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This paper addresses the noticeable increase of 137Cs activity concentrations in soil and fallout in the area surrounding Zagreb (Croatia) that occurred at the time of the 2011 Fukushima accident. This topic is important for public health as 137Cs is highly toxic due to its long half-life of radioactive decay and chemical similarity to potassium. 137Cs concentrations in fallout were much greater than in soil, but remained present longer in the latter. While being detectable in our measurements, 137Cs did not spread through the food chain in amounts exceeding the maximum allowed level of radioactive food contamination. However, more thorough and consistent measurements need to be done in order to establish the precise activity trends of 137Cs in Zagreb soil and fallout.

This article brings the results of a method for quality assurance in gamma-ray spectrometry of seabed sediments. Sediments were collected in selected locations of the South and Middle Adriatic Sea using grab and corer tools. Using our own experimental design, we determined the self-attenuation factors of selected samples. The article also discusses sources of uncertainty in gamma-ray spectrometry, which is another important issue in quality assurance. Together with self-attenuation correction sources of uncertainty are used to calculate the activity concentration for a given sample. The presented procedure demonstrates how a gamma-ray spectrometry experiment should be approached in order to properly account for errors and uncertainties specific to a particular sample.

Thermal waters are known as valuable natural resources of a country. They contain certain degree of natural radioactivity attributable to the elements of the uranium and thorium natural decay series. Among these elements, the most radiotoxic and the most important is radium that exists in several isotopic forms (226Ra and 228Ra). The focus of attention was the content of radium in samples of thermal and mineral spring water from several spas in Croatia. These waters are mainly used for medical, bathing and recreational purposes, and some of them are used for drinking. Measured activity concentrations of 226Ra ranged from 87 to 6200 mBq l(-1) which, in some springs, exceed the maximal permissible level of 1 Bq l(-1) for drinking water. Measured activity concentrations of 228Ra ranged from 23 to 3480 mBq l(-1). The study showed that radium content for the investigated thermal and mineral waters is below the levels at which negative consequences would arise due to ingestion.

The presence of natural radionuclides in Croatian rivers emphasizes the need for its continuous monitoring. Therefore results of 226Ra and 228Ra determination in Croatian river waters are presented in this paper. 226Ra and 228Ra were chosen as a possible source of human exposure due to their high radio-toxicity. Fifty liters of river water samples were collected from the Danube, Drava, Sava, Krka and Neretva rivers twice a year from 2002 to 2006. It is showed that activity concentrations of 226Ra ranged from 6.54 mBq/L to 59.44 mBq/L and 228Ra activity concentrations ranged from 2.57 mBq/L to 20.76 mBq/L. The highest values of both 226Ra and 228Ra were measured in the river Drava, and the lowest values in the river Sava. Statistically significant differences were not observed between radium concentrations from two watersheds (the Black Sea and the Adriatic Sea watershed), nor between 226Ra/228Ra ratio in rivers individually. The number of collected samples is insufficient to make more statistically significant conclusions. However the data obtained in this study could be the baseline for evaluating possible future changes.

This paper gives a review of marine radioecology research in the Adriatic area carried out by the Radiation Protection Unit of the Institute for Medical Research and Occupational Health. Measurements of radioactivity in the Adriatic started in 1963 as a part of an extended monitoring programme of radioactivity in Croatian environment. The main sources of radioactive contamination of the Adriatic Sea are the fallout from past nuclear weapon testing conducted in the atmosphere and the Chernobyl accident. In 2005, the activity concentrations of fission radionuclides were detectable at very low levels in all environmental samples collected on the Adriatic. The 90Sr data obtained from long-term monitoring were used to estimate the upper limit of the Adriatic seawater turnover time, which turned out to be (3.4 +/- 0.4) years. Detailed knowledge about seawater circulation, including the turnover time is essential for planning an overall communal and other wastewater management on the Adriatic coast. The paper concludes with the prospects for future marine radioecological investigations.