U and Th specia ion in i e sedimen s
A. Ma inez-Agui e3, M. Ga cia-León3, M. I ano ich* b
ªFacul ad de Fisica, Uni e sidad de Se illa, Apdo.1065, 41080 Se illa, Spain
bAEA Technology, Ha well Labo a o,y, Oxon, OXll ORA UK
Abs ac
A s udy o he dis ibu ion o so ne na u al adionuclides in di e en chemical ac ions o i e bo om sedimen s
has been ca ied ou . Toe s udy has shown ha he majo i y o he o al U in sedimen s is loca ed in he non- esidual
ac ions, while Th is mo e likely o be p esen in he esidual ones. This di e ence be ween U and Th e lec s
la gely a much highe mobili y o U ela i e o Th in su ace and nea -su ace en i onmen s. Cop ecipi a ion wi h
amo phous e omanganese oxyhyd oxides is he main p ocess o U and Th inco po a ion om he wa e column
in o he soil pa icles. Mo eo e , he dis ibu ion o he adionuclides and he analysis o he Th/U mass a ios in
di e en chemical ac ions o sedimen s has made an unequi ocal connec ion be ween he enhanced U con en in
i e sedimen s and he was es discha ged in o he i e s by he ope a ion o e ilize indus ies.
Keywo ds: Radionuclide pollu ion; U anium (U); Tho ium (Th); Ri e sedimen s; Fe ilize indus ies
l. ln oduc ion
Ri e sedimen s may be ega ded as, a leas , a
empo a y sink o much o he ma e ial which
passes h ough he a ious aqua ic chemical and
biological cycles ope a ing on he ea h's su ace.
Thus, sedimen s become an en i onmen al hos
o many o he was e p oduc s discha ged by
socie y. Toe e ec s o hese man-made emissions,
in so ne si ua ions, can be su icien ly s ong o
a ec highly he composi ion o he deposi ed
* Co esponding au ho .
sedimen s. Once a subs ance has been inco 
po a ed in o a sedimen , i s ul ima e a e depends
on a numbe o e y complex ac o s. An elemen
may be conside ed o be locked pe manen ly in o
a sedimen componen o i may la e be eleased
and ake pa in a ious biogeochemical eac
ions.
Toe undamen al dis inc ions ha ha e been
made in sedimen s geochemis y is ha be ween
ma e ial b ough o he si e o deposi ion in a
solid o m and ha b ough in a dissol ed o m.
In ha sense he dis inc ion o elemen s be ween
esidual and non- esidual ypes is pa icula ly ap
p op ia e o he in es iga ion o adionuclide poi-
'.,,:{�
h ion [1]. Thus, p ocesses in ol ed in he inco 
po a ion o elemen s om pollu ed wa e s esul s
j�:; hei loca ion in he non- esidual ac ions and
hus, hey can usually be conside ed o be a leas
po en ially mobile, i.e. en i onmen ally eac i e in
he chemical and biological p ocesses which occu
in he sedimen s/in e s i ial wa e complex. On
he o he hand, elemen s loca ed in esidual ac
ions can usually be conside ed, a leas o a i s
app oxima ion, o be immobile, i.e. en i onmen
ally un eac i e. Thus, he esidence o an ele
men in a deposi may be only empo a y, and
hei elease in o he ecosys em ep esen s a po
en ial haza d. The ex en o which his elease
occu s depends la gely on he manne by which
his elemen is bound o he sedimen and on how
pa icula kinds o bonds eac o a ious
physico-chemical condi ions.
The abo e conside a ions ha e led o he s udy
o he dis ibu ion o u anium (U) and ho ium
(Th) in di e en ac ions o sedimen s collec ed
a he Odiel and Tin o i e s, which a e loca ed in
Sou hwes Spain. Such sedimen s a e clea ly a 
ec ed by he was es eleased by wo e ilize
ác o ies loca ed in he le ma gin o he Odiel
l e as well as by he phosphogypsum piles s o ed
a he igh ma gin o he Tin o i e [2].
