Natural radionuclides in seafloor sediments of Norway’s continental shelf

Research Notes

One goal of Norway’s integrated ocean management plan is that “Operational discharges (from offshore petroleum activities) will not result in higher levels of naturally occurring radioactive substances”. Is the goal being reached? An interdisciplinary group of scientists are now trying to find out.

By: Hilde Elise Heldal and Andrey Volynkin // Institute of Marine Research.
Hallvard Haanes, Tanya Hevrøy and Hilde Skjerdal // Norwegian Radiation and Nuclear Safety Authority. Henning Jensen and Aivo Lepland // Geological Survey of Norway

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Radium-226 (226Ra) and radium-228 (228Ra) are two naturally occurring radionuclides with physical half-lives of 1 600 and 5.75 years, respectively. They are part of the decay chains of the primordial radionuclides uranium-238 (238U) and thorium-232 (232Th).

Natural sources for these radionuclides to the marine environment include radioactive decay of their parents in the water column and sediments, and supply from land. Levels are also dependent on the source rock. Elevated levels of 226Ra and 228Ra are expected in sediments derived from rocks such as granites and pegmatite, which are important carriers of both uranium and thorium. Factors that decrease Ra levels in Norwegian marine areas are radioactive decay and dilution by inflowing Atlantic water, which has low Ra concentrations.

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Researchers Anders Fuglevik and Hilde Elise Heldal from the Institute of Marine Research sampling sediments in the Barents Sea. Photos: Erlend Astad Lorentzen / Institute of Marine Research

Produced water

An additional anthropogenic source for 226Ra and 228Ra is discharge of produced water from the oil and gas industry. At the Norwegian continental shelf, this corresponds to approximately 400 GBq yearly of each radionuclide. Around 90% of this is discharged to the North Sea. Discharges from the UK oil and gas industry are of similar size (

Produced water contains levels of 226Ra and 228Ra that are up to three orders of magnitude higher than the background levels in the ambient seawater. The levels of natural radionuclides in the produced water vary greatly between different oil and gas fields. This variation may be related to the geological/mineralogical characteristics of the reservoirs. The amount of produced water discharged also varies greatly between different fields, often reflecting how long the field has been in production.


Results from simulations of the dispersion of 226Ra in the marine environment, and experimental studies of the uptake of 226Ra in marine organisms, indicate that the impact of these radionuclides on the marine environment is generally low. However, an environmental study published in 2012 indicates elevated levels of Ra in the upper layers of sediment in the Norwegian Trench and Skagerrak and highlights the need for further work to evaluate impacts of the produced water discharges.


In the NORM project, data on 226Ra and 228Ra from surface sediments of the Norwegian continental shelf collected during the period 2004-2020 have been compiled. Activity concentrations range from 7 to 670 and 6 to 318 Bq/kg dry weight, respectively. The highest levels are found in the northern North Sea. Several large oil and gas fields are located in this area, e.g. the Brage, Gullfaks, Snorre, and Troll Fields, all of which discharge relatively large volumes of produced water and natural radionuclides. The highest levels are considerably higher than what is generally found in the oceans around the world. The data indicate that the oil and gas industry contributes to elevated levels of natural radionuclides in surface sediments in the northern North Sea. Thus, the goal of Norway’s integrated ocean management plans is not being attained.

Apart from the northern North Sea, the levels of 226Ra and 228Ra are fairly similar across Norwegian marine areas. The observed variations may to a large degree be due to local variation in e.g. sediment composition. Statistical analyses of the relationship between radionuclide levels, organic carbon content and sediment grain size will be performed to further investigate this.

Further work

In further work, we will use sediment cores to study potential variations in activity concentrations over the last 50-60 years. The project also includes development of a method using barium (Ba) as a proxy for Ra. Ba is a chemical analogue to Ra, and the amount of data available in the MAREANO database is much larger than for 226Ra and 228Ra. Knowledge of the Ba distribution in sediments in Norwegian marine areas will give deeper insight into the distribution of 226Ra and 228Ra in the marine environment.

Further reading

Dowdall M, Lepland A (2012) Elevated levels of radium-226 and radium-228 in marine sediments of the Norwegian Trench (“Norskrenna”) and Skagerrak. Marine Pollution Bulletin 64, 2069-2076, doi: 10.1016/j.marpolbul.2012.07.022.

DSA-info 2:2021. Kan vi skille mellom forskjellige kilder til naturlige forekommende radioaktive stoffer i det marine miljø? In Norwegian. Available from:

Norway’s integrated ocean management plans — Barents Sea–Lofoten area; the Norwegian Sea; and the North Sea and Skagerrak —Report to the Storting (white paper). Meld. St. 20 (2019-2020),

Facts about the NORM project

  • “Naturally Occurring Radioactive Materials (NORM) in Norwegian marine areas” is funded by the Fram Centre Flagship “Hazardous substances” and the participating institutions.
  • Interdisciplinary project group from the Institute of Marine Research, Norwegian Radiation and Nuclear Safety Authority, and Geological Survey of Norway.
  • Aims at compiling data on natural radionuclides collected within MAREANO, RAME and the environmental monitoring of petroleum activities on the Norwegian continental shelf. The latter is made available to subscribers in the MOD database ( The data will be used to study impacts of discharges of natural radionuclides with produced water.
  • MAREANO maps depth and topography, sediment composition, contaminants, biotopes and habitats in Norwegian waters.
  • RAME (Radioactivity in the Marine Environment) monitors radioactive contamination.
  • The project supports Norway’s contribution of knowledge to international bodies such as OSPAR and AMAP.