Radioecological modelling of Polonium-210 and Caesium-137 in lichen-reindeer-man and top predators

This work deals with analysis and modelling of the radionuclides 210Pb and210Po in the food-chain lichen-reindeer-man in addition to 210Po and 137Cs in top predators. By using the methods of Partial Least Square Regression (PLSR) the atmospheric deposition of 210Pb and 210Po is predicted at the sample locations. Dynamic modelling of the activity concentration with differential equations is fitted to the sample data. Reindeer lichen consumption, gastrointestinal absorption, organ distribution and elimination is derived from information in the literature. Dynamic modelling of transfer of 210Pb and 210Po to reindeer meat, liver and bone from lichen consumption, fitted well with data from Sweden and Finland from 1966 to 1971. The activity concentration of 210Pb in the skeleton in man is modelled by using the results of studying the kinetics of lead in skeleton and blood in lead-workers after end of occupational exposure. The result of modelling 210Pb and 210Po activity in skeleton matched well with concentrations of 210Pb and 210Po in teeth from reindeer-breeders and autopsy bone samples in Finland.The results of 210Po and 137Cs in different tissues of wolf, wolverine and lynx previously published, are analysed with multivariate data processing methods such as Principal Component Analysis PCA, and modelled with the method of Projection to Latent Structures, PLS, or Partial Least Square Regression PLSR

Nordisk kernesikkerhedsforskning Norraenar kjarnöryggisrannsóknir Pohjoismainen ydinturvallisuustutkimus Nordisk kjernesikkerhetsforskning Nordisk kärnsäkerhetsforskning Nordic nuclear safety research Filling knowledge gaps in radiation protec- tion metho

