The sources and fate of 210Po in the urban air: A review

The origin of ²¹⁰Po activity and its fluctuations in the air are discussed in this paper. In the case of atmospheric aerosol samples, a comparison of the ²¹⁰Po/²¹⁰Pb and ²¹⁰Bi/²¹⁰Pb activity ratios makes it possible not only to determine aerosol residence times but also to appraise the contribution of the unsupported ²¹⁰Po coming from other sources than ²²²Rn decay, such as human industrial activities, especially coal combustion. A simple mathematical method makes it possible to observe the seasonal fluctuations of the anthropogenic excess of ²¹⁰Po in the urban air. The average doses of ²¹⁰Po intake with food (including drinking water) and inhalation of urban aerosols are usually lower than those from ²¹⁰Po intake by cigarette smokers and negligible in comparison to total natural radiation exposure.     

Polonium-210 and lead-210 in the terrestrial environment: a historical review

The radionuclides ²¹⁰Po and ²¹⁰Pb widely present in the terrestrial environment are the final long-lived radionuclides in the decay of ²³⁸U in the earth’s crust. Their presence in the atmosphere is due to the decay of ²²²Rn diffusing from the ground. The range of activity concentrations in ground level air for ²¹⁰Po is 0.03-0.3 Bq m⁻³ and for ²¹⁰Pb 0.2-1.5 Bq m⁻³.In drinking water from private wells the activity concentration of ²¹⁰Po is in the order of 7-48 mBq l⁻¹ and for ²¹⁰Pb around 11-40 mBq l⁻¹. From water works, however, the activity concentration for both ²¹⁰Po and ²¹⁰Pb is only in the order of 3 mBq l⁻¹.Mosses, lichens and peat have a high efficiency in capturing ²¹⁰Po and ²¹⁰Pb from atmospheric fallout and exhibit an inventory of both ²¹⁰Po and ²¹⁰Pb in the order of 0.5-5 kBq m⁻² in mosses and in lichens around 0.6 kBq m⁻². The activity concentrations in lichens lies around 250 Bq kg⁻¹, dry mass.Reindeer and caribou graze lichen which results in an activity concentration of ²¹⁰Po and ²¹⁰Pb of about 1-15 Bq kg⁻¹ in meat from these animals. The food chain lichen-reindeer or caribou, and Man constitutes a unique model for studying the uptake and retention of ²¹⁰Po and ²¹⁰Pb in humans. The effective annual dose due to ²¹⁰Po and ²¹⁰Pb in people with high consumption of reindeer/caribou meat is estimated to be around 260 and 132 μSv a⁻¹ respectively.In soils, ²¹⁰Po is adsorbed to clay and organic colloids and the activity concentration varies with soil type and also correlates with the amount of atmospheric precipitation. The average activity concentration levels of ²¹⁰Po in various soils are in the range of 20-240 Bq kg⁻¹.Plants become contaminated with radioactive nuclides both by absorption from the soil (supported Po) and by deposition of radioactive fallout on the plants directly (unsupported Po). In fresh leafy plants the level of ²¹⁰Po is particularly high as the result of the direct deposition of ²²²Rn daughters from atmospheric deposition. Tobacco is a terrestrial product with high activity concentrations of ²¹⁰Po and ²¹⁰Pb. The overall average activity concentration of ²¹⁰Po is 13 ± 2 Bq kg⁻¹. It is rather constant over time and by geographical origin.The average median daily dietary intakes of ²¹⁰Po and ²¹⁰Pb for the adult world population was estimated to 160 mBq day⁻¹ and 110 mBq day⁻¹, corresponding to annual effective doses of 70 μSv a⁻¹ and 28 μSv a⁻¹, respectively. The dietary intakes of ²¹⁰Po and ²¹⁰Pb from vegetarian food was estimated to only 70 mBq day⁻¹ and 40 mBq day⁻¹ corresponding to annual effective doses of 30.6 μSv a⁻¹ and 10 μSv a⁻¹, respectively. Since the activity concentration of ²¹⁰Po and ²¹⁰Pb in seafood is significantly higher than in vegetarian food the effective dose to populations consuming a lot of seafood might be 5-15 fold higher.     

