No description available.

No description available.

The three isomers of dichlorobenzene (DCB) exhibit marked differences in hepatotoxicity following intraperitoneal (ip) administration in male F-344 rats. Plasma GPT activity, measured 24 hours post exposure, was elevated to approximately 4080 units/ml following a 1.8 mmol/kg dose of o-DCB. Conversely, n-DCB produced only a moderate elevation (306 units/ml) following a 4.5 mmol/kg dose, while p-DCB produced no elevation in GPT activity at this dose (24 units/ml). Ultra-structurally, o- and m-DCB induced elevations in GPT activity were associated with a centrilobular pattern of hepatic necrosis. The role of cytochrome P-450 mediated bioactivation in DCB-induced hepatotoxicity was demonstrated by elevated GPT activities following an otherwise nontoxic 0.9 mmol/kg dose of either o- or m-DCB in phenobarbital pretreated animals (16770 and 21540 units/ml, respectively). The paraisomer of DCB showed no induction of toxicity with phenobarbital pretreatment. Hepatic glutathione (GSH) concentrations were reduced 0.5, 3 and 5 hours after a 1.8 mmol/kg dose of either o- or m-DCB, a dose which produces hepatotoxicity only for o-DCB. Pretreatment of animals with phorone depleted hepatic GSH to 15% of control levels within two hours; subsequent ip administration of either o- or m-DCB (1.8 mmol/kg) produced approximately equivalent elevations in GPT activity for both isomers (5749 ± 648 and 4732 ± 857 units/ml, respectively). In vitro incubations of o- and m-DCB with GSH and rat liver cytosolic fraction, suggested that GSH may bind m-DCB without prior bioactivation, thereby reducing the hepatotoxicity of this isomer relative to the more toxic ortho isomer. The interactive hepatotoxicity of the dichlorobenzenes with carbon tetrachloride (CCl₄) was also investigated. Concomitant ip injection of CCl₄ (1.0 mmol/kg) and o-DCB (2.7 mmol/kg) produced a marked inhibition of o-DCB hepatotoxicity, as measured by GPT activity (approximately 200 units/ml vs. 7450 units/ml for o-DCB alone). The mechanism of this inhibition of o-DCB hepatotoxicity was shown to be a reduction in the cytochrome P-450 mediated bioactivation of o-DCB, by CCl₄. A similar inhibition of o-DCB hepatotoxicity was seen following administration of CCl₄ as a pretreatment, via the drinking water. Concomitant ip administration of CCl₄ with either m- or p-DCB also produced a reduction in the metabolism of the dichlorobenzene.

Interstellar chemistry has been a growing field over the last several decades. There is particular interest on the nature and reactivity of interstellar molecules; most notably that of polycyclic aromatic hydrocarbons (PAHs). My thesis focused on the kinetics of unimolecular dissociation of small PAH and PAH-like molecules under interstellar conditions. PAHs (naphthalene (NAP), anthracene (ANT) and pyrene (PYR)), some dihydro- equivalents (1,2-dihydronapthalene (DHN) and 9,10-dihydrophenanthrene (DHP)) and a few other small aromatic organic molecules (indene (IND), ethynylbenzene (EB), propynylbenzene (PB) and benzocyclobutene (BCB)) were studied using imaging photo-electron photo-ion coincidence spectroscopy (iPEPICO) and electron impact mass spectrometry (MS); both mass analyzed ion kinetic energy spectrometry (MIKES) and collision induced dissociation (CID). Experiments were performed at different ionization energies to produce breakdown diagrams for the various fragments. These diagrams are then fit using RRKM theory to determine the zero Kelvin activation energy (E0) and the entropy of activation (Δ‡S); these results are then compared and discussed. All these molecules were compared in order to try and find any overlying trends which could be applied to their role in the interstellar medium (ISM). It was determined that H loss was the dominant fragmentation channel, as it was the only dissociation channel common to the majority of molecules studied. It was also seen that organic fragment loss (C2H2, CH3 and C4H2) was only observed in smaller molecules which indicates that PAHs are not likely a source of these molecules. The small fragment molecules gave insight into the stability of closed ring structures, such as PAHs, through the comparison of the dissociation of closed and open structures. The dihydro-PAHs, selected as a probe to investigate the proposed catalytic role of PAHs in the formation of molecular hydrogen, yielded very interesting results. It was seen that these molecules would readily undergo isomerisation prior to dissociation. This added an unexpected level of difficulty to the calculations but quickly demonstrated how the presence of additional hydrogen atoms could greatly disrupt the dissociations, as it was not the simple process of removing them as it was originally believed. The overall trend observed was that it is the structure, not the size, which has the dominating effect on the dissociation. Ions of similar structure behaved similarly, regardless of a change in mass; isomers, however, had radically different behaviours which can only be attributed to their differing molecular conformations. This observation could aid in the understanding of larger PAHs, those which are believed to exist in the ISM, and what role they may play in the chemistry of the universe.

