Threshold values for the protection of marine ecosystems from NORM in subsea oil and gas infrastructure

This modelling study uses the ERICA Tool and Bateman's equation to derive sediment threshold values for radiation protection of the marine environment relevant to NORM-contaminated products (radium-contaminated scales, 210Pb films and 210Po films) found in subsea oil and gas infrastructure. Threshold values are calculated as the activity concentration of the NORM-contaminated products' head of chain radionuclide (i.e., 226Ra + 228Ra, 210Pb, or 210Po) that will increase radiation dose rates in sediments by 10 mu Gy/h to the most exposed organism at a given release time. The minimum threshold value (corresponding to peak radiation dose rates from the ingrowth of progeny) were for radium-contaminated scales, 0.009 Bq/g of 226Ra, 0.029 Bq/g of 228Ra (in the absence of 226Ra) or 0.14 Bq/g of 228Ra (in the presence of 226Ra), followed by 0.015 Bq/g for 210Pb films, and 1.6 Bq/g for 210Po films. These may be used as default threshold values. Added activity concentrations of the NORM-contaminated products to marine sediments below these threshold values implies a low radiological risk to organisms while exceedances imply that further investigation is necessary. Using contaminated product specific parameterisations, such as Kd values derived for Ra from a BaSO4 matrix in seawater, could greatly affect threshold values. Strong consideration should be given to deriving such data as part of specific radiological risk assessments for these products.