Previous studies have shown that pteris vittata may accumulate substantial quantities of arsenic (As) in its shoots. The present study involved collecting soils from 21 contrasting sites from around England which had been contaminated with arsenic as result of a wide range of human activities and natural causes. These were used to examine growth and As uptake by P. vittata in a series of pot experiments. Initial experiments used soil from 10 fields on a large commercial sewage disposal estate located north east of Nottingham. These soils were highly organic and contained high concentrations of heavy metals (Zn, Cu, - Cd and Pb) but limited contamination with As. In some cases, the presence of high concentrations of heavy metals resulted in poor fern growth and limited removal of,As. With this information in mind, the remairjng 20 soils were collected from historically contaminated areas of England to provide a wide range of sources and severity of As contamination, a range of associated heavy metal concentrations and varying soil types. The results showed that the capacity of P. vittata to remove As from the soil may be severely limited by a range of influential factors in historically contaminated natural soils. Availability of the total As pool present was often very low, ranging between 1.7 and 16.9%. Indeed, soil solution concentrations were below the EU drinking water standard of 50 IJg L,l for all soils, with the Devon Great Consols humic soil having the highest solution As concentration of all soils examined, although this was nevertheless only 0.33 mg L-1 • This is believed to have occurred because the As was predominantly present as a constituent of minerals such as arsenopyrite in the mine spoil soils from the south west of England, or was strongly complexed within clay and iron oxides in the sewage treated soil. The highest percentage As removal was for two orchard soils (13.3 and 9.7%) in which the As present originated from pesticides containing chromated copper arsenate (CCA), a form of As known to be available to P. vittata, which had been applied over extended periods. The frequent co-occurrence of high concentrations of heavy metals in the study soils again adversely affected biomass production and As uptake by P. vittata. Factors such as low soil pH may also have reduced growth in some soils, as well as reducing the availability of As for uptake. High phosphate concentrations in some soils may have acted antagonistically to reduce As uptake, as demonstrated in an experiment in which phosphate Was added to three contrasting soils; low phosphate applications increased biomass and As uptake, whereas higher applications blocked As uptake. An uptake model was developed to predict the uptake of arsenic from field soils by P. vittata and facilitate assessment of the impact of a range of influential factors on the phytoremediation potential of this species. This model allowed the performance of P. vittata to be predicted under a variety of soil conditions and the time-frame required to remove the labile As pool to be estimated depending on whether this was replenished from other pools or not. The overall conclusions were that, although P. vittata may be unable to access and remove the extremely large non-labile pool of As in some soils, this species could provide a valuable tool for removing the labile and, hence potentially hazardous, fraction from contaminated soils.

This study investigates and examines the concentrations of Cd, Cr, Cu, Mn, Ni, Pb and Zn in the Manifold and Derwent floodplain soils, their distribution across the floodplains, transportation along the river channels, bioavailability to grazing grasses, and association with soil pH and organic matter. Six floodplains (2 from the Manifold catchment and 4 from the Derwent catchment) have been chosen as field sites, and 61 paired soil and grass samples have been collected and analysed.

As a consequence of the link of polycyclic aromatic hydrocarbons (PAHs) to adverse health effects in the human population, efforts should be made to reduce or even eliminate them wherever possible. The limited pore water and contaminant movement in tight soils poses problems for traditional soil cleansing processes, which makes remediation of sediments contaminated with persistent PAH one of the more intractable environmental problems. Iimovative, new techniques are required for cleaning up PAHs contaminated sediment. In recent years, the application of electrochemistry to environmental pollution treatment has been thoroughly investigated and electrochemical remediation is shown to be more suitable to the removal of organic pollutants from low-permeability soils and sediments, but problems with removing PAHs still exist because of their low aqueous solubility and high preferential sorption to soils and sediment. The promising results from the complete destruction of PAHs from wastewater permit to consideration of the electrochemical technology as an alternative to PAH contaminated sediment.

