No abstract

A framework for protection of the environment is likely to require a methodology for assessing dose rates arising from naturally occurring radionuclides. This paper addresses this issue for European aquatic environments through a process of (a) data collation, mainly with respect to levels of radioactivity in water sediments and aquatic flora and fauna, (b) the use of suitable distribution coefficients, concentration factors and global data where data gaps are present and (c) the utilisation of a reference organism approach whereby a finite number of suitable geometries are selected to allow dose per unit concentration factors to be derived and subsequent absorbed dose calculations (weighted or unweighted) to be made. The majority of the calculated absorbed dose, for both marine and freshwater organisms, arises from internally incorporated alpha emitters, with 210Po and 226Ra being the major contributors. Calculated doses are somewhat higher for freshwater compared to marine organisms, and the range of doses is also much greater. This reflects both the much greater variability of radionuclide concentrations in freshwater as compared to seawater, and also variability or uncertainty in concentration factor values. This work has revealed a number of substantial gaps in published empirical data especially for European aquatic environments.

In order to put dose-rates derived in environmental impact assessments into context, the International Commission on Radiological Protection (ICRP) has recommended the structuring of effects data according to background exposure levels. The ICRP has also recommended a suite of reference animals and plants (RAPs), including seven aquatic organisms, for use within their developing framework. In light of these propositions, the objective of this work was to collate information on activity concentrations of naturally occurring primordial radionuclides for marine and freshwater ecosystems and apply appropriate dosimetry models to derive absorbed dose-rates. Although coverage of activity concentration data is comprehensive for sediment and water, few, or in some cases no, data were found for some RAPs, e.g. for frogs (Ranidae) and freshwater grasses (Poaceae) for most radionuclides. The activity concentrations for individual radionuclides in both organisms and their habitat often exhibit standard deviations that are substantially greater than arithmetic mean values, reflecting large variability in activity concentrations. To take account of variability a probabilistic approach was adopted. The dominating radionuclides contributing to exposure in the RAPs are (40)K, (210)Po and (226)Ra. The mean unweighted and weighted dose-rates for aquatic RAPs are in the ranges 0.07-0.39 microGy h(-1) and 0.37-1.9 microGy h(-1) respectively.

No abstract

The Chernobyl fallout is an enduring challenge to reindeer husbandry in Norway, and South Sámi reindeer herders in central and southern Norway are as contaminated by (137)Cs as inhabitants close to Chernobyl. Therefore, Norwegian authorities continuously recommend to these reindeer herders the use of countermeasures to reduce their intake of (137)Cs. In this study, the authors have applied data on contamination levels in reindeer, results of dietary surveys, and whole body monitoring data in low and high contaminated areas to estimate the effectiveness of countermeasures and resulting averted doses to the reindeer herders. In the most contaminated area, the various countermeasures applied reduced radiocesium ingestion doses during 1986-2009 by about 73%, to an integrated dose of about 17 mSv. However, to comply with the recommended (137)Cs ingestion dose limit of 1 mSv y(-1), the study indicates that reindeer herders in the most contaminated areas will need to carry on with their countermeasures for another 10-15 y. Furthermore, the study indicates that whole body monitoring is an important tool to assess individual doses and countermeasure effectiveness in long-term management of a contamination situation and that such monitoring may be required to reach long-term reference levels.