Tellurium species in seawater

Abstract

The marine geochemistry of tellurium is unknown, being one of the few elements whose concentrations in seawater have never been reported^1,2. The major problem in studying Te stems from its rarity and the poor sensitivities of most analytical methods (even its crustal abundance is still controversial³). We have developed a very sensitive method allowing accurate measurements to be made of Te(IV), Te(VI) and total Te in seawater and we present here several vertical profiles of these species, which were obtained from the ocean. The Te profiles resemble in part the behaviour of Se and in part that of Po, reflecting the position of Te between Se and Po in Group VIb of the Periodic Table. Te, like Se, is found to be present in two oxidation states, Te(VI) and Te(IV), but their relative stabilities are reversed with respect to Se^4–7. Se(VI), which is thermodynamically stable, and the unstable Se(IV) both exhibit nutrient-type distributions, but the distribution of Te, like ²¹⁰Po⁸, shows evidence of strong scavenging by marine participates, consistent with the chemical speciation of Te(VI) as a hydrosilate (Te(OH)₆), similar to Po(IV)OH₄), rather than as an oxyanion, like Se(VI)O²⁻₄.