Hog manure phosphorus (P) can be recovered as struvite or magnesium ammonium phosphate hexahydrate (MgNH4PO4∙6H2O). The recovered struvite has slow-release properties and may be used as a P-source for crops. Two pot experiments were conducted to evaluate the agronomic effectiveness and seedling toxicity of liquid hog manure-recovered struvite for canola (Brassica spp.) and wheat (Triticum aestivum). While wheat was non-responsive to P application, canola dry matter yield (DMY) from struvite (1.9 g kg-1) was similar to that from monoammonium phosphate (MAP) (1.8 g kg-1) and coated-monoammonium phosphate (CMAP) (1.7 g kg-1). Importantly, when P was seed-placed at the higher rate (15 mg kg-1), canola seedling emergence was significantly greater with struvite (90%) and CMAP (85%) than with MAP (60%). The results demonstrate the potential of struvite as an effective P-source for canola in P-deficient soils, which can be safely applied at higher rates than those currently recommended for seed-placed MAP.

To protect the environment from contaminants, environmental risk assessment (ERA) evaluates the risk of adverse effects to populations, communities and ecosystems. Environmental management decisions rely on ERAs, which commonly are based on a few endpoints at the individual organism level. To bridge the gap between what is measured and what is intended for protection, individual-level effects can be integrated in population models, and translated to the population level. The general aim of this doctoral thesis was to extrapolate individual-level effects of harpacticoid copepods to the population level by developing and using population models. Matrix models and individual based models were developed and applied to life-history data of Nitocra spinipes and Amphiascus tenuiremis, and demographic equations were used to calculate population-level effects in low- and high-density populations. As a basis for the population models, individual-level processes were studied. Development was found to be more sensitive compared to reproduction in standard ecotoxicity tests measuring life-history data. Additional experimental animals would improve statistical power for reproductive endpoints, but at high labor and cost. Therefore, a new test-design was developed in this thesis. Exposing animals in groups included a higher number of animals without increased workload. The number of reproducing females was increased, and the statistical power of reproduction was improved. Individual-level effects were more or equally sensitive compared to population-level effects, and individual-level effects were translated to the population level to various degrees by population models of different complexities. More complex models showed stronger effects at the population level compared to the simpler models. Density dependence affected N. spinipes populations negatively so that toxicant effects were stronger at higher population densities. The tools presented here can be used to assess the toxicity of environmental contaminants at the individual and population level, improve ERA, and thereby the basis for environmental management. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.</p>

Many consumer and medical products contain engineered nanomaterials (ENMs) due to their unique properties arising from their small size of <100 nm in at least one dimension. Although ENMs could greatly improve the quality of daily life, concerns for their health and environmental safety emerged in recent years because the same properties that make ENMs beneficial may also render them toxic. The small size allows ENMs’ entrance into the cell where they may attach to biological molecules and membranes, disrupting their function and/or leading to oxidative stress and/or damage. This thesis focused on silver nanoparticles (AgNPs). Several articles demonstrated that during washing AgNPs are released from the AgNP-impregnated fabrics and could pose a risk to aquatic species. Given that the toxicity mechanisms of AgNPs are yet to be clearly understood this thesis investigated the effects of AgNPs from ‘oxidative stress’ and ‘endocrine disruption’ points of view, using both in vivo and in vitro model fish systems. A 4 d exposure of zebrafish (Danio rerio) embryos to AgNPs increased mortality, delayed hatching, and increased oxidative stress. The silver ion (Ag+) was more effective in eliciting these effects at equivalent silver concentrations. Moreover, the Ag-chelator cysteine reduced the toxicity of both Ag-types. Despite these effects AgNPs or Ag+ did not affect the ability of zebrafish larvae or adults (raised to adulthood in Ag-free water) to increase cortisol levels, but there were differential effects on the expression of corticotropin-releasing factor (CRF)-related genes, suggesting that other physiological processes regulated by CRF may be impacted. Furthermore, a 48 h exposure of rainbow trout (Oncorhynchus mykiss) erythrocytes and hepatocytes to AgNPs or Ag+ increased oxidative stress, but Ag+ was more potent. Moreover, AgNPs elevated lipid peroxidation, while Ag+ increased DNA damage, suggesting different modes of action for the two Ag-types. Cysteine treatment reduced the toxicity of Ag+ and AgNPs, while buthionine sulfoximine, which inhibits glutathione synthesis, increased it, suggesting the importance of glutathione in silver toxicity. Finally, AgNPs increased glycogenolysis in trout hepatocytes independently of the beta-adrenoreceptor or the glucocorticoid receptor.

