title: Evaluation of mercury methylation and methylmercury demethylation rates in vegetated and non-vegetated saltmarsh sediments from two Portuguese estuaries.
abstract: Neurotoxic methylmercury (MMHg) is formed from inorganic divalent mercury (Hg2+). However, it is poorly understood to what extent different mercury (Hg) pools contribute to existent MMHg levels. In this study, ambient concentrations of total Hg (THg) and MMHg as well as rates of methylation and demethylation were measured simultaneously in sediments with and without salt-marsh plant vegetation, which were collected in Guadiana and Tagus estuaries, Portugal. Concurrent processes of Hg methylation and MMHg demethylation were directly monitored and compared by spiking sediments cores with stable isotope tracers of199Hg2+and CH3201Hg+followed by gas chromatographic separation and isotope-specific detection using inductively coupled plasma mass spectrometry. Compared to the Guadiana estuary, where concentrations were comparatively low, THg and MMHg levels varied between vegetated and non-vegetated sediments collected at the Rosário site (ROS) of the Tagus estuary. Methylation (KM) and demethylation rates (KD) were also different between estuaries being dependent on the presence of vegetation. In addition, the type of macrophyte species influenced KMand KDvalues. In fact, the highest KMvalue was found in Sarcocornia fruticosa vegetated sediments at the Castro Marim site in Guadiana (CM, 0.160 day-1) and the lowest KMwas observed in non-vegetated sediments at the Alcochete site in Tagus (ALC, 0.009 day-1). KDvaried by a factor of three among sites with highest rates of demethylation observed in non-vegetated sediments in Guadiana (12 ± 1.3 day-1, corresponding to a half-life of 1.4 ± 0.2 h). This study clearly shows that the presence of vegetation in sediments favors the formation of MMHg. Moreover, this effect might be site specific and further studies are needed to confirm the findings reported here.
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1, 1049-001 Lisboa, Portugal; IPMA-Instituto Português do Mar e Atmosfera, Av. Brasília, 1449-006 Lisboa, Portugal.
authors.forename: Rute
authors.initials: R
authors.lastname: Cesário
authors.affiliation: Water Quality Centre, Trent University, 1600 West Bank Drive, Peterborough, ON K9J 0G2, Canada.
authors.forename: Holger
authors.initials: H
authors.lastname: Hintelmann
authors.affiliation: IPMA-Instituto Português do Mar e Atmosfera, Av. Brasília, 1449-006 Lisboa, Portugal.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Mendes
authors.affiliation: Institute of Inorganic and Analytical Chemistry, University of Muenster, Schlossplatz 2, 48149 Munster, Germany.
authors.forename: Kevin
authors.initials: K
authors.lastname: Eckey
authors.affiliation: Water Quality Centre, Trent University, 1600 West Bank Drive, Peterborough, ON K9J 0G2, Canada.
authors.forename: Brian
authors.initials: B
authors.lastname: Dimock
authors.affiliation: Centro de Biociências e Biotecnologia, Universidade Estadual do Norte Fluminense, Av. Alberto Lamego, 2000, Horto, Campus dos Goytacazes, Rio de Janeiro, Brazil.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Araújo
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1, 1049-001 Lisboa, Portugal.
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Mota
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1, 1049-001 Lisboa, Portugal. Electronic address: joao.canario@tecnico.ulisboa.pt.
authors.forename: João
authors.initials: J
authors.lastname: Canário
mesh_terms: D004784:Environmental Monitoring; D063366:Estuaries; D019015:Geologic Sediments / Q000737:chemistry; D006207:Half-Life; D007554:Isotopes / Q000032:analysis; D008628:Mercury / Q000032:analysis*; D008745:Methylation; D008767:Methylmercury Compounds / Q000032:analysis*; D010944:Plants; D011174:Portugal; D014874:Water Pollutants, Chemical / Q000032:analysis*; D053833:Wetlands
chemical_list: D007554:Isotopes; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Estuaries; Mercury methylation; Methylmercury demethylation; Salt-marsh sediments