Radioactivity in produced water from Norwegian oil and gas installations - concentrations, bioavailability and doses to marine biota

Large amount of produced water containing elevated levels of radionuclides is discharged to the sea in connection with oil and gas production on the Norwegian Continental Shelf. So far no study has been performed to assess the potential radiological effec ts on marine biota in connection with radionuclide discharges to the North Sea. The produced water contains elevated levels of 226Ra and 228Ra. It is normally assumed that when this water, which is poor in sulphate, gets in contact with seawater rich in s ulphate, RaSO4 precipitates. The precipitated salts can then attach to other organic or inorganic particles and sequentially settle to the bottom close to the installation. Data on the speciation of radium, and the effect of major components in produced w ater on the speciation of radium, is however sparse. In today’s oil production, several chemicals are added, i.e. scale and corrosion inhibitors, emulsion breakers and surfactants, sulphide removers, etc. These chemicals are usually organic compounds co mprising functional groups, which may also interact with cations such as Ra2+. Thus, radium may exist in compounds more easily accessible for uptake in biota than the inorganic aqueous or food-borne form. An understanding of how different compounds in pro duced water affect the mobility, bioavailability and sedimentation of radium is essential to determine the fate and effects of radium discharges. For evaluation purposes the behaviour of produced water radium must be compared to radium already present in seawater. An assessment of existing data on natural radioactivity in the North Sea has revealed a lack of data in this area. This project aims at assessing this problem thorough an interdisiplinary study comprising survey of background levels, mobility studies of relevant radioactive isotopes, bioavailability studied at controlled environments, studies on effects on biota, modelling of the discharge, and calculation of doses to biota and humans.