Speciation and Reactivity of Toxic Metals in Anoxic Sediments.

The objective of this research was to determine the influences of metal speciation on the kinetics of toxic metal solid phase transitions and interactions between solid phases and natural waters. Primary emphasis was on sulfidization-desulfidization reactions associated with near interfacial anoxic sediments. The approach utilized both the collection and analysis of natural samples and laboratory experiments. Samples from Chesapeake Bay were studied from organic matter rich and poor sites on a time-dependent basis in collaboration with the ONR-sponsored research of Drs. Donat and Burdige. A time-dependent field study was also conducted in Offatts Bayou, Texas, which is particularly well suited to our objectives because of the major redox changes that occur on a seasonal basis to the deeper basin waters. Sediments in these areas are more spatially heterogeneous in composition than anticipated and can also undergo seasonal variations in their trace metal chemistry. These results, coupled with those of the laboratory experiments, demonstrated the very dynamic nature of toxic metal speciation in sediments during early diagenesis. They point to the need to use considerable caution in the application of limited data bases and simple time-independent models for predictihg potential bioavailability of toxic metals.