Chemical Availability of Cadmium in Mississippi River Sediment1
- Rashid A. Khalid,
- Robert P. Gambrell and
- William H. Patrick2
There is concern that changes in the physicochemical conditions occurring during dredging and disposal of polluted sediments may increase chemical mobility and hence bioavailability of sediment-bound toxicants such as Cd. The objectives of this research were to study the chemical transformations of Cd in freshwater sediment as affected by pH and redox potential under controlled laboratory conditions and predict Cd behavior during dredging and disposal of Cd-contaminated sediments.
Mississippi River sediment suspensions were incubated at four redox potential levels (−150, +50, +250, and +500 mV) at each of three pH levels (5.0, 6.5, and 8.0) and spiked with 0.2 µCi carrier-free 109Cd/g solids. Sediment suspensions were sequentially extracted for easily mobile and potentially available 109Cd fractions. Essentially all of 109Cd extracted from alkaline sediment suspensions was associated with potentially available chelated, insoluble organic-bound and reducible fractions and was not affected by changes in oxidation-reduction conditions. A change from alkaline to acidic pH under moderately oxidized to well-oxidized conditions resulted in 109Cd transformations from potentially available organic forms to more mobile and readily available dissolved and exchangeable forms. This could create potential hazards of disposal of Cd-contaminated dredged sediments due to enhanced availability and leaching of Cd as affected by altered physicochemical environments.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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