A STUDY OF THE METAL-BINDING ORGANIC CONSTITUENTS IN GREAT BAY SEDIMENTARY SYSTEMS
The fact that the concentration of copper in pore fluids exceeds the values predicted by simple solubility products has led to the suggestion that the copper is solubilized by the formation of copper-organic matter complexes. Previous attempts by other workers to form these complexes have utilized material that may not be representative of organics naturally present in sediments. Organic matter was isolated from anoxic sediments of Great Bay estuary in New Hampshire. Pore water, a double-deionized water extract, and an artificial seawater extract were used to isolate organic matter from the sediments. Dissolved organic carbon measurements revealed that the seawater and deionized water extractants removed considerably more material than the pore water isolation procedure. The process responsible for this increased amount of material was suggested to be abrasion of sediment particles during agitation, which resulted in the removal of organic coatings. Negligible effects were noted for temperature and microbial activity. Amicon ultrafiltration studies showed that, compared to pore water, the seawater and deionized water extracts had much more material with molecular weight greater than nominally 500 amu. Reversed-phase liquid chromatography results showed that organics in pore water were more polar than material in the other extracts. It was found that the deionized water removed more organic matter than seawater, but the latter removed organics that were more non-polar. Liquid chromatography in conjunction with atomic absorption spectrometry was employed with the Amicon ultrafiltration system to study copper binding to organic matter. Results indicated that copper complexed with non-polar fractions of all extracts. The quantity of copper retained by ultrafiltration, which was originally thought to be entirely bound to organics, was significantly larger than values obtained previously. It was felt that the discrepancy in binding capacities may be due to the retention of copper hydroxides by the Amicon system. Kinetic studies showed that copper complexation occurred within ten minutes after the addition of metal. EPR investigations revealed the presence of multiple copper(II) species in all samples. Binding studies with iron(II) revealed that this metal complexed with the same fractions of organic matter as did the copper. This indicated that the copper-binding material could bind other trace metals as well.
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