Tobacco was transformed with the nitroreductase (<i>nfsI</i>) gene from<i> Enterobacter cloacae. </i>Nitroreductase (NR) was proposed to reduce TNT to classic type I nitroreductase products and its activity was found to be induced in the presence of TNT. The aim of this study was to characterize these plants with respect to their ability to tolerate, take up and transform TNT from their environment. The product/s of TNT reduction by nitroreductase has not been characterized prior to this study but were analyzed here and found to be 4-hydroxylamino-2,6-dinitrotoluene (4-HADNT). Semi-quantitative RT-PCR analysis of transgenic lines indicated that higher <i>nfsI </i>transcript expression was correlated with greater tolerance to TNT at germination. The most TNT-tolerant transgenic line was established and chosen for further characterization in sterile, aqueous conditions and in soil contaminated with TNT. Vegetative growth was suppressed in wild type plants at 23mg/L TNT whereas transgenic plants were found to remove all TNT from a concentration of 113mg/L TNT and were found to gain biomass at this concentration. This concentration of TNT is above the aqueous solubility limit of TNT and would be presumably be the highest concentration plants would encounter in the field. Following uptake, transgenic seedlings transformed TNT predominantly to 4-HADNT. This product was only detected in the tissue and growth medium of transgenic plants and its high levels appeared to correlate with enhanced tolerance and transformation of TNT. The wild type seedlings produced both isomers of the further reduced product of TNT, the amino-dinitrotoluene (2-ADNT and 4-ADNT). This may be significant, as the 2 isomer of TNT reduced products have been found to be more toxic to other organisms. The phytodetoxification of TNT was also studied with both plant lines in TNT-contaminated soil. The transgenic seedlings were found to tolerate TNT significantly better than the wild type plants at germination and during vegetative growth.

In this work a series of 11 <I>Rhodococcus</I> strains which mineralise the alkylphenone, 3-(2-hydroxyphenyl) propionic acid (OHP) were isolated from a larger strain collection previously isolated from a polluted gasworks in Newcastle, UK. These OHP catabolic pathways had not been subjected to direct selection during strain isolation and therefore are likely to represent the 'native' state of genes within the <I>Rhodococcus</I> genome. To investigate the <I>Rhodococcus</I> population structure, a phylogenetic analysis of the 11 <I>ohp</I> isolates of <I>Rhodococcus</I> and <I>Rhodococcus</I> sp. V49 from pristine soil was made and a biochemical characterisation of their OHP pathways was carried out. The results show a range in the mode of expression of analogous/homologous gene clusters in this group of closely related soil bacteria. The taxonomic analysis demonstrates that of the strains isolated from a polluted gasworks in Newcastle, all 11 are independent isolates of <I>Rhodococcus</I>, including the species <I>R. ruber, R. erythropolis and R. opacus</I>, although they originate from a narrow taxonomic radius. <I>Rhodococcus</I> sp. strain V49 which was isolated from pristine soil in Canada, is also a member of this phylogenetic group which encompasses the 13 described species of <I>Rhodococcus. Rhodococcus</I> sp. V49 is used as a model system in this work for examining <I>ohp</I> catabolic genes, as it has been the subject of previous work. These data argue that the soil environment is finely divided and supports a diverse array of closely related but distinct species from numerous clones. <I>Rhodococcus</I> strain RC291 appeared to exhibit catabolite repression during the initial characterisation of the OHP catabolic pathways.

Nuclear Magnetic Resonance (NMR) imaging has been applied to multiphase systems in order to gain insight into both the usefulness of NMR as a quantitative tool and the mass-transfer processes which govern the rate of removal of nonaqueous phase liquid (NAPL) contaminants from groundwater. A new approach to chemically resolved imaging is proposed. It is shown that by acquiring an image of a system with two different gradients, a system composed of two overlapping peaks can be resolved by employing a deconvolution algorithm based upon CLEAN. This method provides better chemical resolution for systems of overlapping peaks than standard chemical select methods, without the need of resorting to chemical shift imaging. Further extension of NMR imaging has been made through the introduction of a segmentation algorithm for the analysis of three-dimensional images. This method provides an unambiguous partitioning of the void space and may be used to obtain information about the geometry and topology of the system. The application of NMR to specific questions in the field of NAPL research has provided new and useful findings. One-dimensional NMR has been used to obtain saturation profiles during the course of dissolution of NAPL. The results were compared to six different models appearing in the literature. It was found that a conceptual model, the pore diffusion model, provided the best agreement with experimental data. However, none of the models were accurate enough to be predictive. The size and shape of NAPL ganglia are studied during the course of dissolution for the first time via three-dimensional imaging of a model NAPL system.