Abstract The activities of the GAPRAD project are summarised in this report. The background and rationale to GAPRAD are presented and explained. Most notably this relates to a lack of information on naturally occuring radionuclides in terrestrial and aquatic systems that have direct applicability for use in envrionmental impact assessments. Results from field activities are presented from the Dovrefjell area in Norway (terrestrial study) and selected lake and brackish water systems in Finland. The data mainly concern activity concterations of Po-210 in environmental media and selected biota allowing concentration ratios to be derived where appropriate. Furthermore, details in relation to Po-210 uptake and biokinetics in humans based on experimental work conducted within the project are presented. Key words Po-210, environmental impact assessment, levels, transfer, concentration ratios, human biokinetics Electronic report, March 2009 GAPRAD Filling knowledge gaps in radiation protection methodologies for non-human biota Final summary report A report for the NKS-B activity October 2008 Edited by Justin Brown and Runhild Gjelsvik Norwegian Radiation Protection Authority, Norway Contributors: Elis Holm, University of Lund, Sweden Per Roos, Risø national laboratory, Denmark Ritva Saxen, Radiation and Nuclear Safety Authority, Finland Iisa Outola, Radiation and Nuclear Safety Authority, Finland The GAPRAD Activity was presented at the NKS seminar held at the NRPA 28 to 29 th August 2007. The deliverable report entitled "Knowledge gaps in relation to radionuclide levels and transfer to wild plants and animals, in the context of environmental impact assessements, and a strategy to fill them" was submitted to the NKS in December 2007. A status report summaring the activities in the first 6 months of the GAPRAD project was submitted to the NKS in late October 2007. Studies conducted as part of GAPRAD have been presented at an international Conference held in Bergen in 2008 (see The method applied for the deliverable report was simply to access databases and reviews conducted recently in the context of the development of environmental impact assessment approaches. The focus of the work was on natural decay series radionuclides ( 238 U and 232 Th decay series radionuclides with half-lives > 10 days 1 ) This entailed: • Summarising information from the ERICA project (see • Analyses of other recently published data 2.2 An overview of transfer (and for natural activity concentration) knowledge gaps for environmental impact assessment The CR empirical data coverage for selected radionuclides provided by the ERICA project for terrestrial and feshwater environments have been presented in the deliverable report "Knowledge gaps in relation to radionuclide levels and transfer to wild plants and animals, ..."Since the publication of the NKS GAPRAD report, comprehensive overviews of the ERICA transfer data sets have been published in Hosseini et al. For the terrestrial environment, the coverage for Pb is reasonable presumably reflecting the large number of stable element studies that have been conducted on this element. Other radioelements are more poorly characterised with empirical data sets. In the case of Polonium, some information is available for flora but only for the fauna group mammals. In the latter case it should be noted that 1 This half-life cutoff has been selected owing to the fact that radionuclides with half-lives < 10 days have been included in the dose-conversion coefficients (DCC) of their parent radionuclides. In other words secular equilibrium with the parent is assumed and no explicit transfer or DCC for these particular radionuclides are required. 4 although 36 data are available these represent "all mammals" from a single geographical area -the UK. The number of values associated with Thorium is low. In all cases the number of available empirical values is below 20 and for 7 reference categories no information is available at all. A similar situation esists for Uranium although, arguably, floral reference organisms are endowed with reasonable CR information. For radium there are severe data deficiencies for invertebrates, insects, amphibia and reptiles. In the freshwater environment, the data coverage for Pb is extremely poor -no data are available for any reference organism although it may be assumed that an extended review of stable element data might lead to the extraction of at least some information to mitigate this situation. CR values for Th are limited to a small number of data for fish and vascular plants. Although coverage of U and Po is slightly improved on this there are conspicuous data gaps including one for aquatic birds, mammals and insect larvae. Furthermore, there are no reported data for Po in benthic fish or U in bivalve mollusc. A recent report by 2.3 Devising a strategy to mitigate the lack of transfer and activity concentration data In its simplest sense the strategy to mitigate the lack of transfer and activity concentration data involved the focussed experimental studies including field-work and analyses. The following activities were identified as areas where a small effort will reap great dividends : • Determination of Po-210 in soil fauna, small mammals and soil • Characterisation of natural radionuclides (U-238, U-234, Ra-226, Ra-228, Po-210, Pb-210) in fish, brackish waters and sediments Linking the sampling work to national monitoring campaigns should limit associated costs. In view of the fact that it is also important to understand the underlying mechanisms influencing the environmental transfer of natural radionuclide because this will allow us to interpret the data in a more meaningful way, studies will be tailored to fit with this aspiration as far as practicable. The role of skeletal 210 Pb decay on subsequent soft tissue 210 Po concentrations in mammals is still a matter for some debate Both 210 Po and 210 Pb concentrations in water from various parts of the Baltic Sea were lower than in lake waters, although values for 210 Po were in most cases below the detection limit, which was estimated to be 0.002 Bq/kg water. Two parallel analyses were also carried out in various parts of the swan: breast muscle, liver and bones. 210 Po in liver was ten times higher and 210 Pb six times higher than in breast muscle. Activity concentrations of 210 Po and 210 Pb in whole swan were estimated to be 1.0 and 0.4 Bq/kg f.w. In Saduria entomon from the Gulf of Finland, activity concentration of 210 Po was four times higher and 210 Pb almost the same (a little lower) than that in the freshwater mussel (Anodonta sp.). Among the organisms studied, the highest activity concentration of 210 Po was found in the crustacean Saduria entomon. Further information on the sample preparation, analyses methods and detailed results is provided in the aforementioned deliverable report. 6 The data presented above and in the deliverable report were used to derive Concentration Ratios, i.e. activity concentration in organism divided by the activity concentration in water for the main organism categories. A comparison was thereafter made with the values underpinning the ERICA database as presented in Isotopes of plutonium in freshwater environments STUK also conducted a number of analyses on Pu isotopes. These data were not included in the deliverable report owing to a decision to restrict the scope of the report to a consideration of radioisotopes of polonium and lead only. These additional data are reported below. Activity concentration of 239,240 Pu in lake waters varied from 4.9 to 39.5µBq/kg and that of 238 Pu between 1.2 and 2.1 µBq/kg. Activity concentrations of 239,240 Pu and 238 Pu were very low and in many cases below detection limit which was estimated to be about 1µBq/kg. In aquatic plants 239,240 Pu varied between 0.6 and 3.4 mBq/kg f.w., concentrations being highest in water horsetail from lake Siikajärvi and lowest in yellow water lily from lake Vehkajärvi. 238 Pu activity concentrations were up to ten times lower than those of 239,240 Pu. 7 These measurement data were used to derive CR values. As for Po and Pb, the data constitute an important new source of information that may be used to amend existing environmental impact assessment databases pertaining to transfer. A summary of the plutonium CR from the STUK study are presented in Following this preliminary sample preparation and gamma analyses, small (whole body including hair) mammal samples were analysed at RISØ national laboratories according to Po-210 activity concentrations in small mammals have been reported earlier in the aforementioned GAPRAD deliverable report and conference paper (see A preliminary data set on the concentrations of 210 Pb in small mammal samples indicates that the correction required for this will not be great (i.e.<10%). The preliminary data reported on Samples of viper and frog, taken from the Olkiluoto area in 2007, were dried, homogenized, digested and analyzed as a whole animal at the STUK laboratories in Finland. Total amounts of 210 Po and 210 Pb in the viper were 5.3 and 3.1 Bq kg -1 f.w. respectively and those in the frog were 1.68 and 0.93 Bq kg -1 f.w. respectively. More details concerning the analytical procedures, uncertainties and derivation of concentration ratios are provided in the aforementioned Deliverable report. The following data, resulting from the Dovrefjell study were not included in the Deliverable report. 210 Po in soil. Typical activity concentration versus depth profiles in soil are shown in • All profiles exhibit an approximately exponential fall in activity concentrations from elevated levels in humus/surface soils to a "supported" level at depth. This undoubtedly reflects the atmospheric input of 210 Pb followed by the redistribution of the radionuclide to lower soil strata by burial, physical migration and bioturbation. The unsupported activity of • The Supported activity concentration of 9 • Surface activity concentrations (in the range of 84-338 Bq kg -1 d.w. for the humus layer for the 8 cores analysed) seem relatively high for natural site although direct comparison is difficult because activity concentrations are often quoted for different depths of surface soil. - Bunzl & Kracke (1984) Concentration ratios (CRs) There are numerous issues that should be addressed concerning the validity of applying 10 Nonetheless, CR values have been derived from Po-210 in the open literature and there appears to be some value in making a cursory comparison between the present study and these earlier works. Concentration ratios have been derived based upon the uncorrected 210 Po data presented above. The number of data points "n" reflects the number of plant and animal samples used in the derivation of average CRs. Correction factors to transform all biota data to fresh weight have been taken from For those cases where direct comparison is possible it can be seen that Polonium in man Within the framework of GAPRAD a study was set up to establish radiobiological parameters, important in dosimetry, such as fractional uptake parameter gastrointestinal absorption factors f 1 and biological retention times of radioisotopes Po-209 and Po-210 in the body. Gastrointestinal absorption factors have been established in earlier studies with a wide range of results. P.A. In the first part of the study one person was given 50 mBq of Polonium 209 with an oral intake frequency of 24 hours. The goal of this part was to remain the intake frequency until constant radioactive output from urine and feces was maintained, i.e. equilibrium of intake and excretion. 24h urine samples were collected a few times every month until 320 days from the first intake. Then the intake of 209 Po and urine sampling stopped and 24h faeces sampling for a week begun. The results showed clearly a slow decreasing excretion of 209 Po in faeces in the range 0.59%-0.07% of consumed activity. Urine samples analysis showed a fluctuating value of 209 Po excretion with a maximum peak value of about 1 % (ca 17.5 mBq/L) 40 days from the first intake. From this maximum the output activity fluctuates between 0.85 mBq/L-15.91 mBq/L of total intake activity and tends asymptotically against 5.78 Bq/day (5.50 Bq/L). The next step of the project was to distribute an acute oral intake to two persons of 10 Bq and then study the immediate body burden response by spectrometric analysis of urine and feces. In the acute oral intake study, the maximum daily excretion rates in faeces of 18-50 % can be measured 3 days after intake. Urine activity excretion measures an average of 0.15-1 % of ingested activity after 2 days from intake. These results indicate a GI factor of 0.50-0.75. These results correlate well with earlier biokinetic studies of polonium in man. Acknowledgment NKS conveys its gratitude to all organizations and persons who by means of financial support or contributions in kind have made the work presented in this report possible

