• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 91
  • 90
  • 31
  • 26
  • 12
  • 7
  • 4
  • 3
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 300
  • 87
  • 76
  • 62
  • 49
  • 35
  • 32
  • 25
  • 25
  • 23
  • 23
  • 22
  • 20
  • 19
  • 18
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Genotoxicity of complex chemical mixtures

Phillips, Tracie Denise 15 May 2009 (has links)
Complex chemical mixtures are ubiquitous in the environment. Humans are frequently exposed to these mixtures; therefore, it is important to understand potential interactions of chemical mixtures. Mixture interactions may influence the absorption, distribution, metabolism or excretion of the components of a complex mixture. The research conducted for this dissertation has coupled chemical fractionation with in vitro and in vivo bioassays to assess the potential carcinogenic risk of complex mixtures. A non-aqueous phase liquid from a wood treatment plant was separated into acid (AF), base (BF) and neutral fractions (NF). The NF was further enriched using column chromatography to produce a polychlorinated dinbenzo-p-dioxin (PCDD) and a polycyclic aromatic hydrocarbon (PAH) fraction. The genotoxicity of these mixtures were assessed via analytical quantification, in vitro (Salmonella microsome and E. coli prophage induction) and in vivo (32P-postlabeling) bioassays. The NF was further tested to measure bulky DNA adducts and induction of tumor formation. The AF contained the highest level of pentachlorophenol and the highest concentration of total PAHs. Although the carcinogenic PAHs were highest in the PCDD fraction, the highest concentrations of benzo(a)pyrene (BAP), indeno(1,2,3-cd)pyrene and dibenz(a,h)anthracene were detected in the PAH fraction. A positive genotoxic response in Salmonella was induced by the crude extract, the PAH and BF, whereas the AF and BF induced a positive response in the E. coli assay. In vivo, the PAH fraction induced the highest DNA adduct frequencies in the lung. The NF, reconstituted mixture (RM) (which includes equivalent concentrations of seven carcinogenic PAHs in the NF), BAP and the NF amended with BAP (NF+BAP) were all tested in an infant mouse model. At the highest dose, after a 24 hr exposure, NF+BAP had the highest total DNA adducts measured in liver which was three to seven times higher than with other treatments. Adduct levels were comparable to the control after 280 days. The highest incidence of tumors was observed in the liver. At the high dose, NF+BAP elicited the highest incidence of tumors. The results of this research confirm previous studies and indicate that the carcinogenic potential of PAH mixtures may be greater than predicted by chemical analysis.

Biomarkers of exposure to complex environmental mixtures

Naufal, Ziad Sami 15 May 2009 (has links)
Maternal exposure to genotoxic chemicals may produce a variety of adverse birth outcomes. Depending on the dose and duration of exposure, adverse birth outcomes can range from premature or low-birth weight, to congenital abnormalities including neural tube defects (NTDs). The research described in this dissertation focused on several rural counties in Shanxi province, China. Shanxi has one of the highest rates of NTDs in the world. In 2005, the incidence of NTDs in the study counties ranged from 8 to 24 cases per 1,000 births. While some of these birth defects are likely to be related to nutrition, it is also suggested that environmental factors play a significant role. One such factor includes polycyclic aromatic hydrocarbon (PAH) exposure as a result of combustion of coal for indoor heating and cooking. Human populations in Shanxi depend heavily on coal as their main source of energy. This study determined the concentrations of PAHs in house dust, venous blood and placenta of study participants. Dust was collected from homes in the study site. Carcinogenic PAH levels in dust collected from kitchen floors ranged from 12 to 2,000 µg/m2. The genotoxic potential of dust was confirmed by shortterm bioassays. Median concentrations of total PAHs in placenta from children born with NTDs were elevated compared to matched controls and appeared to be associated with the risk of having a child with a NTD. Tobacco smoking was not associated with elevated levels of PAH biomarkers in this study population. Levels of bulky DNA adducts in placenta have also been quantified using 32P-postlabeling. Adduct levels do not appear to be significantly different between cases and controls and were not associated with deletions in enzymes GSTM1 or GSTT1. These data suggest that children born with NTDs may be at increased risk due to exposure to genotoxic PAHs. Studies with a larger number of subjects are needed to further elucidate the relationship between PAH exposure and adverse birth outcomes.

