The Nederlandse Aardolie Maatschappij B.V. (NAM) is the largest gas producer In the Netherlands. The company operates a number of gas/condensate platforms on the Dutch continental shelf in the North Sea. From 8 of these platforms produced water is discharged directly into the sea. An extensive sampling, analysis and testing campaign was carried out in 1989 to characterise physical, chemical and ecotoxicological properties of these streams.

The total volume of water discharged from the NAM platforms was about 210,000 m in 1989. The average volume per platform was relatively small (about 70 m per day), certainly when compared to oil producing platforms. The^ total volume of oil discharged was about 160x10 kg, 50-70% thereof being present in the form of dispersed oil. The total volume of all organic substances, including polar compounds, Was about 400x10 kg.

The complex mixture of organic and inorganic components and their concentrations in the effluents indicate, with effluent EC/LC.- values between 1 and 420 ml/1, an acute toxic hazard to organisms directly exposed to the discharges. Acute toxic effects are, however, not expected beyond a distance of 50 m from the discharge point. A risk of sublethal effects cannot be excluded within distances of several hundred metres to a few kilometres from the discharge points. The dissolved organic components are most probably the prime cause of the acute toxicity, of which the volatile aromatic hydrocarbons are the most significant. These compounds were observed at concentrations of up to 480 mg/1.

Relatively high concentrations of metals were observed in the ' effluents. However, these metals did not contribute significantly to the acute toxicity of the streams. This suggests that metals were not present in a bioavailable form.

All effluents contained components which have the potential to be bioaccumulated by organisms. Polycyclic aromatic hydrocarbons, with concentrations ranging from 0.5 to 70 mg/1, were the major contributors.

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