Polonium-210 and Caesium-137 in lynx (Lynx lynx), wolverine (Gulo gulo) and wolves (Canis lupus).

Wolves, lynx and wolverines are on the top of the food-chain in northern Scandinavia and Finland. (210)Po and (137)Cs have been analysed in samples of liver, kidney and muscle from 28 wolves from Sweden. In addition blood samples were taken from 27 wolves. In 9 of the wolves, samples of muscle, liver and blood were analysed for (210)Po. Samples of liver and muscle were collected from 16 lynx and 16 wolverines from Norway. The liver samples were analysed for (210)Po and (137)Cs. Only (137)Cs analyses were carried out for the muscle samples. The wolves were collected during the winter 2010 and 2011, while the samples for lynx and wolverines were all from 2011. The activity concentrations of (210)Po in wolves were higher for liver (range 20-523 Bq kg(-1) d.w.) and kidney (range 24-942 Bq kg(-1) d.w.) than muscle (range 1-43 Bq kg(-1) d.w.) and blood (range 2-54 Bq kg(-1) d.w.). Activity ratios, (210)Po/(210)Pb, in wolf samples of muscle, liver and blood were in the ranges 2-77, 9-56 and 2-54. Using a wet weight ratio of 3.8 the maximal absorbed dose from (210)Po to wolf liver was estimated to 3500 μGy per year. Compared to wolf, the ranges of (210)Po in liver samples were lower in lynx (range 22-211 Bq kg(-1) d.w.) and wolverine (range16-160 Bq kg(-1) d.w.). Concentration of (137)Cs in wolf samples of muscle, liver, kidney and blood were in the ranges 70-8410 Bq kg(-1) d.w., 36-4050 Bq kg(-1) d.w., 31-3453 Bq kg(-1) d.w. and 4-959 Bq kg(-1) d.w., respectively. (137)Cs in lynx muscle and liver samples were in the ranges 44-13393 Bq kg(-1) d.w. and 125-10260 Bq kg(-1) d.w. The corresponding values for (137)Cs in wolverine were 22-3405 Bq kg(-1) d.w. for liver and 53-4780 Bq kg(-1) d.w. for muscle. The maximal absorbed dose from (137)Cs to lynx was estimated to 3000 μGy per year