2. Samples and adiochemical p ocedu es
Sampling was ca ied ou du ing he summe ,
1989. Sedimen samples we e collec ed along he
Odiel and Tin o i e basins and s o ed in plas ic
b¡igs; hen, a he labo a o y hey we e d ied and
1'9W.de ed be o e he analysis. The loca ion o he
S!lmpling s a ions a e shown in Fig. 1. Th ee sedi
� s om he Odiel i e we e s udied: up
s eam om he e ilize indus ies (S01), a ound
o:n� o he e ilize indus ies (S02) and down
s eam om hem (S03). In he Tin o i e , sedi
men s om wo loca ions we e s udied: one
;; IQUnd he phosphogypsum pile a ea (STl) and
ino he downs eam om his zone nea he con
lu�nce wi h he Odiel i e (ST2). Addi ionally,
a ió he sample (SOT) loca ed downs eam o he
co' luence o bo h i e s was s udied.
S:1bne sequen ial ex ac ion o six sedimen ac
io'ns (Table 1) has been implemen ed o each
sedimen sample (3,4]. The six sequen ially
leached ac ions o he sedimen a e de ined in
Table 1. F ac ions Fl -F4 a e e e ed o as sec
onda y phases expec ed o ep esen he non- e
sidual pa o he sedimen , being ei he an end
p oduc de i ed om he i e wa e /solid in e 
ac ion and exchange p ocesses o pa o he solid
capable o di ec in e ac ion wi h i e wa e and
hus sha ing so ne geochemical and iso opic cha 
ac e is ics wi h he liquid phase. F ac ions F5 and
F6 a e e med esidual phases and a e no ex
pec ed o necessa ily in e ac on a sho ime-scale
wi h he liquid phase, a leas no unde no mal
condi ions ound in he su ace and nea -su ace
en i onmen s.
Once he ac ions we e sepa a ed, hey we e
spiked wi h 236 U and 229Tb and he ex ac ion o
U and Th iso opes was ca ied ou acco ding o
he me hods gi en in [3,4]. U and Th ac i i ies
we e measu ed by a-spec ome y wi h su ace
ba ie o ion implan ed Si de ec o s.
3. Resul s and discussion
Pe cen age dis ibu ion o U and Th in he
di e en ac ions ( aking he con en in he un
ac iona ed sedimen as 100% [2]) a e shown in
Figs. 2 and 3. Wi h he excep ion o samples ST2
o U, he sum o he pe cen ages in he di e en
ac ions ag ees well wi h 100%. Analy ical p ob
lems in chemical sepa a ions o he e ogenei y in
he sedimen sample canno be igno ed.
3.1. U anium
Fig. 2 shows ha U is mainly associa ed wi h
non- esidual ac ions, pa icula ly wi h F2 and
F3 ac ions. Mo e han 40% o U is ound asso
cia ed wi h he ac ion F3 (an excep ion is sam
ple STl wi h 30% in his ac ion). This implies
ha he main p ocess o U inco po a ion om
he liquid phase ( i e wa e ) in o he sedimen s
is he cop ecipi a ion wi h amo phous e oman
ganese oxyhyd oxides. This is a ypical p ocess
obse ed in es ua ine en i onmen s [5].
In sedimen S02 (Fig. 2b), ac ion F3 is s ill
one o he main non- esidual ac ions con aining
>40% o he o al U. Howe e , in his sample a
o
N
� Phosphogypsum pi les
*Fe lllze ac o les
3km
1
Fig. l. Map o he s udied a ea showing he loca ion o he sampling poin s, he e ilize ac o ies and he phosphogypsum s o age
a ea emplacemen s.
high p opo ion o U (- 50%) is also ound in
ac ion F6 ( he p ima y mine al ac ion). This
sample (Fig. 1) was aken in he icini y o a
e ilize ac o y which eleases pa o i s solid
was es di ec ly in o he Odiel i e [2,6]. Conse
quen ly, his sedimen is likely o con ain ma e ial
om he mine als used o he e ilize p oduc-
Table 1
ion. This ma e ial is expec ed o o m a majo
pa o ac ion F6 o he sedimen a his loca
ion.
