Doctor of Philosophy (PhD)
School of Earth & Environmental Sciences - Faculty of Science
Tarin, Pattanan, Distribution, speciation and geochemistry of selenium in contaminated marine sediments - Port Kembla Harbour, NSW, Australia, PhD thesis, School of Earth & Environmental Sciences, University of Wollongong, 2006. http://ro.uow.edu.au/theses/714
Selenium (Se) is an element of concern in Port Kembla Harbour as it was the only element found in harbour fish tissues in the mid-1990s at concentrations that exceeded the Australia New Zealand Food Authority Maximum Residue Limit. This thesis investigated the distribution, speciation, binding phases and geochemical behaviour of selenium in Port Kembla Harbour sediments, which potentially receive selenium pollution from local metal processing and smelting and coal industries. Sedimentary selenium is a potential selenium source for fish and organisms via benthic food chain transfer. Grab surface sediments from 23 sites around the harbour and a total of 14 sediment cores were collected from the contaminated Red Beach area (during 2003-2006) and analysed for selenium concentrations by HG-AAS and also for sediment parameters including grain size composition, pH, redox potential, other trace metals, porewater composition and sediment macrocomponents. Two sequential extraction procedures were used to fractionate the solid-phase selenium into soluble and adsorbed, carbonate, metal oxyhydroxide, organically bound, elemental, organic matter and sulfide, and residual selenium fractions. The selenium behaviour in the different geochemical phases was examined in association with the measured sediment parameters. The selenium concentrations in surface sediments from most harbour sites were low (below 3 ug/g) except those in sediments from the Red Beach area (up to 9.38 ug/g), which is in close proximity to a local copper refinery. Selenium concentrations in the Red Beach sediment cores ranged from 6 to 1735 ug/g, depending on depth and grain size, with peak selenium concentrations observed at 6-10 cm and at 14-16 cm depths. The highest selenium concentration (1735 ug/g), found in the less than 63 um Red Beach sediments, was 100 times higher than the highest sedimentary selenium concentration previously reported in Australia. The sedimentary selenium was concentrated in fine (less than 63 um) grains that are easily mobile. Selenium was correlated mainly with Pb, Cu and Zn in the less than 250 um fraction of the surface sediments and in the less than 63 um fraction of the sediment cores, indicating association from both original ore sources and through post-depositional transformation. The sediment 210Pb dating estimated the sedimentation rate of Red Beach cores to be 0.55 u 0.03 cm/year. Sediment 210Pb dating provided an indication that the deeper sediments were not disturbed and high selenium concentrations in the sediment cores were a result of historical selenium input potentially from a copper smelter. The solid-phase selenium in the Red Beach sediment cores was present mainly as elemental selenium. High proportions of the selenium were also bound to the organic matter in the upper 10 cm region and associated with the residual fraction below 10 cm. Selenite was the major selenium species found in the organically bound selenium fraction. Small proportions of the solid-phase selenium were in soluble and adsorbed fractions, with peak concentrations in the below 10 cm depth region. Minimal amounts of selenium were found to associate with iron-manganese oxyhydroxides and carbonate minerals in the sediment. The Red Beach sediment cores were oxic in the top 2 cm and anoxic below 2 cm depths. The top 2 cm oxic sediment contained low solid-phase selenium concentrations and low porewater selenium concentrations. The anoxic 2-10 cm core region contained the peak solid-phase selenium concentrations but with low porewater selenium concentrations. This layer was enriched with the organic matter, AVS, organically bound selenium, and elemental selenium species, indicating a strong link between organic matter decay processes and the reduction of sulfate and selenium. The below 10 cm-anoxic sediments contained moderate solid-phase selenium, peak porewater selenium and high soluble and adsorbed selenium concentrations, and stable pyritic sulfur species. Selenium was observed to become associated with the residual fraction at the expense of the organically bound and the elemental selenium in this region. This below 10 cm region contained lower proportions of copper, lead and zinc in the residual fraction but significant amounts in the organically bound fractions. The solid-phase selenium correlated with the solid-phase sulfur through the association of their reduced forms: elemental selenium, pyrite and possibly as pyritic selenium. Copper was the only major element that co-extracted with elemental selenium. The reduced selenium forms (elemental and residual) correlated significantly with Cu, Pb and Zn, suggesting possible formation of independent CuSe, PbSe and ZnSe minerals in the sediment. Redox potential, sedimentation rate, organic matter components, sulfur and transition elements are concluded to be the important factors affecting the selenium geochemical behaviour in Red Beach cores.
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