EFFECT OF SHORT-TERM RESUSPENSION EVENTS ON TRACE-METAL SPECIATION INPOLLUTED ANOXIC SEDIMENTS

The effects of the short-term resuspension of a contaminated anoxic es tuarine sediment on solid-phase metal speciation have been studied. Pr eliminary experiments investigated the oxidation rates of model metal sulfide phases to provide mechanistic information for interpreting the observations on the natural sediment. FeS and MnS model phases were p articularly labile and oxidized rapidly in aerated waters. In contrast , CdS, CuS, PbS, and ZnS model phases were kinetically stable over per iods of several hours. The oxidation rate of free sulfide (HS-) was si gnificantly slower than that of FeS and MnS. Upon sediment resuspensio n, the rapid decrease in acid volatile sulfide (AVS) could be accounte d for by the oxidation of iron monosulfide phases. Over prolonged resu spension periods (> 300 min), AVS decreased to values lower than the s imultaneously extracted metals [SEM = Sigma Cd, Cu, Ni, Pb, Zn (1 M HC l extraction, 30 min)] concentration, indicating that a significant fr action of trace metal sulfide phases may he oxidized during resuspensi on events. During 8-h sediment resuspension experiments, SEM(Cu) incre ased from 0.1 to ca. 2 mu mol/g while the SEM measured for the other m etals remained constant. The increase in SEM(Cu) was shown to be an ar tifact of the AVS/SEM analytical procedure. Fe(OH)(3), formed through the oxidation of FeS, dissolved upon acidification to produce Fe3+(aq) , which subsequently oxidized acid-insoluble copper sulfide mineral ph ases in the sediment. The implications of these observations for natur al systems and for the assessment of metal toxicity using AVS/SEM proc edures are discussed.