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Formation and volatilisation of alkyl-iodides and -selenides in macrotidal estuaries

Abstract : The occurrence of alkylated volatile iodide and selenide species was evidenced and investigated in water, sediments and overlying atmosphere of three major European estuaries, such as the Gironde (F), the Rhine (NL) and the Scheldt (B/NL), along with the salinity gradient. For iodine, up to eight volatile species were observed as alkyl-iodides in estuarine waters. The major one (ca. 40%) was methyl-iodide (MeI) with average seasonal concentrations ranging from 1 to 100 pmol l-1. Other species observed were found to correspond to several halomethane derivatives and light alkyl-iodide species. For selenium, dimethyl selenide (Me2Se) was the main compound (ca. 90%) over three methyl-selenides encountered in estuarine waters. Me2Se average seasonal concentrations were found to range between 0.2 and 100 pmol l-1 in the water column. The occurrence of methylated iodides and selenides seems to be mainly related to the algae's biomass turnover as indicated by photosynthetic pigment tracers (i.e. chlorophyll a and phaeopigments) and seasonal variation of surface water concentrations. The production and release of gaseous iodide and selenide compounds may then result from natural biological pathways leading to the methylation of their inorganic form. Finally, significant volatilisation rates were evaluated leading to average seasonal flux rates for total volatile iodide and selenide compounds ranging from 4 to 100 and from 1 to 75 nmol m-2 d-1, respectively. Estuarine mass balance estimated from MeI and Me2Se distributions indicates that volatilisation to the atmosphere represents a primary sink for MeI and Me2Se from estuarine surface waters.
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Submitted on : Tuesday, September 19, 2017 - 12:32:19 PM
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Emmanuel Tessier, David Amouroux, G. Abril, E. Lemaire, O.F.X. Donard. Formation and volatilisation of alkyl-iodides and -selenides in macrotidal estuaries. Biogeochemistry, Springer Verlag, 2002, 59 (1-2), pp.183-206. ⟨10.1023/A:1015550931365⟩. ⟨hal-01590069⟩



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