Sample STl is also o so ne in e es . A his
loca ion (Fig. 1) so ne ma e ial om he phosph
gypsum s o age a ea [2] is discha ged di ec ly in o
he Tin o i e . He e, he la ges ac ion o o al
De ini ion o sedimen ac ions and eagen s used o hei ex ac ion
F ac ion code
Fl
F2
F3
F4
F5
F6
F ac ion
Readily ion exchangeable
Adso bed ions in humic ma e ial and/o amo phous oxides
Cop ecipi a ed wi h amo phous e omanganese oxyhyd oxides
Ca bona es
C ys alline e omanganese oxyhyd oxides
Resis a e (clay) mine als
Reagen
Magnesium chlo ide
Sodium py ophospha e
Tamm's acid oxala e
Sodium ace a e
Co in's eagen
.. u a
80....----------*U b
110---------....
�u e
80.-----------,
.. u d*º .. u
·----------,, 80.-----------
40
Fl Fl F3 F4 F5 F6 Fl Fl 'J F4 FS F6 Fl F2 FJ F4 F/J F6
Fig. 2. Pe cen age dis ibu ion o U in each sequen ially ex ac ed ac ions o samples (a) S01, (b) S02, (e) S03, (d) STl, (e) ST2
and (O SOT.
U esides in ac ion F2 ( > 50%) ollowed by
ac ion F3 (- 30%). Thus, U is inco po a ed in o
he local sedimen p edominan ly by adso p ion
om he liquid phase. A di e en chemical asso
cia ion in he was es mus be esponsible o he
'anomalous' U dis ibu ion obse ed in his s a
ion and ela ed o he discha ges om he phos
phogypsum s o age a ea [2, 7].
In Table 2, concen a ions o U in µ,g/ g con
ained in he main ac ions o he sedimen s a e
shown. I is in e es ing o obse e ha sedimen
samples aken nea he phospha e was e dis-
cha ge a ea o he Odie) i e (SOl, S02, S03
and ST2) ha e i ually iden ical U concen a
ions in ac ions F2 and F3 and hese a e no ice
ably highe han he es o samples (STl and
SOT). This di e ence is much clea e in he case
o ac ion F3. This can be aken as an e idence
o he ex ension o he con amina ion o he
Odie! i e basin (e en he lowes pa o he
Tin o i e bed). Thus, he liquid was es dis
cha ged om he e ilize indus ies a ec he
i e bed ups eam and downs eam om he
indus ies, p obably due o idal mo emen s o
Table 2
U concen a ion in µ,g/ g in he main ac ions o bo om sedimen s om he Odie! and Tin o i e s
F ac ion S01 S02 S03
F2 12.7 ± 0.8 12.1 ± 0.6 13.7 ± 0.9
F3 31.5 ± 3.6 37.5 ± 2.4 34.9 ± 3.5
F5 0.42± 0.04 2.86 ± 0.10 1.92 ± 0.06
F6 1.93 ± 0.07 40.8 ± 2.8 5.89 ± 0.15
he liquid discha ges. In he case o he esidual
phases, i can be obse ed ha samples S02 and
S03 ha e highe U concen a ions in ac ions F5
and F6 han he es o he samples. This di e 
ence is much clea e in he case o ac ion F6 o
sample S02. This sample is loca ed in on o he
e ilize ac o ies and p esen s a U concen a ion
> 1 o de o magni ude highe han he es o
samples. The U concen a ion in his ac ion
dec eases downs eam on he i e bed. This can
be aken as e idence ha he solid pa icles om
he e ilize p oduc ion cha ac e ised by a high
U con en in ac ion F6 ha e eached s a ions
S02 and S03 bu a e no sedimen ed u he
downs eam in he es ua y.
3.2. Tho ium
Fig. 3 shows he pe cen age dis ibu ion o Th
(232 Th) in he six sequen ially ex ac ed ac ions
o sedimen s. I can be obse ed ha Th has a
highe associa ion han U o esidual ac ions F5
and F6, always wi h > 30% in ac ion F6. How
e e , he non- esidual ac ion F3 appea s o be
ano he a ou ed ac ion o Th. Thus, i seems
ha , as o U, cop ecipi a ion wi h amo phous
e omanganese oxyhyd oxides is he main p ocess
o Th inco po a ion om he i e wa e o he
sedimen . Basically, we can make he same com
men s as we did in he case o U. Thus, sample
S02 p esen s a di e en pe cen age dis ibu ion
han he es o samples, wi h > 60% o Th in he
mine al ac ion F6. Mo eo e , ac ion F2 does
no seem o be a a ou ed ac ion o Th. Only
sample STl has -15% o Th in his ac ion
whe eas he es con ain < 5% in he same ac
ion.
