T ans e o Na u al Radionuclides om Soils o Plan s in
a Ma sh Enhanced by he Ope a ion o Non-Nuclea
Indus ies
A. Ma ínez-Agui e/ l. Ga cía-O ellanab & M. Ga cía-Leónb
ªDep. Física Aplicada, EUITA, Uni e sidad de Se illa, Ca e e a U e a, km 1,
41080 Se illa, Spaín
bFacul ad de Física, Uni e sidad de Se illa, Apdo 1065, 41080 Se illa, Spain
ABSTRACT
Two sampling campaigns we e pe o med in 1993 a he ma sh a ea (Odie/
ma sh) loca ed in sou hwes e n Spain, in he ci y o Huel a. Spa ina densi
lo a and subs a e soil ( 5 cm deep) samples we e collec ed in se e a/ loca
ions ac oss he a ea in each campaign. Ac i i y concen a ions o 210Po, U
and Th-iso opes we e de e mined in he plan and he subs a e samples. The
p oduc ion o phospho ic acid om phospha e mine al in he icini y clea ly
enhances he concen a ions o hese adionuclides in ce ain a eas o he
ma sh. Mo eo e , concen a ions in plan s a e a ec ed by he concen a ion
o he same elemen in i s subs a e. Indeed, high concen a ion le els in
plan s a e coinciden wi h high concen a ion in soils. Howe e , concen a ion
a ios ( CR), de ined as he a io be ween he concen a ion o an elemen in
he plan and o ha in i s subs a e, a e highe when subs a e concen a ions
a e low, whe eas low CR alues a e ound in a eas whe e subs a e concen
a ions a e high. Mo eo e , bo h a iables (CR and soil concen a ion)
seem o be non-linea /y ela ed, a leas , in he case o adionuclides om he
238U decay chain.
INTRODUCTION
En i onmen al assessmen s use ood-chain models o de e mine he <lose
o man om adionuclides eleased o he biosphe e. T adi ional ood
chain models equi e a plan /subs a e ans e coe icien , e e ed o as a
concen a ion a io (CR). The concen a ion a io o ans e coe icien
concep , is gene ally accep ed and widely used in en i onmen al anspo
models and desc ibes he amoun s o nuclide expec ed o en e a plan
om i s subs a e.
The CR app oach equi es us o assume ha he plan and subs a e
concen a ions a e linea ly ela ed and ha he line de ining he ela ion
ship goes h ough he o igin. The a iabili y o CR has p e iously been
add essed, bu ew ha e speci ically add essed he linea i y assump ion.
This assump ion implies ha , unde compa able condi ions, he CR o an
elemen is cons an , ega dless o subs a e concen a ion (Sheppa d &
Sheppa d, 1985).
Howe e , plan up ake o elemen s, bo h essen ial and non-essen ial o
g ow h, di e s and may ollow a non-linea ela ionship. Cannon (1952)
has s a ed ha U may be a mic onu ien o highe plan s, which means
ha CR was no linea ly ela ed o he subs a e concen a ion.
Mo dbe g e al. (1976) ob ained CR alues by i ing linea and
hype bolic unc ions o da a ob ained using di e en soil concen a ions
o iso opes in he U-Ra se ies. They showed ha he CR was cons an
o e hei obse ed soil concen a ions. Cannon (1952) also sugges ed a
linea ela ionship exis ing o U be ween plan and soil concen a ions.
Howe e , Mo ishima e al. (1976) epo ed a non-linea ela ionship o
U be ween ege able and soil concen a ions. Lopa kina e al. (1970)
ha e sugges ed ha he linea i y assump ion may hold only o p imi i e
plan o ms. Sheppa d and Sheppa d ( 1985) s udied he linea i y
assump ion o U in plan s and subs a e a wo o e bodies on he
P ecamb ian Shield. They ound ha he ela ionship be ween CR and
subs a e concen a ion obse ed in na i e plan s ends o be hype bolic,
wi h a endency o CR alues o be la ge a lowe subs a e concen
a ions. I appea s, he e o e, ha U may beha e as an essen ial
elemen a low subs a e concen a ions. Many da a sugges ha plan
concen a ions a e un ela ed o soil concen a ions, and when a line is
i ed o he da a, he in e cep is usually g ea e han ze o (Simon &
lb ahim, 1987). Log-no mal dis ibu ions o concen a ion a ios we e
epo ed by Sheppa d and E enden (1988). They p oposed ha he
linea i y assump ion, al hough con a y o wha is usually expec ed o
nu ien s (essen ial) elemen s, may be alid o limi ed anges o soil
concen a ions o o elemen s no physiologically egula ed by plan s.