This thesis takes a multi-scale approach to addressing the issue of air quality and human health impacts attributable to aviation. In particular, processes at the exhaust plume (~ 1 km), local (~ 10 km), regional (~ 1000 km) and global (~ 10 000 km) scale are addressed. At the plume scale, a three-dimensional integral plume model is developed and applied to elucidate aspects of near-field dispersion processes. A new method for approximating dispersion at the local scale is developed, which allows the air quality in the vicinity of large numbers of airports to be rapidly estimated. At the regional and global scales, an atmospheric chemistry-transport model is adapted to understand the intercontinental transport of aircraft pollution. This thesis includes the first estimate of the number of premature mortalities attributable to aviation worldwide. A key finding is that aircraft cruise emissions are more important in terms of their total public health impacts than landing and takeoff (LTO) emissions. On this basis, it may be appropriate to change aircraft emissions regulations, which currently only cover LTO emissions on the assumption that cruise emissions do not degrade air quality.

Traditional forms of risk assessment for pesticide spraying adhere strongly to the ‘positivist’ paradigm, with a reliance on expert knowledge and ‘objective’ scientific experiment methods. This thesis primarily explores how well ideas about increasing the levels of knowledge pluralism, accountability and social context in researching risks, ideas falling within the competing ‘constructivist’ paradigm, are transmitting into practice of risk assessment for agricultural pesticide spraying in the UK. This research explores a variety of discourses on pesticide risk and its assessment, why these differences develop, and how respective groups holding these views mobilise their discourses within the current framework. The research also presents suggestions to potentially integrate these competing epistemological positions. Representatives of relevant ‘acknowledged experts’ (comprised of both governmental and independent expert bodies) and ‘counter-expert’ groups (comprised of pesticide pressure groups and activists) were interviewed, and this was complemented by analysis of published material from the groups in question. Opinions of sampled non-expert, or lay’, communities in Lincolnshire and Cambridgeshire were obtained through a combination of postal surveying and interviewing conducted on doorsteps. The resulting data set revealed a number of specific discourse themes, which were analysed and cross-referenced. The study identifies a notable implementation gap between constructivist ideas and practice; the assessment process is firmly positivistic in approach. Governmental experts, taking a critical position on the health risks associated with pesticide exposure, gravitate towards a linear and technical risk assessment. This approach, stemming from embedded ‘worldviews’, maintains disciplinary integrity, external political relations and economic efficiency. Despite pressure from competing counter-expert groups to account for considerable uncertainties, trust-related problems and long term costs through greater diversity of risk knowledge, current quantitative analysis leaves little scope for its viable inclusion. Limited participatory and communication mechanisms do not enhance civil liberties, but are instead used instrumentally by experts further legitimise technical risk science.

The aim of the experimental work described in this thesis was to investigate the effects of a ubiquitous environmental contaminant, the synthetic platiciser Di-butylphthalate (DBP) on the developing male reproductive tract. Observed changes were compared to those evident in the human males Testicular dysgenesis syndrome (TDS), which is increasing in incidence. To investigate whether DBP treatment induced any TDS-like changes, pregnant rats were gavaged daily with DBP at doses up to 500mg/kg/day from embryonic (e) day e13.5 up to e21.5. Morphological and hormonal parameters (testosterone, inhibin-B) were then assessed in male rats aged e21.5 or in adulthood ± <i>in utero</i> DBP exposure. Concurrently, untreated fetal rat and fetal human testis explants were cultured <i>in vitro</i> ± MBP (Mono-butylphthalate), the DBP metabolite, at levels of up to 1mM, to investigate whether the array of adverse effects seen with the <i>in utero </i>compared ± MBP exposure. The <i>in vitro</i> experiments were restricted to 48h exposure duration, so an additional <i>in vivo</i> treatment regime was established to compare the endopoints induced after just 48h exposure to DBP <i>in utero</i>. Pregnant rats were dosed daily by gavage with 500mg DBP/kg/day on e19.5 and e20.5 only. Morphological and hormonal parameters (testosterone, inhibin-B) were then assessed in male rats aged e21.5 ± 48h. Findings were compared with those from the original <i>in utero</i> studies in which DBP exposure spanned the period e13.5-e20.5. The long-term <i>in utero</i> exposure regime induced an array of changes in the phenotype of the male reproductive tract, evident in e21.5 and adult animals, including testis maldescent (cryptorchidism) and reduced fertility. Changes in testis morphology such as alteration in the distribution of Leydig cells and induction of multinucleated gonocytes at e21.5 were also seen. The production of testosterone in testes at e21.5 was also significantly reduced following the DBP treatment, including a significant reduction in the protein expression levels of the steroidogenic enzyme P450scc. The short-term <i>in utero</i> exposure to DBP regime induced a generally less severe array of changes in the testis at e21.5 male reproductive tract than those seen after 8-day <i>in utero</i> DBP exposure. However, a greater reduction in testis testosterone was seen after short-term exposure than long-term exposure induced, despite less of a reduction in the expression of the steroidogenic protein P450scc. The precise mechanism through which DBP induces its array of developmental abnormalities is still unclear but these studies support the hypothesis that even short term <i>in utero </i>exposure to DBP directly affects the developing testis, probably by acting on Leydig cells and disrupting normal testis endocrinology.

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