Kinetic modelling of radionuclide transfer in northern European marine food chains

摘要

A biokinetic modelling approach with allometric considerations has been used to estimate the trophic transfer of ~(137)Cs and ~(239)Pu in a marine foodchain consisting of 4 trophic levels including phytoplankton, zooplankton, polar cod, and with harp seal as a top predator. The time-dependent transfer of radionuclides within the foodchain is defined by uptake rates, assimilation efficiencies and egestion/excretion rates and can be described by a system of linear 1st order differential equations. The Matlab based software ECOLEGO was used to solve the equation system numerically, and the activity concentration for animals in each trophic level was found as a function of time. For the simulation concerning ~(137)Cs, the preliminary results suggest that equilibrium is not attained for higher trophic levels, i.e. polar cod and harp seal, before time > 2000 days. Biomagnification appears to occur for the lower trophic levels but is not occurring at the highest trophic level, i.e. seal. For ~(239)Pu, transfer to successively higher trophic levels is low – there is a fall of several orders of magnitude between primary producers, represented by phytoplankton, and polar cod representing trophic level 3-4. However, the model predicts that this decreasing trend in activity concentrations along the food-chain is reversed for the highest trophic level, represented by seal. The simulated results for seal display equilibrium activity concentrations about 2 orders of magnitude higher than those observed for polar cod (one of its prey species). However equilibrium (165 years) is not reached during the life span of a seal. The equilibrium ~(137)Cs CFs are approximately 50, 130 and 70 ml/g for zooplankton, polar cod and seal respectively. The predicted equilibrium ~(239)Pu CFs for zooplankton and polar cod are 2.5·10~3 and 25 ml/g. For seal, following a 1 year equilibration period, a CF of approximately 75 ml/g is predicted.