Asphaltenes
Now let’s examine the
chemical structure of Wabasca oil to understand why it is so toxic.
Like most heavy hydrocarbons, the structure of this asphalt-like
substance is similar to a strip of hexagonal chicken wire. It is made
of a long chain-link fence of benzene-rings of 6 carbon atoms and
hydrogen. These links become more difficult to break down (become
more insoluble) and have higher boiling points as they get longer and
heavier.
Figure 8
Hex Chicken Wire Analogy
Figure 9
Molecular Structure of Asphaltene
Source: RERI
These long chains are
called asphaltenes which reportedly comprise about 15% of the
Athabasca bitumens including Wabasca bitumen. They contain sulphur,
vanadium, nickel and Polycyclic aromatic hydrocarbons (PAHs). Some of
these PAHs are known or suspected cancer causing agents or
carcinogens. Wabasca bitumen also contains about 1% nitrogen.
Research in late 2013 at
Oregon State Universityi
has shown that newly discovered nitrated PAHs (NPAHs when combined
with nitrogen) can be hundreds of times more mutagenic than other
known carcinogenic PAHs. This means they can frequently cause DNA
damage in the cells on the salmonella
assay which might indicate a higher cancer causing potential than
other PAHs. These compounds are difficult to biodegrade because
bacteria cannot easily assimilate asphaltenes and they are so recent
identified that they haven’t yet been thoroughly studied in
Athabasca tar sands.
Naphthenic Acids
When heavy hydrocarbon
molecules come into contact with hot water or steam they can release
corrosive Naphthenic Acids (NA). These acids are the principal
contaminants in tar sands waters and are toxic to fish, amphibians
and other organisms.
Figure
10
NA Aquatic Toxicity
Source: Eickhoff
et. al. 2010
Young rainbow trout and crustaceans like Daphnia magna have been shown to be particularly sensitive to NA. Other sub-lethal effects of NA include changes in growth and reproduction as well as hormone disruption. Studies indicate that NA can remain in the environment for many years.
Human Health Concerns are
addressed by the EPA Naphthenic Acid Screening Level Hazard
Characterizationii
sponsored by the American Petroleum Institute High Production Volume
Program. They determined that “No adequate data are available to
assess the repeated-dose, reproductive and developmental toxicity of
the category members.” They did find that NA in SAP oil was
“severely irritating to the rabbit eye and mice skin.”
Furthermore, “No adequate data are available for acute toxicity to
fish and aquatic invertebrates and toxicity to aquatic plants and
chronic toxicity to fish and aquatic invertebrates.”
Naphthenic Acids are
extremely complex containing hundreds of organic acid compounds which
can be measured in a variety of ways. Crude oils routinely are
classified according to Total Acid Number (TAN) which is a rough
indication of Naphthenic Acid concentration. According to ESMAP, “The
TAN of crude oils is an accepted measure of potential corrosivity: it
quantifies the number of milligrams of potassium hydroxide (KOH)
needed to neutralize one gram of sample crude oil. The acidity of a
crude oil has important economic and technical impacts on refining
operations. A TAN exceeding 1mg KOH/g is
commonly considered corrosive; however
corrosion problems can occur in crudes with TAN as low as 0.3 for
several reasons including velocities and the nature of acidic species
present.”iii
Wabasca Heavy has some of
the highest TAN numbers in Canada ranking 6th
out of 29 with a value generally exceeding 1mg KOH/g and a Crude
monitor reading of 1.06 the week before the
Mayflower spill. It also has high sulphur
content (4.14%) which ranks 2nd highest among 29 crude oils from
Canada.iv
i
ECOWATCH/ Oregon
State University | January 6, 2014
Newly
Discovered Compounds Hundreds of Times More Toxic Than Known
Carcinogens
iii
Bacon, Robert and Silvana Tordo 2005
Crude
Oil Price Differentials and Differences in Oil Qualities: A
Statistical Analysis
ESMAP
TECHNICAL PAPER 081 Footnote 7 page 10
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