Many expe imen s designed o measu e CR alues ha e used only a ew
di e en soil concen a ions and hus, canno s a is ically assess he
linea i y assump ion. Simon and Ib ahim (1987) p oposed ha a cu i
linea ela ionship e lec ing a sa u a ion- ype mechanism in plan s was
mo e app op ia e.
A hypo he ical ela ionship o he CR o essen ial and non-essen ial
elemen s o e a ange o subs a e concen a ions is shown in Fig. 1. This
ela ionship means ha plan s eadily ake up elemen s essen ial o plan
g ow h when subs a e concen a ions a e low, whe eas plan up ake o
non-essen ial elemen s is gene ally cons an in his subs a e concen a ion
ange (Timpe ley e al., 1970; Mengel & Ki kby, 1979). A high subs a e
concen a ions, plan up ake o essen ial and non-essen ial elemen s can
ei he be cons an (no oxici y) o can dec ease, leading o oxici y o
dea h. Toxici y begins a a oxici y h eshold, he subs a e concen a ion
a which plan g ow h, and hence up ake, begin o be impai ed. Le hal
subs a e concen a ions o an essen ial o non-essen ial elemen may no
exis , and in ha case, he CR may be cons an o se e a} o de s o
magni ude.
The CR concep is CR = Cp/Cs = cons an , and i is p obably use ul o
non-essen ial elemen s a non- oxic subs a e le els. The lack o co ela
ion be ween plan and subs a e concen a ions o non-essen ial elemen s
could be explained i he elemen is mimicking an essen ial elemen
(Sheppa d & Sheppa d, 1985). This ac would esul in a non-linea ela
ionship be ween he CR and he subs a e concen a ion a low subs a e
concen a ion. This ela ionship could be modelled as:
De icien To!e an
Non Essen iol-
Soil Concen o ion
Toxic
...
Toxici y
Th es íold
Non- oxic
/Le hal
(1)
Fig. l. Hypo he ical ela ionship o CR s soil concen a ion o bo h essen ial and non
essen ial elemen s h ough he de icien o oxic soil-concen a ion ange (Sheppa d &
Sheppa d, 1985).
whe e Cp is he concen a ion in he plan and Cs is he concen a ion in
he subs a e. This esul s in:
Cp a
CR =Cs
= Cs +b. (2)
I he i s ela ionship does no ha e a ze o in e cep (a i-O), his
would mean ha CR (Cp/Cs) is dependen on he subs a e concen a ion.
T acy e al. (1983) s udied he up ake o
226Ra, 21°I>b and U om soils o
ga den p oduce. They obse ed a clea end o inc easing concen a ions in
plan s wi h inc easing concen a ion in soil subs a e. In o de o exp ess
his end quan i a i ely, a linea eg ession analysis was ca ied ou o he
loga i hms o he mean ege able concen a ion s he loga i hms o he soil
concen a ions. This in ol es i ing a unc ion o he o m:
o
CR = acb-i
s '
whe e a and b a e pa ame e s o be de e mined.
(3)
(4)
A alue o b equal o 1.00 would imply a linea ela ionship (CR = Cp/
Cs = c e). They ound ha hei esul s we e no inconsis en wi h he line
a i y assump ion, a leas o concen a ions up o abou 37 Bq g-1 in soil.
The use o concen a ion a ios o p edic plan concen a ions om
low subs a e concen a ion o en i onmen al assessmen pu poses
should be in es iga ed u he o adionuclides known o mimic essen ial
elemen s and should be measu ed unde na u al condi ions (Sheppa d &
Sheppa d, 1985).
This pape e eals a s udy o he dis ibu ion and ans e o
210Po-, U
and Th-iso opes om soils o Spa ina densi lo a (a wild plan species
ypical o ma sh a eas in Eu ope) collec ed om a saline ma sh loca ed in
sou hwes Spain. The p esence, in he icini y, o a e ilize complex
which uses mine al wi h high U concen a ion could allow o a wide soil
concen a ion ange in he s udied a ea (Ma ínez-Agui e & Ga cía
León, 1997). Indeed, he main aim o he wo k is o con ibu e a bi mo e
in he s udy abou how na u al adionuclides a e being inco po a ed in he
plan om i s subs a e concen a ion. Thus, a s udy o he CR ela ion
ship wi h he concen a ion in he soil subs a e will ollow. Al hough his
species is no di ec ly in ol ed in he human ood chain, in o ma ion on
he concen a ion le els and ans e o adionuclides om con amina ed
soils will p o ide impo an da a on he ans e mechanisms in he case o
hose species mo e di ec ly in ol ed in he human die .