Land contaminated with heavy metals such as Cd and Zn can be remediated using a number of different approaches. Many of these strategies are very expensive (e. g. removal and disposal of the soil, covering the soil with uncontaminated soil, extraction with acids or chelates) whilst others provide only short term solutions (e. g. reduction of metal bioavailability by liming or adding organic matter). An alternative approach is the use of hyperaccumulator plants to remove the heavy metals. Phytoremediation, as this process is known, is an attractive method for remediation of contaminated land since it is relatively inexpensive and has the potential through the appropriate selection of plant species to be effective. However, there are many factors that need to be considered for phytoremediation, perhaps the most important is the bioavailability of metals from different component or functional pools within the soil. The bioavailability of heavy metals has been assessed through a variety of approaches, with extraction using chemicals being the most common. Another approach is the isotopic exchange method which has been regularly used for estimating the bioavailable P in soil. This technique relies on the assumption that isotopically exchangeable P is available to a growing plant and yields the so called E-value for a soil. In past studies, particularly in highly P fixing soils, the E-value has been shown to overestimate the soil available P. To overcome this a second procedure based on the measurement of isotope uptake by a plant growing on a spiked soil has been proposed and yields the so called L-value. As well as P, this method has been applied to Ni and only very recently to Cd and Zn using radioisotopes. In the present work, stable isotopes are used for the first time to measure the Cd and Zn available for plant uptake using isotopic exchange principles based on the E and L-values using a contaminated (Great Billings) and a non-contaminated (Countesswells) soil. These values were compared to Cd and Zn bioavailable pool determined using more traditional chemical extraction methods (5 extractants). Of the chemical extractants O. 1M NaNO3,0.01M CaC12,0.5M NaOH, 0.43M CH3COOH and 0.05M EDTA (pH=7.0), the highest amounts of Cd and Zn were extracted by CH3COOH and EDTA. In addition, these two extractants extracted the Cd and Zn amounts close to the Lvalues determined using the isotopic exchange method. An isotope dilution thermal ionisation mass spectrometric (ID-TIMS) method for an accurate and precise determination of Cd and Zn in soils and plants via isotope ratio measurements was developed. This was then validated by quantifying Cd and Zn in soils, plant and animal Certified Reference Materials digested by three different methods. In addition, there was no significant difference between open tube aqua regia, closed microwave bombs and HF digestion procedures which was related to the accurate definitive method of ID. Also, an approach for the sequential isotopic analysis of Cd and Zn on the same filament within the TIMS was developed, allowing more rapid analysis and reducing running time on the instrument. Cd and Zn dual analysis on the same filament proved to be successful and produced results comparable to single analysis. Isotopic ratios of Cd and Zn were used to determine both E and L-values in two soils. Although the E-value determined (in soil solution system) was higher than the L-value (using plants) for the 2 soils tested, the 2 values were generally within agreement. L-values were determined using 3 different plant species, the hyperaccumulator alpine penny cress (T. caerulescens), dandelion (T. officinale) and spring barley (H. vulgare). The available pool of Cd and Zn for plant uptake was determined to be the same for the 3 different plant species examined although plant species had markedly different abilities to uptake metals. In addition to using the plant species to estimate the bioavailable metals, the potential of these plant species for phytoremediation of Cd and Zn was also evaluated. Among the plants tested, only T caerulescens proved to be a Cd hyperaccumulator. However, T. officinale removed an equivalent amount of Cd and more of Zn than the other two plant species; although its Cd and Zn content was not sufficiently high to be considered as a hyperaccumulator. Based on this, dandelion has a good potential for phytoremediation, which lead to an attempt to study Cd and Zn uptake in the rhizosphere of dandelion roots. However, the experiment which used soil between glass plates did not show a clear depletion in Cd and Zn concentrations towards the root surface or if metal concentration was related to the amount of root present in any soil section.

Mining and smelting activities are a major source of arsenic and antimony contamination in the environment. These contaminants have been neglected when such sites are investigated, hence there is a need for their environmental impacts to be assessed. An understanding of bioavailability underpins any such assessment. This measure can only be inferred from traditional chemical techniques and the use of novel bioavailability surrogate measures. This study used a suite of three lux-marked bacterial biosensors as complimentary tools to assess metalloid bioavailability and toxicity in soils contaminated by mining and smelting. This included two constitutively marked metabolic sensors which exhibit inhibition responses to toxicity, and an ars inducible biosensor which reports on metalloid bioavailability. The biosensor responses were first characterised using standard solutions, confirming that they exhibit dose dependent responses which indicate the speciation of bioavailable forms and account for contaminant interactions. The techniques were then applied to assessing a range of environmental samples from sites around the UK, and in Chile, contaminated by either historic or contemporary mining and smelting activities. The results indicated that the metabolic biosensors are powerful tools for assessing the toxicity of bioavailable contaminants while the ars inducible biosensor reports on arsenite bioavailability. The speciation of antimony in the environmental samples resulted in low bioavailable levels, and therefore it played no significant role in determining the biosensor responses. Metal co-contaminants tended to mask the effect of arsenic on the biosensor responses and cation exchange treatment proved a successful technique to mitigate this problem. This work also highlighted the impact of extraction methodology on the chemical composition of soil water and therefore the results obtained.

