The role of Typha sp. in affecting the radium behavior in the water column of a salt coastal lagoon

¹ Instituto de Radioproteçao e Dosimetria, Departamento de Radioproteçao Ambiental, CEP 22780-160 Rio de Janeiro, Brazil
² Departamento de Quimica, Pontificia Universidade Catolica do Rio de Janeiro, rua Marquês de Sao Vicente 225, Gavea, CEP 22453-00 Rio de Janeiro, Brazil

Abstract

The radium accumulation and releasing in Typha Domingenes Pers. foliage in a coastal lagoon was studied by in situ and lab experiments. From leaf sample analysis and lab experiments, adsorption experiments followed by procedure sequential extraction, it was observed the importance of the ionic exchange for the foliar accumulation. The higher the salinity, the lower the accumulation in leaves. Decomposition of leaves was studied by litterbag methods during a period of 6 months. At the end of the experiments the major cation losses were 99% of K, 76% of Na and 51% of Mg. On the other hand the amount of Ca in the residue increased seven times as well as increased the total activity of ²²⁶Ra and of ²²⁸Ra (seven and at least three times, respectively). In agreement with this observation, laboratory experiments showed that the material was able to adsorb quite a 100% of the added Ra and its adsorption capacity was estimated at 5 meq (Ba²⁺)/g_detritus. Radionuclide releasing by sequential extraction of the detritus material followed a little bit different dynamic from the green leaves, showing that important fraction of the radium can be retained in the litter by humidified material.