SAMPLES AND RADIOANAL YTICAL PROCEDURES
Se e al s a ions we e chosen ac oss he Odiel ma sh a ea o Huel a o
sample collec ion. This a ea is clea ly a ec ed by he was es eleased by
wo e ilize ac o ies loca ed in he icini y (see Fig. 2). The a ea is
cons i u ed by ou small islands sepa a ed by ou channels, which a e
a ec ed, due o idal mo emen s, by he in low o he Odiel i e wa e s
(Ma ínez-Agui e & Ga cía-León, 1997). Samples (plan and subs a e)
we e collec ed, du ing he low ide, a he bo de o he channels, in a eas
co e ed wi h wa e du ing he high ide.
A lan :c Ocean
Huel a
Town
Fig. 2. Loca ion o he sampling s a ions in he Odie! ma sh a ea. The loca ions o he
e ilize complex and he phosphogypsum piles a e also gi en.

Abou 1 kg o soil sample was collec ed om each s a ion and s o ed in
plas ic bags. A he labo a o y, hey we e d ied and powde ed be o e he
adionuclide analysis. The bulk d y densi y (g cm -3) and pe cen age o
o ganic ma e we e de e mined in each soil sample. Spa ina densi lo a
samples we e collec ed a he same s a ions and a he same ime as soil
samples. The oo s o he plan s we e sepa a ed in o de o s udy only he
o e g ound pa o he plan s. Once sepa a ed, he samples we e washed
wi h wa e o emo e any ace o solid pa icles. Finally, hey we e ai 
d ied and powde ed o analysis.
Aliquo s o each sample (soil and/o plan ) we e used o Po- and U
and Th-iso opes de e mina ions, sepa a ely. They we e diges ed wi h
concen a ed HN03 and aqua egia and he inal esidue dissol ed in 8M
HN03. Be o e he diges ion, he samples we e spiked wi h known
amoun s o 208Po ac i i ies o 210Po de e mina ion, and o 232U and 229Th
ac i i ies o U and Th iso opes de e mina ions, sepa a ely. Polonium-210
was sepa a ed om ac inides by a sol en ex ac ion me hod which used
TBP ( ibu ylphospha e) as he ex ac an phase. Polonium emained in
he ni ic phase, whe eas ac inides mo ed o he o ganic (TBP) phase
(Ma ínez-Agui e, 1991). The inal Po solu ion was e apo a ed and sel 
deposi ed on o 2.2 cm diame e sil e planche s. Polonium ac i i ies we e
de e mined by .(-spec ome y wi h ion-implan ed de ec o s.
Fo U- and Th-iso ope de e mina ions, an ion-exchange me hod was
used. A e edissolu ion o he esidue wi h 8M HN03, p ecipi a ion o
i on hyd oxides was ca ied ou by adding concen a ed ammonium.
U anium- and Th-iso opes we e sepa a ed and pu i ied in a DOWEX
AG1-X8 (chlo ide o m) esin (Ma ínez-Agui e, 1991). Final solu ions
we e elec opla ed on o 2.2-cm diame e s ainless s eel planche s, sepa
a ely. U anium- and Th-iso opes ac i i ies we e also de e mined by .(
spec ome y wi h ion-implan ed de ec o s.
RESULTS AND DISCUSSION
In Tables 1 and 2, da a on 210Po-, U- and Th-iso opes in soils and Spa ina
densi lo a o each sampling s a ion a e gi en, espec i ely. Table 1 also
includes he pe cen age o o ganic ma e in each soil sample. Mo eo e ,
in Table 3, concen a ion a ios (CR), de ined as he concen a ion o an
elemen in he plan (mBq g-1 d y weigh ) di ided by he concen a ion o
he same elemen in he subs a e (mBq g-1 d y weigh ), a e also gi en.
The nex sec ions discuss sepa a ely, da a on soil and plan concen a ions
and, inally, he CR esul s.
