Seawater radionuclides

This removal may also include diffusion of soluble U(VI) from seawater into the sediment via pore water. Uranium-organic matter complexes are also prevalent in the marine environment. Organically bound uranium was found to make up to 20% of the dissolved U concentration in the open ocean." ° Uranium may also be enriched in estuarine colloids and in suspended organic matter within the surface ocean. " Scott" and Maeda and Windom" have suggested the possibility that humic acids can efficiently scavenge uranium in low salinity regions of some estuaries. Finally, sedimentary organic matter can also efficiently complex or adsorb uranium and other radionuclides. 

Walker MI, McKay WA. 1991. Radionuclide distributions in seawater around the Sellafield pipeline. Estuarine Coastal Shelf Sci 32(4) 385-394. 

SEAWATER Major fallout radionuclides in surface seawater, typical concentrations ... 

There are three classes of radionuclides occurring in seawater ... 

The concentrations of these elements in seawater are extremely low. Radionuclides are primarily used as tracers to study water circulation, par-... 

Measurements of radionuclides in seawater have been used to study a variety of processes, including ocean mixing, cycling of materials, and carbon flux (by proxy). These measurements provide information on both process rates and mechanisms. Because of the unique and well-understood source functions of these elements, models of radionuclide behavior have often led to new understanding of the behavior of other chemically similar elements in the ocean. 

Because many of the radionuclide measurements in seawater require sample sizes of 20-200 liters, it is not practical to distribute true seawater reference materials containing these radionuclides. Furthermore, several of the radionuclide half-lives are only a few days to weeks. A different strategy is clearly required. The most reasonable approach is to prepare a reference material in the field by diluting solutions containing the long-lived parents of the short-lived radionuclides with a volume of seawater similar to the volume used for analyses. 

Reference materials that represent the primary deep-sea and coastal depositional environments and biological materials would solve many of the problems that radiochemists face in analysis of sediments from these settings. Radiochemists require reference materials comprising the primary end member sediment and biological types (calcium carbonate, opal, and red clay from the deep-sea and carbonate-rich, silicate-rich, and clay mineral-rich sediments from coastal environments and representative biological materials). Additional sediment reference material from a river delta would be valuable to test the release of radionuclides that occurs as riverine particles contact seawater. 

Part II considers speciation in specific compartments of the environment viz. the atmosphere, biological systems, soils, sediments and natural waters, and with particular aspects of the speciation of environmentally important radionuclides. Two new chapters have been added to make the coverage even more comprehensive. These new chapters are Chapter 10, Chemical Speciation in Soib and Related Materials by Selective Chemical Extraction by the editors, and Chapter 12, Speciation in Seawater by R.H. Byrne of the University of South Florida. 

It is clear from previous comments that radionuclide speciation studies must consider not only oxidation states and specific inorganic forms but also complex species arising through association with natural organic matter and the possibility of different physical states. The relative importance of these various physicochemical forms will, in practice, be dictated by a combination of the basic elemental characteristics of the radionuclide and the type of environment into which it is placed. Thus in seawater, colloidal organic complex species are likely to be far less dominant than for the same radionuclide in a very low ionic strength freshwater. In the case of soil and sediment interstitial waters or groundwaters,... 

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