The objective of this thesis was to investigate firefighters’ exposures to carcinogens and mutagens. This thesis aimed to (1) characterize firefighters’ exposures during emergency fire suppression, (2) examine the use of silicone wristbands as passive samplers to assess firefighters’ exposures, and (3) assess the ability of post-fire decontamination protocols to reduce firefighters’ exposures. Chapter 1 provides a general introduction and background information on the concepts covered in this thesis. In Chapter 2, I examined air and surface contamination with polycyclic aromatic hydrocarbons (PAHs) and metals, both at fire stations and following emergency fire suppression activities. I also investigated the ability of current laundering methods to remove surficial PAHs and metals from firefighters’ personal protective equipment. In Chapter 3, I assessed the ability of silicone wristband passive samplers to measure firefighters’ exposures to PAHs during live fire training. In Chapter 4, I assessed the ability of three post-fire dermal decontamination methods to remove surface contamination and reduce internal dose. In Chapter 5, conclusions and implications for each chapter are summarized. Future directions for the field are described. The overall conclusions for this thesis were: i. firefighters experience significant occupational exposures to carcinogens during emergency fire suppression and live fire training; ii. the ability of silicone wristbands to properly sample PAHs is altered in a fire environment and correction factors must be determined to improve their utility for exposure assessment; iii. current post-fire dermal decontamination methods, which are intended to reduce firefighters’ exposures, do not reduce their internal dose of PAHs.

No description available.

A groundwater monitoring study was conducted as part of a comprehensive program to remediate a former wood-preserving site that was contaminated with creosote. Twenty-five multi-level samplers (MLSs) were installed on-site and groundwater samples were collected and tested regularly between March 1998 and July 2000. Nearly one-thousand hybrid poplar trees were planted on-site in 1997 to help contain the groundwater plume and enhance phytoremediation. Ten polycyclic aromatic hydrocarbons (PAHs) were monitored along with several terminal electron acceptors (TEAs) and their reduced end products. The focus of the study was to determine the extent of natural biodegradation in the subsurface and assess the role of the poplar trees in site remediation. Since monitoring began, considerable progress has been made remediating the site and the contaminant plume has been shrinking consistently. PAH levels in the groundwater and soil have been reduced and individual MLSs show consistently decreasing contamination. At this point in the study it cannot be conclusively determined what impact the poplar trees are having on the progressing site remediation. However, there is a wealth of evidence indicating that natural biodegradation is playing a major role in site cleanup. Monitoring of TEAs indicates suggests that there are aerobic zones in the site aquifer, but that reduced conditions exist as well. Dissolved oxygen (DO) was found in many MLS ports, but other ports were devoid of both DO and nitrate and contained large quantities of aqueous Fe(II). Oxygen, nitrate and Fe(III) are being reduced on-site and data suggests that they are being used in the biological oxidation of PAHs. Although laboratory studies document the oxidation of PAHs under sulfate-reducing conditions, high aqueous sulfate values were recorded throughout the site, regardless of the level of contamination. Several possible mechanisms are proposed to explain the coexistence of high sulfate and PAHs in the site aquifer. The system may be redox-buffered by excess solid Fe(III) and Mn(III, IV) oxides. Also, dissimilatory sulfate-reducers are strict anaerobes and oxygen-rich rainwater may be toxic to them. The presence of a layer of coal below land surface creates pyrite oxidation conditions similar to those encountered in conjunction with acid mine drainage. The MLSs most affected by the coal layer have less PAHs and DO, lower pH, and higher sulfate and Fe(II) levels than other wells. The oxidation-reduction status of each MLS, based on oxygen, nitrate and Fe(II) measurements, appears to be closely related to the level of PAH contamination, suggesting that PAHs are the primary substrate being biologically oxidized in the site aquifer. These findings tend to support the general belief that the major limitation to natural biodegradation in subsurface environments is the delivery of adequate supplies of suitable TEAs to contaminated zones. / Master of Science