Biodegradation of PAHs in Diesel Fuel by Candida viswanathii in Salty Environment

Yu, Tsung-Lin 29 June 2003 (has links)
Taiwan is an island country. Therefore, it must depend on sea and air transport to communicate with other countried. Especially, the import and export of cargo rely on the sea transport. Nowadays, some ships still use diesel oil as fuel. During the transport, the ship is inevitable for leak, or accidents happening in marine environment. Therefore, in this research, through the man-made sifting way, we will sieve and purify the pure species bacteria, which can degrade the PAHs in diesel fuel floating on the sea surface to decrease its pollution to the marine environment. In this research, eight species of pure bacteria will be sifted to purify. After primarily degrading experiment, we found that the second species of the bacteria performed the best degrading effect. After further identification, it was known that the second species of bacteria was yeast with name of Candida viswanathii. The bacteria were then used to in this study on biodegradation of PAHs in the diesel fuel. According to the experimental results, we found that bacteria could degrade diesel fuel. The OD value and total amount of the bacteria were found to be increased, but showed less degrading effect on PAHs in diesel fuel. However, in the experiment regarding the bacteria against single kind of PAHs, it showed excellent degrading effect on Naphthalene. When the initial concentration of Napthalene was controlled at 10 mg/L, the degrading rates were 0.3 and 0.24 mg/L-day respectively, in two separate experiments. Concerned with the degrading experiment against Anthracene, learned from the chromatography diagram it was observed that the concentration controlled at 10 and 5 mg/L, the production rate of Naphthalene were measured equal to 0.049 and 0.028 mg/L-day respectively. Thus, it was concluded that Anthracene can be degraded by the bacteria, but the degrading rate was slow, and the metabolite might be Naphthalene. As for the Flouranthene, the bacteria presented no degrading effect on it. It was concluded that the bacteria might not degrading ability toward four-ring or above PAHs. In conclusion, it is quite difficult to use single species of bacteria to deal with highly-complicated organic. It is suggested that we should study more about the degrading character of every species of bacteria. After that, we can get better effect by using similar compound bacteria to deal with the PAHs in the diesel oil.

The influence of surfactants on the sorption of phenanthrene in natural waters

Jones-Hughes, Tracey Louise January 2002 (has links)
Polycyclic aromatic hydrocarbons (PAHs) are widely recognised as harmful, persistent organic pollutants, whilst surfactants are more easily degraded but their ubiquitous use both domestically and industrially ensures their presence in natural waters. Owing to both their hydrophobic and hydrophilic properties, surfactants are capable of both adsolubilisation and solubilisation of co-contaminants, hence, their presence in natural waters is considered extremely significant. The purpose of this research was to determine how surfactants and PAHs influence each other in estuaries where both are co-disposed. This study is the first to employ environmentally realistic concentrations of surfactants and to use natural particles in order to determine how changes in surfactant behaviour impinge on the sorption of a representative PAH to sediment. The experimental method employed involved tracing the solubility and sorption of a '''C-labelled PAH (phenanthrene) in the presence of representative surfactants from the three main groups, i.e., anionic, nonionic and cationic. Initially the four compounds were examined in isolation at two temperatures (8°C and 20°C), salinities and particle concentrations. The next stage involved incorporating each surfactant with phenanthrene in the same experiment and repeating the range of variables. Solubility and adsorption of phenanthrene in the presence of Triton X-100, sodium dodecyl sulphate (SDS) or hexadecyltrimethylammonium iodide (HDTMA) proved to be highly complex. The adsorption, expressed as a Freundlich coefficient, KF was generally nonlinear and varied according to surfactant type, salinity, temperature, and contact sequence. The overriding influence, however, was sediment particulate matter (SPM) concentration. On some occasions the surfactants in isolation displayed unusual particle concentration effects (PCE), such as an increase of surfactant in the aqueous phase as the SPM concentration increased. Despite this, they all generally exaggerate the more typical PCE displayed by phenanthrene, where the particle-water partition coefficient is reduced as particle concentration increases. This effect is then modified by temperature and contact sequence, which has important environmental implications with regard to removal or release of compounds stored within sediments. However, overall, at environmentally relevant concentrations, the surfactants appear to enhance sorption, rather than solubility, with HDTMA the most effective surfactant at removing phenanthrene from the aqueous phase.