The temporal variations of (7)Be, (210)Pb and (210)Po in air in England

We have conducted measurements of naturally occurring radionuclides (7)Be, (210)Pb and (210)Po in air at ground level at Chilton, Oxfordshire, England. The sampling and analysis regime for the latter two isotopes has been optimised to minimise uncertainties in measurement due to decay of (210)Po and in-growth of (210)Pb during the sampling and analysis period. Analysis times were reduced by using Cerenkov counting to assay the (210)Bi daughter of (210)Pb. Monthly data collected over a four-year period are presented and discussed. (7)Be activity concentrations appear to peak in spring. (210)Pb activity concentrations also follow a seasonal trend reflecting different (222)Rn emanation rates from soil during winter and summer. Data for (210)Po show no such trend.     

Natural and anthropogenic radionuclides in airborne particulate samples collected in Barcelona (Spain)

Results for naturally occurring ⁷Be, ²¹⁰Pb, ⁴⁰K, ²¹⁴Bi, ²¹⁴Pb, ²¹²Pb, ²²⁸Ac and ²⁰⁸Tl and anthropogenic ¹³⁷Cs in airborne particulate matter in the Barcelona area during the period from January 2001 to December 2005 are presented and discussed. The ²¹²Pb and ²⁰⁸Tl, ²¹⁴Bi and ²¹⁴Pb, ⁷Be and ²¹⁰Pb radionuclide levels showed a significant correlation with each other, with correlation coefficients of 0.99, 0.78 and 0.69, respectively, suggesting similar origin/behaviour of these radionuclides in the air. Caessium-137 and Potassium-40 were transported to the air as resuspended particle from the soil. The ⁷Be and ²¹⁰Pb concentrations showed similar seasonal variations, with a tendency for maximum concentrations during the summer months. An inverse relationship was observed between the ⁷Be, ²¹⁰Pb, ⁴⁰K and ¹³⁷Cs concentrations and weekly rainfall, indicating washout of atmospheric aerosols carrying these radionuclides.     

Levels and transfer of Po and Pb in Nordic terrestrial ecosystems

Recent developments regarding environmental impact assessment methodologies for radioactivity have precipitated the need for information on levels of naturally occurring radionuclides within and transfer to wild flora and fauna. The objectives of this study were therefore to determine activity concentrations of the main dose forming radionuclides ²¹⁰Po and ²¹⁰Pb in biota from terrestrial ecosystems thus providing insight into the behaviour of these radioisotopes. Samples of soil, plants and animals were collected at Dovrefjell, Central Norway and Olkiluoto, Finland. Soil profiles from Dovrefjell exhibited an approximately exponential fall in ²¹⁰Pb activity concentrations from elevated levels in humus/surface soils to “supported” levels at depth. Activity concentrations of ²¹⁰Po in fauna (invertebrates, mammals, birds) ranged between 2 and 123 Bq kg⁻¹ d.w. and in plants and lichens between 20 and 138 Bq kg⁻¹ d.w. The results showed that soil humus is an important reservoir for ²¹⁰Po and ²¹⁰Pb and that fauna in close contact with this media may also exhibit elevated levels of ²¹⁰Po. Concentration ratios appear to have limited applicability with regards to prediction of activity concentrations of ²¹⁰Po in invertebrates and vertebrates. Biokinetic models may provide a tool to explore in a more mechanistic way the behaviour of ²¹⁰Po in this system.     

Study of 210Po and 210Pb in the riverine environments of coastal Karnataka

Activity of ²¹⁰Po and ²¹⁰Pb were measured in soil and sediment samples collected from the major rivers Kali, Sharavathi and Netravathi of Coastal Karnataka. The activity of these two radionuclides were determined by radiochemical separation of ²¹⁰Po and counting the activity using a ZnS(Ag) Alpha counter. The activity of ²¹⁰Pb was higher than that of ²¹⁰Po in the riverine environs. The ²¹⁰Po and ²¹⁰Pb content in sediment was found to increase with silt/clay and organic matter contents. However no significant correlation was found between the activity ²¹⁰Po and ²¹⁰Pb with pH in sediments. The activity of ²¹⁰Po and ²¹⁰Pb and influence of physico-chemical parameters on these radionuclides were studied and discussed in this paper.     

