High level of natural radioactivity in biota from deep sea hydrothermal vents

Hydrothermal vent ecosystems are associated with virtually every area of tectonic activities throughout the deep sea an are thus enriched in natural primitive radionuclides characterizing the magma source i. e. uranium-thorium series. However, the amount of data on radionuclide content in hydrothermal vent biota is very scarce. Various organisms were sampled on the East Pacific Rise and the Mid-Atlantic Ridge in 1996-2001 and 2002. All the samples were analysed through ICP-MS in order to determine their uranium (''238U, ''235U and ''234U) and thorium (''230Th, ''232 Th) contents. In addition''210 Po-Pb were determined in 3 of the samples collected in 2002. Vent organisms are characterized by high levels of U, Th and Pb compared to what is generally encountered in organisms from outside hydrothermal vent ecosystems. ''210 Po appears to be entirely supported by ''210 Pb. These are the first results of a series of on-going work on this topic. Indeed, determination of vent organism concentrations for key elements in the uranium-thorium families has to be carried out in order to precisely determine the radiation exposure they are subject to. This appears especially important at the time where international bodies aim at promoting the development of criteria on the protection of the environment from effects arising from exposures to ionizing radiation. (Author)