Bioremediation of PAHs - Limitations and soultions

Introduction 1.1 Occurrence of polycyclic aromatic hydrocarbons (PAH) in the environment Worldwide industrial and agricultural developments have released a large number of natural and synthetic hazardous compounds into the environment due to careless waste disposal, illegal waste dumping and accidental spills. As a result, there are numerous sites in the world that require cleanup of soils and groundwater. Polycyclic aromatic hydrocarbons (PAHs) are one of the major groups of these contaminants (Da Silva et al., 2003). PAHs constitute a diverse class of organic compounds consisting of two or more aromatic rings with various structural configurations (Prabhu and Phale, 2003). Being a derivative of benzene, PAHs are thermodynamically stable. In addition, these chemicals tend to adhere to particle surfaces, such as soils, because of their low water solubility and strong hydrophobicity, and this results in greater persistence under natural conditions. This persistence coupled with their potential carcinogenicity makes PAHs problematic environmental contaminants (Cerniglia, 1992; Sutherland, 1992). PAHs are widely found in high concentrations at many industrial sites, particularly those associated with petroleum, gas production and wood preserving industries (Wilson and Jones, 1993). 1.2 Remediation technologies Conventional techniques used for the remediation of soil polluted with organic contaminants include excavation of the contaminated soil and disposal to a landfill or capping - containment - of the contaminated areas of a site. These methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling and transport of hazardous material. Additionally, it is very difficult and increasingly expensive to find new landfill sites for the final disposal of the material. The cap and containment method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability. A better approach than these traditional methods is to completely destroy the pollutants, if possible, or transform them into harmless substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (for example, base-catalyzed dechlorination, UV oxidation). However, these methods have significant disadvantages, principally their technological complexity, high cost , and the lack of public acceptance. Bioremediation, on the contrast, is a promising option for the complete removal and destruction of contaminants. 1.3 Bioremediation of PAH contaminated soil & groundwater Bioremediation is the use of living organisms, primarily microorganisms, to degrade or detoxify hazardous wastes into harmless substances such as carbon dioxide, water and cell biomass Most PAHs are biodegradable unter natural conditions (Da Silva et al., 2003; Meysami and Baheri, 2003) and bioremediation for cleanup of PAH wastes has been extensively studied at both laboratory and commercial levels- It has been implemented at a number of contaminated sites, including the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989, the Mega Borg spill off the Texas coast in 1990 and the Burgan Oil Field, Kuwait in 1994 (Purwaningsih, 2002). Different strategies for PAH bioremediation, such as in situ , ex situ or on site bioremediation were developed in recent years. In situ bioremediation is a technique that is applied to soil and groundwater at the site without removing the contaminated soil or groundwater, based on the provision of optimum conditions for microbiological contaminant breakdown.. Ex situ bioremediation of PAHs, on the other hand, is a technique applied to soil and groundwater which has been removed from the site via excavation (soil) or pumping (water). Hazardous contaminants are converted in controlled bioreactors into harmless compounds in an efficient manner. 1.4 Bioavailability of PAH in the subsurface Frequently, PAH contamination in the environment is occurs as contaminants that are sorbed onto soilparticles rather than in phase (NAPL, non aqueous phase liquids). It is known that the biodegradation rate of most PAHs sorbed onto soil is far lower than rates measured in solution cultures of microorganisms with pure solid pollutants (Alexander and Scow, 1989; Hamaker, 1972). It is generally believed that only that fraction of PAHs dissolved in the solution can be metabolized by microorganisms in soil. The amount of contaminant that can be readily taken up and degraded by microorganisms is defined as bioavailability (Bosma et al., 1997; Maier, 2000). Two phenomena have been suggested to cause the low bioavailability of PAHs in soil (Danielsson, 2000). The first one is strong adsorption of the contaminants to the soil constituents which then leads to very slow release rates of contaminants to the aqueous phase. Sorption is often well correlated with soil organic matter content (Means, 1980) and significantly reduces biodegradation (Manilal and Alexander, 1991). The second phenomenon is slow mass transfer of pollutants, such as pore diffusion in the soil aggregates or diffusion in the organic matter in the soil. The complex set of these physical, chemical and biological processes is schematically illustrated in Figure 1. As shown in Figure 1, biodegradation processes are taking place in the soil solution while diffusion processes occur in the narrow pores in and between soil aggregates (Danielsson, 2000). Seemingly contradictory studies can be found in the literature that indicate the rate and final extent of metabolism may be either lower or higher for sorbed PAHs by soil than those for pure PAHs (Van Loosdrecht et al., 1990). These contrasting results demonstrate that the bioavailability of organic contaminants sorbed onto soil is far from being well understood. Besides bioavailability, there are several other factors influencing the rate and extent of biodegradation of PAHs in soil including microbial population characteristics, physical and chemical properties of PAHs and environmental factors (temperature, moisture, pH, degree of contamination). Figure 1: Schematic diagram showing possible rate-limiting processes during bioremediation of hydrophobic organic contaminants in a contaminated soil-water system (not to scale) (Danielsson, 2000). 1.5 Increasing the bioavailability of PAH in soil Attempts to improve the biodegradation of PAHs in soil by increasing their bioavailability include the use of surfactants , solvents or solubility enhancers.. However, introduction of synthetic surfactant may result in the addition of one more pollutant. (Wang and Brusseau, 1993).A study conducted by Mulder et al. showed that the introduction of hydropropyl-ß-cyclodextrin (HPCD), a well-known PAH solubility enhancer, significantly increased the solubilization of PAHs although it did not improve the biodegradation rate of PAHs (Mulder et al., 1998), indicating that further research is required in order to develop a feasible and efficient remediation method. Enhancing the extent of PAHs mass transfer from the soil phase to the liquid might prove an efficient and environmentally low-risk alternative way of addressing the problem of slow PAH biodegradation in soil.