The contamination of soils, particularly by organic pollutants at industrial sites, has required the development of accurate methods of analysis to determine the nature and concentration of the pollutants, thereby allowing appropriate risk assessments and remedial strategies to be implemented. Conventional methods for site assessment generally entail extensive sampling across the whole site, with subsequent sample despatch to a centralised laboratory, where complex, solvent intensive procedures, such as Soxhlet extraction and GC-MS analyses are performed. Since such processes are laborious, expensive, and time-consuming, there has been an increasing demand for rapid and reliable field-based analytical methods for the low-cost and efficient extraction and analysis of organic pollutants from contaminated sites. This thesis describes the development of a field-compatible supercritical fluid extraction (SFE) device and method for extraction of organic contaminants from soil. SFE was chosen due to its reported high extraction efficiency, selectivity and environmentally friendly nature due to the usage of supercritical fluids as opposed to liquid solvents. A compact 72(W)xS7(D)xSO(H) cm, easily-transportable and user-friendly device was developed, based on the use of a reciprocating pump and back pressure regulator system. The optimised method yielded an average extraction recovery of 80% for total polycyclic aromatic hydrocarbons (PABs) when compared to the well-validated laboratory-based Soxhlet extraction method. Tests were performed on a range of natural samples with varying water content (0- 32% w/w) without any sample pre-treatment. In comparison, the only commercially available competing field method, based on solvent shake extraction, yielded recovery values of 20-70% coupled with poor precision. The thesis then describes the optimisation of a field applicable method for analysis of the SFE extracts, based on enzyme linked immunosorbent assays (ELISAs), a method offering speed, low cost and low solvent consumption. Available as a test kit, it was readily amenable to on-site usage requiring only simple equipment. Assay optimisation using an EPA sanctioned P AH immunoassay test kit demonstrated that the kit could function in methanolic SFE extracts diluted in buffer, hence allowing the direct analysis of total P ABs in SFE extracts with minimum sample preparation. Cross-reactivity from parent compounds was found to be an issue for the generation of quantitative data. Nevertheless, the method served as a reliable semi-quantitative technique for rapid screening of P AH levels in the SFE extracts of natural samples obtained from field-based tests. Poor performance of the solvent-shake extraction method linked to immunoassay further vindicated usage of the newly developed field-based SFEI immunoassay method. The thesis concludes by reporting on the successful field-based trials of the coupled SFE/immunoassay method. The SFE system shows promise as a valid tool for the rapid and efficient on-site monitoring of organic contaminants in soil matrices, providing an innovative and alternative approach to the commonly deployed solvent shake extraction method. The combined field-based SFElimmunoassay method is of benefit for the rapid low cost assessment of site contamination, allowing site owners and consultants alike to make rapid and informed decisions regarding site characterisation, monitoring and remediation without recourse to expensive and time consuming laboratory analyses.

The contamination of soil, groundwater and ultimately potable water sources, is a quantifiable risk associated with the sub-surface release of cable oil into the environment. This research has provided the National Grid Transco (NGT) with an evaluation of the feasibility of biological systems as a means of re mediating soil and groundwater contaminated with cable oil. This has been achieved through treatability studies undertaken at three levels of process sophistication; laboratory-scales micro-cosms, a pilot-study to develop full-scale design criteria and a full-scale pilot-study under semi-controlled field conditions. The full-scale pilot-scale study was undertaken together with a simple temporal and spatial model of oil distribution through two contrasting soil blocks. Experimental data obtained in this thesis has shown, for the first time that anaerobic degradation processes are able to offer an effective alternative to aerobic in situ bioremediation for cable oil. Each level of process in this three-phase study has demonstrated anaerobic soil organisms capable of survival on cable oil and mineral salts ~lone. Sulphate reducing micro-organisms are also suggested as playing an important role in the degradation process. Biodegradation of the cable oil of up to 41 % was achieved, in some cases reducing the concentration to below 50ppm threshold required by the Dutch Intervention Values (1994). The study of pollutant migration found that the temporal and spatial distribution of cable oil is specific to soil type and is influenced by the soil structure, particle size distribution and water suction potential. The extent of oil migration in both soils is a function of the volume of cable oil present and is time dependent. The significant outcome of this work is that prior to this study, there have been no reports of higher alkylbenzenes being degraded anaerobically. Consequently, monitored natural attenuation may now be considered by NGT as a feasible remediation option under certain conditions, providing an acceptable, non-intrusive technique for sites contaminated with cable oil.

The intended endpoint for Magnox Electric plc's reactor decommissioning strategy is site clearance and de-licensing, which may require remediation of any 137CS contaminated land on these sites. Phytoextraction might provide a practical and environmentally acceptable method of reducing radioactive waste volumes for disposal. Field trials conducted at Bradwell Nuclear Power Station, Essex, UK and experiments in controlled conditions, using Beta vulgaris, showed that soil-to-plant transfer factors increase as soil 137CS activity concentration decreases, implying that constant 137CS removal rates are possible during site remediation. It was shown that 133CS might be responsible for this effect. Short time-interval multiple croppings were not found to increase the rate of 137 Cs removal. For successful implementation of 137CS phytoextraction plant species need to be identified that can accumulate higher concentrations of 137 Cs than those identified at present. The large variation in 137CS uptake between species tested here suggests that extensive species screening programmes will be required. Soil amendments appear essential to the phytoextraction of aged 137CS and NH/, 133CS+ and K+ were shown to be capable of extracting up to 25 % of the 137CS from soil at a field site. In a 14 month simulated 137CS phytoextraction trial in controlled conditions, over 60 % of 137CS applied to an organic soil was removed using a 20 mg kg-1 CsCl soil amendment suggesting that, where 137CS is sufficiently plant available, phytoextraction might be a useful soil remediation technology. In a desk based BPEO study, composting was identified as the most appropriate option for conditioning the biomass arising from 137 Cs phytoextraction allowing it to be stored at the UK's LLW repository at Drigg, Cumbria. It was concluded that the risk associated with soil amendments of 137 Cs leaching off sites and the poor plant growth conditions likely to be found at field sites would require the use of a greenhouse with soil contained in lysimeters during phytoextraction.

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