Root uptake: Tropical and Subtropical environments

VELASCO, R. H.; JURI AYUB, J.

Quantification of radionuclide transfer in terrestrial and freshwater environments for radiological assessments

International Atomic Energy Agency

Lugar: Vienna, Austria; Año: 2009; p. 207 - 238

Previously, existing reviews of environmental radionuclide transfers were principally limited to temperate climatic zones, as data from other climatic zones were typically unavailable. However, since 1992 new data on tropical environments has become available, and from this new data it appears that though climatic conditions direct influence on radioecological transfer parameters seem to be minimal, its indirect effects can be significant. Climate and parent rock material determine, to a large extent, the characteristics of soil development. In tropical areas, several soil types occur in which radionuclide uptake by crops consistently deviates from the values characteristic in temperate environments. In typical tropical environments, almost all organic material that reaches the soil surface decomposes rapidly, and the surface accumulation of soil organic matter is therefore minimal. Consequently, there is rapid recycling of nutrients and contaminants into the vegetation. In temperate zones the decomposition of organic debris is slower, and the accumulation of soil organic matter is usually greater than the rate of decomposition, resulting in highly organic surface soil. A special analysis was undertaken to determine whether the above factors are significant enough to induce substantial deviations from the parameter values identified as appropriate to temperate conditions, and to suggest transfer factor values applicable for tropical and subtropical conditions. Most of the data analysed and presented in Sections 5.2-5.3 relate to temperate environments. At the same time over previous 15 years more extensive data has been accumulated for tropical and subtropical environments. However, while the data is reasonably extensive, the number of radionuclides considered is limited, the geographical coverage is incomplete, and only a limited number of soil and crop type combinations have been studied. For these reasons, the data has been analysed principally to determine whether there is evidence of systematic enhanced or reduced absorption of radionuclides into plants, under tropical and subtropical conditions.