Anthropogenic 129I in seawaters along the north-central part of the English Channel: Levels and tracer applications
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Abstract: The English Channel (the Channel) represents a major sink and transport pathway of anthropogenic radioactive 129I. Despite this important role, data concerning the distribution of 129I in seawater of the Channel are scarce, and most of existing data are restricted to the eastern part of the Channel. The advection and dispersion of 129I from the French coast toward the central and further the English coast, especially in the Channel west of Cap de La Hague, are not fully investigated. We present results of iodine isotopes (127I and 129I) analyses of surface water samples collected along the central English Channel in October, 2010. The data show high 129I concentrations between Dover Strait and La Hague, followed by a dramatic drop towards the Celtic Sea and reveal the dispersal of 129I towards central and northern part of the Channel. Our observation also implies that the entire British coast is contaminated by 129I. 129I levels in the westernmost English Channel, close to the English coast, may reflect combined influences from La Hague and Sellafield. Evolution of 129I between 2005 and 2010 suggests a strong link to temporal marine discharges from La Hague plant. The discharges from the nuclear reprocessing facility have continued since 2010 and thus an ecological evaluation of 129I radioactive hazards in the environment of the Channel may be needed.
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Key words:
- 129I /
- seawater /
- iodine isotopes /
- English Channel
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Figure 1. Annual liquid 129I discharges (1966−2020) from the La Hague and Sellafield nuclear reprocessing facilities (compiled from He et al. (2014), Sellafield Ltd. (2021), and Orano Recylage (2020)).
Figure 2. Map showing the main surface currents in the North Atlantic Ocean and the Nordic seas. EGC, NCC and NAC refer to the East Greenland Current, the Norwegian Coastal Current and the North Atlantic Current, respectively. The stars show the locations of La Hague and Sellafield.
Figure 3. Location of the water sampling sites collected in this investigation in 2010. Relative locations of the investigated area to the North Atlantic Ocean, Irish Sea, Celtic Sea and the Sellafield site are indicated in the insert. DS refers to the Dover Strait; NBG, the Normand-Breton Gulf. The star refers to the La Hague site.
Figure 4. Longitudinal distribution and correlation coefficient of 127I concentration (a), 129I concentration (b) and 129I/127I concentration ratio (c) in the English Channel surface water.
Figure 5. Distribution of 127I concentration vs. salinity (a), the arrow represents 129I dilution direction; and the relationship between 129I/127I concentration ratio and 129I concentration (b); depth-mean water circulation velocity (daily mean) in the Dover Strait area (c) and wind conditions during 2010 campaign (d). The data of c obtained from website (
https://resources.marine.copernicus.eu/ ) on October 29, 2010.
Figure 6. Distribution of 129I concentration (a) and 129I/127I concentration ratio (b) from the 2005, 2009 and 2010 sampling campaigns with distance from La Hague (Michel et al., 2012; Christl et al., 2015). The horizontal lines represent average values in 2005, 2009 and 2010.
Figure 7. Comparison of 129I concentrations from the sampling campaigns 2005, 2009 and 2010. Sites 1 and 10 (this work) are used because they are close to Sites 903 and 901, respectively (a). b. the location of the 129I seawater sampling sites in 2010 (white dots) and 2005 (blank dots). Red dots represent sampling sites shared by both the 2005 and 2009 cruises. The star shows the location of the La Hague site.
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