Migration of Cs in tributaries,lake water and sediment of Lago Maggiore (Italy,Switzerland) – analysis and comparison with Lago di Lugano and other lakes

This paper describes the behaviour of ¹³⁷Cs in Lago Maggiore and other pre-alpine lakes as a consequence of atmospheric nuclear weapons testing fallout and the fallout from the nuclear accident in Chernobyl. It presents data on the ¹³⁷Cs distribution in tributaries, lake water, bottom sediments and reveals the role of ¹³⁷Cs as a marker of the sedimentation processes. The run-off of ¹³⁷Cs from the watershed to the lake is described with a simple compartment model. Measurements of the activity concentration of ¹³⁷Cs in sediments are compared with the output of a model (diffusion–convection type) which describes the input of ¹³⁷Cs into and its vertical distribution within the sediment. Varying sedimentation rates (0.05–0.90 g (cm² y)⁻¹) in Lago Maggiore are compared with data of other authors. Sedimentation rates and total distribution coefficients (of about 10⁵ L kg⁻¹) in Lago Maggiore are discussed and compared with those of Lago di Lugano, Lake Constance, and Lake Vorsee.     

Plutonium as a chronomarker in Australian and New Zealand sediments: a comparison with Cs

The construction of high resolution chronologies of sediment profiles corresponding to the last 50-100 years usually entails the measurement of fallout radionuclides ²¹⁰Pb and ¹³⁷Cs. The anthropogenic radionuclide, ¹³⁷Cs, originating from atmospheric nuclear weapons testing can provide an important “first appearance” horizon of known age (1954-1955), providing much-needed validation for the sometimes uncertain interpretations associated with ²¹⁰Pb geochronology. However, while ¹³⁷Cs usually provides a strong signal in sediment in the northern hemisphere, total fallout of ¹³⁷Cs in the southern hemisphere was only 25% that of the north and the low activities of ¹³⁷Cs seen in Australian and New Zealand sediments can make its horizon of first appearance somewhat arguable. Low ¹³⁷Cs fallout also limited the size of the 1963-1964 fallout peak, a peak that is usually seen in northern hemisphere sediment profiles but is often difficult to discern south of the equator.This paper shows examples of the use of nuclear weapons fallout Pu as a chronomarker in sediment cores from Australia (3 sites) and New Zealand (1 site). The Pu profiles of five cores are examined and compared with the corresponding ¹³⁷Cs profiles and ²¹⁰Pb geochronologies. We find that Pu has significant advantages over ¹³⁷Cs, including greater measurement sensitivity using alpha spectrometry and mass spectrometric techniques compared to ¹³⁷Cs measurements by gamma spectrometry. Moreover, Pu provides additional chronomarkers associated with changes in the Pu isotopic composition of fallout during the 1950s and 1960s. In particular, the ²³⁸Pu/^239+240Pu activity ratio shows distinct shifts in the early 1950s and the mid to late 1960s, providing important known-age horizons in southern hemisphere sediments. For estuarine and near-shore sediments Pu sometimes has another significant advantage over ¹³⁷Cs due to its enrichment in bottom sediment relative to ¹³⁷Cs resulting from the more efficient scavenging of dissolved Pu in seawater by sediment particles.     

Accumulation of Cs in puddle sediments within urban ecosystem

The role of puddle sediments as a final depot of ¹³⁷Cs horizontal migration within the urban landscape is studied using the example of Ekaterinburg city, Russia. Radioactive contamination in the city appeared due to fallout after atmospheric testing of nuclear weapons and nuclear accidents. Contamination density of ¹³⁷Cs in the region was assessed from archive data to be about 5.1 kBq/m², of which the maximum activity concentration (<30 Bq/kg) is associated with the upper 15 cm soil layer. Results of the survey reported here indicate a mean ¹³⁷Cs activity concentration in puddle sediments of 80 Bq/kg, with a maximum value of 540 Bq/kg. It is estimated that horizontal migration has led to about a fourfold concentration of ¹³⁷Cs in puddle sediments.     