Soil subs a e
In gene al, by conside ing he le els o all adionuclides om he 238U
decay chain, a easonably wide ange o ac i i y concen a ion in he soil
samples, is ound. The e a e samples wi h low concen a ions o
238U and
descendan s, which can be conside ed as clea ly non-enhanced by he
e ilize indus ies. In gene al, concen a ion le els in hese samples a e
below 70 mBq g-1, le els simila o hose ypical in undis u bed soils
( anging om 10 o 50mBqg-1, UNSCEAR, 1988). These samples we e
collec ed in s a ions u he away om he e ilize indus ies, in he wes
pa o he Sal és island along he Pun a Umb ia i e . Also, e y low
concen a ion le els we e ound in wo s a ions a he eas side o he
Bacu a island opposi e he e ilize indus ies. This ac mus be ela ed o
he composi ion o he sample. Indeed, alues o densi y and o ganic
ma e (see Table 1) in bo h samples e lec ha high amoun s o sandy
pa icles, wi h low ac i i y concen a ions, a e con ained in such samples.
So ne o he samples e eal in e media e concen a ion le els (clea ly
highe han backg ound, bu no e y high) o all adionuclides om he
238U decay chain, anging om abou 100 o 300 mBq g-1. These samples
a e loca ed along he eas pa o he Enmedio island and he wes pa o he
Bacu a island, washed by he Moja e a channel. Finally, he e a e samples
wi h much highe concen a ion le els han he es o he samples. The
le els a e, in gene al, abo e 400 mBq g-1 o all adionuclides om he 238U
decay chain. These samples a e loca ed in he eas pa o he Sal és island
and he sou h o he No he n ma sh in he Odiel i e , all o hem along he
Odiel i e ups eam and downs eam om he e ilize indus ies. The
di e ence ound in he samples collec ed a he eas side o he Sal és island
mus , again, be ela ed o he composi ion o he samples. Thus, i can be
seen ha hose samples wi h low concen a ions (15 and 17) ha e densi y
and o ganic ma e alues e y di e en om he o he samples (16 and 18)
ha ha e qui e high concen a ions o adionuclides.
In gene al, excep ing he case o samples wi h di e en composi ion, he
di e ences in ac i i y concen a ion be ween samples seem o depend on
he loca ion o he sampling si es, which indica es he in luence o he
in low o Odiel i e wa e s o e each a ea. Thus, he bag o con aminan s
mo es ups eam and downs eam o he Odiel i e . Pa o i is clea ly
mo ing o he Odiel ma sh h ough he no h o he Bacu a island ha
la e lows in o he Moja e a channel.
We can also compa e ou esul s wi h o he da a ob ained in soils om
he a ea o Huel a, bu in he Tin o ma sh a ea (see Fig. 2) and a ound
he phosphogypsum piles (Boli a e al., 1995). Le els below 40 and
60mBqg-1 o 210Po and 238U, espec i ely, in s a ions loca ed in he eas
TABLE 1
Ac i i y Concen a ions (mBqg-1) o so ne Na u al Radionuclides om he U and Th Decay Chains in Soil Samples om he Odie! Ma sh
Collec ed in Feb ua y (F) and No embe (N) 1993
Code
O.M.(%)
21op0
238U 234u 232Th 230Th 22sTh
Fl
165 ± 7 189 ± 8
NI
10.8 199 ± 10 181 ± 8 197 ± 8 48.1 ± 2.5 186 ± 9 73.0 ± 7.0
N2
11.5 778 ± 41 698 ± 35 747 ± 37 88.1 ± 6.8 922 ± 52 160 ± 15
N3 14.8 643 ± 28 728 ± 32 751 ± 33 103 ± 5 898 ± 42 149 ± 13
N4 14.6 580 ± 26 540 ± 21 594 ± 23 61.1 ± 4.0 533 ± 26 144 ± 13
N13
15.4 222 ± 11 196± 7 217 ± 8 29.8 ± 1.8 112 ± 9 59.3 ± 6.3
