Chemical binding of heavy metals in anoxic river sediments

Acid volatile sulfides (AVS) in sediments are available for binding with di valent cationic metals through the formation of insoluble metal-sulfide com plexes, thereby controlling the metal bioavailability and subsequent toxici ty to benthic biocommunities. However, when the molar concentrations of sim ultaneously extracted metals (SEM) were greater than AVS, the unexpectedly low or nondetectable levels of metal in pore water could also be found. Thu s, except AVS. additional binding, phases in sediments were supposed to pro vide the binding sites for SEM. The aims of this study are to realize the spatial distribution of AVS, SEM, and other binding phases of heavy metals in anoxic sediments of the Ell-Re n river and to elucidate what may be the main additional binding phases exc ept AVS in the anoxic river sediments. By comparing the spatial distributio ns or SEM,. AVS ratio with various binding phases in extremely anoxic sedim ents (redox potential was between -115 and -208 mV), both organic matter an d carbonates could be considered to be the main additional binding phases o f SEM other than AVS. In addition. AVS appeared to have the priority to bin d with SEM. By comparing the binding phases of heavy metals before and afte r AVS extraction, it could be found that Fe-oxides could also be considered to be the main additional binding phase associated with Zn in slightly ano xic sediments (redox potential was between -50 and -130 mV), while organic matter with Cu being the next. (C) 2001 Elsevier Science Ltd. All rights re served.