Effect of short-term resuspension events on the oxidation of cadmium, lead, and zinc sulfide phases in anoxic estuarine sediments

The stability of metal sulfides to oxidation in seawater was investigated in short-term (24 h) resuspension experiments using natural sediments and synthetic metal sulfide phases. Using acid volatile sulfide (AVS) measurements, ZnS, PbS, and CdS phases were shown to be resistant to oxidation. The AVS in resuspended, highly anoxic, contaminated sediments was rapidly oxidized with <6% remaining after 24 h. This was inconsistent with their high particulate lead and zinc content, which should stabilize sulfide against oxidation, suggesting that a large proportion of these metals (73-95%) were nonsulfide phases. When zinc was added to the sediments in a soluble ionic form, ZnS was quantitatively formed; however, lead and zinc solid phases, equilibrated with the sediments for several months, exhibited varying degrees of sulfide formation (10-76%). The results were consistent with the rapid formation of metal sulfide coatings that armor the particles against further sulfidization. It appears that reactive sulfide phases play a limited role in controlling the speciation of many metals entering sulfide-rich sedimentary environments. The initial form of the metals may be of greater importance.