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 i n short-term (24 h) resuspension experiments using natural sediments and sy nthetic metal sulfide phases. Using acid volatile sulfide (AVS) measurement s, ZnS, PbS, and CdS phases were shown to be resistant to oxidation. The AV S in resuspended, highly anoxic, contaminated sediments was rapidly oxidize d with <6% remaining after 24 h. This was inconsistent with their high part iculate lead and zinc content, which should stabilize sulfide against oxida tion, suggesting that a large proportion of these metals (73-95%) were nons ulfide phases. When zinc was added to the sediments in a soluble ionic form , ZnS was quantitatively formed; however, lead and zinc solid phases, equil ibrated with the sediments for several months, exhibited varying degrees of sulfide formation (10-76%). The results were consistent with the rapid for mation of metal sulfide coatings that armor the particles against further s ulfidization. It appears that reactive sulfide phases play a limited role i n controlling the speciation of many metals entering sulfide-rich sedimenta ry environments. The initial form of the metals may be of greater importanc e.