Plutonium in temperate and Arctic lakes

摘要

Plutonium has been studied in different lake systems, spanning clear-water oligotrophic lakes in the high arctic to humic-rich dystrophic lakes in the temperate regions. Correlations between radiocaesium, ~(210)Pb and the plutonium inventory in the lake sediments have been studied. In the high arctic lakes, we find higher inventories of plutonium, radiocaesium and ~(210)Pb than expected from fallout data and the annual flux of ~(210)Pb at these latitudes. We hypothesize that this is due to the lakes acting as traps for wind-driven material which is caught by the water surface during the period of the year when the lakes are ice-free. The influence of the Thule accident in these lakes was also studied with respect to resuspension of debris from the catchment area to the lakes. Judging from the plutonium isotopic composition and ~(239+240)Pu/~(137)Cs ratio, no detectable plutonium from the accident was found in the lakes of the Thule region. The dystrophic lake studied shows very high levels of fallout plutonium (130-220 μBql~(-1), annual variation) in the water. This plutonium is largely associated with humic colloids (77% in the fraction between 1 μm and 100 kD) and so the fate of these colloids obviously plays an important role in determining the behaviour and fate of plutonium in this fresh water system.