Thesis (M.Sc. (Chemistry)) --University of Limpopo, 2017 / The presence of polycyclic aromatic hydrocarbons (PAHs) in the environment is of major concern since these compounds are highly persistent, toxic and wide spread pollutants. The aim of this study was to evaluate the levels of PAHs in water and sediment samples collected from Blood and Mokolo Rivers in Limpopo Province, South Africa. Liquid-liquid extraction (LLE) was used for the extraction of PAHs from water, whereas PAHs in sediments were extracted using optimised microwaveassisted extraction (MAE). Furthermore, ultrasonication and a combination of ultrasonication and mechanical agitation were used for the extraction of PAHs from sediments samples. The quantification of sixteen (16) PAHs in water and sediment was carried out using gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode and by GC-flame ionisation detector (GC-FID). Concentrations of PAHs in sediments were higher than in water. The highest concentrations of PAHs were obtained in Mokolo River sediments, with the concentration ranging between 0.044 and 51.9 mg/kg. The levels of PAHs recorded in Blood River sediments were lower than those obtained in Mokolo River with concentrations ranging between 0.014 and 3.10 mg/kg. In water samples, higher levels of PAHs were observed in Mokolo River (between 0.0219 and 1.53 µg/L) while lower concentrations were recorded in Blood River (between 0.0121 and 0.433 µg/L). In water and sediment samples from both Rivers, higher molecular weight (HMW) PAH compounds (4-6 rings) were found at greater concentration levels than lower molecular weight (LMW) PAHs (2-3 rings), and this can be attributed to pyrogenic activities in the study areas. The efficiencies and accuracy of the methods for the extraction of PAHs were determined by assessing the recoveries of samples spiked with known amount of standards (for water samples), while a certified reference material (CRM) was used for sediments. Percentage recoveries ranged from 67.6 to 115% for LLE and 83.8 to 125% for MAE for both sample types. Diagnostic ratio was used for the source identification of PAHs in sediment samples. Several PAHs ratios indicated that both pyrogenic and petrogenic could be the sources of these compounds in both rivers. Toxic equivalency factors (TEFs) and benzo(a)pyrene equivalent (BaPE) were used to quantitatively estimate the PAHs potential human health risk. The assessment of ecotoxicological risk indicated that the v sediment samples collected from Mokolo River are at high toxicity risk while sediments from Blood River are at low sediment toxicity risk. / Water Research Commission (WRC), National Research Foundation (NRF) and Sasol Inzalo Foundation

During the past 30 years, numerous studies have focused on the toxicities of polycyclic aromatic hydrocarbons (PAH). Laboratory and field studies have helped elucidate the detrimental effects of these chemicals on growth, reproduction and immune response. Polycyclic aromatic hydrocarbons are in the priority list of chemicals to be studied by different governmental agencies and universities and understanding their mechanisms of action is the focus of the current research. The manuscripts presented in this dissertation are focused on the effects and mechanism of action of PAH on disease susceptibility. After a dietary exposure to PAH for up to 50 days (chapter II) and samplings after 3, 7, 14, 28 and 50 days, a number of biomarkers of PAH exposure were measured: Fluorescent aromatic compounds (FACs) in bile, ethoxyresorufin-o-deethylase (EROD) in liver microsomes, cytochrome P450 1A immunohistochemistry in liver and kidney and adduct formation in liver. Additionally markers of oxidative stress were measured: comet assay in blood, protein nitration in kidney and F2-isoprostanes in kidney. Oxidative stress was a probable factor in PAH induced responses in fish adapted to long-term PAH exposures and aryl hydrocarbon activation was not necessarily involved in this process. Disease challenge with Aeromonas salmonicida (chapter III) resulted in differences in mortalities that demonstrated that fish exposed to PAH were more susceptible to disease than fish not exposed to PAH. Determination of gene expression in head kidney of fish exposed and not exposed to PAH challenged with A. salmonicida using microarray and RT-PCR technologies 2, 4, 10 and 20 days after challenge (chapter IV), suggested that PAH exposure was associated with down regulation of interleukin 8, transport associated protein 1, NF-kB modulator, recombination activating gene and major histocompatibility complex II two days after challenge in fish exposed to PAH. The transcript levels were closer to control levels 20 days after challenge, this indicated a recovery from the effect of PAH exposure. / Graduation date: 2006

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Restricted until October 2006. Bibliography: leaves 99-106.