Variation of short-lived beta radionuclide (radon progeny) concentrations and the mixing processes in the atmospheric boundary layer

Radon is emitted to the atmosphere with quasi constant emission rates depending on the radium concentration in the earth's crust and soil physical properties. In this way, the ²²²Rn and ²²⁰Rn concentration in air reflects significantly the thickness of the atmospheric boundary layer (ABL). The aerosol-associated, beta-emitting progeny nuclides of ²²²Rn were measured daily in the framework of the atmospheric radioactivity monitoring program of NIMH at Sofia. The ²¹⁴Pb concentration was estimated from the measured short-lived beta activity of 24-h filter samples, changed daily at 6:00 GMT. The impact of some meteorological factors such as wind direction, wind velocity, humidity, and temperature on short-lived beta radionuclides is estimated, and the results show no simple statistical relationship. A seasonal pattern was observed with winter minima and late summer-early autumn maxima. High variability in daily morning concentrations and mean monthly values was observed. There were well pronounced differences between years. The height of the convective ABL was estimated from daily radio-soundings at 12:00 GMT for the period 2001-2006 and from seven soundings per day during the experimental campaign in Sofia in October 2003. In general, concentrations of short-lived ²²²Rn progeny nuclides decreased with increased convective ABL height.     

Aspects on the analysis of 210Po

There has been little development regarding analysis of polonium (Po) in environmental samples since the 1960ies. This is due to the straightforward spontaneous deposition of this element on silver (Ag), nickel (Ni) or copper (Cu) without any radiochemical separation. For many years, no radiochemical yield determinant was used and it was generally supposed that the yield was 100% after two depositions. Counting was often done using ZnS scintillation counter coupled to a photomultiplier tube. However, the use of the yield determinants ²⁰⁸Po and ²⁰⁹Po and the development of alpha spectrometry showed that the yield was lower. Furthermore, the tendency of Po to volatilize at low temperatures constrains the sample preparation techniques; dry-ashing cannot be used. But during the wet-ashing procedure, there are still some losses.The aim of this study was to evaluate the Po losses during wet-ashing by the use of a double-tracer technique. We have found that the losses were about 30% when open glass beakers were used and about 17% when the samples were digested in microwave oven. When long-necked bottles (Kjeldahl flasks) were used, a loss of about 20% was registered.It has also been observed that ²¹⁰Pb to some extent is plating out together with its daughter nuclide Po during the electrochemical deposition. This will result in a systematic error since an unknown amount of supported ²¹⁰Po will be produced from the ²¹⁰Pb decay depending on the fraction of ²¹⁰Pb being deposited on the disc and the waiting time between deposition and measurement of the sample. A further consequence of this is that in the assessment of the ²¹⁰Pb content in the sample, very often the remaining liquid is stored after deposition for build-up of ²¹⁰Po. Since some ²¹⁰Pb is lost on the disc, the result for ²¹⁰Pb will be too low. Both these systematic errors give rise to a too high ²¹⁰Po/²¹⁰Pb ratio. The fraction of ²¹⁰Pb which is plating out has been assessed in this study for different matrices and is about 50-90%. During the measurement by solid state Si-detectors, some Po is evaporated in the vacuum conditions contaminating the detectors. Experiments have here been done by heating the discs after deposition which indicate that less Po is evaporated from Ag than from Ni. The losses from Ag are less than that from the other metals probably due to a deeper penetration into the surface of Po. We conclude that in most aspects, Ag is better to use than the other plating metals.     

