Dynamic model for tritium transfer in an aquatic food chain

Abstract

Tritium ((3)H) is released from some nuclear facilities in relatively large quantities. It is a ubiquitous isotope because it enters straight into organisms, behaving essentially identically to its stable analogue (hydrogen). Tritium is a key radionuclide in the aquatic environment, in some cases, contributing significantly to the doses received by aquatic, non-human biota and by humans. The updated model presented here is based on more standardized, comprehensive assessments than previously used for the aquatic food chain, including the benthic flora and fauna, with an explicit application to the Danube ecosystem, as well as an extension to the special case of dissolved organic tritium (DOT). The model predicts the organically bound tritium (OBT) in the primary producers (the autotrophs, such as phytoplankton and algae) and in the consumers (the heterotrophs) using their bioenergetics, which involves the investigation of energy expenditure, losses, gains and efficiencies of transformations in the body. The model described in the present study intends to be more specific than a screening-level model, by including a metabolic approach and a description of the direct uptake of DOT in marine phytoplankton and invertebrates. For a better control of tritium transfer into the environment, not only tritiated water must be monitored, but also the other chemical forms and most importantly OBT, in the food chain.

Tritium dynamics in large fish – a model test

“…The updated AQUATRIT model [4] was successfully tested for small fish. In the absence of the experimental data for large fish, it was agreed in 2009 with researchers from Atomic Energy of Canada Limited to use their planned experiments with large trout for a blind test of AQUATRIT model.…”

“…One such scenario involved the prediction of time-dependent tritium concentrations in freshwater mussels that were subjected to an abrupt change in ambient tritium levels [3]. An updated model concerning the dynamics of tritium transfer in aquatic food chain (AQUATRIT model) was developed and reported recently elsewhere [4]. The experimental data for tritium in large fish are not reported and consequently, AQUATRIT model cannot be tested.…”

“…In practice, the assessment of K 0.5 is based on fish bioenergetics models and the detailed description is given in a recent paper [4]. For rainbow trout, the model parameters are considered as those used in the specific bioenergetics models based on experimental verification [6,7].…”

Advanced nuclear reactors and tritium impacts. Modeling the aquatic pathway

“…The Specific Activity Ratio (SAR) is defined as the ratio between SA of OBT in the animal and SA of HTO in water. Previous work defined values of SAR and other transfer factors for different aquatic organisms from European rivers (Galeriu et al, 2009;Gontier and Siclet, 2011;Galeriu and Melintescu, 2010;Fontugneet al, 2005;Franco et al, 2006;Gleizon et al, 2009;Heling and Bezhenar, 2009;Howard et al, 2012;IAEA, 2008;Melintescu and Galeriu, 2011;Miyamoto et al, 2002). These values should not be used to tropical organisms without significant increasing in the uncertainty of model results.…”

“…This parameter allows evaluating the transfer coefficients used to assess OBT dynamics, so the uncertainty is propagated into the model. Other critical parameter is the OBT biological loss rate (K 0.5 ) that is the half-live of tritium on OBT form in the organism, so it is crucial to determine the dynamic of OBT concentration in different aquatic organisms (Galeriu et al, 2009;Melintescu and Galeriu, 2011). Laboratory experiments to Fig.…”