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300 V. Hansen et al. / Science of the Total Environment 412-413 (2011) 296–303
August
April
I-127 iodide (ppb) I-127 iodate (ppb) I-127 iodide/iodate
a b c
I-127 iodide (ppb) I-127 iodate (ppb) I-127 iodide/iodate
d e f
Fig. 2. Distribution of 127 I − , 127 IO 3 and 127 I − / 127 IO 3 − (a–f) in the surface water of Skagerrak, Kattegat and Baltic Sea for samples collected in August 2006 and April 2007.
3.2. 129 I-iodide and 129 I-iodate in surface water of Baltic Sea, Kattegat
and Skagerrak
The concentrations of 129 I (as iodide and iodate) and their ratios
for August 2006 and April 2007 sampling campaigns are listed in
Tables 1 and 2. The spatial distribution of 129 I (as iodide and iodate),
129 I-iodide/ 129 I-iodate, 129 I/ 127 I Iodide (10 − 8 ) and 129 I/ 127 I Iodate
(10 − 8 ) in surface water is shown in Figs. 3 and 4.
The distribution of 129 I species seems homogenous for both 129 Iiodide
and 129 I-iodate, where the decrease in their concentrations follows
the surface water mass from the Skagerrak to the north part of
the Baltic proper (Fig. 3a, b, d and e). Similar to the behavior of 127 Iiodide,
the 129 I-iodide is the dominant species compared to iodate.
Maximum value of 129 I-iodide over 1000×10 8 atoms/L at the Skagerrak
basin, whereas the minimum value is around 25×10 8 atoms/L
and occurs in the Baltic Proper. For the 129 I-iodate, the range for minimum
and maximum values is at 1.1–9.3×10 8 atoms/L and
4–777×10 8 atoms/L in the Skagerrak and Baltic Proper respectively.
The ratio between the 129 I-iodide/ 129 I-iodate is up to five times
higher than for the 127 I-iodide/ 127 I-iodate and the spatial pattern contains
more differentiation within the Baltic Sea during August than
during April (Fig. 3c and f). Maximum ratio of 95.6 appears in the
Arkona Basin and West Gotland Sea during August and this maximum
is also persistent during April, (Tables 1 and 2 and Fig. 3). The minimum
ratio of 129 I-iodide/ 129 I-iodate is normally below 1, as observed
for the 127 I-iodide/ 127 I-iodate, and occurs within the Skagerrak–Kattegat
Basins.
Other interesting results in the surface waters are the ratios between
the two isotopes species (Fig. 4). In both sampling campaigns,
the 129 I-iodide/ 127 I-iodide values are decreasing going from the Skagerrak
into the Baltic Proper, except for sample in August which show
a rather low ratio in the north part of Skagerrak (Fig. 4a and c). For
the 129 I-iodate/ 127 I-iodate, the gradual decrease from the Skagerrak
to the Baltic proper is apparent in the two sampling campaigns, but
also shows some areas that have values higher or lower than the general
trend (Fig. 4b and d).
4. Discussion
4.1. Iodide and iodate in surface water of Skagerrak and Kattegat
Despite the limited number of sampling sites used here, the general
trend in variability of iodide and iodate ( 129 I and 127 I) is, to a large
extent, linked to water transport and environmental conditions. It is
important to mention that 129 I − and 129 IO 3 − concentrations (Tables 1
and 2) are 2–5 orders of magnitude higher than marine environment
level of the pre-nuclear era (10 −12 for 129 I/ 127 I ratio) (Hou et al.,
2009). Previous studies (Hou et al., 2002, 2009; Aldahan et al., 2006,
2007; Alfimov et al., 2004; Yi et al., 2011) have shown that a part of
129 I released into marine environment from La Hague (France) and
Sellafield (UK) reprocessing plants is transported to the North Sea
by the Atlantic Current and a part of this enters the Baltic Sea through
the Skagerrak and Kattegat Basins.
Earlier publication by Yi et al. (2011) on the distribution of total
iodine isotopes along the same sampling sites analyzed here shows
rather strong dependence of iodine distribution on type of water
masses. More details are, however, exposed by using the chemical
speciation of the iodine isotopes. The relatively gradual decrease of
the total concentration of both isotopes ( 127 I and 129 I), from Skagerrak
and northern Kattegat to the Baltic Sea indicated by Yi et al.
(2011) seems to be partly confirmed by the chemical speciation
(Figs. 2 and 3). We observe also complicated distribution patterns
revealed by the speciation analysis suggesting a complex transport
and mixing of the high salinity water of the North Sea with the relatively
low salinity water of the Baltic Sea (Fig. 5a and c). Occurrence
of strips or pockets of iodide-rich water within the generally low