Biosphere transport

BIOSPHERE TRANSPORT (HAZARDOUS SUBSTANCE TRANSPORT THROUGH THE BIOSPHERE)... 

Prediction of the consequences of degradation release conventionally involves data and models for three steps of analysis geosphere transport, biosphere transport, and biosphere consequences. I will discuss these and add two others analysis, rather than assumption, of repository degradation, and consideration of the geosphere/biosphere interface and its effect on biosphere consequences. These refinements to safety assessment procedures, when developed and implemented, can be expected to aid validation of results. 

Radioactivity that enters the biosphere is subject to transport by a variety of pathways and mechanisms that need to be reflected in migration models for this regime. Factors to consider in biosphere transport models are similar in type to those considered for geosphere transport, but details will differ substantially. Pathways are more numerous in the biosphere, and phenomena such as weathering may change the physical and chemical properties of the nuclides. Such changes may alter the environmental behavior and biological consequences of the radioactivity. 

Models of biosphere transport have been developed. 5,6) As is the case for geosphere transport models, the data base for parameters in the biosphere models is limited. The scope of available data is being expanded, (7-9) but careful assessment is needed of the validity of the data, the validity of the models, and the need for the data and models to be site-specific. One site-specific factor to consider is the possibility that geosphere migration could extend for considerable distances from the repository radioactivity might therefore enter the biosphere in an environment different from that of the repository site. 

Prediction of biosphere consequences is coupled with modeling of biosphere transport.(5 6 The key factors in the transition from biosphere transport to biosphere consequences are the assumptions made concerning man s interaction with his environment. The interactions depend, of course, on man s activities and the presence of nuclides with which he can interact. 

Ear from being just the processing of water on Earth, this cycle is the basis for a wide range of meteorologic, geochemical, and biological systems. Water is the transport medium for all nutrients in the biosphere. Water vapor condensed into clouds is the chief control on planetary albedo. The cycling of water is also one of the major mechanisms for the transportation of sensible heat (e.g. in oceanic circulation) and latent heat that is released when water falls from the air. 

Knorr, W. and Heimann, M. (1995). Impact of drought stress and other factors on seasonal land biosphere CO2 exchange studied through an atmospheric tracer transport model, Tellus, Ser. B, 47, 471-489. 

As reactive P is transported through the terrestrial system, it is assimilated into plants and subsequently into the rest of the biosphere (2). Although many elements are required for plant life, in many ecosystems P is the least available and, therefore, limits overall primary production (Schindler, 1977 Smith et al., 1986). Thus, in many instances the availability of P influences or controls the cycling of other bioactive elements. When organisms die, the organic P compounds decompose and the P is released back into the soil-water system. This cycle of uptake and release may be repeated numerous times as P makes its way to the oceans. 

Water is the most abundant substance on the surface of the earth and the major constituent of all living organisms. Life on earth would not be possible and the biosphere would not exist without water. Water plays a key role in the sustenance of living organisms, since it is essential for all living processes, transporting nutrients to wherever they are required in their bodies, and removing from them their waste products. Thus, since it plays... 

As yet there have been no reports that the actinides in the biosphere become complexed in a chemical form which would facilitate their transport through the food chain to man. All the available evidence indicates that solutions of the actinides hydrolyze to give polymeric forms which exhibit limited mobility in cellular systems. There are, however, many complexing agents in the biosphere which could form stable complexes with the actinides, such complexes could alter the transport of the actinides in microenvironments but these microenvironments have yet to be identified. 

Since there is now considerable concern in the technologically advanced countries concerning the contamination of the environment by actinides, such as plutonium, americium and curium, this review attempts to present an understanding of how the actinides could concentrate and/or become transported through the biosphere to man. 

Most of the naturally occurring chelating agents are substituted hydroxamates which are produced by a variety of protista so that iron(III) subsequently becomes available for biochemical processes. Neilands (73) has suggested that the hydroxamates facilitate the transport of iron across cell membranes. The distribution of hydroxamates in the biosphere appears limited. However, if there was a wider distribution of hydroxamates in the environment then the management of actinide wastes could become a problem of horrifying dimensions if these chelators facilitated the transport of actinides across cell membranes. 

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