Pu, Cs-137 and excess Pb-210 in Russian arctic sediments

The activity ratios of Pu and radiocesium isotopes have been used to delineate the major sources (such as global and close-in (debris) fallout, nuclear fuel reprocessing and fabrication plant effluents) in the environment. We have measured Pu-238, Pu-239,Pu-240, Cs-137, and excess Pb-210 concentrations in 107 surficial sediments as well as in 5 sediment cores collected in the summer months of 1993 and 1994 from the Ob and Yenisey Rivers (Russia) and the Kara sea. A comparison of the sediment core inventories of Pu-239,Pu-240 and Cs-137, along with the Pu-238/Pu-239,Pu-240 activity ratios, with those expected from global fallout allows us to estimate the relative amounts, if any, of reactor-derived Pu-238 and Pu-239,Pu-240 dumped reactor sites in the study area. In surficial sediment samples collected in 1993 and 1994, the Pu-239,Pu-240 concentrations varied between 4.2 and 856 mBq kg(-1), with a mean of 239 mBq kg(-1). In samples with a measurable Pu-238, the Pu-238/Pu-239,Pu-240 activity ratios varied between 0.010 and 0.069, with an average value of 0.035 +/- 0.014. This range can be compared to the average Pu-238/Pu-239,Pu-240 activity ratio of 0.030 for the year 1993 from nuclear weapons testing and SNAP fallout obtained from soil studies, indicating very little (less than or equal to 5%) additional sources of Pu-238 to the sediments in the study area. The inventories of Pu in the 5 sediment cores from the study area varied between 2.67 +/- 0.67 and 24.5 +/- 2.2 Bq m(-2), with a mean value of 8.83 Bq m(-2). The Cs-137 concentrations in the upper 3 cm of the sediments varied between below detection limit to 71.4 Bq kg(-1), with a mean of 14.9 Bq kg(-1). The Cs-137 inventories in the 5 sediment cores varied between 156.7 +/- 28.3 and 1600 +/- 153.3 Bq m(-2), with a mean value of 583.3 Bq m(-2). The mean ratio of inventories of Pu to that of Cs-137, 0.015, is comparable to the values in other places in the Arctic region. There is a significant correlation between total organic carbon and concentrations of Cs-137, Pu-239,Pu-240 and Pb-210, suggesting that organic matter-enriched fine particles are a likely carrier phase for these nuclides. The ratio of Cs-137/Pu-239,Pu-240 also suggests that most of these nuclides are derived from global fallout.