Date of Award

Winter 2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Committee Director

Gregory A. Cutter

Committee Member

David J. Burdige

Committee Member

Peter N. Sedwick

Abstract

Toxic trace elements such as cadmium, lead, chromium, and arsenic released by human activities can accumulate in marine and estuarine sediments, where these metals are often sequestered until local environmental changes (e.g., redox, salinity, and/or pH) allow these elements to be reintroduced into the food web. In order to assess the extent of toxic trace element contamination in sediment, numerous leaching schemes have been developed that separate sediment-bound trace metals into operationally defined geochemical phases. These "phase speciation" leaching schemes are typically designed with the purpose of being used on either oxic or anoxic sediments. However, natural sediments often contain prominent redox boundaries; therefore, it is useful to develop a single phase speciation leaching scheme which can be used on both oxic and anoxic sediments.

A six step leaching scheme was developed in order to separate sediment-bound trace elements into five operationally defined phases: exchangeable, oxide, acid volatile sulfide (AVS), organic, and pyrite. The efficacy of five of the six leaching steps (oxide, AVS, organic #1 and #2, and pyrite) was evaluated using standard reference sediments (NIST 2702 and BCR-701) and actual sediment samples. Overall, the results show that the six step leaching process compared well with other frequently utilized phase speciation leaching schemes ("Tessier" and "optimized BCR"). With the exception of some surface sediment oxides carrying over into the AVS phase, the leach AVS and pyrite results compared well with H2S generation sediment sulfide analysis methods. The organic phase extractions were about three times more effective (∼60% removal efficiency) at removing labile organic material (e.g., proteins and humic and fulvic acids) in sediment than refractory organics (e.g., protokerogens) (∼20% removal efficiency). The six step leach method was applied to bulk sediments obtained from three estuaries with differing geochemical environments (salinity and sediment C and S concentrations). The sediment phase speciation results for the major (Fe, Mn, and Ca) and trace metals (Cd, Pb, Cr, and As) of interest are similar to those reported by other workers for similar environments, with the majority of the trace metals being located in the oxide and organic phases.

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DOI

10.25777/wbpd-pj88

ISBN

9781267837035

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