Radiossensibilidade gama de Cladonia substellata Vainio (lÃquen) e o conseqÃente efeito sobre rochas calcÃrias / Gamma radiosensibility of Cladonia substellata vainio (lichen) and the consequent chelating effect on calcareous rocks

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Soil is an unconsolidated surface that recovers the rocks and maintains animal and plant life on Earth. It is formed from climatic and biotic relationship, modified by topography that acts on original material, over a long period of time. Concerning biotic activities, one may emphasize that performed by lichens, which allow the succession of rocky substratum colonization, since they can live directly on rocks, weathering them. When submitted to different doses and kinds of radiation, lichens are stimulated to produce their substances in differentiated amounts from the ones that would be produced without radiation intervention. The objective of this research was to determine the possible changes in usnic acid (USN) production by the lichen Cladonia substellata, submitted to different doses of gamma radiation, and to determine the chelating capacity of those thalli, when deposited over calcareous rocks. Samples of C. substellata (2,5g) were submitted to Co-60-irradiador source, dose rate of 9,06Gy.h-1, receiving doses of 5; 7; 10; 15; 20; 30; 40; 50; 60 e 80Gy, and kept on Petri dishes, over triturate limestone. During the period of incubation, the lichen samples were sprayed with deionized water, three times a week. Lichen samples were collected at 1, 2; 3; 7; 15; 30; 60 and 90 days, and analyzed by Thin Layer (TLC) and High Performance (HPLC) chromatographies. The control rock samples (not submitted to lichens) and, the ones that were in contact with irradiated C. substellata at 10, 30 and 80Gy, were analyzed by X ray diffratometry. The results pointed out an increase in USN production directly proportional to the higher doses, up to 10Gy. Since, there was a tendency for reduction in production, a very reduced biosynthesis at 80Gy occured. This corroborates the X ray diffratometry experiments, which showed to be more easily chelated when limestone samples were placed under C. substellata irradiated at 10Gy. The rock submitted to irradiated lichen at 80Gy, showed low content of USN, remained in a similar form to control material. It was possible to conclude that C. substellata increases its USN biosynthesis in proportion to elevation of gamma radiation dose, but there exists a limit for that. The chelating action of USN on limestone was proportional to produced amount of this compound, that can be extrapolated to natural conditions, where excessive radiation can have influence on pedogenesis and ecological succession

ASSUNTO(S)

engenharia nuclear cladonia substellata raios gama, Ãcido Ãsnico, rochas calcÃrias, cladonia substellata pedogenesis usnic acid calcareous rock pedogÃnese gamma rays

ACESSO AO ARTIGO

Documentos Relacionados