S. Penttila et al., THE OCCURRENCE AND BIOAVAILABILITY OF RADIOACTIVE CS-137 IN SMALL FOREST LAKES IN SOUTHERN FINLAND, Environmental pollution, 82(1), 1993, pp. 47-55
Following the Chernobyl accident in late April 1986, central Finland w
as subjected to considerable radioactive fallout. The radioactive isot
ope of caesium, Cs-137, was potentially the most harmful isotope in th
e fallout because of its long half-life (30 years). Cs-137 activities
remained unexpectedly low within the biota (algae, zooplankton, aquati
c moss, fish) of some humic forest lakes in southern Finland compared
to the clear water lakes within the same district. This observation su
ggested that humic substances, by binding Cs-137 chemically, may reduc
e its bioavailability in lake water. Our laboratory experiments (throu
ghflow systems; gel chromatography) demonstrated that binding of Cs-13
7 by humic substances was negligible in untreated lake waters; only wh
en most of the alkali metals had been removed with an ion exchange res
in was any binding of Cs-137 by low molecular humic fractions apparent
. Instead, the concentrations of cations (especially potassium) were o
f overwhelming importance for the bioavailability of Cs-137 within the
lacustrine ecosystems. The concentrations of Cs-137 within food chain
s are expected to stay at a high level for many years especially in la
kes with long water renewal times.