UPTAKE OF RADIOACTIVE NUCLIDES
&LL
the close manner shown by calcium and strontium (2, 64). The study of
the interaction of caesium and potassium has been hindered by the fact that
1.6 pe Sr°/gCa in
verage to abou t
» i
strontium
eeper penetration of
rease by a out
w rooted crops to dec
wide fallou
ldwor
ults of surveys of
eriments in
exp
ld
fie
s; so also did the
toxic symptoms may readily be induced by relatively high ratios of caestum
to potassium. Cline & Hungate (72) found that the growth of plants was
considerably reduced by 0.2 mM caesium in the presence of 0.07 mM potassium after 16 days. Uhler (73) showed that within a few hours respiration
may be reduced by 7.5 mM caesium. The suggestion that two mechanisms
the
ab sorption from
tamination and
he first
are operative for the absorption of caesium, one at relatively low concentrations, the other at higher levels (74), may therefore be due to the
llout.—T
with world-wide fa
ect conta
dir
of
if the importance
to 9 hie
occurrence of toxic effects under the latter circumstance. Cline (75) has,
however, established that over extended periods the absorption of carrierfree caesium 137 (which will give rise to no toxic symptoms) bears no constant relationship to that of potassium; whereas the ratio of caesium 137 to
potassium in tissues equalled that in the external solution when 10 mdf
potassium was applied, caesium 137 reached leaves to less than one-fiftieth
of the extent of potassium when the concentration of the latter ion was
0.02 mdf. Comparable results have also been obtained in short experiments,
cdlAE
rontium 89
of the ratios of st
cause the haif lt ‘
‘5 1957 and 1958. Be
in any sample ot
atio to strontium 90
Information’ o
.
r of 2 in this period
re: ore
diet could the
is transferred to
:.
und that the rate
fo
s
1 Britain it wa
°
summer (27).
fallout during the
s thus between one
ntium 90 to milk wa
use
in which, however, interpretation is less certain because of the occurrence
ons trials ca
ispension of weap
of exchange reactions (76). The dissimilar behaviour of the two ions
misphere, t ons
out the Northern He
els of strontiam
d decreases in the lev
n In ne
does not, however, justify the conclusion that they enter plants by separate
mechanisms, The ionic radii of the two ions contrast markedly; this could
contaminatio
grtance of direct
ntamina:
cause them to be retained to differing extents on sites of the same type.
1959 the co
at during 1958 and
direct contamin®
the
was mainly due to
situation appears
posit (66) and the
ed States about| a
is (67). In the Unit
these years has be
< in the summer of
Uncertainties as to the basic nature of metabolic processes whereby ions are
actively accumulated make it unwise to suggest any final conclusion.
Caesium 137 which was deposited on foliage of plants appears to be
retained relatively similarly to strontium 90, and like strontium it is readily
removed from foliage by rain (32). The concentration of caesium 137
within different tissues which results from direct contamination, however,
factors whic ir
ve proportionality
°
rate of fa ne
Itural products to the
e
n
cu
y such cal
il (2, 65 to 71). An
ac ors
can contrast very markedly with that caused by strontium 90. This is due
to the mobility of caesium 137 within tissues; thus nearly 30 per cent of
the caesium 137 which has been deposited on the foliage of potatoes may
reach the tubers, as compared with less than 1 per cent of strontium 89
and seasonal
anges in weather
has
“en
milk, which
} into plants. With
an
s
onal complication
viewpoint, additi
and the consumpt
tle
cat
x pattern of
from the imprecise”
uncertainties result
The effects of t est
ulations are based.
estimates are mas
erably reduced when
nger in 4 large . ;
1 entire year or lo
(45). It appears possible that in permanent pastures caesium 137 may
Legerer
OM
remain in the plant-base region, readily accessible for absorption for an
appreciably longer time than strontium 90 (77). More detailed investiga-
is y
culations which sat
n carried out. Cal
ore
for
e
lu
va
practical
ye of considerable
am
nt
co
l
ta
en
nm
viro
nsequences of en
soils is fixed in this way; the operative process appears to be entrapment of
the caesium ion in the lattice structures of clay minerals, possibly illite.
ium is not related
S
Caesium 137 in the soil—Caesium 137 moves downwards in undisturbed
soil to a considerably smaller extent than strontium 90 (2); after 3 years
more than 90 per cent of the caesium 137 which has been added to thesoil
surface may remain in the upper 5 cm (78). The most important contrast
have estimated that 95 to 99 per cent of the caesium 137 in typical Swedish
ever, it is well es
4 within them. How
1
to that of potassium
EP EY SELE
tions must, however, be carried out before any general conclusions are
warranted.
in the behaviour of the two ions in the soil, is however, that caesium 137
is usually bound in forms inaccessible to plants (2). Fredriksson et al. (79)
r
esiuM 137
by plants and fe
am is readily absorbed
a
+
gern UT
ce
some *ag
287
ae
ee
vee gee ee ep
Foe
*
ee gps
me
gee ae Fe tees ge
ee a et
pat,
so