F5 20.9 290 ± 31 360 ± 22 364 ± 22
N5 15.2 213 ± 10 232±9 248 ± 10 41.2 ± 3.0 208 ± 11 48.0 ± 3.3
N6 11.4 141 ± 7 147 ± 6 161 ± 6 31.0 ± 1.8 104 ± 5 14.0 ± 3.7
N7 13.1 130± 7 158 ± 6 179 ± 7 30.3 ± 2.2 125 ± 7 36.2 ± 2.5
N8
9.2 64.6 ± 4.0 64.8 ± 3.2 71.9 ± 3.5 26.6 ± 1.9 41.0 ± 2.6 30.9 ± 2.6
N9
9.7
188 ± 10 127 ± 5 142± 5 24.4 ± 1.6 101 ± 5 35.0 ± 4.0
FIO 12.9 25.1 ± 1.7 95.1 ± 4.9 116±6
NlO 12.7 27.9 ± 2.0 106±4 122± 5 23.6 ± 1.6 28.4 ± 1.9 22.5 ± 1.6
N23
14.5 210 ± 11 245±8 281 ± 9 41.4 ± 3.1 216 ± 13 62.1±5.4
N20 9.8 233 ± 11 258 ± 9
Nl8 17.3 565 ± 23 601 ± 21
Fl7 9.4 108±6 142 ± 10
N17 4.8 41.0 ± 3.2 17.6 ± 0.8
Fl6 13.7 367 ± 34 434 ± 16
Nl6 15.5 441 ± 20 511 ± 18
Nl5 4.6 131 ± 7 94.1 ± 3.7
Fl2 15.6 163 ± 9 147± 6
Nl2 9.3 44.2 ± 2.5 44.8 ± 1.6
Fll 13.3 124 ± 8 124 ± 6
Nll 9.2 194±9 75.4 ± 2.6
Nl9
5.7
54.4 ± 3.7 30.1±1.2
Fl4 12.5 40.5 ± 2.3 36.9 ± 1.6
N14 9.4 54.7 ± 3.9 37.8 ± 1.6
N21 1.1 16.2 ± 2.5 17.9 ± 0.8
N22 2.3 37.2 ± 2.5 32.4 ± 1.3
283 ± 10 44.l ± 3.6
630 ± 21 56.4 ± 3.8
163 ± 12
18.8 ± 1.0 26.5 ± 2.5
498 ± 23
523 ± 19 68.l ± 4.5
101 ±4 17.1±1.2
158±6
48.4 ± 1.8 26.7 ± 1.6
138 ±7
87.4 ± 3.0 22.0 ± 1.4
34.7 ± 1.4 15.4 ± 1.0
43.4 ± 1.8
43.7 ± 1.8 22.4 ± 1.6
19.3 ±0.9 4.9 ± 0.3
36.7 ± 1.4 11.8±0.7
256 ± 16
443 ± 22
30.0 ± 2.7
554 ± 23
87.4 ± 4.7
28.l ± 1.7
71.0 ± 3.7
31.7 ± 1.9
42.8 ± 2.7
8.8 ± 0.5
16.0 ± 0.9
78.5 ± 6.4
120 ± 12
32.8 ± 2.9
100 ± 12
46.3 ±4.5
25.0 ± 1.7
28.9 ±4.l
16.4 ± 1.3
22.5 ± 0.4
4.3 ± 0.9
13.3 ± 1.1
232Th/23su = 2_57e3su)-o.4ss
and
232Tb/230Tb = 3.14(23ºTh)-o.sos,
wi h eg ession coe icien s o -0.8623 and -0.9267, espec i ely.
(6)
(7)
These ela ionships may e lec ha hese ac i i y a ios emain
cons an only o concen a ions o 238U and 230Tb abo e so ne
200 mBq g-1• F o concen a ions below his alue, con amina ion o
adionuclides om he 232Tb decay chain seems o be undis inguished.
Spa ina densi lo a
The same adionuclides we e analysed in samples o Spa ina densi lo a,
whose esul s a e p esen ed in Table 2. The ac i i ies ange, in gene al,
om 2 o 50 mBq g-1 o 210Po and U iso opes, wi h he ac i i y concen
a ions o 21ºPo being highe han hose o U-iso opes in mos samples.
The e is a di e ence o one o de o magni ude be ween he highes and
he lowes concen a ions. As in he case o soil subs a es, he highes
concen a ions in Spa ina densi lo a we e ound a he No he n ma sh
and a he eas side o he Sal és island. Thus, in gene al, he highes
adioac i e concen a ions in plan s a e ound in hose collec ed in a eas
wi h he highes adioac i e concen a ion in he soil subs a e, and he
lowes in hose wi h he lowes concen a ions in he subs a e. Concen
a ions o 230Tb a e gene ally lowe han hose o 210Po and U-iso opes.
Howe e , he same pa e n o dis ibu ion is obse ed. Concen a ions o
adionuclides om he 232Tb decay chain a e clea ly much lowe han
hose o adionuclides om he 238U decay chain ( anging om 0.26 o
4.14 o bo h Th iso opes). In gene al, he concen a ion o 228Tb is highe
han ha o 232Tb. This ac should be ela ed wi h he highe mobili y o
228Ra. Howe e , i is also ue ha he adioac i e concen a ion o bo h
iso opes in plan s collec ed in he No he n ma sh and in he eas side o
he Sal és island a e highe han in hose samples collec ed in o he
s a ions.
