Recent evolution of 129I levels in the Nordic Seas and the North Atlantic Ocean

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 10⁸atoms·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.

Estimating the impact from Fukushima in Southern Spain by 131I and Accelerator Mass Spectrometry detection of 129I

After the Fukushima accident, large amounts of radionuclides were discharged to the atmosphere. Some of them travelled long distances and were detected in places as far from Japan as Spain a few days after the accident. One of these radionuclides was ¹³¹I. Its isotope ¹²⁹I (T1/2 = 15.7 × 106 years) was also expected to follow the same pathway. In this work, we present the results for the ¹²⁹I concentration in the same atmospheric samples from Seville (Spain) where ¹³¹I activity was measured in 2011 by Baeza et al. (2012). ¹²⁹I concentrations in aerosol and gaseous samples showed concentrations in the order of 104 and 105 atoms/m³, typically higher in the gaseous form with respect to the aerosol form. Also ¹²⁹I in rainwater was measured, showing concentrations in the order of 10⁸ atoms/L. The results show a very good agreement with the ¹³¹I profile, showing that, if background from other sources is not relevant, it is possible to estimate the impact of similar events years after them thanks to the sensitivity of techniques like Accelerator Mass Spectrometry.