Thus, tri-, tetra-, and pentacyclic (hopanes) terpanes,
and particularly 17α(H)21β(H) hopane, that are
degraded at the ultimate stage of petroleum degradation (10–15 years after their input into the environment) are selected as endogenous standards.
(ii) Petroleum chemical composition (Head et al. 2003).
(iii) Petroleum physical state (cf. emulsion water-in-oil and
oil-in-water).
(iv) Nutrient concentration: The petroleum input in the
ecosystem corresponds to an important carbon supply
that generates a major imbalance of C/N and C/P
ratios.
(v) Dioxygen concentration: The aerobic biodegradation is
usually more rapid than the anaerobic one.
(vi) Several physical factors such as hydrodynamism, pH,
temperature, salinity. For example, Bacteria (Margesin
and Schinner 2001) and Archaea (Aiken et al.;
Rudolph et al. 2001; Khelifi et al. 2010) oxidize
hydrocarbons at low and elevated temperatures. In
the same way, Bacteria (Bertrand et al. 1993; Gauthier
et al. 1992; Fernandez-Linarez et al. 1995; Margesin
and Schinner 2001) and Archaea (Bertrand et al. 1990;
Al-Mailem et al. 2010) degrade hydrocarbons at high
salt concentrations.
(vii) The presence of emulsifying compounds that may be
chemical (dispersal agents) or biological (biosurfactants).
In the water column, biodegradation is essentially
aerobic. In the sediments, it is aerobic in the superficial
layer (less than 2–3 mm in coastal areas) and anaerobic in
deeper layers where it is extremely slowed down. For
instance, in an in situ experiment conducted in coastal
sediments at 20 m depth, Miralles and collaborators (2007)
showed, 16 months after implementation in the sediment of
Arabian Light crude oil, an important biodegradation of
n-alkanes (80–90 %) and isoprenoids (55–60 %) under
oxic conditions. Under anoxic conditions, biodegradation
is markedly lower, for instance, that of eicosane (saturated
hydrocarbon C 20 ) is 90 % in oxic zone and 17 % in sediment
anoxic layer. It is important to note that in vitro aerobic
biodegradation of the same hydrocarbon by hydrocarbonoclastic single strains or communities isolated from the
same site is substantially faster: eicosane is 90 % biodegraded
within 24 or 48 h (time scale is no more month but hour).
To explain hydrocarbon evolution within sediments, the
action of microorganisms (bioturbation) must be also taken
into account (Grossi et al. 2002; cf. Sect. 14.2.4). They exert
two antagonistic effects: the first one is burying in the
sediment anoxic layers which may lead to hydrocarbon
sequestration in a zone where biodegradation becomes
impossible and the second one is resuspension in the water
column and sediment oxygenation (tunnel formation) that
increases the hydrocarbon availability and favors aerobic
biodegradation processes.
16.8.3 Bioremediation of Contaminated Sites
16.8.3.1 Bioremediation of Marine Ecosystems;
Physical, Chemical, and Biological
Treatments
Means to fight against accidental and huge oil spills can be
grouped into three categories (Fig. 16.43): mechanical means
(pollution confinement by setting up barriers and oil recovery
(Fig. 16.44), chemical means (in situ burning; washing
contaminated substrates with pressurized water, cold or
warm; use of dispersal agents; etc.), and biological means
(Atlas 1995; Swannell et al. 1996; Bocard 2007; Singh et al.
2012; Dash et al. 2013). Treatments susceptible to be
implemented depend on the nature of petroleum products
discharged at sea. For instance, in the case of Erika shipwreck
in December 1999 that occurred in the Atlantic off Belle-Ile,
the spilled oil, 19000 tons of heavy fuel oil “N
2”, was not
crude oil but a refining product, highly viscous and rich in
aromatic compounds, resins, and asphaltenes (saturated:
25 %; aromatics: 55 %; resins: 13 %; asphaltenes: 7 %)
(Vandecasteele 2008). This product was poorly biodegradable; biodegradation undertaken in laboratory under optimal
conditions was less than 10–15 %. Under such conditions, the
only solution to decontaminate the affected areas was the
implementation of mechanical and physicochemical means
(washing rocks, oil recovery with shovels and buckets, etc.).
A similar situation took place with the pollution generated by
the Prestige shipwreck (2002).
In different circumstances, implementation of
microbiological fighting means can be considered. This
means are regrouped under the term bioremediation; they
rely on metabolic capacities of hydrocarbonoclastic
microorganisms. Biostimulation and bioincrease strategies
that were developed for coastal area bioremediation are very
difficult to implement in open sea where it is impossible to
keep nutrients in contact with the oil spill and where
hydrocarbonoclastic bacteria concentrations are extremely
low. Furthermore, up to now, the efficiency of these
treatments in open sea was never demonstrated. In contrast,
promising results were obtained on the coastline through
biostimulation or by combining bioaugmentation and
biostimulation.
Bioaugmentation (or Bioincrease)
Microorganisms, isolated from the environment and/or
modified by genetic engineering, must satisfy criteria
already mentioned:
(i) To have a large metabolic activity spectrum enabling
the degradation of the different components present in
the petroleum product.