I seems in e es ing o s udy he ela ionship be ween hese adio
nuclides. In Fig. 5(a), adioac i e concen a ions o bo h U iso opes a e
plo ed. I can be clea ly obse ed ha bo h iso opes a e qui e well linea ly
ela ed ( = 0.996), as was ound in he case o he soil subs a e samples.
Mo eo e , again he slope o he line (1.073 ± 0.018), o a y-axis in e cep
ze o (0.174 ± 0.262), would gi e he 234U /238U ac i i y a io o he plan .
Thus, he e is again a sligh excess o he daugh e iso ope. The ela ion-

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Fig. 5. Rela ionship be ween concen a ions o adionuclides om he
238U
decay chain in Spa ina densi lu a samples (a) 234U s.
238U,
(b)210po YS. 238U, (e) 230Tb s. 238u, (d) 228Th s. 232Th, (e) 232Th s. 238u and ( ) 232Th s. 230Th.
ship be ween he concen a ions o 210Po and ha o 238U [see Fig. 5(b)], is
no clea . Howe e , he e is s ill a clea end o inc easing 210Po concen
a ions when concen a ions o 238U inc ease ( = 0.8515). Compa ing
he U concen a ion in he plan wi h he y-in e cep o his line
(5.59 ± 1.45), he la e mus be conside ed clea ly di e en o ze o. This
y-in e cep e lec s he a ia ion in he 210Po/238U ac i í y a io wi h he
238U concen a íon in he plan . Thus, o a low U concen a íon (back
g ound le els), he e is an excess o 210Po compa ed o 238U. This excess
dec eases o secula equílíb íum o high 238U concen a íons. In ac , o
plan s wi h enhanced concen a ions, bo h adionuclídes a e p ac ically in
secula equilib ium.
Agaín, a linea ela ionship ( = 0.8223) can be ound be ween he 23ºTh
and 238U concen a ion in he plan s [see Fig. 5(c)]. In his case, he alue
close o ze o o he y-in e cep (0.368 ± 1.39) gi es a 23ºTh/238U ac i i y
a io qui e cons an ac oss all he a ea (0.638 ± 0.110). This alue o he
ac i i y a io e lec s a clea de ici y o 230Th in he plan s, opposi e o ha
ound in soils. This di e ence be ween ac i i y a ios in soils and plan s
can be explained by he lowe mobili y o Th compa ed o U.
Bo h Th iso opes om he same decay chain (232Th and 228Th) a e also
linea ly ela ed ( = 0.8950), as can be obse ed in Fig. 5(d). The alue o
he y-in e cep , gi es p ac ically secula equilib ium be ween iso opes in
all samples.
Mo e ín e es ing seems o be he ela ionship o he 232Th concen a
ions wi h he 238U and 230Th concen a ions [see Fig. 5(e) and 5( )]. The
concen a ion o 232Th in he plan clea ly inc eases as he concen a ion
o U and/o 23ºTh inc eases, ollowing linea ela ionships ( eg ession
coe icien s o O. 7220 and 0.9248, espec i ely). As hey a e iso opes o he
same elemen , he ela ionship be ween bo h Th iso opes is much be e .
In bo h cases, he y-axis in e cep is nea ly ze o, gi en 232Th/238U and
232Th/23ºTh ac i i y a ios o 0.087 ± 0.021 and 0.143 ± 0.015, espec
i ely.
Concen a ion a ios
We we e also ín e es ed in he s udy o he biological up ake and ans
e o hese adionuclides om he soil subs a e o he plan . Thus, we
ha e calcula ed he expe imen al alues o he concen a ion a ios o
each adionuclide in each s a ion. The esul s a e p esen ed in Table 3.
Fo 210Po, concen a ion a ios anging om 0.026 ± 0.002 o
0.948 ± 0.082, wi h a mean alue o 0.172 ± 0.204, we e ound. The
s anda d de ia ion o his mean alue e lec s he high dispe sion o he
da a. In ac , di e ences abo e one o de o magni ude a e ound.
