Description
Mercury (Hg) is a ubiquitous heavy metal with a complex environmental fate, which is dictated by the element’s intrinsic properties as well as the characteristics of the surrounding environment. Due to its high propensity to bioaccumulate and known neurotoxic effects, Hg remains a contaminant of concern monitored in a range of environmental matrices and associated biological receptors. The here presented work addressed knowledge gaps pertaining to Hg behaviour in the marine environment including the sediment-water interface, legacy pollution, ecotoxicology, and large-scale environmental fate. The individual chapters investigated the lability, bioavailability, toxicity and bioaccumulation of Hg, with the aim to offer novel empirical insights.Chapter 1 quantitatively explored the interactions of Hg with pristine marine sedi- ments through tracer tests. The results confirmed the assumption, based on Hg behaviour in freshwater environments, that organic matter significantly impacts Hg ad- sorption. Further experiments also suggested that an increase in porosity may result in an increased physical retention of Hg contamination in sediments.
The lability of legacy Hg contamination was explored in Chapter 2, which comple- mented an offshore benthic survey conducted with the Scottish Marine Directorate around the sites of two former oil platforms. This study used DGT passive samplers, and a new thermofractionation method, to evaluate the environmental mobility of the discharged Hg compounds. While total concentrations of Hg in impacted sediments were elevated (in comparison with reference sites), both the DGT and thermofrac- tionation analyses suggested very limited lability. The development of Hg-specific DGTs and their various areas of application over the last 20 years were further ex- plored in Chapter 3.
In aiming to bridge the gap between the chemically inferred bioavailability and biolog- ical effects, Chapter 4 used Artemia to assess the impact of organic matter coexposure on Hg toxicity. Artemia nauplii and unhatched cysts were exposed to Hg together with different types and concentrations of dissolved organic matter (DOM). The results indicated that coexposure may significantly increase bioaccumulation and subsequent toxicity for filter feeding organisms such as Artemia. Unhatched cysts were unaffected by DOM coexposure.
How high trophic marine animals handle chronic exposure to environmental Hg was investigated in Chapter 5, by analysing tissue samples from a stranded bottlenose dolphin. Marine mammals are known to detoxify Hg through biocrystallisation of mercury selenide (HgSe), which is presumed to be biochemically inert. Using scanning electron microscopy, the first high resolution three-dimensional images of these crys- tals were captured, with the largest measuring ~5 μm.
The systemic movement of Hg in aquatic environments was explored in Chapter 6 by employing an existing fugacity-based model to simulate the mercury dynamics in the Sea of Azov. The computed results indicated large influxes through riverine inflow as well as the atmospheric Hg concentration ~6 ng/m3, which reflected the legacy pollution by heavy industry and its potentially adverse effects on the local population and ecosystem.
The results of this work highlighted the interconnectivity and ubiquity of Hg, identified hotspots of contamination, and appraised their individual impact on larger ecosystems. Further, the employed techniques showcased the multifaceted nature and interdisciplinarity of environmental research.
| Period | 08 Aug 2024 |
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| Examinee | Christoph Gade |
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| Degree of Recognition | National |