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Over the last decades, arsenic (As) contamination of soil-plant-water systems has become a major concern for Bangladesh and West Bengal, India. The geochemistry of the sediment depositional environment which subsequently, on sediment burial, give rise to elevated As in Holocene groundwater’s of Southeast Asia, may provide clues to unravelling the mechanistic basis and spatial heterogeneity of this phenomenon. The Sundarbans mangrove ecosystem, Bangladesh, is a modern analogue, and indeed forms a continuum with, the Holocene sediments of concern and thus studying As cycling in surface Sundarbans sediments. Similarly, rice paddy fields in many regions of the Bengal Basin form a continuum with Holocene sediments. Sediment cores were collected from a wide range of locations within the Sundarbans to study surface spatial, as well as down the profile (~1 m), As distribution and it’s association with other geochemical parameters. Pore and surface water, and Diffusive Gradients in Thin films (DGT) were sampled from 4 different interlocked sub-habitats over 0.29 km2: major river bank, main tributary, forest floor and minor tributary. Further experiments were conducted to observe As dynamics in mangrove surface sediments on application of mangrove detritus. Finally 3 interlinked experiments (field manuring, soil batch culture, greenhouse growth trials) were conducted to assess the effect of farm-yard manure (FYM) and rice straw, at a field application rate practised in Bangladesh (5 t/ha), on As mobilization in soil and subsequent assimilation by rice. As concentration in mangrove sediment down the profile was found to be more associated with elevated Fe and Mn than with organic matter (OM), with significant spatial variations among the locations. Sediment particle size was an important factor determining As retention and mobilization, which is also true for deeper Bengal Bay sediments. Proximity to mangrove vegetation and to water bodies was found to have significant effect on As dynamics. Porewaters from coarse textured, low OM riverbank sediment were high in As, but with only a small pool of As for resupply from the solid phase, showing similarities with grey aquifer sediments compared to fine textured and high OM content forest floor sediments. The As column dynamics study showed that As release into porewater was strongly associated with Fe release, indicating the strong association of the 2 elements, with OM playing a major role in their dissolution. The desorption studies also showed OM driving As mobilization within short time. Due to strong redox cycling very little evidence of As methylation was observed in biologically active mangrove porewaters. But we found 10-fold increase in dimethylarsinic acid (DMA) production compared to a non-amended control using the same sediments treated with mangrove detritus in the laboratory. OM amendments lead to considerable mobilization of As into both soil porewaters and standing surface waters in rice paddy. In a greenhouse rice cultivation experiment, flooding initially caused greatly enhanced As mobilization in porewater (< 24 d), but the effects of flooding on As mobilization decreased during later rice growth, particularly at grain fill. However, OM amendment did not cause significant As accumulation in grain and straw compared to control. It was noted in field trials and greenhouse studies that OM fertilization greatly enhanced As mobility to surface waters, which may have major implications for fate of As in paddy agronomic ecosystems.

Effective techniques for assessing soil environmental pollution are required to develop protective policy. Chemical methods have been traditionally used to determine total concentration of pollutants and biologically linked measurements have been used to assess the bioavailable fraction of pollutants. Bioluminescence-based microbial bioassays have been shown to respond to the bioavailable fractions. Growth and bioluminescence of lux-marked E. coli HB101 and P. fluorescens 10586r were characterised and optimised for freeze-drying culture. Freeze-drying cultures have been used effectively because of their ease of use, rapid assay response and sensitivity to a wide range of pollutants. An assessment of Zn and Cd amended soil was investigated. Two different techniques (centrifugation and Rhizon sampler) were used to obtain the interstitial pore water of soils. The concentrations of Zn and Cd were significantly higher in the soil solution extracted using the centrifugation technique compared to the Rhizon sampler technique. The biosensors responded to the free metal concentrations in the soil solution. An assessment of the toxicity of 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol, individually and in combinations, was tested in deionised water (pH 5.5), soil solutions, and soils using lux-marked E. coli HB101 and P. fluorescens 10586r. Toxicity interaction responses of the mixture chlorophenols were predicted using a model. Synergistic interactions were observed for the response of P. fluorescens 10586r pUCD60-7 to all combinations of chlorophenol tested, while the response of E. coli HB101 pUCD607 varied with the matrix solutions tested. Bioavailability of naphthalene was studied using cyclodextrin-based extractions caused to the luminescence response of Pseudomonas fluorescens KH44 pUTK21. Increasing the concentrations of beta-cyclodextrin (b-CD) and hydroxylpropyl-b-cyclodextrin (HPBC) in the extract solutions increased the apparent concentration of naphthalene in the soil solutions. The luminescence response of P. fluorescens HK44 was associated with bioavailable of naphthalene.

The objective of this research was to determine the potential of two anti-atrazine single-chain antibodies (scAbs) to detect very dilute atrazine concentration, specifically in the nanomolar and sub-nanomolar ranges. Analysis of environmental pesticide contamination is routinely done by high performance liquid chromatography (HPLC), gas chromatography (GC) and mass spectrometry (MS). However, since the mid eighties there have been an increasing number of reports describing the use immunoassays to detect environmental pollutants. Although immunoanalysis using whole antibodies has been shown to be almost as effective as GC/MS (Thurman et al., 1990) the technology is still not widely used for pesticide analysis. This thesis will describe the increased sensitivity of single-chain antibody fragments, compared to whole antibodies, to detect low concentrations of atrazine and related triazines. The effect of monomeric and dimeric scAb conformations on the ability of enzyme linked immunosorbent assays (ELISAs) to detect atrazine and related triazines is investigated. The thermal and chemical stability of the scAbs, and a modified scAb containing an interchain disulphide bond, are compared with the parent monoclonal antibodies (MAbs) to determine their suitability in an environmental ELISA assay system. The expressions in Escherichia coli (E. coli) of two different anti-atrazine scAbs and related antibody fragments are studied, and an optimised expression protocol for these antibody fragments obtained. Three potentially toxic amino acid residues identified in one of the variable heavy (VH) domains (Knappik & Pluckthun, 1995) are mutated to less toxic amino acids, and their effects on antibody fragment expression observed.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Herbert E. Allen, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Ph.D. / Environmental Science and Engineering / Chromate-containing precipitates can affect the mobility of toxic Cr(VI) in the subsurface, control its concentration in groundwater, limit its bioavailability, and impede remediation of chromium contaminated sites. This dissertation focuses on two iron-chromate precipitates, KFe [subscript 3](CrO4)[subscript 2](OH)[subscript 6] (the chromate analog of the sulfate mineral jarosite) and KFe(CrO4)[subscript 2].2H2O, that we identified in a soil contaminated by chrome plating solutions. The precipitates were identified using scanning and transmission electron microscopy, as well as powder x-ray diffraction. KFe[subscript 3](CrO4)[subscript 2](OH)[subscript 6] occurs as small (2-5 um) crystals interspersed within the bulk soil. KFe(CrO4)[subscript 2].2H2O forms crusts of larger crystals (10-50 um) in cracks and fractures of the soil. / Due to highly mathematical nature of the abstract, only the first paragraph is shown.