Mo eo e , i is in e es ing o no ice ha di e en alues o his ac o
depend on he ac i i y concen a ion o he soil subs a e. Thus, high
concen a ion a ios appea in s a ions wi h low ac i i y concen a ions
in he subs a e, and low in mo e con amina ed s a ions. The same
occu s in he case o all adionuclides om he 238U decay chain. Fo
bo h U iso opes (238U and 234U), he expe imen al concen a ion a ios
ange om 0.022 ± 0.002 o 0.269 ± 0.03 l o 238U and om
0.024 ± 0.002 o 0.272 ± 0.032 o 234U, wi h mean alues o
0.083 ± 0.061 and 0.082 ± 0.060, espec i ely. Again, in bo h cases, he
concen a ion a io (CR) depends on he ac i i y concen a ion o he
elemen s in he soil subs a e. The same is ound in he case o he
concen a ion a io o 23ºTh. I anges om 0.010 ± 0.001 o
0.202 ± 0.022, wi h a mean alue o 0.065 ± 0.057. Thus, i seems ha
he beha iou o he concen a ion a io, which means he up ake by
plan s o adionuclides om i s subs a e, depends on he ac i i y
concen a ion o he elemen in he soil subs a e.
In he case o bo h Th iso opes om he 232Th decay chain, he
concen a ion a io anges om 0.014 ± 0.004 o 0.065 ± 0.008 o 232Th
and om 0.011 ± 0.001 o 0.084 ± 0.022 o 228Tb, wi h mean alues
0.036 ± 0.018 and 0.042 ± 0.025, espec i ely. The dispe sion o he da a
seems o be no as high as ha o adionuclides om he 238U decay
chain. Howe e , we mus conside ha , in his case, he ange o Th
concen a ion in he soil subs a e is no as wide as in he case o U and
daugh e s.
In o de o s udy he beha iou o he concen a ion a ios o hese
adionuclides, concen a ion a ios e sus he ac i i y concen a ion a he
adionuclide in he soil subs a e ha e been plo ed in Fig. 6 o 238U and
daugh e s and in Fig. 7 o 232Th and 228Tb. The CR alues clea ly
dec ease when he ac i i y concen a ion in he subs a e soil inc eases. In
ac , he da a can be modelled by i ing unc ions o he o m:
CR = aC� (8)
Thus, i b = O, his would mean ha he concen a ion a io is cons an ,
ega dless o he ac i i y concen a ion in he soil subs a e. Func ions o
his ype ha e been i ed o 210Po, 238U, 234U and 230Tb, and hese esul s
a e p esen ed in Table 4. Thus, o all adionuclides om he 238U, he b
alue o he hype bolic unc ion is clea ly di e en om ze o,
-0.750 ± 0.097, -0.445 ± 0.081, -0.438 ± 0.082 and -0.573 ± 0.098 o
210Po, 234U, 234U and 23ºTh, espec i ely. Howe e , he linea i y assump
ion may i be e in he case o U iso opes. Thus, i seems ha all hese
adionuclides ollow he beha iou o an essen ial elemen o he plan
TABLE4
Concen a ion Ra io (CR) Fi ed Func ions o Radionuclides om he 238U Decay Chain
Radionuclide
210p0
23su
234u
230Th
CR =aC
CR = 4.06 c;º·750
CR = 0.59 c;º·445
CR = 0.588 c,0·438
CR = 0.717 c,0573
l.96
0.239
0.247
0.349
0.097
0.081
0.082
0.098
-0.8296
-0.7137
-0.7030
-0.8256
C, means he concen a ion o he adionuclide in he soil subs a e.
g ow h. Mo eo e , i ac i i y concen a ions in he soil subs a e abo e
200mBqg-1 a e only conside ed, he CR alue would be appa en ly
cons an . Thus, conside ing only hose s a ions wi h high ac i i y concen
a ions in he soil subs a e, CR alues o 0.050 ± 0.023, 0.046 ± 0.020
and 0.023 ± 0.011 a e ob ained o 210Po, U-íso opes and 23ºTh, espec
i ely. In his case, i he CR alue is used o p edic plan concen a ions
om subs a e concen a ion, i will unde p edic plan concen a ion
when he subs a e concen a ion is less han ,..._, 200 mBq g-1. Sheppa d and
Sheppa d (1985) ound ha he CR o na u al U in na i e plan s a he
" 'T
. :T •
º·'
,
.. :
I
"
� º·'i
o.,�,-
.,_ ..
�--.-------� --. ------�---+- --·--+--
0.30
0.25
0,20
0::: 0,15
u
0,10
0.05
0.00
200
T
1
T
I
1!
· .} I
_{_
.! I
·. I
Pi. ·I.
...
