Pyritization of Trace Elements in Sediments of the Jiaozhou Bay, Qingdao, China

To determine the pyritization characteristics of reactive trace elements in different anoxic marine sediments, 4 undisturbed cores were sampled by a diver in May 2003. The chemical speciations of the trace elements versus depth were performed using modified sequential extraction procedures from Huerta-Diaz and Morse (1990).Resultsindicate that the degree of trace metal pyritization (DTMP) of most trace metals increased with increasing DOP. However, for As, Hg and Mo, the DTMP/DOP values were generally above the 1∶1 ratio line irrespective of the type of sedimentary environment involved, whereas the transition metals Cu, Zn, Cd, Cr, Co and Ni displayed a close to linear increase in DTMP with DOP and moderate incorporation into pyrite. Pb and Mn were also gradually incorporated into the pyrite phase but without reaching the DTMP levels exhibited by the above metals. These results are consistent with the chemical attributes of these different classes of trace elements. Availability of organic matter content and sedimentary rate are apparently important factors controlling the incorporation of Cu, Zn, Co, Ni, Cr, Cd and Mn into pyrite in Jiaozhou Bay. The authors conclude that special attention must be paid to during dredging activities to protect the pyrite fraction from being oxidized, especially where activity is carried out down to 20 cm in river delta sediments.