B. Oregioni

AMS measurements of 14C and 129I in seawater around radioactive waste dump sites

Abstract According to a recent IAEA compilation of inventories of radioactive wastes dumped in the world ocean, a total of 85 PBq of radioactive wastes were dumped, in the Atlantic (45 PBq), the Pacific (1.4 PBq) and the Arctic (38 PBq) Oceans and their marginal seas between 1946 and 1993, mostly in the form of low-level wastes. 3 H, and 14 C formed an important part of the beta-activity of these dumped wastes. Because of its long half-life, 14 C will be the main constituent in possible leakages from the wastes in the future. On the other hand, 14 C and 129 I are important radioactive tracers which have been artificially introduced into the oceans. Small amounts of 14 C and 129 I can be easily measured by accelerator mass spectrometry (AMS) on mg-size samples of carbon and iodine extracted from 500 ml seawater samples. The high analytical sensitivity enables one therefore to find even trace amounts of 14 C and 129 I which could be released from radioactive wastes, and to compare the measured levels with the global distribution of these radionuclides. The IAEAs Marine Environment Laboratory (IAEA-MEL) has been engaged in an assessment program related to radioactive waste dumping in the oceans since 1992 and has participated in several expeditions to the Atlantic, Arctic, Indian and Pacific Oceans to sample seawater, biota and sediment for radiological assessment studies. In the present paper, we report on methods of 14 C and 129 I measurements in seawater by AMS and present data on the NE Atlantic, the Arctic and the NW Pacific Ocean dumping sites. A small increase of 14 C was observed at the NE Atlantic dumping site.

A new Certified Reference Material for radionuclides in Irish sea sediment (IAEA-385)

A new Certified Reference Material (CRM) for radionuclides in sediment (IAEA-385) is described and the results of the certification process are presented. Eleven radionuclides ((40)K, (137)Cs, (226)Ra, (228)Ra, (230)Th, (232)Th, (234)U, (238)U, (238)Pu, (239+240)Pu and (241)Am) have been certified and information mass activities with 95% confidence intervals are given for seven other radionuclides ((90)Sr, (210)Pb((210)Po), (235)U, (239)Pu, (240)Pu and (241)Pu). Results for less frequently reported radionuclides ((60)Co, (99)Tc, (134)Cs, (155)Eu, (224)Ra and (239)Np) and information on some activity and mass ratios are also reported. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in sediment samples, for the development and validation of analytical methods and for training purposes.

Isotope studies in the Caspian Sea.

Oceanographic and isotopic investigations in the Caspian Sea and the analyses of the available data on the discharge to the sea and the observed sea level changes suggest that climatically caused changes of river inflow are the major cause of the sea level fluctuations over the last century. Hydrogen-3 and 3H-3He data indicate that the deep basins of the sea are rapidly ventilated, although the hydraulic turnover time of the sea is approximately 200 years. The concentration levels of the anthropogenic radionuclides 90Sr, 137Cs and 239,240Pu in the water column can be explained by global fallout and therefore, at the sampling sites visited, there were no signs of dumping of radioactive wastes. The anthropogenic radionuclide data support the idea of fast exchange of water masses in the Caspian Sea. The isotopic and oceanographic data collected during the cruises have shown potential to allow for a better understanding of the water circulation in the Caspian Sea.

Anthropogenic Radionuclides in the Caspian Sea

Analysis and interpretation of the distribution of anthropogenic radionuclides 90Sr, 137Cs, and 239,240Pu in the Caspian Sea water are presented. These radionuclides are shown to be of environmental importance and to be useful for studying water mass dynamics.

Temporal evolution of 137Cs, 237Np, and 239+240Pu and estimated vertical 239+240Pu export in the northwestern Mediterranean Sea

The evolution of 137Cs, 237Np and 239+240Pu at the DYFAMED station (NW Mediterranean) is discussed in relation to physical processes, downward fluxes of particles, and changes in the main input sources. The data set presented in this study represents the first complete 237Np vertical profiles (0.12-0.27μBqL-1), and constitutes a baseline measurement to assess future changes. A similar behavior of Cs and Np has been evidenced, confirming that Np behaves conservatively. While the 137Cs decrease has been driven by its radioactive decay, the vertical distribution of 237Np has not substantially changed over the last decade. In the absence of recent major inputs, a homogenization of their vertical distribution occurred, partly due to deep convection events that became more intense during the last decade. In contrast, 239+240Pu surface levels in the NW Mediterranean waters have fallen in the past four decades by a factor of 5. This decrease in surface has been balanced by higher concentrations in the deep-water layers. A first estimate of the downward 239+240Pu fluxes in the NW Mediterranean Sea is proposed over more than two decades. This estimation, based on the DYFAMED sediment trap time-series data and published 239+240Pu flux measurements, suggests that sinking particles have accounted for 60-90% of the upper layer (0-200m) Pu inventory loss over the period 1989-2013. The upper layer residence time of Pu is estimated to be ~28years, twice as long as the residence time estimated for the whole western Mediterranean (~15years). This difference highlights the slow removal of Pu in the open waters of the NW Mediterranean and confirms that most of the Pu removal occurs along the coastal margin where sedimentation rates are high.

Anthropogenic radionuclides in biota samples from the Caspian Sea

Abstract Samples of fish flesh collected in 1999 in the south-western Caspian Sea in the Baku area, important for caviar production (sturgeon – russkyi osyotr, sevruga and beluga), as well as for consumption (roach and carp) were analysed for anthropogenic strontium, caesium, plutonium and americium, and natural polonium. The highest massic activities of 137 Cs were found in sevruga and beluga flesh (1.2–1.8 Bq/kg wet weight (ww)), while 90 Sr levels were between 5–12 mBq/kg ww, and plutonium and americium levels were close to limits of detection (∼0.2 mBq/kg ww). The observed plutonium and strontium levels are in the same range as in the Mediterranean Sea, whereas caesium has been accumulated in conditions of lower salinity in larger proportions. The 210 Po levels in fish were between 0.2–3 mBq/kg ww, in a fresh caviar (spawn) sample they were higher by a factor of 4 than in sturgeons, but comparable with levels observed in other species. The highest radionuclide levels, by one to two orders of magnitude, were measured in a macroalgae sample. The distribution of radionuclides seems to be more related to the species than to environmental conditions. The estimated concentration factors (CFs) for strontium and plutonium in fish and algae are in a reasonable agreement with IAEA recommended values. Caesium in the same species has been accumulated in larger quantities, so that the resulting CF is higher by a factor of two. The highest CFs were found for macroalgae, documenting that algae are suitable biomonitors of radioactive contamination. The measured activities of radionuclides in biota samples do not represent any radiological risk from their consumption.

Recent IAEA reference materials and intercomparison exercises for radionuclides in the marine environment

Abstract Results of the recent intercomparison exercises on Irish Sea sediment (IAEA-385) and a mixed fish sample from the Irish and North Seas (IAEA-414) are compared and discussed. Both materials have been designed for the determination of anthropogenic and natural radionuclides in marine samples. Several anthropogenic and natural radionuclides were analyzed by over 100 laboratories. The data were evaluated and recommended and information values for several radionuclides have been derived. Both materials will be issued as IAEA reference materials (RMs). IAEA-385 will replace IAEA-135 (Irish Sea sediment), which is out of stock. Ongoing and planned intercomparison exercises for determination of radionuclides in seawater (IAEA-418), marine biota (IAEA-437, IAEA-415, IAEA-438 and IAEA-442) and sediment (IAEA-410 and IAEA-412) are presented as well.