Thesis for the Degree of Doctor of Philosophy - DTU Orbit

FIGURE 5. Time series data of 129 I concentration in the
Skagerrak (red circle), Kattegat (blue star) and Baltic Proper
(green dot) based on results from this study (2006 and 2007) and
published data from 1992 to 2001 listed in Supporting Information
Table S-3.
year of 2000 and even much higher than the value (56 × 10 8
atoms/L) in 1992 (5).
Influence of the release function from the reprocessing
facilities on the distribution of 129 I in the studied region with
time is captured through constructing a delayed arrival
response. Transit time for the radioactive plume from
Sellafield and La Hague to the Baltic Sea was intensively
discussed (3, 13, 14) and the estimate varies in different
literatures. We have set, arbitrarily, a 3 year delay for 129 I
discharged from Sellafield and 2 years from La Hague to
arrive at the Baltic Proper and calculated the delayed release
function (details presented in the Supporting Information
Figure S-5). The pattern of marine discharges function agrees
well with the 129 I time series in the Skagerrak. The relatively
strong increase in the discharge between 1992 and 2002 is
manifested in the measurements reported from Skagerrak
and also in the Kattegat and Baltic Proper. The year of 2000
represents a turning point in the Kattegat and in the Baltic
Proper. Owing to long period of water stagnation, in particular
deep portions of the Kattegat and Baltic Proper, 129 I may
accumulate and thus the response to the discharge function
would be sluggish and not scaled to the release function.
129 I Inventory Estimation. Published data on 129 I inventory
in the Baltic Sea were sparse, averaged for the whole water
mass and scaled to the year of 2001 at that time (1, 6). Here
we update the inventory estimation based on our data set,
where contribution from each water mass is calculated by
averaging 129 I concentration from different layers, multiplying
by the corresponding water volumes in each basin. The results
show that the inventory of 129 I in August 2006 (24.2 ( 15.4
kg) is much higher than that in April 2007 (14.4 ( 8.3 kg)
within the Baltic Proper. In the Kattegat, a similar inventory
of 129 I for August (5.5 ( 1.8 kg) and April (5.1 ( 3.8 kg) was
obtained. The estimated inventory of 129 I in the Skagerrak
reservoir is 11.4 ( 0.4 kg, in which over 80% resides in the
surface and intermediate layers.
A simplified calculation is set up to simulate 129 I inventory
in the Baltic Proper based on the assumption that the source
of 129 I in the Kattegat is only attributed to Sellafield and La
Hague marine discharges (for the detailed model see Supporting
Information Table S-4 and Figures S-5, S7, and S9).
129 I input from fresh water system such as rivers and
precipitation and 129 I sink for sediment were also estimated.
The natural inventory of 3.2× 10 -4 kg for the Baltic Sea (3)
was adapted into the model as initial value and was run from
908 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 45, NO. 3, 2011
1968 to 2006 as liquid emission from Sellafield nuclear
reprocessing facility was insignificant during the period of
1952-1965.
The modeled result shows that there has been 21 kg 129 I
in the Baltic Proper by 2006 as liquid form and 1 kg trapped
in the sediment. The estimates are rough because the few
number of 129 I data and large variability in the Kattegat water
body. Although effect of water and air exchange, mixing and
diffusion were ignored in the model simulation, the results
provide inventory approximations that can be helpful for
future prediction by prolonging time series of input condition.
A relatively large error (up to 60%) is expected to associate
the simulated inventory of 129 I and the impact on adapting
such estimate in radioactive risk assessments is marginal.
This is because the isotope bioavailability and transport
between the different ecological compartments (water,
sediment, and biota) are still poorly investigated. Furthermore,
extensive anoxia conditions and disturbance of the
thermohaline and the water mass layering can be potential
processes associating a future global warming effect on the
region. Development of such new conditions in the Baltic
Sea is predicted to enhance releases of iodine bound in the
sediment and most likely the load of the 129 I in the water
column. Therefore, further evaluation of bioavailability of
the isotope in the ecosystem is indispensible for a sustainable
future environmental assessment and risk management
impact in the region.
Acknowledgments
The authors thank Lars Andersson and Bodil Thorstensson
and all the crew and scientific team on board of the research
vessel Argos for the help during the sampling expeditions.
Funding for the sampling was provided by the Swedish
Meteorological and Hydrological Institute (SMHI) and for
the analyses by the Tandem Laboratory, Uppsala University.
X.L.Hou appreciates the support by “BaiRen” Project of CAS
(Grant No. KZCX2-YW-BR-13).
Supporting Information Available
Description of chemical separation and measurement for 129 I
and 127 I, data plotting and model parameters with nine figures
and four tables as noted in the text. This material is available
free of charge via the Internet at http://pubs.acs.org.
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