Determination of concentration profiles of methyl mercury compounds in surface waters of polar and other remote oceans by GC-AFD

The concentration of monomethyl mercury (MeHg+) and dimethyl mercury (Me2Hg ) was determined in surface sea-water samples of the Antarctic and Arctic O cean as well as of other remote areas (South Atlantic and South Pacific) du ring expeditions of the German research vessel "Polarstern" A purge and tra p/gas chromatographic system, equipped with an atomic fluorescence detector (AFD), was used. For the analysis of MeHg+ conversion into the volatile me thylethyl mercury by reaction with tetraethyloborate prior to the purging p rocess was carried out. The detection limit for both methylated mercury com pounds was 5 pg Hg/L, which allowed their determination in most ocean water samples even in those of the Antarctic and Arctic Ocean. A north-south con centration profile in the Atlantic Ocean, covering a distance from 51 degre es N to 58 degrees S, was also examined, which resulted in the most extende d set of data in the environment for these important heavy metal species. I n anthropogenically influenced areas of the North Atlantic from 51 degrees N to about 40 degrees N concentrations of methylated mercury in the range o f 100-3000 pg/L were found. The contents of these species were significantl y lower in remote areas, represented by a range of <5 pg/L to 150 pg/L. Con centrations of the methylated mercury species were compared with those of s ubstances often used as biomass indicators, e.g. chlorophyll-a and adenosin e triphosphate. A positive correlation was found, in general, in remote are as between the contents of methylated mercury and these parameters for bioa ctivity, demonstrating the biogenic origin of MeHg+ and Me2Hg, respectively . The concentration of MeHg+ normally exceeded that of Me2Hg, except at loc ations with especially high bioactivities. This result indicates that Me2Hg may be the main primary biogenic product. Oceanographic conditions are ver y well reflected by concentration profiles of methylated mercury. For examp le, in biologically very active upwelling regions peak concentrations of Me 2Hg and MeHg+ were found, whereas in parts of the Antarctic Ocean, totally covered by ice, the concentration of methylated mercury was determined to b e below the detection limit.