Submitted to: Journal of Geochemical Exploratin
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2010
Publication Date: 12/25/2010
Citation: Bitterli, C., Banuelos, G.S., Schulin, R. 2010. Use of transfer factors to characterize uptake of selenium by plants. Journal of Geochemical Exploration. 107:206-216. Interpretive Summary: The radioactive selenium isotope 79Se can be a component of radioactive waste produced in nuclear power plants. The accidental release of 79Se in the environment from power plants or nuclear waste repositories, and subsequent transfer of 79Se into soils, plants and food chain, are relevant concerns in Europe. In environmental risk assessment models, the ability of plants to take up Se is often characterized by means of soil-to-plant transfer factors (TF). However, these recommendations take little or no account of the variability in plant Se accumulation among plant species and differences in Se distribution between plant parts. Also such factors as soil type, form of Se, climatic conditions, as well as the chemical form in which Se is present in the soil, are not taken into consideration. This paper reviews the current knowledge on Se uptake by plants and compiles published data on the transfer of Se from soils and nutrient solutions into plants. The data were categorized according to the form of Se supply, i.e. when added in as either selenate or selenite to nutrient solutions or soils, or whether plant Se accumulation was studied on soil containing only natural-occurring Se (native Se). Differences observed in the transfer of Se from soil into plants appear to result primarily from differences in the solubility of Se species in soil and only to a minor degree from differences in plant uptake efficiency among these species. Situations where radioactive Se has been accidentally released into the environment may be better represented by TF values for experimentally added Se than by TF values computed for native soil Se.
Technical Abstract: Models used for the assessment of risks relating to the eventual leakage of nuclear waste repositories have been developed by various agencies including the International Atomic Energy Agency. While focusing on other radionuclides, little attention has been given to the assessment of the environmental behavior of radioactive selenium isotope (79Se) in these models. Given that radio-selenium is an important component of nuclear waste, it is planned to upgrade the Terrestrial-Aquatic Model of the Environment (TAME) model in order to close this gap. The planned upgrade of TAME requires the knowledge of transfer factors describing the soil-to-plant transfer of Se in terms of the ratio between the concentration of Se in a plant (numerator) and its concentration in the soil (denominator) in which the plant is growing. This paper presents the results of a literature survey in which we screened available publications for data relating Se concentrations in plants to Se concentrations in soils or hydroponic (nutrient) solutions. The aim of this paper is to give modelers a more realistic and comprehensive basis for selecting Se soil-to-plant transfer factors that are more appropriate for the particular scenarios to be modeled. Values of the soil-to-plant transfer factor (TF) for Se were found to lie between 0.01 and 100 with few exceptions. Transfer factor values derived from studies in which Se was added to soil as selenate or selenite were generally found to be one or more orders of magnitude higher for a given plant species and plant part than TF values derived for “native Se”. From these values we determined the respective soil-to-plant transfer factors, and evaluated the role of experimental growth conditions on Se soil-to-plant transfer. As a result, we established a data basis of classified soil-to-plant transfer factors and their variation with experimental parameters. The large variability in TF values suggests that it is still important to understand the complexity of the soil-plant system when selecting TF values to assess risks arising from the transfer of accidentally released 79Se from soil into plants.