A blind test of the MOIRA lake model for radiocesium for Lake Uruskul, Russia, contaminated by fallout from the Kyshtym accident in 1957

This paper presents results of a model-test carried out within the framework of the COMETES project (EU). The tested model is a new lake model for radiocesium to be used within the MOIRA decision support system (DSS; MOIRA and COMETES are acronyms for EU-projects). This model has previously been validated against independent data from many lakes covering a wide domain of lake characteristics and been demonstrated to yield excellent predictive power (see H?kanson, Modelling Radiocesium in Lakes and Coastal Areas. Kluwer, Dordrecht, 2000, 215 pp). However, the model has not been tested before for cases other than those related to the Chernobyl fallout in 1986, nor for lakes from this part of the world (Southern Urals) and nor for situations with such heavy fallout as this. The aims of this work were: (1) to carry out a blind test of the model for the case of continental Lake Uruskul, heavily contaminated with 90Sr and 137Cs as a result of the Kyshtym radiation accident (29 September 1957) in the Southern Urals, Russia, and (2) if these tests gave satisfactory results to reconstruct the radiocesium dynamics for fish, water and sediments in the lake. Can the model provide meaningful predictions in a situation such as this? The answer is yes, although there are reservations due to the scarcity of reliable empirical data. From the modelling calculations, it may be noted that the maximum levels of 137Cs in fish (here 400 g ww goldfish), water and sediments were about 100,000 Bq/kg ww, 600 Bq/l and 30,000 Bq/kg dw, respectively. The values in fish are comparable to or higher than the levels in fish in the cooling pond of the Chernobyl NPP. The model also predicts an interesting seasonal pattern in 137Cs levels in sediments. There is also a characteristic "three phase" development for the 137Cs levels in fish: first an initial stage when the 137Cs concentrations in fish approach a maximum value, then a phase with relatively short ecological half-lives followed by a final phase with long ecological half-lives more or less corresponding to the physical decay of radiocesium.     

Distribution of environmental Cesium-137 in tree rings

Environmental ¹³⁷Cs concentrations in tree rings grown since 1914 and 1929 were measured and compared with the record of ¹³⁷Cs deposition from weapons fallout. ¹³⁷Cs was found in tree rings formed prior to 1945 when the first nuclear weapon test was conducted. The radiocesium record in wood is not correlated with that of fallout deposition.     

Temporal variation of Cs and Pu in the sea of Japan

Concentrations of the anthropogenic ¹³⁷Cs and ^239,240Pu in surface water of the Sea of Japan were in the ranges of 2·7–3·8 mBq l^-1 and 1·3–8·0 μBq l^-1, respectively, in 1993–1994, which are in the same order of magnitude as those in the North Pacific. The time-series data indicated a marked increase of surface ¹³⁷Cs in 1986 and 1987 after the major radioactive dumping and the Chernobyl fallout in 1986 and then rapidly decreased thereafter. The apparent half-residence time of ¹³⁷Cs in the surface water was estimated to be about 3 years for excess ¹³⁷Cs and 16 years for a rather long time-scale transport, respectively. For ^239,240Pu in the surface water, no systematic temporal variation was observed over the past two decades, which may reflect rapid recycling of deeper Pu. The results revealed that most of the recent radioactivity in water columns of the Sea of Japan was of global fallout origin from atmospheric nuclear testing and partly the Chernobyl fallout. No clear signal about the effect of radioactivity from Russian dumping was observed.     

Uptake of radionuclides and stable elements from paddy soil to rice: a review

The critical paths for radionuclides and the critical foods in Asian countries differ from those in Western countries because agricultural products and diets are different. Consequently, safety assessments for Asian countries must consider rice as a critical food. As most rice is produced under flooded conditions, the uptake of radionuclides by rice is affected by soil conditions. In this report, we summarize radionuclide and stable element soil-to-plant transfer factors (TFs) for rice. Field observation results for fallout ¹³⁷Cs and stable Cs TFs indicated that while fallout ¹³⁷Cs had higher TF than stable Cs over several decades, the GM (geometric mean) values were similar with the GM of TF value for ¹³⁷Cs being 3.6 × 10⁻³ and that for stable Cs being 2.5 × 10⁻³. Although there are some limitations to the use of TF for stable elements under some circumstances, these values can be used to evaluate long-term transfer of long-lived radionuclides in the environment. The compiled data showed that TF values were higher in brown rice than in white rice because distribution patterns for elements were different in the bran and white parts of rice grains.     