Lead-210 and Beryllium-7 fallout rates on the southeastern coast of Brazil

Total ²¹⁰Pb and ⁷Be fallout rates were measured on the coastal region of Niteroi, Brazil. The monthly depositional flux of ²¹⁰Pb and ⁷Be varied by a factor of 26, from 1.7 to 43.3 mBq cm⁻² year⁻¹ and ∼27, from 7.5 to 203.5 mBq cm⁻² year⁻¹, respectively. The relatively large oscillations in the depositional flux of ²¹⁰Pb at this study site were likely due to variations in air mass sources, while the ⁷Be fluctuations may be driven by a combination of weather conditions. Local geology could support the periodic high fluxes of ²¹⁰Pb from continental air masses, as shifting oceanic wind sources were affirmed by the uncorrelated ²¹⁰Pb and ⁷Be fallout activities and ⁷Be/²¹⁰Pb ratios. The ²¹⁰Pb atmospheric deposition was found to be in agreement with local sediment inventories, an important consideration in geochemical studies that estimate sedimentation processes.     

Factors affecting 210Po and 210Pb activity concentrations in mussels and implications for environmental bio-monitoring programmes

The activity of ²¹⁰Po and ²¹⁰Pb was determined in mussels of the same size (3.5-4.0 cm shell length) sampled monthly over a 17-month period at the Atlantic coast of Portugal. Average radionuclide concentration values in mussels were 759 ± 277 Bq kg⁻¹ for ²¹⁰Po (range 460-1470 Bq kg⁻¹ dry weight), and 45 ± 19 Bq kg⁻¹ for ²¹⁰Pb (range 23-96 Bq kg⁻¹ dry weight). Environmental parameters and mussel biometric parameters were monitored during the same period. Although there was no seasonal variation of radionuclide concentrations in sea water during the study period, the concentration of radionuclide activity in mussels varied seasonally displaying peaks of high concentrations in winter and low concentrations in summer. Analysis of radionuclide data in relation to the physiological Condition Index of mussels revealed that ²¹⁰Po and ²¹⁰Pb activities in the mussel (average activity per individual) remained nearly constant during the investigation period, while mussel body weight fluctuated due to fat storage/expenditure in the soft tissues. Similar variation of radionuclide concentrations was observed in mussels transplanted from the sea coast into the Tejo Estuary. However, under estuarine environmental conditions and with higher food availability throughout the year, transplanted mussel Condition Index was higher than in coastal mussels and average radionuclide concentrations were 210 ± 75 Bq kg⁻¹ (dry weight) for ²¹⁰Po and 10 ± 4 Bq kg⁻¹ (dry weight) for ²¹⁰Pb, therefore lower than in coastal mussels with similar shell length. It is concluded that the apparent seasonal fluctuation and inter-site difference of radionuclide concentrations were mostly caused by mussel body weight fluctuation and not by radionuclide body burden fluctuation. This interpretation can be extended to the apparent seasonal fluctuation in concentrations of lipophilic and lipophobic contaminants in mussels, and provides an explanation for occasional high concentrations of ²¹⁰Po and man-made contaminants measured in mussels far from pollution sources.     

210Pb as a tool for establishing sediment chronologies: examples of potentials and limitations of conventional dating models

For aquatic sediments, the use of ²¹⁰Pb originating from the decay of atmospheric ²²²Rn is a well-established methodology to estimate sediment ages and sedimentation rates. Traditionally, the measurement of ²¹⁰Pb in soils and sediments involved laborious and time-consuming radiochemical separation procedures. Due to the recent development of advanced planar (‘n-type’) semi-conductors with high efficiencies in the low-energy range which enable the gamma-spectrometric analysis of the 46.5 keV decay line of ²¹⁰Pb, sediment dating using this radionuclide has gained renewed interest.In this contribution, potentials and limitations of the ²¹⁰Pb methodology and of the models used for estimating sediment ages and sedimentation rates are discussed and illustrated by examples of freshwater and marine sediments. Comparison with the use of ¹³⁷Cs shows that the information which may be gained by these two tracers is complementary. As a consequence, both radionuclides should be used in combination for dating of recent sediments. It is shown that for various sedimentation regimes additional information from other sources (e.g. sediment lithology) may be needed to establish a reliable chronology. A strategy for sediment dating using ²¹⁰Pb is recommended.     

