407969
Radatwn Hotany, 1970, Vol 10, pp. 29'S to 295. Pergamon P ess. Prnted in Great Britain.
SHORT COMMUNICATION
Comparative Uptake of Thorium-230, Radium-22%6, Lead-216
and Poloniun2i0 by Plants
(Received 18 Fuly 1969)
Wire the uptake of 9°Th, ™4Ra, **°Pb and
9Po, the long-lived radionuclides of uranium
series, by plants from nutrient solution and soil
has been reported, (-#19.11,13.19 no quantitative
data are available on their entry and translocation measured under closely comparable conditions. Since this information is likely to be of
value in establishing the relative significance
ot different: nuclides as sources’ of natural
radioactivity in plant populations, we have
examined these aspects in nutrient culture
experiments. Strontium-89, a fission product
nuclide of radiobiological significance, was
included for comparison.”
Red kidney beans (Phaseolus oulgaris L.) var.
Local were grown in water culture and when 15
days old the plants were transferred to polythene jars containing 1000 ml fresh nutrient
solution. The nutrient solution contained Kt,
3-0; Catt, 8.0; Mgtt, 3-0; NO,-, 10:0;SO,- -,
3-0; H,PO¢, 1:0; m equiv/l together with
micronutrients Fe, Mn, Cu, Zn, B and Mo. The
pHof the solution was 5-0. Each radionuclide
constituted a separate treatment and was added
in carrier free state at the activity level of 0-25
pCi/L to five replicate jars. The experiment
was conducted in a growth room where tem-
perature was maintained at 2341°C, relative
humidity at 65 {2 per cent and the plants were
illuminated in 12 hr periods at 800 ft-c. The
duration of the treatment was 15 days and the
transpiration losses from the solution were made
up daily with distilled water.
Atter treatment, roots were separated from
sheots and the entrained solution was removed
from roots by blorting. The tissues were dried
at 90°C and wet ashed usingnitric acid to obtain
clear extracts which were taken up for radioassay. ™*Ra and ™°Pb were assayed by gamma
spectrometry using a well-type 3x3 in. Nal
(Tt) crystal integral line assembly, and a 512channel pulse height analyser attached to an
oscilloscope and computer readout typewriter.
For the assay of®*Ra, measurements were made
of the 610 KeV peak of its daughter **Bi after
allowing "Bi to attain equilibrium with **Ra
in a sealed ampoule.“ %°Pb was assayed by
measurementof its gamma peak at 47 KeV.
"™°Th was coprecipitated aé fluoride with
neodymium carrier and its alpha activity was
measured in a low background ZnS (Ag)
scintillation counter.) For assay of ™°Po and
*Sr aliquots of the extracts were dried and
counted in a low background alpha <cintillation
counter and a Geiger-Muller counter respectively.Since each plant tissue sample contained only one radionuclide no interference
froin other nuclides occurred during radioassay.
The radioassay data were corrected for background and processed to compute per cent
uptake, concentration factor and transport
index for each nuclide (Table 1).
Data presented in Table 1 indicate that
accumulation of ®°Th, @*Pb and "°Po occurs
predominantly in roots and only very small
amounts of these nuclides are translocated to
shoots, Over comparable periods, the accumulation of **Ra in roots is 2-3 times lower than
that of the other nuclides of uranium series.
However, the mostsignificantdifference between
™4P4 and other nuclides is in the extent oftheir
upward transport which for radium is 50-200
293
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