Natural and anthropogenic radionuclides in the marginal seas of Siberia: implications for the fate and removal of pollutants

Abstract

Natural and anthropogenic radionuclides have been widely used to trace the sources and fate of radioactive pollutants in the marine environment. In this study, particle-reactive radionuclides such as ... Ph and 214 Th have been employed for scavenging studies. The inventories of Pu and radiocesium and activity ratios of Pu (such as 238PU/239,24OPu) have been utilized to determine the sources and transport of anthropogenic pollutants. Water soluble tracers such as Ra isotopes and radiocesium have been used to determine the water mass movements as well as residence time of water masses. This will help to define the processes related to estuarine mixing over the continental shelf which control radioactive and other pollutants entering surface waters of the Arctic Ocean. 21OPb and 214 Th concentrations were measured in a suite of water samples (dissolved and particulate phases) from the marginal seas of the Russian Arctic (Pechora, Kara, Laptev, and East Siberian Seas) in order to better understand scavenging within the water column. To elucidate the sources of Pu and 131CS to the study area, Pu and "'Cs concentrations and 238PU/239,240puactivity ratios were measured in water samples. Concentrations of Ra isotopes were also determined for the estimation of the residence time of river water entering the Kara Sea. The model-derived scavenging parameters for 114 Th and "OPb clearly indicate particle concentrations, influenced by resuspension, ice melt, and continental runoff, primarily control the removal of these nuclides. Concentrations and inventories of Pu and "'Cs as well the activity ratio of "IpU/219,l4OpU suggest two main sources of Pu and "'Cs to the waters over the Siberian shelf. an oceanic source, likely from Sellafield and La Hague nuclear reprocessing plants, and a riverine source emanating from estuarine sediments . 21lpU/219,24OPu activity ratios suggest all of the Pu entering into shelf waters by way of Siberian rivers is from Global Fallout. The Pu concentrations are also primarily controlled by the particle concentrations in the water column. River water residence times for the surface and subsurface waters of the Kara Sea were estimated, using2l'Ra/22'Ra activity ratios, to be on the order of one year and 30 years, respectively.