Thorium Concentrations in Terrestrial and Freshwater Organisms: A Review of the World Data

Abstract

An overview of data on thorium concentrations in terrestrial animals, as well as freshwater organisms is presented. Concentrations of 232Th in both animals and fish vary widely, reflecting environmental thorium concentrations. Thorium concentrations in the regions with a normal thorium background in animal tissues were in a range from 0.9 × 10–4 to 2.1 × 10–2 Bq/kg, and from 3.1 × 10–2 to 1.4 × 10–1 Bq/ kg in the areas with high thorium concentrations in the soil. Significantly higher values were observed in wild animals’ tissues. The highest 232Th concentrations were found to be in the skeleton, followed by lungs, kidneys, liver and finally muscles. It has been shown that thorium accumulation is higher in species occupying a higher position in the trophic chains. In areas with normal thorium background, the concentration of 232Th in fish can reach 1.0 × 10–1 Bq/kg (fresh mass), and in areas of high thorium background this value can be up to 100 times higher. The obtained results show the importance of study on the thorium transfer along the food chains and the need to consider observed regularities when assessing the consequences of radioactive contamination of the environment.