Cellular internalization is a highly regulated process controlled by proteins in the plasma membrane. Large and hydrophilic compounds, in particular, face difficulties conquering the plasma membrane barrier in order to gain access to intracellular environment. This puts serious constrains on the drug industry since many drugs are hydrophilic. Several methods aiming at aiding the cellular internalization of otherwise impermeable compounds have therefore been developed. One such class, so-called cell-penetrating peptides (CPPs), emerged around twenty years ago. This group constitutes hundreds of peptides that have shown a remarkable ability in translocating diverse molecules, ranging from small molecules to large proteins, over the cell membrane. The internalization mechanism of CPPs has been questioned ever since the first peptides were discovered. Initially, the consensus in the field was direct translocation but endocytosis has gradually gained ground. The confusion and the disunity within this research field through the years proceeds from divergent results between research groups that hamper comparison of the peptides. This thesis aims at characterizing several well-established CPPs with comprehensive studies on cellular toxicity, secondary structure and cellular internalization kinetics. The results demonstrate that CPPs act in general in a low or non-toxic way, but the apparent toxicity is both peptide- and cell line-dependent. Structural studies show that the CPPs have a diverse polymorphic behavior ranging from random coil to structured β-sheet or α-helix, depending on the environment. The ability to change secondary structure could be the key to the internalization property of the CPPs. Internalization kinetic studies of CPP conjugates reveal two sorts of internalization profiles, either fast curves that cease in few minutes or slow curves that peak in tens of minutes. Furthermore, improved synthesis of CPP conjugates is demonstrated. In conclusion, the studies in this thesis provide useful information about cytotoxicity and structural diversity of CPPs, and emphasize the importance of kinetic measurements over end-point studies in order to give better insights into the internalization mechanisms of CPPs. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.</p>

SirT1 is a class III histone deacetylase that has beneficial roles in various diseases related to aging such as cancer, diabetes and neurodegenerative disease. Resveratrol is a natural compound that mimics most of the beneficial effects attributed to SirT1. Resveratrol has toxicity towards cancer cells and has been reported to be a direct activator of SirT1. Interestingly, SirT1 over-expression has also been reported to be toxic. We set out to determine if resveratrol toxicity is mediated through activation of SirT1. We have assessed resveratrol toxicity in embryonic stem cells and mouse embryonic fibroblast (MEFs) across different SirT1 genotypes. Our data indicates that SirT1 is not implicated in resveratrol toxicity in either normal or transformed MEFs. Thus, resveratrol toxicity does not appear to be mediated by SirT1.

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 41-45). / v, 45 leaves, bound 29 cm

This project developed methodology for in vitro toxicity assessment of contaminated sites using the Promega?? MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxy-methoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay performed on human cells (HepG2 and Skin fibroblasts). The project included the development of a method for extracting contaminants from soil based on leaching and centrifugation. A number of solvents and surfactants were assessed for their suitability as extracting agents. The Zwitterionic surfactant CHAPS ({3[(3-Cholamidopropyl) dimethylammonio] propanesulphonic acid}), which is an irritant in vivo, was found suitable for in vitro toxicity assessment applications. CHAPS was found to be the least toxic surfactant in vitro when tested on skin fibroblasts (NOEC: 1800??577 ppm, IC50: 4000??577 ppm) and HepG2 cells (NOEC: 833??289 ppm, IC50: 5300??287 ppm). The chosen surfactant was used in three different methods for extraction of Toluene and Xylene spiked in 2 g and 10g soil. The combination comprising of 0.1% (s/w) CHAPS and cosolvent 1% (w/w) Isopropanol, at their respective NOEC (No Observed Effective Concentration) toxicity values, showed good recovery of the nonpolar organic compounds in comparison to the recovery by 0.1% CHAPS and 0.5% CHAPS. The study found additive interactions to be the most common form of toxicity for 16 concentration combinations of Formaldehyde (polar), Toluene and Xylene (nonpolar) when compared to predicted toxicity (R2=0.943, P&lt0.0001). When assessing the in vitro toxicity of unknown (blind) contaminated soil samples, the Hazard Index (HI) predicted from the chemical analyses results showed a relatively good correlation (R2&gt0.7062, n=26) when compared to the experimental toxicity results on HepG2 cells. Furthermore, the comparison of Australian Health Investigation Levels (HIL) with in vitro toxicity testing gave similar correlation (R2&gt0.6882, n=26) on HepG2 cells. The overall project suggests the potential application of the zwitterionic surfactant (CHAPS) in sampling contaminants from soils in an in vitro toxicity assessment. This study demonstrates the application of in vitro toxicity assessment using human cells for the prediction of toxic risk as a sentinel to human toxicity from a contaminated site.

