I. LITERATURE REVIEW OF OFFSHORE OIL AND GAS DRILLING
34
The chemical fate of metal emissions from the various offshore drilling activities also depends
on the physico-chemical and bathymetric conditions of the marine environment. Indeed,
according to several characteristics of this environment such as redox conditions, marine currents
and type of sediments; the behavior of each trace or major metallic element is variable. There is
competition between several biogeochemical processes that govern the mobility and transfer,
biodegradation and chemical speciation, toxicity and bioavailability of these elements in the
marine environement.
The main metals present in the aqueous sludge, in terms of quantities and environmental impact,
are arsenic, barium, mercury, zinc, chromium, cadmium, copper, iron, nickel and lead present in
the barite (BaSO4; additive) or in the material removed from the geological formations through
which the borehole was drilled. The bioavailability and toxicity of barium to marine organisms is
low due to its low solubility in the water column and in sediments.
Thus, the different organic pollutants as aromatic hydrocarbons and inorganic as metals (trace or
major), depending on their concentrations and their toxicity thresholds, can cause acute toxic
effects to certain less resistant species in the ecosystem. They can also have long-term toxic
effects due to their bioaccumulation and biomagnification in the food chain up to humans via the
consumption of seafood products. This mechanism leads to marine and terrestrial Ecotoxicity as
well as that of Human Toxicity, which are two categories of impacts analyzed within the
framework of the Life Cycle Assessment applied to offshore drilling in the following chapters.
34
The chemical fate of metal emissions from the various offshore drilling activities also depends
on the physico-chemical and bathymetric conditions of the marine environment. Indeed,
according to several characteristics of this environment such as redox conditions, marine currents
and type of sediments; the behavior of each trace or major metallic element is variable. There is
competition between several biogeochemical processes that govern the mobility and transfer,
biodegradation and chemical speciation, toxicity and bioavailability of these elements in the
marine environement.
The main metals present in the aqueous sludge, in terms of quantities and environmental impact,
are arsenic, barium, mercury, zinc, chromium, cadmium, copper, iron, nickel and lead present in
the barite (BaSO4; additive) or in the material removed from the geological formations through
which the borehole was drilled. The bioavailability and toxicity of barium to marine organisms is
low due to its low solubility in the water column and in sediments.
Thus, the different organic pollutants as aromatic hydrocarbons and inorganic as metals (trace or
major), depending on their concentrations and their toxicity thresholds, can cause acute toxic
effects to certain less resistant species in the ecosystem. They can also have long-term toxic
effects due to their bioaccumulation and biomagnification in the food chain up to humans via the
consumption of seafood products. This mechanism leads to marine and terrestrial Ecotoxicity as
well as that of Human Toxicity, which are two categories of impacts analyzed within the
framework of the Life Cycle Assessment applied to offshore drilling in the following chapters.