Environ. Sci. Technol. 2008, 42, 9225–9230
Modeling Fallout of Anthropogenic 129I E D V A R D E N G L U N D , * ,† A L A A L D A H A N , ‡ ¨ RAN POSSNERT,† EEVA HALTIA-HOVI,§ GO XIAOLIN HOU,¶ INGMAR RENBERG,| AND TIMO SAARINEN§ Tandem Laboratory, Uppsala University, Box 529, SE-751 20 Uppsala, Sweden; Department of Earth Sciences, Uppsala University, Villav. 16, SE-752 36 Uppsala, Sweden; Department of Quaternary Geology, 20014 University of Turku, Finland; Risø National Laboratory for Sustainable Energy, NUK-202, Technical University of Denmark, DK-4000 Roskilde, Denmark; and Environmental Assessment Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
Received April 10, 2008. Revised manuscript received September 5, 2008. Accepted September 9, 2008.
Despite the relatively well-recognized emission rates of the anthropogenic 129I, there is little knowledge about the temporal fallout patterns and magnitude of fluxes since the start of the atomic era at the early 1940s. We here present measurements of annual 129I concentrations in sediment archives from Sweden and Finland covering the period 1942-2006. The results revealed impression of 129I emissions from the nuclear reprocessing facility at Sellafield and La Hague and a clear Chernobyl fallout enhancement during 1986. In order to estimate relative contributions from the different sources, a numerical model approach was used taking into account the emission rates/ estimated fallout, transport pathways, and the sediment system. The model outcomes suggest a relatively dominating marine source of 129I to north Europe compared to direct gaseous releases. A transfer rate of 129I from sea to atmosphere is derived for pertinent sea areas (English Channel, Irish Sea, and North Sea), which is estimated at 0.04 to 0.21 y-1.
references therein). Additionally, two other facilities located in central Europe, at Karlsruhe in Germany (operated during 1970-1989) and at Marcoule in France (operated during 1959-1997), have released 129I. Gaseous emission from the Marcoule facility was as much or even higher than that from the Sellafield and La Hague, whereas emission from the Karlsruhe facility is considered negligible (10). Besides emission from the European facilities, there is a possibility that north Europe may have received an unquantified amount of 129I from the reprocessing facilities in Russia, particularly the Mayak (11). Apart from the reprocessing facilities, the above-ground nuclear weapon tests that culminated during the early 1960s were also a source of radioactive 129I, but the contribution was insignificant compared to the emissions from the nuclear reprocessing facilities (9). Furthermore, large parts of Europe including Sweden were affected by fallout from the Chernobyl accident in 1986 (12). Although the total release of 129I from the Chernobyl accident was small in comparison to that from the reprocessing facilities, the fallout was strongly localized in time and space. The distribution pattern of the Chernobyl 137Cs fallout has been shown to vary by more than 100 times between low and high radioactively contaminated areas in Scandinavia. In comparison to the above-mentioned sources of 129I, emissions from conventional nuclear reactors seem to be negligible (13, 14). Despite increasing concentrations of 129I in the environment, which today are up to 106 times the prenuclear values in north Europe, there is a limited number of published records about the temporal distribution of the isotope (6, 8). Here we present new results on 129I distribution in sediment archives from Sweden and Finland covering the period between 1942 and 2006 (Figure 1). The data from these archives together with that from Englund et al. (8) provided proxy information for 129I deposition from the atmosphere of north Europe over a period of 60 years. The proxy data were further utilized to numerically model the relative temporal variability of the 129I anthropogenic fallout over north Europe.
Sampling and Analytical Techniques The sediment archives used in this study were collected from two sampling sites (lakes) that were chosen for their
Introduction The amount of naturally produced radioactive 129I (t1/2 ) 15.7 Myr) is presently overwhelmed by anthropogenic emissions of the isotope. Environmental hazards of the isotope are not clearly foreseeable, which imply that further evaluation is indispensable until a comprehensive assessment of the situation is established. Studies of 129I distribution in fresh and marine water and sediment of north Europe have revealed that the isotope is enriched by several orders of magnitude in comparison to the natural concentrations (1-8). Among the many anthropogenic 129I sources, emissions from the nuclear reprocessing facilities located at Sellafield (UK) and La Hague (France) are pointed out as the main ones. Emissions from these facilities started in 1952 (Sellafield) and 1966 (La Hague) and are still going on ((9), and * Corresponding author fax: +46-18-555736; phone: +46-184713899; e-mail:
[email protected]. † Tandem Laboratory, Uppsala University. ‡ Department of Earth Sciences, Uppsala University. § University of Turku. ¶ National Laboratory for Sustainable Energy, Denmark. | Umeå University. 10.1021/es8009953 CCC: $40.75
Published on Web 11/18/2008
2008 American Chemical Society
FIGURE 1. Location of the sampling sites: (A) Lake Nylandssjo¨n, (B) Lake Lehmilampi, and (C) the additional modeled archive of Englund et al. (8) at Lake Loppesjo¨n. The arrows indicate the general circulation pattern in the North Sea; see, e.g., Otto et al. (33). The main sources of 129I to the sampling sites are shown as stars, i.e., the nuclear fuel reprocessing facilities in Sellafield and La Hague, and the Chernobyl nuclear plant. VOL. 42, NO. 24, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Sediment profiles for Lake Nylandssjo¨n concentrations: (a) 129I and 137Cs concentrations (137Cs is decay corrected to 1986), (b) dry mass accumulation rate, and (c) 129I flux in sediment as concentration (t) × accumulation rate(t); the error margins include both accumulation and 129I concentration variability. Tabulated values are provided in the Supporting Information (Table S1).
FIGURE 3. Sediment profiles for Lake Lehmilampi: (a) 129I and 137Cs concentrations, (b) dry mass accumulation rate, and (c) 129I flux in sediment. Measurements at the lower part are performed on merged samples of up to 5 years. Tabulated values are provided in the Supporting Information (Table S2). undisturbed varved chronology and marked 32 kBq m-2 differences in 137Cs Chernobyl fallout (Figures 2 and 3). Considerably higher 137Cs fallout was received at Lake Nylandssjo¨n (12) as opposed to the negligible fallout of ∼0.5 kBq m-2 at Lake Lehmilampi (15). Details of each sampling site are presented in Table 1. Both sites have been targeted for many years for the high-resolution varve chronology and environmental and paleoclimatic investigations (16-19). The sediment cores used in this study were collected in winters of 2006 and 2007 with a crust-freeze sampler. Subsamples (sediment varves) were sliced in a freeze room and subsequently freeze-dried. The varves were typically 3-4 mm thick in Lake Nylandssjo¨n and 1-4 mm in Lake Lehmilampi. In order to clearly mark the Chernobyl fallout peak during 1986, the 137Cs was measured on dried portions of the samples using γ-spectroscopy (error