Development of a Method for GC/MS Analysis of PAHs and Alkylated PAHs for Use in Characterization and Source Identification of PAH Contaminated Sites

Vestlund, Hanne January 2014 (has links)
Polycyclic aromatic hydrocarbons (PAHs) are toxic and carcinogenic environmental contaminants originating from different sources; petrogenic, pyrogenic or biogenic. Depending on the source of contamination there will be different ratios of PAHs and the effects on the environment will differ. Petrogenic sources will be higher in concentration of alkyl substituted PAHs (APAHs) while pyrogenic sources will be higher in parent PAHs. In the present study a GC/MS method was developed to separate and calibrate PAHs, dibenzothiophenes and alkyl substituted PAHs in a mix containing 49 standards. The method was able to differentiate between PAHs and APAHs with the same mass number; up to six different compounds with the same mass number was separated. The developed method was used to analyse six different soil samples from various contamination sites. PAHs, APAHs and dibenzothiophenes were identified and quantified in all samples. In order to establish the source of contamination, the distribution pattern, the ratio between different PAHs, and the ratio between APAHs and parent PAHs were used. There was a higher ratio of APAHs/PAHs and a lower ratio between the parent PAHs in the soil samples from sites contaminated with oils compared to the other samples, indicating petrogenic source. / Polycykliska aromatiska kolväten (PAH) är giftiga och cancerframkallande miljögifter som härstammar från olika källor; petrogena, pyrogena eller biogena. Olika föroreningskällor kommer att ha olika förhållanden av PAH och effekterna på miljön kommer att skilja. Petrogena källor innehåller högre koncentrationer av alkylsubstituerade PAH (APAH) medan pyrogena källor kommer att ha högre koncentration av PAH. I denna studie har en GC/MS-metod utvecklats för att separera och kalibrera PAH, dibensotiofener och alkylsubstituerade PAH i en blandning innehållande 49 standarder. Metoden kunde skilja mellan PAH och alkylsubstituerade PAH med samma masstal; upp till sex olika föreningar med samma masstal särskildes. Den utvecklade metoden användes för att analysera sex olika jordprover från olika föroreningsplatser. PAH, APAH och dibensotiofener identifierades och kvantifieras i samtliga prover. För att fastställa föroreningskällan användes fördelningsmönstret för APAH och PAH, förhållandet mellan olika PAH och ration mellan APAH och PAH. Det fanns en högre kvot APAH/PAH i jordprover från områden som var förorenade med olja, vilket indikerar på petrogena föroreningskällor.

Trace analysis of halogenated polycyclic aromatic hydrocarbons from an electronic waste recycling area and Guangzhou, China

Gonzales, Leah R. 15 June 2011 (has links)
Halogenated Polycyclic Aromatic Hydrocarbons (X-PAHs) are ubiquitous contaminants that are thought to be generated by processes such as chemical industries and incomplete combustion, including waste incineration and electronic waste (e-waste) burning. X-PAHs are a concern for environmental and human health because they are toxic, mutagenic, and are expected to be more lipophilic than the parent compounds. To study these compounds in the environment, an analytical method was developed, utilizing large-volume injection via a programmable temperature vaporizing (PTV) inlet, using environmental samples from an e-waste area and in Guangzhou, China. The concentrations of 26 X-PAHs were measured in atmospheric particulate matter (PM), house dust (HD), and sediment. In general, the X-PAH concentrations in PM were low, with concentrations ranging from <0.078 to 41.81 pg/m³. There was no significant difference in X-PAH concentrations in PM between the e-waste area and Guangzhou. These concentrations are of the same order of magnitude as previous studies of X-PAHs in PM. These data suggest that e-waste activities are not a significant source of X-PAHs in atmospheric PM. The concentrations of X-PAHs in HD samples ranged from <0.0372 to 3575 pg/g dry weight. In general, there was no significant difference between E-waste and Guangzhou HD concentrations. The profiles of X-PAHs in PM and HD were different, suggesting that there are additional sources for X-PAHs inside homes other than outdoor air. The concentrations of X-PAHs in sediment samples from an e-waste site ranged from <104 to 2890 pg/g dry weight. The X-PAH profile in sediment more closely resembled the X-PAH profile of PM. / Graduation date: 2011

Concentrations and sources of polycyclic aromatic hydrocarbons in sediment cores of southern continental shelf of Kaoping submarine canyon