(ii) To be adapted to the geographical area affected by the
pollution. Hydrocarbonoclastic communities that are
734
J.-C. Bertrand et al.
and particularly 17α(H)21β(H) hopane, that are
degraded at the ultimate stage of petroleum degradation (10–15 years after their input into the environment) are selected as endogenous standards.
(ii) Petroleum chemical composition (Head et al. 2003).
(iii) Petroleum physical state (cf. emulsion water-in-oil and
oil-in-water).
(iv) Nutrient concentration: The petroleum input in the
ecosystem corresponds to an important carbon supply
that generates a major imbalance of C/N and C/P
ratios.
(v) Dioxygen concentration: The aerobic biodegradation is
usually more rapid than the anaerobic one.
(vi) Several physical factors such as hydrodynamism, pH,
temperature, salinity. For example, Bacteria (Margesin
and Schinner 2001) and Archaea (Aiken et al.;
Rudolph et al. 2001; Khelifi et al. 2010) oxidize
hydrocarbons at low and elevated temperatures. In
the same way, Bacteria (Bertrand et al. 1993; Gauthier
et al. 1992; Fernandez-Linarez et al. 1995; Margesin
and Schinner 2001) and Archaea (Bertrand et al. 1990;
Al-Mailem et al. 2010) degrade hydrocarbons at high
salt concentrations.
(vii) The presence of emulsifying compounds that may be
chemical (dispersal agents) or biological (biosurfactants).
In the water column, biodegradation is essentially
aerobic. In the sediments, it is aerobic in the superficial
layer (less than 2–3 mm in coastal areas) and anaerobic in
deeper layers where it is extremely slowed down. For
instance, in an in situ experiment conducted in coastal
sediments at 20 m depth, Miralles and collaborators (2007)
showed, 16 months after implementation in the sediment of
Arabian Light crude oil, an important biodegradation of
n-alkanes (80–90 %) and isoprenoids (55–60 %) under
oxic conditions. Under anoxic conditions, biodegradation
is markedly lower, for instance, that of eicosane (saturated
hydrocarbon C 20 ) is 90 % in oxic zone and 17 % in sediment
anoxic layer. It is important to note that in vitro aerobic
biodegradation of the same hydrocarbon by hydrocarbonoclastic single strains or communities isolated from the
same site is substantially faster: eicosane is 90 % biodegraded
within 24 or 48 h (time scale is no more month but hour).
To explain hydrocarbon evolution within sediments, the
action of microorganisms (bioturbation) must be also taken
into account (Grossi et al. 2002; cf. Sect. 14.2.4). They exert
two antagonistic effects: the first one is burying in the
sediment anoxic layers which may lead to hydrocarbon
sequestration in a zone where biodegradation becomes
impossible and the second one is resuspension in the water
column and sediment oxygenation (tunnel formation) that
increases the hydrocarbon availability and favors aerobic
biodegradation processes.
16.8.3 Bioremediation of Contaminated Sites
16.8.3.1 Bioremediation of Marine Ecosystems;
Physical, Chemical, and Biological
Treatments
Means to fight against accidental and huge oil spills can be
grouped into three categories (Fig. 16.43): mechanical means
(pollution confinement by setting up barriers and oil recovery
(Fig. 16.44), chemical means (in situ burning; washing
contaminated substrates with pressurized water, cold or
warm; use of dispersal agents; etc.), and biological means
(Atlas 1995; Swannell et al. 1996; Bocard 2007; Singh et al.
2012; Dash et al. 2013). Treatments susceptible to be
implemented depend on the nature of petroleum products
discharged at sea. For instance, in the case of Erika shipwreck
in December 1999 that occurred in the Atlantic off Belle-Ile,
the spilled oil, 19000 tons of heavy fuel oil “N
2”, was not
crude oil but a refining product, highly viscous and rich in
aromatic compounds, resins, and asphaltenes (saturated:
25 %; aromatics: 55 %; resins: 13 %; asphaltenes: 7 %)
(Vandecasteele 2008). This product was poorly biodegradable; biodegradation undertaken in laboratory under optimal
conditions was less than 10–15 %. Under such conditions, the
only solution to decontaminate the affected areas was the
implementation of mechanical and physicochemical means
(washing rocks, oil recovery with shovels and buckets, etc.).
A similar situation took place with the pollution generated by
the Prestige shipwreck (2002).
In different circumstances, implementation of
microbiological fighting means can be considered. This
means are regrouped under the term bioremediation; they
rely on metabolic capacities of hydrocarbonoclastic
microorganisms. Biostimulation and bioincrease strategies
that were developed for coastal area bioremediation are very
difficult to implement in open sea where it is impossible to
keep nutrients in contact with the oil spill and where
hydrocarbonoclastic bacteria concentrations are extremely
low. Furthermore, up to now, the efficiency of these
treatments in open sea was never demonstrated. In contrast,
promising results were obtained on the coastline through
biostimulation or by combining bioaugmentation and
biostimulation.
Bioaugmentation (or Bioincrease)
Microorganisms, isolated from the environment and/or
modified by genetic engineering, must satisfy criteria
already mentioned:
(i) To have a large metabolic activity spectrum enabling
the degradation of the different components present in
the petroleum product.
(ii) To be adapted to the geographical area affected by the
pollution. Hydrocarbonoclastic communities that are
734
J.-C. Bertrand et al.