Voltammetric behavior of MoS2-4 and SbS3-4 as possible components of "dissolved sulfide" in oxic natural waters

Nanomolar concentrations of dissolved sulfide have been observed in O-2- hearing natural waters. The sulfide consists of oxidation-resistant, unknown chemical components that might include metal-sulfide complexes, elemental sulfur in various forms or organic sulfur compounds. Here we show that thioanions are also plausible components. Tetrathiomolybdate and tetrathioantimonate ions deposit respectively 3 and 4 equivalents of HgS at mercury electrodes. In cathodic stripping voltammetry, a common method to quantify nanomolar sulfide in nature, MoS42- and SbS43- would therefore contribute to "total dissolved sulfide." Limited evidence suggests that thioanions may be powerful complexing agents that would be capable of affecting trace metal speciation and bioavailability in natural waters.