Contaminant status of the North Sea

Abstract

From the Executive Summary: “The main contaminants associated with the oil and gas industry in the North Sea come from produced water and drill cuttings. Produced water is now the main source, having overtaken drill cuttings since the change from oil based muds (OBMs) to other, less harmful alternatives and since the maturity of the production fields.

Cuttings Piles

There is a wide range of metals in cuttings piles. However, in most cases the reported concentrations of the “Red List” metals are low…

Produced Water

The hydrocarbon-producing areas of the North Sea can be divided into three regions. The northern and central areas produce both oil and gas while the southern North Sea predominantly produces gas with some fields also producing condensate. Higher quantities of corrosion inhibitors, gas treatment products and scale inhibitors are discharged into the North Sea than chemicals of any other functional group.

Biota

There are two main sources of potential biological effect upon marine organisms that are associated with oil and gas production activities: those caused by production discharges, i.e. produced water, and those associated with drilling activities. Operational aerial emissions may also give rise to deposition of contaminants (in particular the lower molecular weight compounds such as naphthalene and pyrene) on the sea surface.

Exposure of marine organisms to contaminants occurs by two routes, either through passive diffusion or active uptake processes via surface membranes, or through absorption from the gut in association with fatty materials. Organisms spending the majority of their life-cycle in the water column are therefore likely to receive the highest exposure to contaminants that remain in solution. Contaminants that are/or become readily associated with suspended particles are likely to become associated with the sediments. The main exposure route for particle bound contaminants will be through direct ingestion by various benthic species or indirectly when these same species are consumed by other organisms. In addition, those organisms living in close association with the sediments may also absorb contaminants from interstitial water.

The biological effects of platform activities are wide-ranging. The contaminants in produced water plumes may have direct effects on populations of both pelagic invertebrate and vertebrate species in the vicinity of the discharge and also indirect effects via bioaccumulation and bioconcentration of contaminants through the food chain. Drilling activities primarily have effects on the benthic fauna directly underneath and some distance from a platform, but they also potentially have impacts on fish species that live in close association with the sediment and feed upon invertebrate populations that may be contaminated.

The effects of contaminants upon biological systems can be manifested at a number of different levels of organisation ranging from the cellular and organ level through to changes in the sizes of populations and ultimately to altered diversity and functioning within the community of interacting populations. Changes that occur at the cellular and organ level may provide an ‘early warning system’ of more dramatic and possibly irreversible effects upon populations or communities. The occurrence of various biological effects following exposure to contaminants that are predominantly associated with oil and gas exploration and production activities are discussed in relation to data from laboratory studies and from monitoring programmes.”