In Table 3, Th concen a ions in µ,g/ g in he
main ac ions o he sedimen s a e shown. I can
be obse ed ha , excep ing sample S03, he Th
ST1 ST2 SOT
8.69 ± 0.54 11.2 ± 0.8 6.86 ± 0.30
4.51 ± 0.26 33.3 ± 2.1 14.1 ± 0.7
0.35 ± 0.02 0.90± 0.04 0.92 ± 0.06
1.68 ± 0.13 2.77 ± 0.11 2.44 ± 0.14
con en in he non- esidual ac ions F2 and F3 is
qui e simila in all s a ions. S a ion S03 has a
highe concen a ion o Th in bo h non- esidual
ac ions. This is mo e e iden in he case o
ac ions F3, wi h - 1 o de o magni ude highe
concen a ions in sample S03 han in he case o
he es o samples. I seems ha he dissol ed Th
is quickly cop ecipi a ed on he i e bed. Thus,
Th con ained in he liquid discha ges seems o
a ec only he sedimen s closes o he e ilize
indus ies. In he case o he esidual ac ions,
samples S02 and S03 p esen highe concen a
ions in bo h ac ions han he es o samples,
whe eas he es ha e simila Th concen a ions.
Thus, i can be concluded ha he i e sedimen s
nea he e ilize indus ies ha e inco po a ed
Th de i ed om he liquid and solid was es bu i
does no each s a ions u he ups eam o
downs eam along he i e .
3.3. Th / U mass a ios
In e ac ion o non- esidual ac ions wi h solu
ion is essen ially e lec ed in he Th/U mass
a io. I is well known ha Th is a pa icula ly
insoluble elemen in na u al wa e s and i is usu
ally ound associa ed wi h solid ma e . Thus, his
a io is ypically much below uni y in wa e s and
abo e uni y in solid pa icles. These ac s can be
clea ly ob ained by s udying he alues o such
a io in he main ac ions o sedimen s om he
Odiel and Tin o i e s which a e p esen ed in
Table 4.
In he case o non- esidual ac ions F2 and F3,
and excep ing ac ion F3 o sample S03, he
Th/U mass a io is much below uni y and ypical
o liquid phases. In ac , hese alues a e simila
o hose ound in wa e samples om he same
i e s [2). Toe excep ion o phase F3 o sample
S03 seems o be ela ed o he ac ha Th is

, TII a
80,------------.
,n d
801------------,
20
F F2 F3 F4 F5 F6
,Th b
80.-----------
% Tlo e.
ao----------
Fl F2 F3 F4 F5 F6
,T11 C
80.-----_.;;..----.......
..,n
80...----------
FI F2 F3 F4 FS F6
Fig. 3. Pe cen age dis ibu ion o Th in each sequen ially ex ac ed ac ions o samples (a) S01, (b) S02, (e) S03, (d) ST1, (e) ST2
and (0 SOT.
Table 3
Th concen a ion in µ.g/g in main ac ions o bo om sedimen s om he Odie! and Tin o i e s
F ac ion S01 S02 S03 STl ST2 SOT
F2 0.79 ± 0.08 0.74 ± 0.06 1.31 ± 0.08 1.10 ± 0.12 0.59 ± 0.05 0.70 ±0.05
F3 7.71 ± 0.51 3.97 ±0.22 38.4 ± 4.0 2.02 ± 0.14 5.05 ±0.39 5.88±0.36
F5 1.89 ± 0.13 1.41 ± 0.07 6.22 ±0.33 0.68±0.08 1.44 ± 0.11 0.96±0,07
F6 4.83 ± 0.22 12.7 ± 1.1 15.8 ± 0.80 4.36± 0.31 4.21 ± 0.33 6.61 ±0.63
Table 4
To/U mass a io in main ac ions o bo om sedimen s om he Odie! and Tin o i e s
F ac ion S01 S02 S03
F2 0.062 ± 0.007 0.061 ± 0.006 0.096 ± 0.009
F3 0.245 ± 0.032 0.10 ± 0.009 1.10 ± 0.16
F5
4.5
± 0.5
0.493 ± 0.030 3.24 ± 0.20
F6 2.50 ± 0.15 0.311 ± 0.034 2.68 ± 0.15
quickly cop ecipi a ed on he su ace o sus
pended ma e which a e deposi ed downs eam
a such a poin and no u he downs eam. I is
also in e es ing o obse e ha his a io is much
lowe in ac ion F2 han in F3. This could be
in e p e ed by he ac ha Th is no easily adso 
bed on o solid pa icles compa ed wi h U. In ac
all s a ions p esen simila alues o his a io in
ac ion F2, independen ly o he concen a ion o
U and/o Th in he ac ion. In he esidual
ac ions F5 and F6 he Th/U mass a io o all
samples, excep sample S02, has alues abo e
uni y and close o he ypical alue o nea 
su ace ocks o 3.5 [8]. Toe excep ion o bo h
esidual ac ions o sample S02 con i ms he U
en ichmen ela i e o Th ypical o he phos
pha e mine al u ilised in he e ilize p oduc ion
[7].
