Description: Solid phase extraction (SPE) has become a widespread method for isolating dissolved organic matter (DOM) of diverse origin such as fresh and marine waters. This study investigated the DOM extraction selectivity of 24 commercially available SPE sorbents under identical conditions (pH = 2, methanol elution) on the example of Suwannee River (SR) water and North Sea (NS) water by using DOC analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Proton nuclear magnetic resonance (1H NMR) spectroscopy was employed to assess leaching behavior, and HLB sorbent was found to leach substantially, among others. Variable DOC recoveries observed for SR DOM and NS DOM were primarily caused by the respective molecular composition, with subordinated and heterogeneous contributions of relative salinity. Scatter of average H/C and O/C elemental ratios and gross alignment in mass-edited H/C ratios according to five established coarse SPE characteristics was near identical for SR DOM and NS DOM. FTMS-based principal component analysis (PCA) provided essentially analogous alignment of SR DOM and NS DOM molecular compositions according to the five established groups of SPE classification, and corroborated the sorption-mechanism-based selectivity of DOM extraction in both cases. Evaluation of structural blanks and leaching of SPE cartridges requires NMR spectroscopy because FT-ICR mass spectrometry alone will not reveal inconspicuous displacements of continual bulk signatures caused by leaching of SPE resin constituents.

Description: Oceans constitute one of the most important reservoirs for mercury. In order to provide a first insight into the concentrations of Hg species in the Atlantic sector of the Southern Ocean a sampling campaign was carried out south of the Polar Front. Water samples taken at discrete depths from the surface down to 300 m at six stations were analysed for total Hg (HgT), methylmercury (MeHg) and other interpretative parameters such as salinity, temperature, dissolved and particulate organic carbon, dissolved oxygen, chlorophyll and inorganic nutrients. Results showed a high spatial variability in the concentrations of HgT and MeHg. HgT (0.93±0.69 ng L−1) and MeHg (0.26±0.12 ng L−1) levels were similar or higher than those reported in previous works in high latitude studies. The highest values were found at a location (−53°, 10°E) south of the South Polar Front, an area of strong gradients caused by the mixing of different water masses. Vertical profiles showed a great variability even for those stations sampled at the same location or an area dominated by the same oceanographic features. A decrease of HgT and a consequent increase in MeHg with depth was observed in some sites, suggesting the occurrence of Hg-methylation process, while at other stations, a concurrent decrease or increase of both mercury species was observed. In spite of these differences, an overall positive correlation between HgT and MeHg was observed. Differences between vertical profiles of Hg species were attributed to favourable environmental conditions for Hg methylation. The highest proportion of MeHg (% of HgT) was observed in sites with low dissolved oxygen or highest estimated remineralization rates. The results obtained in this study show that the Hg distribution and speciation in the Atlantic sector of the SO is comparable (or in some sites higher) to the ones published for the other open ocean regions. However, the concentrations of MeHg in this area are more dependent on the environmental conditions than on the total concentration of Hg present in the water.