Year

2009

Degree Name

Doctor of Philosophy

Department

School of Earth and Environmental Sciences

Abstract

Mercury was investigated in multiple environmental compartments of the remote oceanic island of Tutuila in southern Polynesia, to examine prevalent lines of thought on how Hg is distributed in the environment at the global scale. Research shows that Hg is highly mobile in the environment, and that the atmosphere is the principal reservoir from which Hg is ultimately deposited to aquatic systems. Since the poisonings at Minamata and Niigata fifty years ago, Hg is a highly studied element, and the neurotoxicity and accumulation of Hg in the biosphere at levels that pose risks to human health are well documented. The ubiquity of Hg in the global environment is not as well known. Direct experimental evidence for Hg in remote regions of the globe is rare, which hinders our understanding of the extent of Hg proliferation and weakens arguments that Hg is a contaminant of global concern. To assess the prevalence of Hg in the remote global environment, this study provided experimental evidence for Hg in rainfall and in coral reef biota, at a remote oceanic location thousands of kilometres from any Hg emission source. Other environmental compartments of soils, erosion materials, and reef sediments were investigated to examine Hg transport and distribution on this remote island where there was little previous data on the occurrence of Hg. Trace-elements field and analytical protocols were maintained throughout to ensure integrity of the data set. Speciation analysis was applied to most field samples to determine proportions of inorganic and organic Hg in environmental media, to examine potential sites of Hg methylation, and to accurately assess the prevalence of the highly toxic methylmercury compared to the relatively less toxic inorganic species. Mercury in Tutuila rainfall was the same, or slightly higher than, Hg in rainfall from comparably remote sites in the northern hemisphere, indicating that Hg is well-mixed and distributed globally via the atmosphere. Mercury residues in top-trophic fish from Tutuila reefs were far above allowable world health standards. Results for Hg in rainfall and predator fish support concerns for global proliferation of Hg, and are consistent with evidence that world-wide, Hg deposition has increased since the onset of industrialisation. Evaluation of transport and distribution of Hg on Tutuila strongly suggested that atmospheric wet deposition is a significant source of Hg to aquatic environments of this remote oceanic high island. Patterns of Hg transport and distribution indicated that the geologic base or regional volcanism were not likely to be significant sources of Hg on Tutuila. The potential for human habitation and a modern material economy as a non-point source of Hg to reef systems in remote global locations, due to Hg in consumer goods, vehicles, and building materials, was identified, though this appeared to be highly localised. Although Hg in rainfall and in top-trophic reef fish indicated that the flux of Hg to remote Tutuila is significant, Hg did not occur at levels above established regulatory or health standards in the other compartments investigated. Mercury in lower-trophic fish, reef sediments, and water column, at pristine sites do not yet appear to be significantly impacted by the globalisation of Hg. At the study site under the influence of anthropogenic disturbance, slightly elevated Hg was found in the water column, sediments, and fish, compared with pristine sites, but concentrations were still generally lower than established threshold levels of concern, except for a few benthic-feeding fish. Overall, study results supported that the proliferation of Hg via atmospheric processes is of global relevance. Notwithstanding the weight of mounting evidence, international consensus on worldwide controls of Hg use and emissions remains elusive. Timely global actions on controls for Hg emissions, the use of Hg in consumer goods, and controls on artisanal uses of Hg, appear warranted.

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