200
<-00 800 800
C8 (mBq/g)
234u
I
j _
,oo 600
C. (mBqlgJ
800
O.JO :T
, 1 b
º·" .T
0.20
+-,-! ..
0:::: 0,15 J".1
ü ' �
0.25 '.
º·'° ·
,!
0.15 T
5 '
º·" l.
200
o.o, 'i:_ . I
..
I1í ··--]I;
J[
0.00 ¡
O 200
I
J: I
-- --- --- ---_]l_ -
,oo 600 800
C.(mBq/g)
·�-- -- -· -- -- ---------•.---
'
'°º '
600
C.(mBq/g)
' --,
800 1000
Fig. 6. Concen a ion a ios s. he ac i i y concen a ion o he elemen in he soil
subs a e o
(a) 210Po, (b) 238U, (e) 234U and (d) 23ºTh.
P ecamb ian Shield appea ed o be dependen upon subs a e concen a
ion below ""20 µgg-1. They assumed he use o he CR concep o p edic
U concen a ion in plan s o be alid when subs a e concen a íons a e
highe han abou 20 µgg-1• In ou case, his ac seems o be ue o ali
adionuclides om he 238U decay chain. The case o bo h Th iso opes
om he 232Th decay chain is no e y clea . The CR alues (see Fig. 7)
seem o be mo e o less cons an compa ed wi h hose o adionuclides
om he 238U decay chain, wi h mean alues o 0.036 ± 0.017 and
0,16 232Th
•
0,14
0,12
0,10
a::: 0.08
III
0,06 T I I
0,04 1
]: I l:
0,02 ]:
:q I I
º·ºº'
o20
40
60 80 100 120
C. (mBq/g)
b
0,10
• 1
!
+ I
1
0,05 -'--
I
II lI ! I
I
I I
0,00 +-���--.-�-.---..-----,--���--.�-.---..---.-�-,
o 20 40 60 80 100 1W 1� 100 100
C.(mBq/g)
Fig. 7. Concen a ion a ios s. he ac i i y concen a ion o he elemen in he soil
subs a e o (a) 232Th and (b) 228Th.

0.042 ± 0.025 o 232Th and 228Th, espec i ely . Howe e , he ange o
ac i i y concen a ion o hese adionuclides in he soil subs a e, should
be conside ed ca e ully.
Thus, i seems ha , when s udying he up ake o adionuclides by plan s
om i s subs a e concen a ion, i is necessa y o conside a easonably
wide ange o ac i i y concen a ion in he soil subs a e. O he wise,
no hing can be clea ly p edic ed. l seems ha a leas hose adionuclides
om he 238U decay chain beha e as essen ial elemen s o he g ow h o
he plan . Howe e , whe he hese elemen s a e essen ial o a e mimicking
essen ial elemen s canno be de e mined wi hin his s udy.
CONCLUSIONS
Concen a ions o 210 Po, U- and Th-iso opes in Spa ina densi lo a and
soil subs a e samples collec ed om a saline we ma sh ha e been s udied.
The ac i i y concen a ions show clea ly he in luence ha he adio
ac i i y con ained in he phospha e ock used o he phospho ic acid
p oduc ion has o e he concen a ion o na u al adionuclides in ce ain
zones o he ma sh, a ec ing he plan s and he soils. Indeed, he s a ions
mo e in luenced by he Odiel wa e s p esen he highes concen a ions in
soils and plan s.
Concen a ion a ios o all adionuclides in he plan we e de e mined.
The concen a ion a io o an elemen seems o be dependen on he
ac i i y concen a ion o he same elemen in i s soil subs a e. Thus, high
CRs appea in plan s g owing in soils wi h a low concen a ion o adio
nuclides, whe eas low CRs appea in plan s g owing in soils wi h high
concen a ions. Mo eo e , he ela ionship be ween he CR and he
ac i i y concen a ion o he soil subs a e seems o be hype bolic, a leas
in he case o adionuclides om he 238U decay chain. As a consequence,
i he CR alue is used o p edic plan concen a ions om subs a e
concen a ion, i will unde p edic plan concen a ion when he subs a e
concen a ion is less han "'200mBq g-1. Howe e , in he case o 232Tb
and 228Tb, he na ow ange o ac i i y concen a ion o hese adio
nuclides in he soil subs a e, could be he eason o he appa en
cons ancy o he CR wi h subs a e concen a ion.
ACKNOWLEDGEMENT
This wo k was pa ially suppo ed unde EC con ac FI 3P-CT920035.
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