Plutonium and americium concentrations in sea water and in sinking particles

Vertical fluxes of 239+240Pu and 241Am and temporal changes in their inventories in the northwestern Mediterranean Sea have been examined through high-resolution water column sampling coupled with direct measurements of the vertical flux of particle-bound transuranics using time-series sediment traps. Water column profiles of both radionuclides showed well-defined sub-surface maxima (2391240Pu between 100-400 m; 241Am at 100-200 m and 800 m), the depths of which are a result of the different biogeochemical scavenging behavior of the two radionuclides. Comparison of deep water column (0-2,000 m) transuranic inventories with those derived from earlier measurements demonstrate that the total 2391240Pu inventory had not substantially changed between 1976-1990 whereas 241Am had decreased by approximately 24%. Enhanced scavenging of 241Am and a resultant, more rapid removal from the water column relative to 239+240Pu was also supported by the observation of elevated Am/Pu activity ratios in sinking particles collected in sediment traps at depth. Direct measurements of the downward flux of particulate 239+240Pu and 241Am compared with transuranic removal rates derived from observed total water column inventory differences over time, show that particles sinking out of deep waters (1,000-2,000 m) could account for 26-72% of the computed total annual 239+240Pu loss and virtually all of the 241Am removal from the water column. Upper water column (0-200 m) residence times based on direct flux measurements ranged from 20-30 yr for 239+240Pu and 5-10 yr for 241Am. The observation that 241Am/239+240Pu activity ratios in unfiltered Mediterranean seawater are six times lower than those in the north Pacific suggests the existence of a specific mechanism for enhanced scavenging and removal of 241Am from the generally oligotrophic waters of the open Mediterranean. It is proposed that atmospheric inputs of aluminosilicate particles transported by Saharan dust events which frequently occur in the Mediterranean region could enhance the geochemical scavenging and resultant removal of 241Am to the sediments.

(Table 1) Concentration of plutonium isoptopes in dry matter of bottom sediments from the Kerch Straight area in December 2007

A study of redistribution of alpha-radioactive isotopes of plutonium, 239,240Pu and 238Pu in coastal ecosystems off the northern Black Sea coast for quantitative characterization of modern radioecological situation in these waters with respect to plutonium was the aim of this work.

Geochemistry and radionuclide content of sediment and water samples obtained from the Ob and Irtysh river, Russia

This paper reports the results of the investigations of 2006-2007 on the distribution and migration forms of artificial radionuclides and chemical elements in the Ob-Irtysh water system. Three regions were studied. One of them is a local segment of the Ob River upstream from the confluence with the Irtysh River; its investigation allowed us to estimate the general radioecological state of the aquatic environment affected by the activity of the Tomsk 7 plant. The second region is a local segment of the Irtysh River upstream from its confluence with the Ob River, where the influence of emissions from the NPO Mayak could be estimated. The third region is the water area of the Ob River after its confluence with the Irtysh River. It characterizes the real level of radioactive and chemical contamination of the middle reaches of the Ob River. In order to explain horizontal variations in the distribution of radionuclides in the upper layer of bottom sediments collected at various sites, the results of sorption-kinetic experiments with radioactive tracers in the precipitate-solution system were used. The investigation of the migration forms of trace elements and radionuclides occurring in river water was based on the method of tangential-flow membrane filtration. Chemical element contents were determined in 400-ml water samples. A set of Millipore polysulfone membranes with pore sizes of 8, 1.2, 0.45, 0.1, and 0.025 µm was employed. Taking into account the ultralow specific concentrations of radionuclides in the water, they were analyzed in 300-500 litre samples using Millipore polysulfone membranes with pore sizes of 0.45 µm and 15 kDa. This allowed us to estimate the percentages of cesium-137 and plutonium-239, 240 in the suspended particulate fraction, colloids, and dissolved species.

(Table) Specific activities of 137Cs, 90Sr and 239,240Pu in surface waters obtained during cruises BP06-BP09, Indian Ocean

One of the main sources of anthropogenic radionuclides in the ocean is the global fallout resulting from the nuclear tests that had been conducted by the United States, the former Soviet Union, and other countries between 1945 and 1990 mainly in the Northern Hemisphere. The most extensive fallout was observed in the middle latitudes of the Northern Hemisphere in 1963 immediately after the nuclear tests of 1961-1962 conducted by the United States and the Soviet Union. In 2006-2009, under the auspices of an agreement between the Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences and the National Center of Antarctic and Marine Research of the Ministry of Earth Sciences of India, cooperative geological and geochemical investigations were organized in several regions of the Indian Ocean. During these expeditions, the spatial distribution of anthropogenic radionuclides was investigated in the water of the Indian Ocean. The main results of these investigations are reported in this paper.