210Po in the marine environment with emphasis on its behaviour within the biosphere

The distribution and behaviour of the natural-series alpha-emitter polonium-210 in the marine environment has been under study for many years primarily due to its enhanced bioaccumulation, its strong affinity for binding with certain internal tissues, and its importance as a contributor to the natural radiation dose received by marine biota as well as humans consuming seafoods. Results from studies spanning nearly 5 decades show that ²¹⁰Po concentrations in organisms vary widely among the different phylogenic groups as well as between the different tissues of a given species. Such variation results in ²¹⁰Po concentration factors ranging from approximately 10³ to over 10⁶ depending upon the organism or tissue considered. ²¹⁰Po/²¹⁰Pb ratios in marine species are generally greater than unity and tend to increase up the food chain indicating that ²¹⁰Po is preferentially taken up by organisms compared to its progenitor ²¹⁰Pb. The effective transfer of ²¹⁰Po up the food chain is primarily due to the high degree of assimilation of the radionuclide from ingested food and its subsequent strong retention in the organisms. In some cases this mechanism may lead to an apparent biomagnification of ²¹⁰Po at the higher trophic level. Various pelagic species release ²¹⁰Po and ²¹⁰Pb packaged in organic biodetrital particles that sink and remove these radionuclides from the upper water column, a biogeochemical process which, coupled with scavenging rates of this radionuclide pair, is being examined as a possible proxy for estimating downward organic carbon fluxes in the sea. Data related to preferential bioaccumulation in various organisms, their tissues, resultant radiation doses to these species, and the processes by which ²¹⁰Po is transferred and recycled through the food web are discussed. In addition, the main gaps in our present knowledge and proposed areas for future studies on the biogeochemical behaviour of ²¹⁰Po and its use as a tracer of oceanographic processes are highlighted in this review.     

Activities of Po and Pb in the water column at Kuala Selangor, Malaysia

Natural radionuclides, such as ²¹⁰Po and ²¹⁰Pb were measured in the water samples collected from six stations at Kuala Selangor, Malaysia. Results for ²¹⁰Po and ²¹⁰Pb in dissolved and particulate phases have showed the difference in distribution and chemical behavior. The fluctuation activities of ²¹⁰Po and ²¹⁰Pb depend on wave action, geology and degree of fresh water input occurring at study areas and probably due to different sampling dates. The distribution coefficient, K_d, values of ²¹⁰Po and ²¹⁰Pb ranged from 2.0 × 10³ l g⁻¹ to 265.15 × 10⁵ l g⁻¹, and from 3.0 × 10³ l g⁻¹ to 558.16 × 10⁵ l g⁻¹, respectively. High K_d values of ²¹⁰Po and ²¹⁰Pb indicated that a strong adsorption of ²¹⁰Po and ²¹⁰Pb onto suspended particles, and the sinking of both nuclides on the seabed at study locations were controlled by the characteristics of suspended particles.     

90Sr, 210Po and 210Pb in lichen and reindeer in Norway

Concentrations of ⁹⁰Sr, ²¹⁰Po and ²¹⁰Pb in lichen and reindeer were studied in central (Østre Namdal) and southern Norway (Vågå) during 2000–2003. The study focussed on potential differences in concentrations of these nuclides in reindeer of different ages. Concentrations of ⁹⁰Sr in bones of ∼10 year old adult females were about 40% higher than those in calves' antlers (⁹⁰Sr concentrations in antlers and bones of calves are similar), while the available data from Vågå suggest that ⁹⁰Sr concentrations in reindeer calves decreased with an effective ecological half-time of 9.03 ± 0.06 years during 1988–2002. Furthermore, ⁹⁰Sr concentrations were 50–80% higher in bone of reindeer of a similar age from Vågå compared to those from Østre Namdal. Concentrations of ²¹⁰Po and ²¹⁰Pb in muscle and liver tissues were comparable to those reported for reindeer in other Nordic areas, with no significant difference in ²¹⁰Po and ²¹⁰Pb concentrations between adults and calves or between reindeer from the two different study areas.     

