Recherche d'éléments radioactifs naturels dans quelques lichens foliaces

Samples of Parmelia sulcata and Xanthoria parietina from different biotopes have been analysed for elements of the series of uranium 238 and thorium 232. These species have been used as bio-monitors in different cases : urban areas, coal fired power plant, tip for uranium-mining residues. The concentration of most of these elements in lichens is decreasing as follows : radium waste-disposal site > area with uranium-rich soil > urban area > rural area. Road traffic was not found to increase notably the presence of radioactive lead in the environment. The two foliose lichens seem to have a comparable concentration ability, but Parmelia sulcata appeared to be more reliable. Some of the elements under investigation could be particularly problematic from a sanitary point of view : the intake limits in case of inhalation are very low and the atmospheric deposition is not negligeable .. this is particularly so for lead 2 10 and thorium 228. These elements should not only be monitored on a spatial basis, but investigated al regular intervals in time since their global abundance seems to have increased in the last decades. The authors have presented the papers reviewed on a synoptic table .. they also give the results of analyses on different species sampled in an area with a uranium-rich soil : these results could be considered as a reference for natural maximal concentrations. The expia nations of the tables are also given in english.