Sammendrag
Risk assessments of radionuclides/trace elements in aquatic freshwater system are in most cases based on the total concentration of the elements. However, in aquatic systems trace elements and radionuclides are present in different physico-chemical forms ranging from low molecular mass (LMM) species to colloids, pseudocolloids and particles. The mobility and bioavailability will depend on the speciation of the trace elements/radionuclides. To reduce uncertainties and improve the predicting power of models, data on the trace element speciation should be included in the risk assessment models. A number of different techniques are available for speciation purposes in water. For in situ fractionation an on line size- and charge fractionation system has proven very applicable. This system uses filtration (membrane)/ultrafiltration (hollow fibre) coupled to ionic exchange columns for charge fractionation. For larger sample volumes tangential flow systems can be used. This system is particularly useful for determination of different physico-chemical forms in unstable water qualities (e.g mixing zones) when it is essential to perform the fractionation in the field. The collected fractions can later be analysed in the laboratory using e.g. ICP-MS, ICP-OES, gamma spectrometry etc. To link the physico-chemical forms of trace elements to the uptake in biota, in vivo bioassays are a useful tool as the uptake and distribution of the tested elements can be determined. Using well defined radioactive tracers the distribution and the kinetics can easily be followed. The present work presents the uptake of 60Co at different early life stages (just fertilized, roe, fry/alevins) of salmon (Salmo salar). Early life stages were exposed to high ionic strength freshwater containing 60Co. The uptake at the different stages was followed in a period of 8 days. Using autoradiography the accumulation sites of 60Co in the eggs/fish could be identified. Gamma measurements were performed using a NaI detector (Wizard). In addition, rainbow trout (Oncorhynchus mykiss)(approx.600g) was injected (dorsal aorta) with 60Co2+ and 60Co-citrate to identify the accumulation sites and redistribution between organs. The results indicated that in the experimental water used, approx 95% of the added 60Co was found as positively charged 60Co. The uptake study showed that accumulation of 60Co occurred at all life stages and the digital autoradiography indicated that there were accumulation sites within the egg, most probably attached to the growing embryo (Figure 1). In the fish injected with 60Co, 60Co was still found in the blood 28 days after. Also, 60Co seems to accumulate in the kidney of the fish.