Thesis for the Degree of Doctor of Philosophy - DTU Orbit

Partition of iodine ( 129 I and 127 I) isotopes in soils and marine sediments
Violeta Hansen a, *, Per Roos a , Ala Aldahan b,c , Xiaolin Hou a , Göran Possnert d
a Risø National Laboratory for Sustainable Energy, NUK-202, Technical University of Denmark, Frederiksborgvej 399, P.O.B. 49, DK-4000 Roskilde, Denmark
b Department of Earth Science, Uppsala University, SE-758 36 Uppsala, Sweden
c Department of Geology, United Arab Emirates University, Al Ain, United Arab Emirates
d Tandem Laboratory, Uppsala University, SE-751 21 Uppsala, Sweden
article info
Article history:
Received 16 May 2011
Received in revised form
12 July 2011
Accepted 19 July 2011
Available online xxx
Keywords:
Iodine-129, 127
Speciation
Iodine humic substances
ICP-MS
AMS
1. Introduction
abstract
The bioavailability of radioactive pollutants in the environment
plays a decisive role in relation to the environmental pollutant
impact, and in particular to the internal and external doses to
humans. The bioavailability of a pollutant is generally related to its
speciation and accordingly, chemical species of radionuclides can
be a determining factor affecting their environmental impact and
hazard. Iodine-129 can also be released in reactor accidents due to
its high volatility, and can in this context serve as a retrospective
tracer shedding new light on the environmental behavior of the
radiologically much more important, but also much more shortlived
131 I. Practices of speciation analyses for radionuclides are
a relatively recent implement and the literature data are rather
* Corresponding author. Technical University of Denmark, Risø National Laboratory
for Sustainable Energy NUK-202, Frederiksborgvej 399, P.O.B. 49, 4000
Røskilde, Denmark.
E-mail address: violeta.hansen@risoe.dk (V. Hansen).
0265-931X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jenvrad.2011.07.005
Journal of Environmental Radioactivity xxx (2011) 1e9
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity
journal homepage: www.elsevier.com/locate/jenvrad
Natural organic matter, such as humic and fulvic acids and humin, plays a key role in determining the
fate and mobility of radioiodine in soil and sediments. The radioisotope 129 I is continuously produced and
released from nuclear fuel reprocessing plants, and as a biophilic element, its environmental mobility is
strongly linked to organic matter.
Due to its long half-life (15.7 million years), 129 I builds up in the environment and can be traced since
the beginning of the nuclear era in reservoirs such as soils and marine sediments. Nevertheless, partition
of the isotope between the different types of organic matter in soil and sediment is rarely explored. Here
we present a sequential extraction of 129 I and 127 I chemical forms encountered in a Danish soil, a soil
reference material (IAEA-375), an anoxic marine sediment from Southern Norway and an oxic sediment
from the Barents Sea. The different forms of iodine are related to water soluble, exchangeable, carbonates,
oxides as well as iodine bound to humic acid, fulvic acid and to humin and minerals. This is the first
study to identify 129 I in humic and fulvic acid and humin. The results show that 30e56% of the total 127 I
and 42e60% of the total 129 I are associated with organic matter in soil and sediment samples. At a soil/
sediment pH below 5.0e5.5, 127 I and 129 I in the organic fraction associate primarily with the humic acid
while at soil/sediment pH > 6 129 I was mostly found to be bound to fulvic acid. Anoxic conditions seem to
increase the mobility and availability of iodine compared to oxic, while subaerial conditions (soils)
reduces the availability of water soluble fraction compared to subaqueous (marine) conditions.
Ó 2011 Elsevier Ltd. All rights reserved.
scarce. The concentrations of the radioactive isotope 129 I have been
and are still increasing in the environment since the beginning of
the atomic era in the late nineteen forties (Hou et al., 2009a;
Englund et al., 2010; Aldahan et al., 2007a; Lo’pez-Gutie’rrez
et al., 2004). As iodine is a biophilic element its distribution in
the environment merits investigation (Hou et al., 2003, 2009a;
Aldahan et al., 2007a). The isotope has a half-life of (15.7 million
years) and it is naturally formed by cosmic-ray-induced spallation
of xenon in the upper atmosphere, spontaneous fission of 238 U and
in minor quantities, by neutron bombardment of tellurium in the
geosphere. Thermal neutron induced fission of 235 U is another
minor natural source of 129 I in the lithosphere. Presently, the source
of additional 129 I in the environment is mainly from human nuclear
activity such as nuclear reprocessing facilities, nuclear weapons
testing and accidents associated with nuclear power plants.
Contributions of 129 I from nuclear weapon tests (57e63 kg of 129 I),
the Chernobyl accident (1.3e6 kgof 129 I) and nuclear power plants
are relatively insignificant (Hou et al., 2009a; Englund et al., 2010
and Andersson et al., 2009). Discharges from nuclear reprocessing
facilities into the marine and atmospheric environments represent
Please cite this article in press as: Hansen, V., et al., Partition of iodine ( 129 I and 127 I) isotopes in soils and marine sediments, Journal of Environmental
Radioactivity (2011), doi:10.1016/j.jenvrad.2011.07.005