es9911115_si_001.pdf (123.51 kB)
Mercury Speciation in the Presence of Polysulfides
journal contribution
posted on 2000-04-21, 00:00 authored by Jenny Ayla Jay, François M. M. Morel, Harold F. HemondEnvironmental mercury methylation appears modulated by
sulfide concentrations, possibly via changes in mercury
availability to sulfate reducing bacteria, the major agents
of this process in aquatic systems. Consequently, there has
been much recent interest in quantifying the chemical
speciation and lipid solubility of mercury in the presence
of sulfide and of polysulfides, which form by reaction of sulfide
with elemental sulfur or as intermediates in sulfur cycling.
We quantify a large increase in the solubility of cinnabar
(HgS(s)) in the presence of elemental sulfur, particularly at
high pH. Based on our data and those of Paquette and
Helz, we propose that the complex, Hg(Sx)22-, dominates
the speciation of Hg(II) in such waters. At lower sulfide
concentrations and at high pH, the data are best fitted by
considering also the formation of the species HgSxOH-.
Octanol−water distribution (Dow) experiments confirm the
charged nature of the dominant mercury−polysulfide
complexes and imply the presence of a minor lipophilic
polysulfide complex, such as HgS5. The recently reported
decrease in Dow with increasing sulfide concentration
also occurs in the presence of polysulfides.