[en] In this chapter, radioecological data are provided that can support the assessment of potential internal doses via the human food chain arising as the consequence of a large-scale pulsed inputs into marine systems. The objectives of this chapter are: • To analyse the data on temporal changes of concentration ratio (𝐶𝑅) in fish; • To quantity timescales required for contaminated marine biota to return to pre-accident levels; • To analyse the temporal changes of 137Cs activity concentrations in the seawater and bottom sediments; • To develop a simple model for the spatiotemporal changes in sediment-water distribution coefficient (𝐾_d) values. The data help to understand the behaviour and bioavailability of radiocaesium distributed in the coastal areas during the pre-accident and post-accident periods.

[en] Highlights: • Radioactive contamination of pristine marine and terrestrial ecosystems • Legacy from nuclear weapon testing in extremely isolated atolls • ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu isotope ratios to asses origin of contamination • ²⁴¹Am/²⁴¹Pu activity ratio to determine age of contamination The Bikar and Bokak Atolls, located in the northern Marshall Islands, are extremely isolated and consist of pristine marine and terrestrial ecosystems. Both atolls may have experienced significant radioactive deposition following the nuclear weapon testing conducted at Bikini and Enewetak proving grounds. Here we report activity concentrations of artificial radionuclides (²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, ²⁴¹Am, ¹³⁷Cs and ⁹⁰Sr) in marine and terrestrial samples collected from Bikar and Bokak Atolls. Artificial radionuclides in soil from the Majuro Atoll are also reported and form a radiological baseline against which the levels at the other atolls can be compared. We observed low levels of artificial radionuclides in soil from Majuro and Bokak, but significantly higher levels in soil from Bikar. The residual radioactivity in the Bikar environment is comparable to the levels previously reported for other nearby atolls, including Taka and Utrik, but lower than for Rongerik, Rongelap, Bikini and Enewetak. An analysis of ²⁴⁰Pu/²³⁹Pu isotope ratios and estimations of the dates of contamination from ²⁴¹Am/²⁴¹Pu activity ratios both indicated that the Bikar Atoll was contaminated mainly by radioactive fallout from the Castle Bravo test in 1954. We compare the results of our measurements at Bikar and Bokak to data from other atolls in the Marshall Islands and to regions of the world affected by both global and regional fallout from atmospheric nuclear weapons testing and nuclear accidents.

[en] The ARGOS decision support system is used for consequence assessment and decision support following a nuclear, radiological or chemical emergency. This paper will focus on the radiological domain. The ARGOS system is in operation or being commissioned in 8 European countries, as well as in Canada, Brazil and Australia. Since the initial version was released 15 years ago, the system has developed from a simple data presentation application to a sophisticated platform which integrates radiological monitoring data, atmospheric dispersion models and calculation of doses in the food chain and the urban environment. (author)

[en] Highlights: • Update of ¹²⁹I distribution in Central North Atlantic (NA) and the Nordic Seas. • Evolution of ¹²⁹I from 2002 to 2012 is associated to changes in releases from NFRPs. • Results suggest deep water formation in the eastern area of the Nordic Seas. • ¹²⁹I from NFRPs partly reaches Central NA and are not carried northwards by the NCC. Most of the anthropogenic radionuclide ¹²⁹I released to the marine environment from the nuclear fuel reprocessing plants (NFRP) at Sellafield (England) and La Hague (France) is transported to the Arctic Ocean via the North Atlantic Current and the Norwegian Coastal Current. ¹²⁹I concentrations in seawater provides a powerful and well-established radiotracer technique to provide information about the mechanisms which govern water mass transport in the Nordic Seas and the Arctic Ocean and is gaining importance when coupled with other tracers (e.g. CFC, ²³⁶U). In this work, ¹²⁹I concentrations in surface and depth profiles from the Nordic Seas and the North Atlantic (NA) Ocean collected from four different cruises between 2011 and 2012 are presented. This work allowed us to i) update information on ¹²⁹I concentrations in these areas, required for the accurate use of ¹²⁹I as a tracer of water masses; and ii) investigate the formation of deep water currents in the eastern part of the Nordic Seas, by the analysis of ¹²⁹I concentrations and temperature-salinity (T-S) diagrams from locations within the Greenland Sea Gyre. In the Nordic Seas, ¹²⁹I concentrations in seawater are of the order of 10⁹ at·kg^{− 1}, one or two orders of magnitude higher than those measured at the NA Ocean, not so importantly affected by the releases from the NFRP. ¹²⁹I concentrations of the order of 10⁸ atoms·kg^{− 1} at the Ellet Line and the PAP suggest a direct contribution from the NFRP in the NA Ocean. An increase in the concentrations in the Nordic Seas between 2002 and 2012 has been detected, which agrees with the temporal evolution of the ¹²⁹I liquid discharges from the NFRPs in years prior to this. Finally, ¹²⁹I profile concentrations, ¹²⁹I inventories and T-S diagrams suggest that deep water formation occurred in the easternmost area of the Nordic Seas during 2012.