Search

There is growing global concern about the impact of microplastics on the marine environment, with evidence emerging that plastic pellets can be a vector for potentially toxic elements (PTE). In this thesis, PTE content was first investigated in petroleum based (polyethylene, polypropylene and polyethylene terephthalate) and bio-based (poly(hydroxybutyrate-co-hydroxyvalerate)) virgin plastic pellets. Various elements associated with plastics'™ manufacture were detected. Next, sorption experiments were conducted to assess the capacity of virgin and laboratory-weathered pellets to take up As, Cd, Cr and Pb from controlled media of deionised, fresh and artificial seawater, with analysis by ICP-MS (Agilent 7700x instrument). All types of plastics showed the ability to take up the PTE studied and the total amounts were in the order Pb > As > Cd > Cr when single element solutions were studied and Pb > Cd > Cr > As from a multi-element solution. It was found that weathered pellets took up greater amounts of PTE than virgin ones. The surface of virgin, laboratory-weathered and beached pellets collected from Kuwait and Scotland were then imaged and their chemical composition determined using a scanning electron microscope with energy-dispersive EDS analyser (JEOL JSM-6010LA). Analysis revealed changes in pellet morphology following weathering. Elements detected were associated with aspects of plastic production or taken up from the ambient environment. Beached pellets were identified by ATR-€“FTIR as predominantly polyethylene and polypropylene. When examples were subjected to sequential cold acid digestion followed by microwave extraction, larger amount of PTE were released by the cold digestion step, indicating the analytes were relatively weakly bound. Samples from Kuwait released higher amounts of PTE than samples from Scotland. In vitro bioaccessibility of PTE to simulated fish stomach was estimated using two methods, a modified SBET and a 0.1 M HCl extraction. Lead was found to be the most bioaccessible of the PTE studied.

Bisphenol A (BPA) is a high production volume chemical that is used widely in the production of polycarbonate plastics, epoxy resins, flexible polyvinyl chloride (PVC) plastics, and thermal paper. It is an endocrine disrupting chemical (EDC) and is considered as an emerging pollutant in the marine environment due mainly to plastic litter. This study developed analytical methodology for the measurement of BPA in marine waters and sediments so that ambient concentrations and the partition coefficients that influence environmental fate and toxicity of BPA in the marine environment could be determined. The experimental partition coefficients (octanol-water partition coefficient (Kow), water solubility (Sw), and sorption capacity (Kd and Koc)) of BPA were affected by water conditions (salinity, pH and temperature). The sorptive process was not affected by only water conditions, but also solid properties (organic carbon (OC) and minerals (silica and calcium)) in the solid samples. The calculation equations to estimate each partition coefficient studied at any specific water conditions were also provided. These equations demonstrate the use of simple and inexpensive proxies (e.g., salinity, pH and temperature) along with the modelling programme EPI Suite™ to assess environmental impacts associated with these partition coefficients. A climate change scenario was used as a case study to illustrate the effects of changing environmental conditions on the behaviour of BPA in the marine environment. The concentrations of BPA were analysed using high performance liquid chromatography (HPLC). The extraction and pre-treatment methods to measure BPA in marine samples (seawater and sediments) were developed. For seawater, the extraction methods studied were conventional solid-phase extraction (SPE), dispersive liquid-liquid microextraction (DLLME), and molecularly imprinted solid-phase extraction (MISPE). The accelerated solvent extraction (ASE) was used to extract BPA from the marine sediment prior to clean-up of the sample with MISPE cartridges, and analysis with HPLC.

The ability to find, mine, extract and smelt metallic ores has been central to technological development throughout history. Demand for metals is projected to increase in the coming decades and the supply of metals such as lithium, copper, indium, neodymium and tantalum have become strategically important in the manufacture of energy-efficient 'green' products and renewable energy generators. However, mining is accompanied by an environmental cost; mining accounts for almost 34% of total worldwide solid waste generated. Historically poor disposal practices in the industry have created a legacy of tailings piles, polluted rivers and health impacts that have the potential to impact surface water quality for centuries after the cessation of mining, primarily through the continued interaction of meteoric and groundwater with mine waste and mill tailings dumped on-site. Arsenic is a toxic metalloid that is commonly present in trace to minor amounts in ores of gold, mercury, lead and zinc as the mineral arsenopyrite (FeAsS) or as substitutions within other sulphide minerals. Consequently, arsenic (As), a known carcinogen, is a contaminant of concern in many mining districts and a useful indicator of water quality. Arsenic exists in natural waters as both As(III) and As(V) oxyanions, whose relative abundance is controlled by pH and redox conditions. The toxicity and mobility of dissolved As in water draining mine tailings is directly related to the inorganic arsenic species present. However, at many sites arsenic contamination of surface water is accompanied by other toxic metals, which are released with arsenic from the weathering and dissolution of sulphide minerals. To investigate the effect of other metal species, on arsenic speciation, field measurements of As(III) /As(V) ratios in surface water were made at selected historical mining sites with elevated levels of dissolved arsenic and of one or more toxic metals. Data are presented from nine contaminated mine sites in Scotland, Alaska and Colombia, representing different types of ore deposits and ore processing sites that have elevated As signatures. At these sites, antimony, mercury or cadmium is present as a secondary contaminant in surface water at levels near or above the USEPA MCL. In addition to arsenic species separation, major and trace elements, vii anions and stable isotopes were determined at each sample point, along with a full suite of in-situ water parameters. Local site variables, including bedrock geology, ore mineralogy, groundwater geochemistry and soil chemistry, contribute to the complexity of As speciation at each study location. It was determined that As(III) is the dominant species in water draining mine adits and tailing piles, instead of the more thermodynamically favoured As(V) species. As(III) is more mobile than As(V) and persists up to 300 metres downstream, before transformation to the more oxidised form. Better understanding of As mobility has the potential to improve remediation strategies at other contaminated mine sites.