RESUMO
Seasonal trends of benthic methylmercury (methyl-Hg) production were examined in both littoral and open water sites of three lakes (Escondido, Moreno, and Morenito) in the North Andean Patagonia region of Argentina. Potentials of methyl-Hg production were measured by amending sediment samples with inorganic (197)Hg(II), incubating for either 24 and 32 h at room temperature, and subsequently assaying the radiolabelled organomercury produced. Seasonal variations of benthic methyl-Hg production were studied but no significant correlation was observed. Lake littoral sites exhibited up to two fold higher methyl-Hg production potentials in most cases. Sediment from lakes Moreno and Morenito generally exhibited much lower (up to 10 fold) methyl-Hg production potentials than those from Lake Escondido, possibly due to differences in particulate and dissolved organic matter quantity and quality, which is higher in Lake Escondido and primarily allochthonous, whereas in lakes Moreno and Morenito is primarily autochthonous. This study represents the first to directly examine benthic microbial Hg(II)-methylation in aquatic ecosystems of Patagonia.
Assuntos
Ecossistema , Mercúrio/análise , Compostos de Metilmercúrio/análise , Poluentes do Solo/análise , Argentina , Monitoramento Ambiental , Sedimentos Geológicos/química , Radioisótopos de Mercúrio/química , Compostos de Metilmercúrio/química , Estações do Ano , Poluentes do Solo/químicaRESUMO
The absolute 4pi-betagamma coincidence counting has been used to measure the activity concentrations of 54Mn and 203Hg, and the Sum-Peak method was used for 125I. 54Mn and 125I radionuclides have been part of international key-comparisons coordinated by the Bureau International des Poids et Measures (BIPM) in 2003/2004, while 203Hg is part of the traceability programme of the National Laboratory for Ionizing Radiation Metrology (LNMRI)/Brazil. Three different detectors were used for the Sum-Peak method: 3''x3'' NaI(Tl) and 5''x5'' well NaI(Tl) scintillation detectors and a planar germanium detector. Direct measurements were made of the photon emission probabilities of the 35.5-, 834.8- and 279.2-keV gamma-rays of 125I, 54Mn and 203Hg to give values of (0.0667+/-0.0014), (0.9997+/-0.0055) and (0.8161+/-0.0005), respectively. The half-lives of 203Hg and 54Mn were also determined by means of a 4pigamma ionization chamber (203Hg) and by the reference source method using a HPGe detector (54Mn) to give values of (46.639+/-0.023) days and (312.1+/-0.9) days, respectively.