RESUMO
Activity ratios (A.R.) of 234U/238U and activity concentration of 238+234U and 239+240Pu were measured in collected seawaters and sand beach samples from various locations along of littoral of Mexican state of Veracruz. Uranium and plutonium were separated and concentrated in a liquid-liquid partition chromatography, afterwards, detected and analyzed by means of alpha spectrometric technique. The 234U/238U activity ratio (AR) ranges from 0.72 to 1.11 in sand beach and from 0.77 to 1.22 in seawater. The activity concentration was found in sea water from 0.31 to 1.94 Bq/L for 234+238U and from 15 to 137 µBq/L for 239+240Pu, in sand beach samples was found to be from 0.64 to 3.86 Bq/kg for 234+238U and from 33 to 249 µBq/kg for 239+240Pu.
Assuntos
Plutônio , Monitoramento de Radiação , Urânio , Plutônio/análise , Urânio/análise , México , Areia , Monitoramento de Radiação/métodosRESUMO
The uranium (U) and plutonium (Pu) content with depth in a sediment core collected in the continental shelf off the mouth of the Santiago River in the Mexican Pacific was studied to evaluate the contamination effects of the effluent of the Santiago-Lerma River as it moves into the sea. The large mass of terrestrial detritus delivered by the river influences the physicochemical and geochemical processes in the seafloor. Abnormal concentrations of U and Pu in sediments were examined as indicative of the effects of anoxic conditions. One of the indicators of pollution of seawater is the bacterial activity of the shallow seabed layer; and among the prevailing bacteria, the magnetotactic ones induce the formation of euhedral and framboidal shapes (pyrite). These pyrite entities are by-products of anoxic environments loaded with decomposing detrital material and are very abundant in the surface layers of the sediment core analyzed. The pyrite formation is the result of a biochemical reaction between iron and organic sulphur reduced by bacteria, and the pyrite entities precipitate to the seafloor. In the same upper zone of the profile, 238U is readily immobilized, while 234U is oxidized and dissolved in seawater by the effect of hot atom chemistry. This may cause the activity ratio (AR) 234U/238U disequilibrium (near 0.41). Furthermore, in the shallow layer of the sediment core, an abnormally high concentration of 239+240Pu was detected. In this upper layer, the activity concentrations found were 3.19 Bq kg-1 for 238U, 1.32 kg-1 for 234U and 2.78 Bq kg-1 for 239+240Pu. In the lower fractions of the sediment core, normal values of AR 234U/238U (≈1) were found, with traces of 239+240Pu.