IODINE SPECIATION IN THE WATER COLUMN OF THE BLACK-SEA

Iodine speciation was determined on water samples collected from the upper 250 m of the Black Sea during 11-14 June 1988. Iodate, iodide and total iodine were determined by three separate voltammetric methods. In most samples, the sum of iodide plus iodate equalled the total iodine. In four samples obtained near the oxic/anoxic nonsulfide interface, however, the sum of the iodide plus iodate was less than the total iodine (range 17-38% lower). Thus, a third form of iodine is present. Addition of sulfite to the samples did not increase the iodide concentration which would be expected if I2 or OI- were present. It is suggested that the third form of iodine is organic and probably of high molecular weight (peptide or aromatic?). The differences with the previous results of WONG and BREWER (1977, Geochimica et Cosmochimica Acta, 41, 151-159) can be attributed to different methods used and to differences in the water column chemistry of the Black Sea over time and perhaps season. In the previous work, O2 and H2S coexisted in the zone between the oxic and sulfidic zones whereas in this work, O2 and H2S were not present in the zone between the oxic and sulfidic zones.