Synthese und Eigenschaften von Tetrastilbenylmethanen und Tristilbenylcarbokationen

Das Ziel dieser Arbeit war die Entwicklung neuartiger organischer Materialien, die eine Absorption im NIR-Bereich besitzen. Zu diesem Zweck wurden höher konjugierte Carbinole und Tetrakis(stilbenyl)methane synthetisiert und aus den Carbinolen mit Trifloressigsäure Carbokationen-Salze hergestellt. Die Darstellung der Oligomeren erfolgte durch eine konvergente Synthesestrategie, bei der die meisten der synthetisierten Vorstufen in mehreren Folgereaktionen eingesetzt werden konnten. Als Schlüsselschritt der Synthesen wurde fast ausschließlich die Horner-Reaktion angewendet. Die Vorteile lagen dabei in der leichten Zugänglichkeit der Edukte, in hohen Produktausbeuten und vor allem in der hohen trans-Selektivität der Reaktion. Die effektiven Konjugationslängen (EKL) der Carbinole und Carbokationen wurden mit Hilfe der Fitfunktion berechnet. Mit zunehmender Ausdehnung des p-Systems wird der HOMO-LUMO Abstand des energieärmsten p-p*- Übergangs geringer und die Absorption zum sichtbaren Bereich hin bathochrom (langwellig) verschoben. Die Substitution mit einem Dialkylamino-Rest bewirkt ebenfalls eine bathochrome Verschiebung der Absorptionsbande.Umgekehrt verhält es sich bei den Carbokationen. Hier absorbieren die dialkylaminosubstituierten Verbindungen bei kürzerer Wellenlänge als die alkoxysubstituierten, da bei der Herstellung der Kationen aus den Carbinolen ,zuerst der Sickstoff als elektronenreichste Stelle protoniert wird. Dabei hat die Menge an zugesetzter Trifluoressigsäure einer entscheidende Einfluß auf die Bildung der Carbokationen aus den Carbinolen (s. Tabele 4-3). Während bei den alkoxysubstituierten Carbinolen das Gleichgewicht zwischen Carbinol und Carbokation schon nach Zusatz von ca 4 % Trifluoressigsäure erreicht ist, benötigt man bei den dialkylaminosubstituierten Carbinolen eine wesentlich höhere Säurekonzentration (10 %) zur vollständigen Protonierung (n = 4). Beiden Systemen ist gemein, daß nach Überschreiten der benötigten Gleichgewichtskonzentration an Trifluoressigsäure, eine Erhöhung der Säuremenge einen Abbau des Chromophos zur Folge hat. Offensichtlich wird dann die Doppelbindung protoniert, ein Vorgang der allerdings reversibel ist und keine Isomerisierungen beinhaltet.E/Z-Isomerisierungen finden allerdings durch Bestrahlungen mit Licht der Wellenlänge l = 366 nm statt. Bei dem Tetrakis(stilbenyl)methan 25a liegt das photostationäre Gleichgewicht bei ca 1/9 (Z/E), bei dem Tris(stilbenyl)methanol 19a liegt es bei 1/7 (Z/E).

Cellular and molecular effects of cross reacting material 197 (CRM197) on HT-29 colon cancer cell line

Cross Reacting Material 197(CRM197) is a Diphteria toxin non toxic mutant that had shown anti-tumor activity in mice and humans. CRM197 is utilized as a specific inhibitor of heparin-binding epidermal growth factor (HB-EGF), that competes for the epidermal growth factor receptor (EGFR), overexpressed in colorectal cancer and implicated in its progression. We evaluated the effects of CRM197 on HT-29 human colon cancer cell line behaviour and, for CRM197 recognized ability to inhibit HB-EGF, its possible effects on EGFR activation. In particular, while HT-29 does not show any reduction of viability after CRM197 treatment, or changes in cell cycle distribution, in EGFR localization or activation, they show a change in gene expression profile analyzed by microarray. This is the first study where the CRM197 treatment on HT-29 show the alteration of a specific and selected number of genes.

Experimental investigation of the reactions 25 Mg(alpha,n)28 Si, 26 Mg(alpha,n)29 Si, 18 O(alpha,n)21 Ne and their impact on stellar nucleosynthesis

In der vorliegenden Dissertation werden die Kernreaktionen 25Mg(alpha,n)28Si, 26Mg(alpha,n)29Si und 18O(alpha,n)21Ne im astrophysikalisch interessanten Energiebereich von E alpha = 1000 keV bis E alpha = 2450 keV untersucht.rnrnDie Experimente wurden am Nuclear Structure Laboratory der University of Notre Dame (USA) mit dem vor Ort befindlichen Van-de-Graaff Beschleuniger KN durchgeführt. Hierbei wurden Festkörpertargets mit evaporiertem Magnesium oder anodisiertem Sauerstoff mit alpha-Teilchen beschossen und die freigesetzten Neutronen untersucht. Zum Nachweis der freigesetzten Neutronen wurde mit Hilfe von Computersimulationen ein Neutrondetektor basierend auf rn3He-Zählrohren konstruiert. Weiterhin wurden aufgrund des verstärkten Auftretens von Hintergrundreaktionen verschiedene Methoden zur Datenanalyse angewendet.rnrnAbschliessend wird mit Hilfe von Netzwerkrechnungen der Einfluss der Reaktionen 25Mg(alpha,n)28Si, 26Mg(alpha,n)29Si und 18O(alpha,n)21Ne auf die stellare Nukleosynthese untersucht.rn