Erratum tipped in before chapter 1. / Bibliography: leaves 226-248. / xv, 248 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Shows that pretreatment with peroxisome proliferators protects mice against the acute hepatotoxicity of paracetamol, in addition to a number of other toxicants. / Thesis (Ph.D.)--University of Adelaide, Dept. of Clinical and Experimental Pharmacology, 1999

In strongly acidic soils (pH <4.5) aluminium (Al) becomes soluble in quantities that can lead to Al phytotoxicity. It is estimated that approximately 30 % of the worlds’ potentially arable lands are acidic, with Al toxicity the most limiting factor for plant growth on acid soils. With increasing use of marginal land in cropping systems, this area could reach 70 %. Cell wall pectin provides up to 70 % of the root cation exchange capacity. Pectin is suggested to control a number of physiological properties of the plant cell wall such as porosity, charge density, microfibril spacing and pH. The ability of pectin to bind cations is not only important for the uptake of nutrients but is implicated in metal toxicity, in particular Al. Despite over a century of research, the mechanisms of Al toxicity are yet to be fully elucidated or agreed upon. Gluconacetobacter xylinus is a gram-negative, soil dwelling bacterium which produces extracellular cellulose. It is an established archetype for the study of cellulose biogenesis. In the presence of pectin in the growth medium, the bacterium can form cellulose-pectin composites. Recently, the bacterium has been used to form composites as model cell walls to understand plant cell wall deposition. Additionally, bacterial cellulose composites in their natural hydrated state mimic the hydration state of primary plant cell walls. The aim of this project was to attempt to incorporate this novel cell wall analog into laboratory investigations into metal interactions with plant cell walls. Preliminary work was undertaken to optimise the bacterial culture medium, growth conditions, analysis of the composites and developing an overall general methodology. The medium buffering system was altered, growth under non-optimal pH conditions was evaluated and Al was successfully incorporated into the composites. Appropriate sample preparation for scanning electron microscopy (SEM) of the composites was determined. This work resulted in the successful production of bacterial cellulose-pectin composites with 30 % w/w pectin incorporation. The effect of Al on the tensile properties of the composites was examined. Aluminium had no effect on the stress/strain profiles, confirming the hypothesis that pectin is not the main load bearing component of the cell wall. The composites were used to investigate the effects of Al and other trace metals (copper (Cu), gadolinium (Gd), lanthanum (La), ruthenium (Ru) and scandium (Sc)) on the hydraulic conductivity of the composites. Hydraulic conductivity was reduced to ≈ 30 % of the initial flow rate by 39 μM Al and 0.6 Cu μM, ≈ 40 % by 4.6 μM La, 3 μM Sc and 4.4 μM Ru, and ≈ 55 % by 3.4 μM Gd. These metal concentrations were selected based on the concentrations causing a 50 % reduction in root elongation in cowpea (Vigna unguiculata L.). This study demonstrated that all the trace metals caused a similar decrease of hydraulic conductivity, despite the different concentrations of the metals used. Scanning electron microscopy showed changes in pectin porosity with metal binding which may account for the decreases in hydraulic conductivity observed. As the composites could not be used as a model material in all investigations, pectin-only systems were employed in a rheological study to investigate the effect of increasing concentrations of Al, Ca, Cu or La at pH 4 on pectin (degree of esterification 30 %, 1 % w/v) gel physical strength. Comparing similar saturation levels, La formed the weakest gel, followed by Ca, which was similar to Al, while the strength of Cu gels was almost an order of magnitude stronger than the other cations. This study was the first to investigate Al and La pectate gel strength. The swelling of the gels also varied, with Ca gels being the most swollen. Pectin was also used to determine the exchange selectivity of Al, Cu, Gd, La, Ru and Sc toward Ca pectate. The order of selectivity was found to be Sc>Gd>La>Cu>Ru>Al. There were some parallels between this sequence and the rhizotoxicity data of the metals, suggesting that the strength with which metals bind to pectin is an indication of their rhizotoxicity. Through the use of synthetic pectate gel systems new information was discovered about the strength of pectin gels and the selectivity of trace metals towards pectin. These findings were in keeping with those of a number of related studies, as well as with studies of plant root tissue. Overall, the novel bacterial cellulose-pectin cell wall analog was successfully integrated into research into Al and other metal toxicity in plants, and offers a useful system that can overcome some of the difficulties encountered when using plant cell wall tissue. Further research may be warranted on manipulating the growth system to produce composites in the presence of the metal (ie. metal added to the growth medium), as opposed to post-formation treatments. Moreover, the production of a three way composite of cellulose, hemicellulose and pectin would likely be another useful analog for plant cell wall material.

Thesis (M.Sc. (Zoology & Entomology)) - Rhodes University, 2007.