137Cs in marine samples from the Brazilian southeastern coastal region

The present work presents the results of ¹³⁷Cs concentration in seawater, fish and sediments samples collect in 11 sampling points, crossing the Brazilian Southeastern coastal region, from Vitória (ES) to Santos (SP), on a routine basis from 1997 to 2002. This monitoring program was carried out by the Instituto de Radioproteção e Dosimetria (IRD/CNEN/MCT), in cooperation with the Instituto de Estudos do Mar Almirante Paulo Moreira (IEAPM/Brazilian Navy), aiming at determining artificial radionuclides in marine samples. Additionally to the ¹³⁷Cs results, ⁹⁰Sr concentrations in fish samples from 1998 to 2002 are also reported.The ¹³⁷Cs in seawater follows a lognormal distribution, with a geometric mean of 1.8 Bq m^-3 and a geometric standard deviation of 1.4 (n=54), decay corrected to June/2002. For ¹³⁷Cs levels in fish samples a geometric mean of 0.19 Bq kg⁻¹ and a geometric standard deviation of 2.9 (n=39), decay corrected to June/2002, with a range of 0.03 to 1.7 Bq kg⁻¹, were obtained. Based on the ¹³⁷Cs mean concentration in fish as well as in seawater, a transfer factor of 1 × 10² was calculated, which is quite in agreement with the recommended value found in the Safety Report Serie 19.     

Establishment of control site baseline data for erosion studies using radionuclides: a case study in East Slovenia

The aim of the present study was to establish a reference site and its soil characteristics for use of fallout radionuclides in erosion studies in Slovenia. Prior to this study, no reference site and baseline data existed for Slovenia for this purpose. In the agricultural area of Gori?ko in East Slovenia, an undisturbed forest situated in Šalamenci (46°44’N, 16°7’E), was selected to establish the inventory value of fallout ¹³⁷Cs and to establish a baseline level of multi-elemental fingerprint (major, minor, trace elements including heavy metals) and naturally occurring radionuclides in soils. A total of 20 soil profiles were collected at four 10 cm depth increments for evaluation of baseline level of ¹³⁷Cs inventory. An exponential distribution for ¹³⁷Cs was found and the baseline level inventory was established at 7300 ± 2500 Bq m⁻² with a coefficient of variation of 34%. Of this mean present-day inventory, approximately 45% is due to the Chernobyl contribution.The physical degradation of soils through erosion is linked with biochemical degradation. This study introduces an approach to establishment of the naturally occurring radionuclide and elemental fingerprints baseline levels at a reference site which can provide comparative data to those from neighbouring agricultural fields for assessment of soil redistribution magnitude using fallout radionuclides. In addition, this information will be used to determine the impact of soil erosion processes and agricultural practices on soil quality and redistribution within agricultural landscapes in Slovenia.     

Application of the ERICA Assessment Tool to freshwater biota in Finland

In recent years there has been growing international interest in the assessment of doses and risks from ionising contaminants to biota. In this study the ERICA Tool, developed within the EC 6th Framework Programme, was applied to estimate incremental dose rates to biota in freshwater ecosystems in Finland mainly resulting from exposure to the Chernobyl-derived radionuclides ¹³⁷Cs, ¹³⁴Cs and ⁹⁰Sr. Data sets consisting of measured activity concentrations in fish, aquatic plants, lake water and sediment for three selected lakes located in a region with high ¹³⁷Cs deposition were applied in the assessment. The dose rates to most species studied were clearly below the screening level of 10 μGy h⁻¹, indicating no significant impact of the Chernobyl fallout on these species. However, the possibility of higher dose rates to certain species living on or in the bottom sediment cannot be excluded based on this assessment.     

