title: Methylmercury production in the water column of an ultraoligotrophic lake of Northern Patagonia, Argentina.
abstract: Methyl-mercury (CH3Hg+) production was studied in freshwaters from lake Moreno, an ultraoligotrophic system belonging to Northern Patagonia. Hg2+ labelled with high specific activity 197Hg was spiked to water samples in concentrations of 10 ng l(-1), and incubated in laboratory for 3d time trends under different conditions. Experimental water was sampled daily to evaluate CH3(197)Hg+ production. Lake water used in the experiments was sampled just below the upper limit of the metalimnion ( approximately 30 m depth), where maximum values of chlorophyll a have been measured previously. Sampling was performed in late autumn, when the plankton fraction <50 microm exhibited mercury concentrations up to 260 microg g(-1) dry weight. The experiments analysed lake water filtered through 50, 20, and 0.2 microm (filter-sterilized) mesh nets. ASTM grade 1 water was also incubated for control. All the experiments were run in an environmental chamber under controlled temperature and light regime. High Hg2+ conversion to CH3Hg+, up to 50%, was measured in lake water, in a process stimulated by light. CH3Hg+ production was two-fold higher after 3d of incubation with illumination compared to total darkness. Sterile lake water showed conversions up to 30%, while the planktonic components seem to enhance the CH3Hg+ production. Overall, our results provide evidence that lake Moreno waters favour CH3Hg+ production in processes stimulated by light. Although biotic components certainly contribute to enhance mercury methylation, water chemistry plays a key role in this process. We hypothesize that dissolved organic matter, particularly its quality, could be decisive.
authors.affiliation: Laboratorio de Análisis por Activación Neutrónica, Comisión Nacional de Energía Atómica, Centro Atómico Bariloche, Av. Bustillo km 9.5, 8400 Bariloche, Argentina. ribeiro@cab.cnea.gov.ar <ribeiro@cab.cnea.gov.ar>
authors.forename: Sergio
authors.initials: S
authors.lastname: Ribeiro Guevara
authors.forename: Claudia P
authors.initials: CP
authors.lastname: Queimaliños
authors.forename: María Del Carmen
authors.initials: Mdel C
authors.lastname: Diéguez
authors.forename: María
authors.initials: M
authors.lastname: Arribére
mesh_terms: D001118:Argentina; D005618:Fresh Water / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry / Q000302:isolation & purification; D008631:Mercury Radioisotopes; D008767:Methylmercury Compounds / Q000737:chemistry* / Q000302:isolation & purification; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000302:isolation & purification
chemical_list: D008631:Mercury Radioisotopes; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury