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This study was carried out in the Carnon valley, which is located in Cornwall, south-west England. A river runs through the Carnon valley while former settlement ponds for processing tin and copper ore from the Wheal Jane mine are found on the floodplain. Tailings and waste rocks have accumulated on the floodplain to a height of about 6 meters. The valley is physically divided by a country road into the Middle valley and the Lower valley. Plant growth on tailings in the Middle valley, where tailings heaps were bulldozed, is visibly different from plant growth in the tailings and coarse waste rock observed in the Lower valley. The Lower valley, which features hummocks and hollows, appears to be less rehabilitated than the Middle valley. However, flora diversity in the Lower valley is considerably higher compared to the Middle valley, where a relatively homogeneous vegetation coverage is dominated by a few species. Other noticeable differences between the Lower and Middle valleys are a relative consistent soil compaction and the absence of visible ponds in the Middle valley. This research aims to identify the main drivers and limiting factors in the natural rehabilitation process and local biodiversity development in the middle and lower sections of the Carnon Valley. Through close year-round recording of natural plant species and colonies and habitat survey in the evolving terrain, it was attempted to correlate biota to progressive structural amelioration of the site. Species success was observed in relation to habitat evolution, restrictions imposed by residual toxicity of the former metal-mining terrain, advantages gained by artificial topographic diversity present on abandonment, and the stages reached in the dynamic progression of the combination of all of these features. By observing and recording the outcome of natural revegetation and identifying the impacts of abiotic factors, recommendations are made about the significance of such abandoned mine-sites in relation to ecological conservation value of such former disturbed land, and derive proposals for its onward management. We conclude that, on the site, complex interwoven processes occur of which we observe the state at one moment in time. The volume of data collected in the Carnon Valley is probably greater than available for any other known mine site of comparable history and size. While the data enabled inference of important biotic progressions, this study suggests that the 9 approaches may be applied to other abandoned mine sites, especially for assessment of natural attenuation of residual toxic legacies and ways to engineer future biotic rehabilitation patterns. The potential development of abandoned mine sites to re-establish natural biodiversity is thus recommended, together with a strategy for monitoring of future rehabilitation progression. The study consists of a field survey to record the present vegetation assemblage pattern, laboratory experiments to investigate soil features, data interpretation with statistical software, and evaluation of the interrelationship between emerging vegetation patterns and soil features. Extensive field work was undertaken within a one-year period, observing the highly heterogeneous vegetation community in a state of succession towards natural rehabilitation. The study generated up-to-date, detailed insight into year-round biodiversity development, notably of species diversity and seasonal stages of its development. Both transect surveys and quadrat surveys were carried out to capture general and spatial vegetation distribution variances. Fifty-seven quadrats, deemed to be representative, are surveyed in terms of plant species present and physical and chemical properties of the soil. While the natural vegetation of areas surrounding the valley has already been mapped, it is possible to build a factually-based picture of the progression of on-site species-assembly in relation to taxa that are, or are not, present in the surrounding landscape’s natural vegetation. This revealed that, out of a total of 87 species found in the valley, 9 are classified as very rare species in Cornwall. The presence of local rare species suggests the Carnon valley and other post-mining sites potentially have a significant ecological conservation value. This diversity and biotic taxonomic content of the former mine site highlights the importance of allowing natural biotic colonisation to continue in the wider interest of biodiversity conservation and utilisation of such sites as future biotic reserves. Vegetation survey revealed a host of unusual species assemblage settling on the contaminated soil, which is especially true in the community around ditches. The significantly high species richness and presence of rare species in the ditch community indicates the potential of an edge effect, which has a benefit for biodiversity and may be applied in mine site rehabilitation. The prominent high species richness in the core area (excluding the ditch community) of the Lower valley (75 species compared to 18 10 species in the Middle valley) emphasizes the value of heterogeneity. Bulldozing and human disturbance proved to be effective to improve vegetation coverage, but failed to promote biodiversity recovery. To investigate the effect of chemical contaminants on vegetation development, data is interpreted with ordination techniques such as redundancy analysis (RA) and principal component analysis (PCA). Both techniques indicate that arsenic and copper have a negative impact on vegetation development. Absorbed arsenic or phosphate exchangeable arsenic were found to be the most influential fractions of total arsenic in the soil which affect local species richness and biodiversity. Controlling arsenic fractionation is therefore an important strategy towards supporting vegetation recovery. The thesis postulates that sites with mine waste have special conservation value and that an edge effect may exist -from observing relatively high species diversity in zones along ditches. Water availability has great influence in ditch community development, but is remains unclear how it interacts with other factors to contribute to biodiversity development. The study shows the potential of natural rehabilitation, which should be considered as an option when planning for rehabilitation of former mine sites.

Analytical chemistry together with photophysical studies is a powerful tool for the detection and quantification of crucial chemical species involved in the environment and biological processes. Among analytical techniques, luminescent chemosensors are widely used in the development of new solutions to long-standing problems. Here, the main focus of this research is the recognition and quantification of important biological and organic/inorganic anions utilizing luminescent molecular sensors. The first part of this work is focused on the recognition of ATP due to its pivotal role in many biological processes. Bisantrene, a molecule comprising imidazolium hydrazone receptor moieties and anthracene as a central fluorophore, was employed as a new sensor for ATP in water at neutral pH by displaying amplified fluorescence. This process was selective to ATP while other nucleotide phosphates such as AMP, GTP, UTP, and CTP did not elicit sensor response. Also, this sensor was used to sense other small anions such as F-, Cl-, AcO-, H2PO4- and HP2O73- in an organic solvent, where the sensor shows fluorescence quenching. The second project is focused on the recognition and sensing of various phosphates and carboxylates in water using a metal-sensor coordination system. The sensors are based on fluorescent carboxamidequinoline chemosensors derivatized by phenol and benzothiazole. These sensors form non-fluorescent complexes with Eu3+ where the fluorescence is recovered when the phosphate anion sequesters the Eu3+ from the complex. The present sensors show selectivity for biological phosphates such as ATP, ADP, and AMP. Arsenate (HAsO42-) is a highly toxic analyte to living organisms, and efforts toward sensing arsenate are an important area of research. The third project is aimed at the detection of arsenate (HAsO42-) in water by luminescence spectroscopy using a lanthanide/transition metal dyad. We have synthesized a cryptand molecule which binds Eu3+and displays a ligand-sensitized luminescence. This intense luminescence is quenched upon addition of Zn2+, only to be restored in the presence of arsenate. This lanthanide/transition metal dyad was used for the detection of arsenate in water utilizing an Off-to-On intensity switching of Eu3+ luminescence.

Arsenic is a widespread contaminant of aquatic systems worldwide, and though the toxic effects on vertebrates are well understood, the impacts of chronic arsenic exposure on lower trophic levels of insects have received little attention. The overall goal of this dissertation was to investigate the sublethal effects of arsenic on aquatic primary consumers, and how they could transfer arsenic from aquatic to terrestrial environments. I investigated the effects of arsenic on survival, growth, and reproduction of Chironomus riparius. There was a significant increase in the time between male and female emergence when exposed to 1000 μg/l as larvae, and a significant decrease in the number of eggs produced per egg mass. Total arsenic body burdens decreased 72% between larval and adult stages. Larvae of Culex tarsalis and Culex quinquefasciatus exposed to arsenate or arsenite were assayed against Bacillus thuringiensis var. israelensis or Lysinibacillus sphaericus microbial pathogens to determine shifts in survival curves resulting from arsenic accumulation. Arsenic did not affect growth and survival of these mosquitoes compared to controls. Culex tarsalis was the more sensitive species, but both species were tolerant to arsenic exposure. X-ray absorption spectroscopy was used to map the localization and biotransformation of arsenic in various life stages of C. riparius and Cx. tarsalis. Chironomus riparius larvae accumulated arsenic in the midgut, while adults had arsenic distributed throughout the exoskeleton. There was evidence for reduction of arsenate to arsenite, and production of an As-thiol. In Cx. tarsalis, arsenic was found throughout the larval and adult bodies. Behavioral assays on Cx. tarsalis revealed no effects of prolonged arsenic exposure on frequency or duration of measured behaviors, including time spent resting, gliding, diving, and swimming. There was a limited effect of exposure on predator avoidance behaviors, but interactions made patterns difficult to discern. The trophic transfer potential of arsenic from aquatic to terrestrial environments was evaluated by feeding contaminated Cx. tarsalis to aquatic and terrestrial predators. Results suggest that overall the trophic transfer of arsenic is more likely to occur within an aquatic system, although transfer to terrestrial predators may play an important role in arsenic cycling during periods of mass emergence of insect prey.

The removal of arsenic toxicity from water is accomplished by a preliminary preoxidative step transforming the most toxic form, arsenite (As (III)), to the least toxic form, arsenate (As (V)). The potential of As (III) oxidation to As (V) was initially investigated in batch reactors using the chemoautotrophic Thiomonas arsenivorans strain b6 under varying initial As (III) and cell concentrations and at optimal pH and temperature conditions (pH 6.0 and temperature 30°C). The strain b6 completely oxidized As (III) to As (V) during exponential growth phase for lower levels of As (III) concentrations (≤ 100 mg/L) but continued into stationary phase of growth for higher levels (≥ 500 mg/L). Other important factors such as oxygen and carbon limitations during biological As (III) oxidation were also evaluated. The biokinetic parameters of the strain b6 were estimated using a Haldanesubstrate inhibition model with the aid of a non-linear estimation technique. Microbial As (III) oxidation was further investigated in continuous-flow bioreactors (CSTR and biofilm reactor) under varying As (III) loading rates. Both the reactors achieved As (III) oxidation efficiency exceeding 99% during the steady-state conditions. The reactors were also able to recover from an As (III) overloading phase establishing the resilient nature of the microorganism. The basic mass balance expressions on As (III) and biomass along with the Monod model were used to linearly estimate the biokinetic parameters in the CSTR study. However, in the biofilm study, a steady-state flux model was used to estimate the same parameters. The performance of the model was very good in simulating the transient and steady-state conditions. Finally, the potential application of one-stage and two-stage reactor systems was investigated for the near complete removal of arsenic. Activated alumina was used as the adsorbent for the As (V) produced by the biological oxidation of As (III). The two-stage reactor process performed better than the one-stage reactor system in lowering the arsenic level below the detection limit (1 mg/L) for at least eight days of operation. However, pH fluctuations and probable competition from ions such as PO43- , SO42-, and Cl- severely impacted the performance of the reactors. Further study is needed to improve the overall efficiency of the reactor systems for achieving complete removal of arsenic for a longer operating time.

In vitro gastrointestinal methods can potentially provide a rapid and inexpensive measure of bioaccessible arsenic which in turn can be used to conduct more accurate and site-specific human health risk assessments of contaminated soils. However, in order for in vitro methods to become widely accepted as tools that accurately assess soil As exposure through the oral ingestion pathway, a better understanding of the fractions of soil arsenic that are measured by the in vitro extraction and the underlying soil properties associated with As bioaccessibility (BA) are needed. In this study, nineteen soils with a wide range of soil properties were spiked with 250 mg/kg As. Bioaccessible As was then determined using The Ohio State University in vitro gastrointestinal method (OSU-IVG) and soil As was fractionated using a four-step sequential extraction. There was a wide range in As BA; from 27.3 to 206 mg/kg with a mean of 94.7 mg/kg in the gastric phase, and from 29.0 to 210 mg/kg in the intestinal phase with a mean of 98.6 mg/kg. Highly significant (P < 0.0001) relationships existed between bioaccessible As and the combination of soil pH and Fe extracted by citrate bicarbonate dithionite (Fecbd) or soil pH and Fe extracted by acid ammonium oxalate (Feox). Soil pH explains more of the variation in bioaccessible As (r2 = 0.67) than Fecbd (r2 = 0.45) or Feox (r2 = 0.38). The sequential extraction results indicate that As extracted from non-specifically sorbed (F1) and specifically sorbed (F2) fractions provide a good measure of pH and iron oxide (Fecbd and Feox) controlled As BA (GE, r2 = m = 1.06; IE, r2 = 0.94, m = 1.07). However, the addition of amorphous or poorly-crystalline oxides of Fe (F3) and well-crystallized oxides of Fe (F4) as extractable As fractions to F1 and F2 dies not improve the correlation with bioaccessible As. Therefore, the total As content of soil overestimates and is a poor indication of bioaccessible As. The largest contribution to bioaccessible As is the specifically sorbed (F2) fraction of soil As. Because F2 As is the largest contribution to bioaccessible As, it is the strong linear relationship between F2 and soil pH that controls the relationship between bioaccessible As and soil pH. Accurate and site specific HHRAs are necessary in order to prevent the use of overly conservative assumptions that would result in unnecessary site remediation. The use of As BA in HHRA as determined by valid in vitro methods supported by soil property and As fractionation results could potentially provide enormous cost and time savings for superfund site managers while assuring protection to public health.

Spectroscopic and kinetic studies of arsenite oxidase and DMSO reductase, both members of the DMSO reductase family of mononuclear molybdenum enzymes, have been undertaken to provide a better understanding of how the physical and electronic structure of the molybdenum center relates to the oxygen atom transfer chemistry catalyzed by each enzyme. Protein film voltammetry of arsenite oxidase shows that the molybdenum center displays highly concerted two-electron oxidation-reduction activity with a reduction potential of +254 mV vs. SHE and spectrophotometric reductive titrations of arsenite oxidase have revealed the heretofore unresolved reduction potentials of the [3Fe-4S] and [2Fe-2S] Rieske-type iron-sulfur centers of the enzyme. Stopped-flow kinetic studies of the reaction of oxidized R. sphaeroides DMSO reductase with the general reductant sodium dithionite is biphasic, with an intermediate species formed that is determined to be that of the catalytically relevant MoV enzyme form. UV-visible spectral deconvolution of enzyme-monitored turnover reactions using DMSO reductase with the oxidizing substrates (DMSO or TMAO) and the reductant sodium dithionite clearly reveals the mechanistic differences of catalytic oxygen atom abstraction between them where a stable Ered-substrate complex is only observed for reaction with DMSO. The pH-dependence of UV-visible spectra for DMSO reductase intermediates was also examined and only the spectrum of reduced enzyme is found to be particularly sensitive to pH. The spectrum of the high pH reduced enzyme implies dissociation of the Q pterin in reduced enzyme and further studies suggest that this Q pterin dissociation may stabilize an Eox•DMS intermediate which accumulates to an increasing degree as pH increases and is responsible for the observed pH-dependence of steady-state enzyme activity. Spectroscopic and kinetic analysis of the W116F mutant shows that, in contrast to previous studies, the functional form of the enzyme has a bis-dithiolene molybdenum center. Resonance Raman has also been employed to further characterize W116F DMSO reductase forms and shows that both oxidized and reduced species are vibrationally analogous to those of the wild-type enzyme. This provides further evidence of full bis-dithiolene coordination to the molybdenum in the mutant active center.