oil produced by weathering is from 5- to 50-fold greater than the quantity produced by weathering of equal volumes of light and medium crude oils.
From page 49...
... Because viscous oils tend to break into large droplets,59 the OPAs resulting from these oils would tend to be large, and if their density is greater than that of the receiving water, they would settle to the bottom. This formation of large OPAs is a major distinction between diluted bitumen, which rapidly weathers to a viscous residue, and commonly transported crude oils.
From page 50...
... ENVIRONMENTAL BEHAVIOR This section addresses how oil spills behave in and potentially impact specific environments, with particular attention to how spills of diluted bitumen may be similar to or distinct from those of other commonly transported crude oils. The toxicity of diluted bitumen is reviewed in a following section.
From page 51...
... Research at the Bemidji site has provided a wealth of information on the rates and limitations of the microbial processes that biodegrade oil, and this information has been integrated into a mathematical model that informs decisions about remediation of subsurface oil spills. SOURCE: Delin et al.69
From page 52...
... Removal of oily vegetation and soils severely disturbed the riparian and floodplain ecosystems, even though this was done manually in all but the most heavily oiled locations, where excavation was necessary. In terrestrial ecosystems, spills of diluted bitumen and of light or medium crude oils present similar challenges for cleanup.
From page 53...
... Inland Lakes and Reservoirs Inland lakes and reservoirs vary greatly in depth, exposure to wind and currents, suspended matter, and submerged and emergent aquatic vegetation, all of which potentially affect the behavior and impacts of oil spilled into these environments. Spilled oil may enter a lake or reservoir along a shoreline, or from tributaries.
From page 54...
... . Unless the water is deep enough that submergence of oil poses an issue, diluted bitumen and commonly transported crude oils pose many similar challenges following release in wetlands, but three factors specific to diluted bitumen can be mentioned.
From page 55...
... The answers to these questions are likely to be different for diluted bitumen compared to other commonly transported crude oils. Estuaries and Coastal Zones Pipeline spills can readily reach coastal zones if they occur in tributaries or along estuaries, or at coastal processing facilities.
From page 56...
... Despite the chemical and physical differences between the heavy crude oil spilled at Refugio and diluted bitumen, several aspects of the event provide for a valuable point of comparison for this study, which led to a site visit from members of the study committee. Unanticipated Complexities The May 19, 2015, rupture to Line 901 occurred on the inland side of a four-lane highway during daylight hours, though an earthen berm paralleling the highway prevented motorists from seeing the oil.
From page 57...
... Valentine 1.0 km, a scale that is too large to quantify the processes occurring in the coastal zone. While waves in coastal areas tend to bring the crude oil to the beach, there are situations where regional, longshore, and rip currents transport crude oil offshore and parallel to the shoreline and deposit it miles away from where it was released (Box 3-3)
From page 58...
... tend to penetrate very little within the sediment. High adhesion of heavy crude and weathered diluted bitumen oils further reduces their mobility in porous media, making them as amenable to recovery as other crude oils.
From page 59...
... The effects of the spill were limited due to favorable conditions for recovery:77 •  here was sunny weather with little stormwater flow (slowed the movement of T oil in storm drains and facilitated evaporation of oil)
From page 60...
... Also of concern are the 3- to 5-ring (unsubstituted TABLE 3-1  Five-Year Average Concentrations and Ranges of BTEX in Various Crude Oils in Percent Volumeii Light Crude Medium Crude Heavy Crude Diluted Bitumen Benzene 0.22 0.42 0.12 0.16 (<0.01-0.38)
From page 61...
... A summary of PAH concentrations in some commonly transported crude oils and diluted bitumen is presented in the previous chapter (Table 2-2)
From page 62...
... Concentrations of 3- and 4-ring unsubstituted parent and alkyl PAHs are similar or higher in Cold Lake Blend in comparison to other commonly transported crudes as listed in Table 2-2 in Chapter 2, although that blend contains higher levels of total phenanthrenes, fluorenes and chrysenes compared with light and medium crude oils. Therefore, based on the limited available research, it is expected that exposure to diluted bitumen would cause similar or higher chronic toxicity to fish embryos, although further chemical characterization of diluted bitumen along with more toxicity studies in other fish species would be required to confirm this.
From page 63...
... Overall the toxicity (chronic and acute) of fresh and weathered diluted bitumen and its residues to freshwater, estuarine, and marine species at various life stages is at this time very understudied compared with other commonly transported light and medium crude oils.
From page 64...
... This section aims to compare potentially hazardous characteristics of diluted bitumen with those of other commonly transported crude oils and identify whether diluted bitumen may pose similar or distinct human health risks. Inhalation and dermal exposure are typically immediate concerns for the first responders and the public in the vicinity of the spill.
From page 65...
... were detected at levels of concern at a drinking water treatment plant forcing the closure of the water intakes. Given the similar concentrations of BTEX in diluted bitumen and other commonly transported crude oils in the U.S.
From page 66...
... Therefore, there may be chemicals of toxicological concern unique to diluted bitumen that have not yet been characterized. This consideration is an important caveat for an assessment of relative human health risk for diluted bitumen spills compared to spills of commonly transported crude oils: an assessment based only on known BTEX concentrations must be considered incomplete and therefore tentative.
From page 67...
... Diluted bitumen products will initially float with the lack of turbulence in fresh water, and at that time they can be cleaned to levels of low toxicity, but are persistent and can cause chronic sheening that can trigger the need for extensive treatment, particularly in inland areas where natural removal processes are slow. Photo Credit: U.S.
From page 68...
... pyrene levels in Cold Lake diluted bitumen are 3.01 µg/g compared to the light and medium crudes ranging from 0.25–0.74 µg/g. As mentioned above there also are many unknown compounds in crude oils for which we do not know the environmental fate, bioavailability and potential impact to organisms.
From page 69...
... However, the potential toxicological risks to humans and animals, particularly longerterm exposures, are currently unknown compared to commonly transported crude oils. CONCLUSIONS In some respects the environmental effects of diluted bitumen spills resemble those of spills of other commonly transported crude oils, as long
From page 70...
... The loss of the lighter fraction and resultant potential for submergence of residual oil manifests more quickly and will involve a greater fraction of the spilled oil than in the case of light and medium crude oils. Toxicity of the residual bitumen has received little study, although toxic effects of both organic substances and associated metals have been observed in the vicinity of oil sands deposits in western Canada.
From page 71...
... Until there is more toxicological research specifically targeting diluted bitumen, the acute, chronic, sub-lethal and longer-term toxicities of diluted bitumen relative to conventional crude oils will be poorly known.


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.