Environ. Sci. Technol. 2001, 35, 1579-1586
129
I from the Nuclear Reprocessing Facilities Traced in Precipitation and Runoff in Northern Europe
N A D I A B U R A G L I O , † A L A A L D A H A N , * ,‡ GO ¨ RAN POSSNERT,† AND INGEMAR VINTERSVED§ Tandem Laboratory, Uppsala University, Box 534, S-751 21 Uppsala, Sweden, Institute of Earth Science, Uppsala University, S-752 36 Uppsala, Sweden, and Swedish Defence Research Agency, FOI, 172 90 Stockholm, Sweden
A huge amount of radioactive 129I has been released into the environment from the nuclear energy industry, atomic weapon tests, and nuclear accidents. In this study, we present weekly and seasonal data on 129I measured in precipitation and runoff of northern Europe during 1998 and 1999. The 129I concentration is at 108-109 atoms/L in precipitation and (2-5) × 108 atoms/L in runoff water, and it is 3-4 orders of magnitude higher than in the prenuclear era. Snow shows lower 129I concentration than rain, and there is apparently a positive correlation between surface air temperature and 129I. Precipitation chemistry, expressed as the content of Cl, SO4, and NO3 and atmospheric ozone, exhibits weak negative correlation with 129I values. Our 129I data on precipitation suggest significant influence of the northern European atmosphere by the discharges from the nuclear reprocessing facilities at Sellafield and La Hague.
Introduction Presently there are several studies clearly indicating that anthropogenic 129I discharges from the European nuclear reprocessing facilities (particularly at Cap La Hague and Sellafield) have overwhelmed its natural prenuclear abundance (1-3). The major pathway of anthropogenic 129I into the environment is through oceanic discharges into the Irish Sea from Sellafield and into the English Channel from La Hague and direct releases into the atmosphere. The main form of released iodine from these sources to the atmosphere is as alkyl iodides e.g. CH3I (4-6). The iodides transform into water-soluble molecules (e.g. HI, IO) and/or molecules (e.g. IO3-) adsorbed to aerosols that are brought back to the earth surface by wet and dry fallout. In addition to chemistry, the dry and wet fallout of iodine depends on factors, such as aerosol type and size and meteorological conditions (precipitation rate and chemistry, wind speed, temperature) (e.g. see ref 5). The effect of these factors was not fully explored with respect to the behavior of 129I in the atmosphere. For example, the concentration of stable iodine was found to be decreasing during the course of a single rain event and with inland distance from the seacoast (5, 7). This behavior was not verified for 129I as pointed out by a recent study of Moran * Corresponding author phone: +46-18-4713095; fax: +46-18555920; e-mail:
[email protected]. † Tandem Laboratory, Uppsala University. ‡ Institute of Earth Science, Uppsala University. § Defense Research Establishment. 10.1021/es001375n CCC: $20.00 Published on Web 03/13/2001
2001 American Chemical Society
et al. (7). A possible explanation may be due to the different sources and chemical forms of 127I and 129I that imply some differences in their natural pathways in nature. Nevertheless, a complete annual record of atmospheric 129I variability is not available in published literature and in particular at regions that usually constitute major repository of atmospheric contaminant, such as northern Europe. For example, release of sulfur from the source points at middle latitudes has strongly affected north Europe through acid rain deposition during the 20th century. A similar situation is apparently rising with respect to the fallout pattern of radioactive releases, and many questions, with respect to quantities, sources, distribution, and regional and global environment impact, need to be investigated. In this study, we present monthly and seasonal results on 129 I in precipitation (rain and snow) and runoff from Sweden covering the years 1998 and 1999. In this part of Europe the main sources of moisture are the north Atlantic and the Arctic Oceans and the Baltic Sea, which are apparently severely contaminated by anthropogenic 129I (1-3, 8, unpublished data). We have also considered the effects of meteorological conditions and the chemistry of precipitation on the distribution of 129I.
Samples and Analytical Technique Sampling. Twenty-four rainwater and nine snow samples have been collected at Uppsala (Sweden) during 1998 and 1999 (Figure 1) and four rain samples in Northern Italy in 1998 (Table 1). All the samples have been taken in an open field and mostly during one single precipitation event. In a few cases the rain samples contain 2 days rainwater and for two times the sample is an accumulation of more than 3 days events (Table 1). Surface water has been collected during February and June 1998 and during February 1999 from the river Fyris in Uppsala at 10 different locations along its 15-km course (Figure 1). The first two sampling campaigns were done in a rainy weather period, while the last sampling was performed after 2 weeks of dry and cold weather and some of the stations (stations 1, 2, and 10) were completely frozen at the surface. All the samples have been stored in polyethylene bottles, kept in a dark and cold room (3 °C), and chemically treated within 1 month after sampling. Sample Preparation and AMS Measurements. The chemical extraction of iodine from water samples is carried out in a clean room laboratory and follows the procedure described in ref 9. All the samples have been stored in polyethylene bottles securely closed and kept in a cold dark room. Before the extraction, the samples are equilibrated to room temperature and filtered through 0.45 µm. After adding 1-2 mg of KI carrier to 100-200 mL of water, respectively, and acidification by HNO3 to pH 2, the solution is transferred into a separation funnel. The iodide is oxidized to iodine by 30% H2O2 and extracted into CCl4, while further extraction of possible iodate speciation is achieved by addition of chloride hydroxylamine (HONH3Cl) and CCl4. The iodine is then back-extracted into the water phase and precipitated as AgI that is mixed with niobium and pressed in a copper holder for the accelerator mass spectrometry (AMS) measurement. Extraction of iodine using the above-described chemical method has also been performed on the water sample (number 5) of the International Round Robin Exercise and given a value 1.21 ( 0.09 × 107 atoms/g in agreement with the consensus one (10). The 129I/127I measurements were performed at the Uppsala EN-tandem accelerator, and technical details are discussed VOL. 35, NO. 8, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Map showing location of the precipitation sampling sites in Sweden and in Italy (rectangles) and other relevant sites used in the text. The underlined numbers represent 129I concentration (×108 atoms/L) in surface water (27 and references therein). The numbers 1-3 are locations of the meteorological stations in central Sweden from which chemistry data were used: 1 ) Aspvreten, 2 ) Kindlaho1 jde, and 3 ) Ja1 draa˚s. The enlarged portion of the map shows the sampled parts (see Table 1) of the river Fyris in Uppsala and the exact location of the precipitation sampling station (triangle). elsewhere (11). Our AMS background for 129I/127I is presently at 4 × 10-14 (from a natural AgI crystal and Woodward iodine) and 10-13 for a chemically processed KI carrier. The measured ratio of the samples of this study was always higher than 7 × 10-12. We used the NIST (SRM 4949C.Iodine129) standard which was diluted at our laboratory at ratios of (0.2-2) × 10-11. Our total analytical error, including the chemistry and the statistics, is typically