Inventories of Pu, Cs, and excess Pb in sediments from freshwater and brackish lakes in Rokkasho, Japan, adjacent to a spent nuclear fuel reprocessing plant

We investigated the vertical profiles of ^239+240Pu, ¹³⁷Cs, and excess ²¹⁰Pb (²¹⁰Pb_ex) in sediment core samples obtained from two freshwater lakes and two brackish lakes situated near the first commercial spent nuclear fuel reprocessing plant in Rokkasho, Japan, before the final test of the plant using actual spent nuclear fuel. The inventory of ^239+240Pu in those lakes was larger than that in soil in Rokkasho, which indicated the inflow of ^239+240Pu from the catchment area in addition to direct deposition on the lake surfaces. The ¹³⁷Cs inventory in sediments of the brackish lakes was lower than that in the soil, which showed that part of the ¹³⁷Cs was removed from the sediments by the brackish water or that it was not deposited into the sediments, because of the high solubility of Cs in brackish water. The ¹³⁷Cs inventory in sediments of the freshwater lakes was higher than that of the brackish lakes, and comparable with that in soil except for one core sample out of four. The ^239+240Pu/¹³⁷Cs ratio in freshwater lake sediments was higher than that in soil, and that indicated that part of the ¹³⁷Cs was lost from the sediments. The low inventory of ¹³⁷Cs may be attributable to competition for absorption sites in sediments with ammonium ions formed in the reducing environment which occurs from summer to fall in the sediments. Those data will be used as background data on the artificial radionuclides in the lakes to assess the effect of released radionuclides on their concentrations.     

Foliar uptake of Cs from the water column by aquatic macrophytes

A transplant experiment was performed to determine the relative importances of root uptake from the sediments and foliar uptake from the water column in determining the accumulation of ¹³⁷Cs by aquatic macrophytes. Uncontaminated individuals of three species, Brasenia schreberi, Nymphaea odorata and Nymphoides cordata, were transplanted into pots containing either contaminated sediments (i.e. 1.2 Bq ¹³⁷Cs g⁻¹ dry mass) or uncontaminated sediments (i.e. < 0.1 Bq g⁻¹ dry mass) and immersed in Pond B, a former reactor cooling pond where ¹³⁷Cs concentrations in surface waters range from 0.4 to 0.8 Bq liter⁻¹. The plants in uncontaminated sediments rapidly accumulated ¹³⁷Cs from the water column and after 35 days of immersion had ¹³⁷Cs concentrations in leaves that were: (1) not statistically significantly different from those for plants in contaminated sediments; and (2) similar to those for the same species growing naturally in Pond B. The similarity in ¹³⁷Cs concentrations between naturally-occurring plants and those in pots with uncontaminated sediments suggests that foliar uptake from the water column is the principal mode of Cs accumulation by these species in Pond B.     

The partitioning of sellafield-derived radiocaesium in scottish coastal sediments

Sequential leaching of Clyde Sea Area and Loch Etive sediments suggests that partitioning of Sellafield (formerly Windscale)-derived ¹³⁷Cs is related, to a larger than expected extent, to the concentration of sedimentary oxides, organics and, less importantly, carbonates. These components act to prevent ¹³⁷Cs release from clay mineral exchange sites. Leaching of wet sediments appears to provide quite different and presumably more realistic information on nuclide associations relative to that produced by leaching dry ground sediments. The latter ¹³⁷Cs partitioning data appear to overestimate the degree of ¹³⁷Cs fixation in these coastal deposits. Because of the observed partial association of ¹³⁷Cs with nonclay constituents, diagenetic remobilisation of the nuclide is in theory feasible and a preliminary study suggests its occurrence to a minor degree.     

Deposition of 134,137Cs from Chernobyl fallout on Norway spruce and forest soil and its incorporation into spruce twigs