4. Conclusions
Toe U and Th dis ibu ion in di e en ac
ions o bo om sedimen s om he Odiel and
Tin o i e s has p o ided much in o ma ion on
hei en i onmen al beha iou . Unde es ua ine
condi ions U and Th occu mainly in he non- e
sidual ac ions al hough Th ends o eside mo e
in esidual ac ions han U. These di e ences
be ween U and Th e lec la gely he much highe
solubili y (and hence mobili y) o U ela ed o Th
in su ace and nea -su ace en i onmen s. Toe
sedimen ac iona ion and analysis p esen ed
he e has made an unequi ocal connec ion
ST1 ST2 SOT
0.127 ± 0.016 0.053 ± 0.006 0.102 ± 0.009
0.448 ± 0.040 0.152 ± 0.015 0.417 ± 0.032
1.94 ± 0.25 1.60 ± 0.14 1.04 ± 0.10
2.60 ± 0.27 1.52 ± 0.13 2.71 ± 0.30
be ween he enhanced U con en and espec i e
Th/U mass a ios in i e sedimen s close o he
e ilize ac o ies and he was es discha ge poin
in he Odiel and Tin o i e s.
Re e ences
[1] R. Ches e and S.R. As on, The pa i ioning o ace
me als and ansu anics in sedimen s, in Techniques o
Iden i ying Specia ion in Aqua ic En i onmen s, IAEA,
Vienna, 1981, pp. 173-193.
[2] A. Ma inez-Agui e, M. Ga cia-León and M. l ano ich,
Toe dis ibu ion o U, Th and 226Ra de i ed om he
phospha e e ilize indus ies on an es ua ine sys em in
Sou hwes Spain, J. En i on. Radioac i i y, 22 (1994)
155-177.
[3] M. I ano ich and R.S. Ha mon, U anium Se ies Dise
quilib ium: Applica ions o Ea h, Ma ine and En i on
men al Sciences, Cla endon P ess, Ox: o d, UK, 2nd edn,
1992.
[4] A. Ma inez-Agui e, Radiac i idad na u al en di e ses
compa imen os na u ales de Andalucía, PhD hesis,
Se ille Uni e si y, Spain, 1991 (in Spanish).
[5] E.R. Sholko i z, Floccula ion o dissol ed o ganic and
ino ganic ma e du ing he mixing o i e wa e and
seawa e , Geochim. Cosmochim. Ac a, 40 (1976)
831-845.
[6] A. Ma inez-Agui e and M. Ga cia-León, Na u al a
dioac i i y enhancemen s by human ac i i ies in i e s o
he Sou h o Spain, J. Radioanal. Nucl. Chem. Le ., 155
(1991) 97-106.
[7] A. Ma inez-Agui e, M. Ga cia-León and M. I ano ich,
Iden i ica ion and e ec s o an h opogenic emissions o
U and Th on he composi ion o sedimen s in a
i e /es ua ine sys em in Sou hem Spain, J. En i on.
Radioac i i y, 23 (1994) 231-248.
[8] J.J.W. Roge and J.A.S. Adams, Handbook o Geochem
is y, Wedepohl Sp inge Ve lag, Be lin, 1969.