Sediment radionuclide transport

Radionuclide transport in natural waters is strongly dependent on sorption, desorption, dissolution, and precipitation processes. The first two sections discuss laboratory investigations of these processes. Descriptions of sorption and desorption behavior of important radionuclides under a wide range of environmental conditions are presented in the first section. Among the sorbents studied are basalt interbed solids, granites, clays, sediments, hydrous oxides, and pure minerals. Effects of redox conditions, groundwater composition and pH on sorption reactions are described. 

Surface complex models (SCMs) are now finding widespread application in the fields of pollutant retention behaviour (Zachara etal., 1989,1992), the soil chemistry of plant nutrient retention (Goldberg and Sposito, 1984 Goldberg and Glaubig, 1986 Goldberg and Traina, 1987) and the retention of radionuclides by sediments and transport of pollutants by colloids (Davis and Kent, 1990 Dzombakand Morel, 1990 Goldberg, 1992). 

Radionuclide transport in an aqueous environment probably is related to community metabolism (9). The concentration of radionuclides increases in the plant biomass, with an accompanying loss from water or sediment, when the photosynthesis-to-respiration (P/R) ratio exceeds one (Figure 5). When this ratio fell below one, a net gain of radionuclides in the sediment and water accompanied by a loss in plants was observed. 

Walling, D.E., Rowan, J.S., Bradley, S.B., 1989. Sediment-associated transport and redistribution of Chernobyl fallout radionuclides. In Hadley, R.F., Ongley, E.D. (fids.). Sediment and the Environment. lAHS Publ. no. 184, pp. 37 5. 

The short4ived particle reactive radionuclides of the U/Th series also have enormous potential for tracking particle source and transport in ocean margins. Mass balances comparing inventories in sediments with supply can be used to determine import or export of particles to an area. Such approaches are increasingly important in understanding the fates of particle-reactive contaminants whose sources are often enhanced in the coastal ocean. Studies of especially when supplemented by other... 

Heussner S, Cherry RD, Heyraud M (1990) Po-210 and Pb-210 in sediment trap particles on a Mediterranean continental margin. Cont. Shelf Res 10 989-100 Heyraud M, Cherry RD (1983) Correlation of Po-210 and Pb-210 enrichments in the sea-surface microlayer with neuston biomass. Cont Shelf Res 1 283-293 Honeyman BD, Santschi PH (1989)The role of particles and colloids in the transport of radionuclides and trace metals in the oceans. In Environmental particles. Buffle J, van Leewen HP (eds) Lewis Publishers, Boca Raton, p 379-423... 

Srinath T, Verma T, Ramteke PW, Garg SK (2002) Chromium biosorption and bioaccumulation by chromate resistant bacteria. Chemosphere 48 427-435 Stephen JR, Macnaughton SJ (1999) Developments in terrestrial bacterial remediation of metals. Curr Opinion Biotechnol 10 230-233 Tabak HH, Lens P, van Hullebusch ED, Dejonghe W (2005) Developments in bioremediation of soils and sediments polluted with metals and radionuclides 1. Microbial processes and mechanisms affecting bioremediation of metal contamination and influencing metal toxicity and transport. Rev Environ Sci Bio/Technol. 4 115-156... 

By combining the findings of Cacchione, Drake and the results reported here, a coherent model can be proposed to explain the deposition inventory of the radionuclides. The down-canyon current transports large quantities of sediment toward the radioactive waste disposal site at 4000 m. Within the upper canyon, fine material is transported the furthest. Near the mouth of the canyon, sediment erosion of the walls occurs due to the down-canyon currents meeting a proposed opposing on-shore bottom current. The eroded material from the walls is transported and the finer material is deposited in eddies formed where the two currents meet. 

In this article we plan to focus on two aspects (i) the transport of radionuclides to the ocean floor and the processes which govern their distribution in deep-sea sediments and (ii) the application of deep-sea sediments to retrieve historical records of large scale phenomena, e.g. long term changes in the rate of production of nuclides by cosmic rays. Even while discussing these aspects, our emphasis will be mainly on the processes rather than on the details of the chronometric method. 

Due to preferential scavenging and lateral transport of a daughter radionuclide, the activity of daughter Ap can be greater than that of the parent Ap in sediments. The inputs of daughter radionuclides that are not directly from the in situ decay of the parent (supported) are termed unsupported or excess activity. The unsupported Ap is equal to the supported A ) minus the Ap, as shown in the theoretical radionuclide profiles in figure 7.3. Moreover, the curve for the unsupported Ap decreases with depth more than the supported Ap because it is not being produced in situ from the parent. Consequently, the excess activity of a radionuclide can be used to calculate the time elapsed since the particles with unsupported Ap were last at the surface, relative to a particular depth (A). However, to calculate this it must be assumed that the sedimentation rate and supply of unsupported Ap has remained constant over time. 

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