The aims of the present research are to describe the amounts, and the variation with time, of ¹³⁴Cs and ¹³⁷Cs in spruce-twigs (P. abies karst.) and in the soil of a spruce forest in Switzerland following deposition of the Chernobyl fallout. The activity of the twigs was subdivided into 3 compartments: the activity on their surfaces (i.e. the activity which can be removed from the twigs along with their natural wax coating), the activity incorporated into the needles and, finally, the activity incorporated into the wood. These compartments were separately sampled 6 times over a period from 54 to 233 days after the Chernobyl incident. Twigs which sprouted in two successive years (1985, 1986) were sampled and were found to show different behaviours. The activities associated with the 1986 twigs were roughly constant with time, while those of the 1985 twigs decreased exponentially, with half-lives around 150 days. The mean activity associated with 1 g (dry) of 1985 twigs is 724 mBq ¹³⁷Cs g⁻¹, of which 58% is incorporated into the twig wood, 17% into the needles and 25% associated with the adhering aerosol. ¹³⁷Cs on the surface of the needles was found to be water-insoluble. It is believed to be strongly adsorbed on to the soil-derived fraction of the aerosol residing on the needle surface and thus provides a tracer for studying the behaviour of natural aerosols on such surfaces.The same soil profile was measured before and after the Chernobyl incident, allowing direct comparison between nuclear weapons and Chernobyl fallout. The latter is mainly (56%) stored in the litter layer, with only 4% below a depth of 13 cm; it has penetrated into the soil to a much lesser extent than weapons fallout. The forest soil inventory of ¹³⁷Cs showed 2600 Bq m⁻² from nuclear weapons fallout and 6200 Bq m⁻² from Chernobyl.The ¹³⁴Cs/¹³⁷Cs activity ratio of the Chernobyl fallout was found to be 0·58 ± 0·01; the activity ratios in the different compartments investigated prove that incorporation of Cs into spruce occurred exclusively by uptake through the needles. A rough estimate indicates that in a spruce forest the activity stored in the twigs is half that stored in the soil.     

Evidence of the radioactive fallout in the center of Asia (Russia) following the Fukushima Nuclear Accident

It was recently reported that radioactive fallout due to the Fukushima Nuclear Accident was detected in environmental samples collected in the USA and Greece, which are very far away from Japan. In April-May 2011, fallout radionuclides (¹³⁴Cs, ¹³⁷Cs, ¹³¹I) released in the Fukushima Nuclear Accident were detected in environmental samples at the city of Krasnoyarsk (Russia), situated in the center of Asia. Similar maximum levels of ¹³¹I and ¹³⁷Cs/¹³⁴Cs and ¹³¹I/¹³⁷Cs ratios in water samples collected in Russia and Greece suggest the high-velocity movement of the radioactive contamination from the Fukushima Nuclear Accident and the global effects of this accident, similar to those caused by the Chernobyl accident.     

Determining floodplain sedimentation rates using Cs in a low fallout environment dominated by channel- and cultivation-derived sediment inputs, central Queensland, Australia

Fallout ¹³⁷Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of ¹³⁷Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total ¹³⁷Cs inventories calculated from the detailed profile data. Information on the rates of ¹³⁷Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection–diffusion model to account of ¹³⁷Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for ¹³⁷Cs being known and without having to assume that ¹³⁷Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total ¹³⁷Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, ¹³⁷Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites.     

Cs, Pu concentrations and the Pu/Pu atom ratio in a sediment core from the sub-aqueous delta of Yangtze River estuary

A sediment core collected from the sub-aqueous delta of the Yangtze River estuary was subjected to analyses of ¹³⁷Cs and plutonium (Pu) isotopes. The ¹³⁷Cs was measured using γ-spectrometry at the laboratories at the Nanjing University and Pu isotopes were determined with Accelerator Mass Spectrometry (AMS), measurements made at the Australian National University. The results show considerable structure in the depth concentration profiles of the ¹³⁷Cs and ^239+240Pu. The shape of the vertical ¹³⁷Cs distribution in the sediment core was similar to that of the Pu. The maximum ¹³⁷Cs and ^239+240Pu concentrations were 16.21 ± 0.95 mBq/g and 0.716 ± 0.030 mBq/g, respectively, and appear at same depth. The average ²⁴⁰Pu/²³⁹Pu atom ratio was 0.238 ± 0.007 in the sediment core, slightly higher than the average global fallout value. The changes in the ²⁴⁰Pu/²³⁹Pu atom ratios in the sediment core indicate the presence of at least two different Pu sources, i.e., global fallout and another source, most likely close-in fallout from the Pacific Proving Grounds (PPG) in the Marshall Islands, and suggest the possibility that Pu isotopes are useful as a geochronological tool for coastal sediment studies. The ¹³⁷Cs and ^239+240Pu inventories were estimated to be 7100 ± 1200 Bq/m² and 407 ± 27 Bq/m², respectively. Approximately 40% of the ^239+240Pu inventory originated from the PPG close-in fallout and about 50% has derived from land-origin global fallout transported to the estuary by the river. This study confirms that AMS is a useful tool to measure ²⁴⁰Pu/²³⁹Pu atom ratio and can provide valuable information on sedimentary processes in the coastal environment.     