Direct comparison of 210Po, 234Th and POC particle-size distributions and export fluxes at the Bermuda Atlantic Time-series Study (BATS) site

Particle-reactive, naturally occurring radionuclides are useful tracers of the sinking flux of organic matter from the surface to the deep ocean. Since the Joint Global Ocean Flux Study (JGOFS) began in 1987, the disequilibrium between ²³⁴Th and its parent ²³⁸U has become widely used as a technique to measure particle export fluxes from surface ocean waters. Another radionuclide pair, ²¹⁰Po and ²¹⁰Pb, can be used for the same purpose but has not been as widely adopted due to difficulty with accurately constraining the ²¹⁰Po/²¹⁰Pb radiochemical balance in the ocean and because of the more time-consuming radiochemical procedures. Direct comparison of particle flux estimated in different ocean regions using these short-lived radionuclides is important in evaluating their utility and accuracy as tracers of particle flux. In this paper, we present paired ²³⁴Th/²³⁸U and ²¹⁰Po/²¹⁰Pb data from oligotrophic surface waters of the subtropical Northwest Atlantic and discuss their advantages and limitations. Vertical profiles of total and particle size-fractionated ²¹⁰Po and ²³⁴Th activities, together with particulate organic carbon (POC) concentrations, were measured during three seasons at the Bermuda Atlantic Time-series Study (BATS) site. Both ²¹⁰Po and ²³⁴Th reasonably predict sinking POC flux caught in sediment traps, and each tracer provides unique information about the magnitude and efficiency of the ocean's biological pump.     

Seasonal variations of aerosol residence time in the lower atmospheric boundary layer

During a one year period, from Jan. 2002 up to Dec. 2002, approximately 130 air samples were analyzed to determine the atmospheric air activity concentrations of short- and long-lived (222Rn) decay products 214Pb and 210Pb. The samples were taken by using a single-filter technique and gamma-spectrometry was applied to determine the activity concentrations. A seasonal fluctuation in the concentration of 214Pb and 210Pb in surface air was observed. The activity concentrations of both radionuclides were observed to be relatively higher during the winter/autumn season than in spring/summer season. The mean activity concentration of 214Pb and 210Pb within the whole year was found to be 1.4+/-0.27 Bq m(-3) and 1.2+/-0.15 mBq m(-3), respectively. Different 210Pb:214Pb activity ratios during the year varied between 1.78 x 10(-4) and 1.6 x 10(-3) with a mean value of 8.9 x 10(-4) +/- 7.6 x 10(-5). From the ratio between the activity concentrations of the radon decay products 214Pb and 210Pb a mean residence time (MRT) of aerosol particles in the atmosphere of about 10.5+/-0.91 d could be estimated. The seasonal variation pattern shows relatively higher values of MRT in spring/summer season than in winter/autumn season. The MRT data together with relative humidity (RH), air temperature (T) and wind speed (WS), were used for a comprehensive regression analysis of its seasonal variation in the atmospheric air.     

High (210)Po atmospheric deposition flux in the subtropical coastal area of Japan

Bulk atmospheric deposition fluxes of (210)Po and (210)Pb were measured at three coastal regions of Japan, the Pacific Ocean coastal area of the Japanese mainland (Odawa Bay), the Chinese continental side of Japanese coastal area (Tsuyazaki), and an isolated island near Okinawa (Akajima). Wet and dry fallout collectors were continuously deployed from September 1997 through August 1998 for periods of 3 to 31 days depending on the frequency of precipitation events. Annual (210)Pb deposition fluxes at Odawa Bay (35 degrees N 139 degrees E), Tsuyazaki (33 degrees N 130 degrees E) and Akajima (26 degrees N 127 degrees E) were 73.3+/-8.0, 197+/-35 and 78.5+/-8.0 Bqm(-2)y(-1), respectively. Higher (210)Pb deposition was observed at the Chinese continental side of Japanese coast than at the Pacific Ocean coastal site. The high (210)Pb atmospheric flux at the Chinese continental side coast was thought to be attributable to (222)Rn-rich air-mass transport from the Chinese continent during the winter monsoon. In contrast, the annual (210)Po deposition fluxes at the three study sites were 13.0+/-2.3 (Odawa Bay), 21.9+/-4.4 (Tsuyazaki) and 58.4+/-7.7 (Akajima)Bqm(-2)y(-1), respectively, indicating unusual high (210)Po deposition at Akajima during winter. Anomalous unsupported (210)Po input was observed during summer 1997, suggesting unknown source of (210)Po at this area.     

