Determination of methylmercury using liquid chromatography – photochemical vapour generation – atomic fluorescence spectroscopy (LC-PVG-AFS) : a simple, green analytical method

Acknowledgements The authors thank P S Analytical for financial support for the project. In addition, the author would like to thank Dr Nick Ralston for providing the tuna samples used in the method validation, as well as Jonas Kunigkeit and Jasmina Allen for their help in the lab.Peer reviewedPostprin

Methylmercury varies more than one order of magnitude in commercial European rice

P.M. thanks the Royal Thai Government for funding and C.C.B. thanks the School of Natural and Computing Science and PS Analytical for funding.Peer reviewedPostprin

Quick and robust method for trace determination of MeHg in rice and rice products without derivatisation

Peer reviewedPostprin

Prévision des éruptions volcaniques par l'analyse chimique des fluides hydrothermaux d'arc insulaire : Guadeloupe (Petites Antilles) et Nisyros (Grèce)

This study investigates two hydrothermal systems in volcanic island arcs, Guadeloupe (Lesser Antilles) and Nisyros (Greece). At Guadeloupe spring water and fumarolic gas samples were collected in 1997, while at Nisyros three surveys were undertaken (1997, 1998 and 1999), covering fluid sampling, diffuse soil CO2 flux, soil temperature and soil thermal gradient determinations. The chemical and isotopic composition of gas emissions (H2O, CO2, H2S, H2, N2, CH4, CO, Ar, He, dD(H2O), d18O(H2O), d18O(CO2), d13C(CO2), and d34S(H2S)) and thermal waters (Na, K, Mg, Ca, HCO3, Cl, SO4, SiO2, B, dD(H2O), d18O(H2O), and d34S(SO4)) is used, after merging these new data sets with existing data, to elaborate a geochemical model for both hydrothermal systems, which provide the necessary basis for adequate volcanic surveillance. In addition, based on diffuse soil CO2 and soil temperature measurements, the release of hydrothermally related thermal energy is quantified for the Nisyros system. In both systems, Guadeloupe and Nisyros, fumaroles discharge hydrothermal fluids lacking in highly acid gases, such as SO2, HCl and HF. Their outlet temperatures are buffered to 100 ºC. However, isotopic results point to a contribution of andesitic magmatic water. Water stable isotopes indicate boiling, mixing and condensation processes occurring in the subsurface. Assuming chemical equilibrium between gas constituents in the aquifer, and quenching of this equilibrium during upflow of the fluids, the equilibrium temperature of the aquifer and the temperature of vapor separation are estimated. Considering these geothermometric findings, and the alteration phenomena of the gas discharges the isotopic composition of the parent geothermal liquid is traced back for both systems. The thermal spring system at La Soufrière volcano (Guadeloupe) includes (1) sulphate waters produced through absorption of hydrothermal vapors into shallow groundwaters, (2) Ca-Na-Cl springs which testify for mixing of sulfate waters with deep Na-Cl hydrothermal liquids and (3) conductively heated groundwaters. Highsalinity Na-Cl geothermal liquids circulate in the Bouillante geothermal reservoir of Guadeloupe at temperatures close to 250 ºC. These liquids undergo boiling and mixing with groundwater and/or seawater before they discharge as Na-Cl thermal springs. The Na-Cl thermal waters discharging along the coast of Nisyros seem to be fed by seawater with minor contributions of condensed steam outflows from the geothermal system. Repeated surveys of diffuse soil CO2 flux, soil temperature and soil thermal gradient surveys in the southern part of the Lakki plain of Nisyros allow to elaborate several distribution maps of these parameters. These combined measurements - CO2 flux, soil temperature and soil thermal gradient - permit to understand the mechanism of heat transfer through the soil and to quantify the flux of hydrothermally related thermal energy released from the surveyed area. It amounts to 58MW for 1.3 km2. No significant time variations in CO2 and thermal fluxes took place from 1997 to 1999, suggesting that the hydrothermal system was close to steady state conditions during that time

Geochemistry of the thermal springs and fumaroles of Basse-Terre Island, Guadeloupe, Lesser Antilles

The purpose of this work was to study jointly the volcanic-hydrothermal system of the high-risk volcano La Soufriere, in the southern part of Basse-Terre, and the geothermal area of Bouillante, on its western coast, to derive an all-embracing and coherent conceptual geochemical model that provides the necessary basis for adequate volcanic surveillance and further geothermal exploration. The active andesitic dome of La Soufriere has erupted eight times since 1660, most recently in 1976-1977. All these historic eruptions have been phreatic. High-salinity, Na-CI geothermal liquids circulate in the Bouillante geothermal reservoir, at temperatures close to 250 degrees C. These Na-CI solutions rise toward the surface, undergo boiling and mixing with groundwater and/or seawater, and feed most Na-CI thermal springs in the central Bouillante area. The Na-Cl thermal springs are surrounded by Na-HCO3 thermal springs and by the Na-Cl thermal spring of Anse a la Barque (a groundwater slightly mixed with seawater), which are all heated through conductive transfer. The two main fumarolic fields of La Soufriere area discharge vapors formed through boiling of hydrothermal aqueous solutions at temperatures of 190-215 degrees C below the ``Ty'' fault area and close to 260 degrees C below the dome summit. The boiling liquid producing the vapors of the Ty fault area has SD and delta(18)O values relatively similar to those of the Na-CI liquids of the Bouillante geothermal reservoir, whereas the liquid originating the vapors of the summit fumaroles is strongly enriched in O-18, due to input of magmatic fluids from below. This process is also responsible for the paucity of CH;I in the fumaroles. The thermal features around La Soufriere dome include: (a) Ca-SO4 springs, produced through absorption of hydrothermal vapors in shallow groundwaters; (b) conductively heated, Ca-Na-HCO3 springs; and (c) two Ca-Na-Cl springs produced through mixing of shallow Ca-SO4 waters and deep Na-Cl hydrothermal liquids. The geographical distribution of the different thermal features of La Soufriere area indicates the presence of: (a) a central zone dominated by the ascent of steam, which either discharges at the surface in the fumarolic fields or is absorbed in shallow groundwaters; and (b) an outer zone, where the shallow groundwaters are heated through conduction or addition of Na-Cl liquids coming from hydrothermal aquifer(s)

Geochemical evidence for mixing of magmatic fluids with seawater, Nisyros hydrothermal system, Greece

The chemical and isotopic compositions (deltaD(H2O), delta(18)O(H2O), delta(18)O(CO2), delta(13)C(CO2), delta(34)S, and He/N-2 and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9+/-0.5parts per thousand for delta(18)O and -11+/-5parts per thousand for deltaD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid-vapor separation conditions obtained through gas geothermometry. The H-2-Ar, H-2-N-2, and H-2-H2O geothermometers suggest reservoir temperatures of 345+/-15 degreesC, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260+/-30 degreesC is indicated by gas equilibria in the H2O-H-2-CO2-CO-CH4 system. The largest magmatic inputs seem to occur below the Stephanos-Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton-Polybotes Megalos craters receive a smaller contribution of magmatic gases