The radiological impact of the Chernobyl debris compared with that from nuclear weapons fallout

Our basic knowledge of the radiological impact of fallout from nuclear accidents is based on the experience gained from the study of nuclear weapons fallout. Radioecologically, the most important radionuclides generated by the Chernobyl accident were ¹³⁷Cs, ¹³⁴Cs, ¹³¹I and, to a lesser degree, ⁹⁰Sr. These nuclides are well known from global fallout, although in different relative amounts to those observed in the Chernobyl debris. Another important difference between the fallout from Chernobyl and that from nuclear weapon tests is that their seasonal and geographical distributions were quite dissimilar. A number of examples show how these differences influenced transfer factors and thus population doses. Special emphasis is paid to the contamination of milk and cereal products.Furthermore, it is shown how the composition of the Chernobyl debris changed with distance from Chernobyl, due to the differences in volatility of the various radionuclides involved. Finally, the paper compares the dose equivalents received from unit releases (1 P Bq ¹³⁷Cs) of global fallout and of Chernobyl accident debris.     

137Cs budget during the period of 1960s in a small drainage basin on the Loess Plateau of China

A sediment profile with a thickness of 28.12 m in a failed reservoir in a small catchment of the Yuntaishan Gully in the Loess Plateau of China consisted of 44 flood couplets deposited during the period from 1960 to 1970 with total volume of 2.36 x 10(6)m(3). Specific sediment yields for a flood event varied from 300 t km(-2) to 14,400 t km(-2) and annual sediment yields varied from 2500 t km(-2) in 1966 to 40,000 t km(-2) in 1964 with a mean value of 12,700 t km(-2)a(-1) for the period. Average annual (137)Cs concentrations of the sediments increased from 0.92 Bq kg(-1) in 1960 to 4.82 Bq kg(-1) in 1963, then decreased to 1.53 Bq kg(-1) in 1970. The total (137)Cs activity in the reservoir sediments was 9.22 x 10(9) Bq, which accounted for 31.9% of the total (137)Cs fallout precipitation of 2.89 x 10(10) Bq within the catchment during the period. The proportion of the (137)Cs loss from the catchment to the (137)Cs fallout precipitation within the catchment in a year varied between 8.01% and 66.8%, and it was 20.9% for the peak (137)Cs deposition year of 1963 and 52.0% in 1964. By analysis of the (137)Cs budget in the catchment for the (137)Cs peak precipitation period from 1962 to 1964, the (137)Cs surface enrichment coefficient Gamma should be much less than 0.23. And for calculation of soil losses on the cultivated land in the inter-gully area by using the Mass Balance Model II, the value of Gamma should be 0.05-0.1.     

99Tc in the sub-arctic food chain Lichen-Reindeer-man

The deposition, migration and annual variations of ⁹⁹Tc fallout in carpets of lichen collected during the period 1956–1981 have been investigated. The transfer of ⁹⁹Tc to reindeer and man has also been studied. Technetium showed a shorter mean residence time than ¹³⁷Cs in the lichen carpet. The activity ratio ⁹⁹Tc/¹³⁷Cs was generally lower than the theoretical fission ratio of 1·43 × 10⁻⁴. The maximum concentration of ⁹⁹Tc in lichens occurred in 1967 (ca. 60 mBq kg⁻¹) but in 1975 higher values were found than would have been predicted from fallout. The average depth integrated concentration of ⁹⁹Tc at 62·3°N, 12·4° E in 1972 was 540 ± 100 mBq m⁻². The studies of reindeer tissues show that technetium has a short mean residence time in the muscle tissues (ca. 5 days) and is not accumulated like ¹³⁷Cs. The committed dose equivalent from ⁹⁹Tc to the local Lapp population engaged in reindeer breeding is negligible.