Reinvestigation of airborne 210Pb, 137Cs and 207Bi in Vienna (Austria) after atmospheric nuclear weapons tests

Reconstruction of atmospheric 210Pb and 137Cs activity concentrations occurring in Vienna immediately after the atmospheric nuclear weapons tests shall answer the question, whether artificial 210Pb has been produced by fusion devices using lead materials. If so, 207Bi also can be expected. In 1962, weekly average values for 210Pb were between 0.08 +/- 0.02 and 1.31 +/- 0.30 mBq/m2, 137Cs amounts up to 5.1 +/- 0.6 mBq/m3. 207Bi remains below the detection limit, viz. < 0.5 mBq/m3. Bimonthly averages for the periods 1962-1964 and 1974-1975 show 137Cs activity concentrations with typical springtime maxima occurring together with low 210Pb values and 207Bi < 0.02 mBq/m3. Annual averages of 210Pb are varying between 0.27 and 0.53 mBq/m3, independent of whether atmospheric tests have been performed or not. Comparison of the activity ratios 207Bi/210Pb, 207Bi/137Cs and 210Pb/137Cs with published data, leads to the conclusion that no evidence exists for a significant production of 210Pb by nuclear explosions, neither after the Soviet tests in 1961-1962 nor after the Chinese tests in 1973-1976.     

Polonium (210Po) and lead (210Pb) in marine organisms and their transfer in marine food chains

The determination of ²¹⁰Po and ²¹⁰Pb was performed in marine organisms from the seashore to abyssal depths, encompassing a plethora of species from the microscopic plankton to the sperm whale. Concentrations of those radionuclides ranged from low values of about 5 × 10⁻¹ Bq kg⁻¹ (wet wt.) in jellyfish, to very high values of about of 3 × 10⁴ Bq kg⁻¹ (wet wt.) in the gut walls of sardines, with a common pattern of ²¹⁰Po > ²¹⁰Pb.These radionuclides are primarily absorbed from water and concentrated by phyto- and microzooplankton, and then are transferred to the next trophic level along marine food chains. Investigation in epipelagic, mesopelagic, bathypelagic and abyssobenthic organisms revealed that ²¹⁰Po is transferred in the marine food webs with transfer factors ranging from 0.1 to 0.7, and numerically similar to those of the energy transfer in the marine food chains. As ²¹⁰Po preferentially binds to amino acids and proteins, its transfer in food chains likely traces protein transfer and, thus, ²¹⁰Po transfer factors are similar to ecotrophic coefficients. ²¹⁰Pb is transferred less efficiently in marine food chains and this contributes to increased ²¹⁰Po:²¹⁰Pb activity ratios in some trophic levels.     

210Pb and 210Po in Finnish cereals

A survey was carried out on the activity concentrations of ²¹⁰Pb and ²¹⁰Po in cereal grains produced in Finland. The cereal species were wheat (Triticum aestivum), rye (Secale cereale), oats (Avena sativa) and barley (Hordeum vulgare), which account for 90% of the Finnish consumption of cereal products. The survey consisted of 18 flour and 13 unprocessed cereal samples and one hulled grain sample from 22 flour mills. According to the results, the mean ²¹⁰Pb/²¹⁰Po concentrations in wheat grains, wheat flour, rye flour, oat grains and barley grains were 0.29, 0.12, 0.29, 0.36 and 0.36 Bq kg⁻¹, respectively. Combined with the consumption rates of the products, we assess that the mean effective doses from ²¹⁰Pb and ²¹⁰Po in cereal products for the adult male and female population are 22 and 17 μSv per year, respectively.