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.     

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.     

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.     

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.     

Behavior of 137Cs in soils of transitional bogs

Specific features of ¹³⁷Cs accumulation, transformation, and migration in humus-peaty and peaty-gley soils of transitional bogs are discussed with reference to the southwestern part of the Russian Federation, which was most heavily contaminated after the Chernobyl accident. The influence of physicochemical soil properties and concentrations of typomorphic elements on these processes is characterized. It is concluded that bog soils accumulate ¹³⁷Cs in the form of hardly movable compounds and, as a consequence, transitional bogs are transformed into critical ecosystems.     

210Pb deposition in the far East Asia: controlling factors of its spatial and temporal variations

In order to better understand the behavior of ²¹⁰Pb deposition in Far East Asia, comprehensive data of monthly ²¹⁰Pb deposition, which includes several time-series and spatial distribution data at 14 stations in Japan and 2 stations in Taiwan, were analyzed. Pb-210 deposition at most of the sites exhibited a typical seasonal change with higher values in winter and lower values in summer; especially, the greatest ²¹⁰Pb deposition in the world occurred in winter at sites beside the Japan Sea. The deposition behavior of ²¹⁰Pb in Far East Asia differed between winter and summer. The meteorological phenomenon peculiar to winter of the Japan Sea side, i.e., formation of the Japan Sea convergence zone, might cause the high ²¹⁰Pb concentration in rainwater, as may heavy snowfall. The ²¹⁰Pb concentration in rainwater showed long-term variability, although this differed between winter and summer. This long-term variability may be related to climatological factors such as El Niño.     

Comprehensive Analysis of Radioactive and Chemical Contamination of Water Bodies in the Area of Radium-Industry Waste Storage

Genotoxicity and cytotoxicity of water samples from the creeks flowing through the area of radium mining waste storage into the Ukhta River and from this river were assessed using biological tests with Allium schoenoprasum L. Chemical analysis of the samples indicated that concentrations of parent heavy natural radionuclides, ²¹⁰Pb, and ²¹⁰Po do not exceed the allowable level. Of ten heavy metals, only Zn and Mn concentrations exceeded MACs. The results of biological tests provided evidence for the significantly increased genotoxicity of water samples. The mitotic index increased with an increase in the concentration of Zn ions and manifested an inverse dependence on the activity of ²³⁸U. The genotoxic effect linearly depended on Zn concentration. Possible mechanisms responsible for the induction of these biological effects are discussed.     

The combined effect of uranium and gamma radiation on biological responses and oxidative stress induced in Arabidopsis thaliana

Uranium never occurs as a single pollutant in the environment, but always in combination with other stressors such as ionizing radiation. As effects induced by multiple contaminants can differ markedly from the effects induced by the individual stressors, this multiple pollution context should not be neglected. In this study, effects on growth, nutrient uptake and oxidative stress induced by the single stressors uranium and gamma radiation are compared with the effects induced by the combination of both stressors. By doing this, we aim to better understand the effects induced by the combined stressors but also to get more insight in stressor-specific response mechanisms. Eighteen-day-old Arabidopsis thaliana seedlings were exposed for 3 days to 10 μM uranium and 3.5 Gy gamma radiation. Gamma radiation interfered with uranium uptake, resulting in decreased uranium concentrations in the roots, but with higher transport to the leaves. This resulted in a better root growth but increased leaf lipid peroxidation. For the other endpoints studied, effects under combined exposure were mostly determined by uranium presence and only limited influenced by gamma presence. Furthermore, an important role is suggested for CAT1/2/3 gene expression under uranium and mixed stressor conditions in the leaves.