Li, Kun-je 30 July 2007 (has links)
This study investigated distributions and the concentrations of polycyclic aromatic hydrocarbons (PAHs) in the sediment cores in southern continental shelf of Kao-Ping submarine canyon. The sediment cores collected were analyzed for PAHs to reconstruct historical record of PAH contamination and to find out the possible sources, trends and fluxes. The findings demonstrated the average concentrations of PAHs in the northern continental shelf of Kao-Ping submarine canyon were higher than in the southern continental shelf. The average concentrations of £U51 PAHs and £U16 PAHs ranged from 578 to 697 and from 132 to 173 ng/g , respectively. Because particle sedimentation rates and PAH sources were different along cores, vertical distributions of PAH concentrations among cores were not the same. Identification by diagnostic ratios and result of hierarchical cluster analysis (HCA) suggesting PAHs in the core of northern continental shelf were from pyrogenic and petrogenic sources, while those in the cores of southern continental shelf were from petrogenic source. Compared with sediment quality guidelines (SQGs), most of the sample sediment cores are below the outlined criteria. Only the PAH concentrations of the sediments between 2-16 cm in the core L27 were higher than the Threshold Effect Level (TEL) value. Total PAH concentrations in this study were lower than those from other coastal areas in literature. According to the PAH concentrations along cores in the southern continental shelf, significant increase of total PAH concentrations was evident in the early 1900s. Our results also demonstrate that PAH concentrations and sources in the southern continental shelf area related to the increasing industrial activities in Kao-Ping coastal area.

The distribution of Persistent Organic Compounds in the sediments of the Coastal Areas along the Southwestern Taiwan

Jiang, Jheng-jie 30 August 2006 (has links)
This study is to measure the concentrations of polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers (PBDEs) in the sediments of the coastal areas along the southwestern Taiwan. Sediment samples were collected and analyzed to investigate the possible sources and characteristics. The concentration of PAHs and PBDEs ranged from 15 to 907 and from N.D. to 92 ng/g dry wt, respectively, and congener compositions for PBDEs were dominated by BDE-209 (68.8-77.9%). Total PAH concentrations we found in coastal sediments were lower than those of other studies in the world. The highest £UPAH values were observed at Kaohsiung coastal areas, while the lowest £UPAH values were found at Tainan coastal areas. Total PBDE concentrations in coastal sediments were lower than those in river sediments. Sources of PBDEs in those sediments from coastal areas were different from those of river sediments because compound compositions in both areas were different. Both total PAH and total PBDE concentrations were significantly correlated with total organic carbon (TOC) and mean particle size (r=0.51, -0.42, p<0.01; r=0.80, -0.85, p<0.01). In comparison with sediment quality guidelines (SQGs), the PAH concentrations of all sediment samples were lower than those outlined in the criteria, that suggests no evident adverse biological effects caused by PAHs. According to the results of hierarchical cluster analysis (HCA) and principal component analysis (PCA), the stations can be clustered into three groups. In general, PAHs in sediments of Kaohsiung coastal area were mainly contributed from combustion sources, while those in Kao-ping estuary were mainly from petrogenic sources. However, both sediments in Tainan and Hsinda harbor coastal areas were mainly contributed from biogenic sources.

The Influence of Ionic Strength on the Partition Coefficient of Polycyclic Aromatic Hydrocarbons and Dissolved Organic Matter

Wang, Hui-Ling 24 June 2000 (has links)
ABSTRACT Hydrophobic organic pollutants (HOPs) are in general characterized by high toxicity, long environmental half-life and high bio-accumulation factors. Due to their hydrophobicity, HOPs tend to sorb onto particulates in natural aquatic environment and their degradation pathways and rates are altered with the change of the reaction media and the settlement of these particles. The influence of the dissolved organic matters (DOMs), termed as the third phase, on the sorption partition coefficient is observed because of their interactions with HOPs. This binding (between DOM and HOP) increases apparent solubility and mobility of the HOP and the sorption coefficient of HOP in aquatic system is reduced. On the purpose of obtaining data closer to the real world, many aquatic factors, such as the concentration and types of DOM, pH value and ionic strength, are studied intensively recently. Nevertheless, it is difficult to clarify the influence of ionic strength because the relationship between binding constant of DOM-HOP and ionic strength is ambiguous in the literature. As such, by applying fluorescence quenching method, we investigate the influence of ionic strength on the partition coefficient (Kdom) of PAHs (phenanthrene¡Bpyrene)-humic acid (HA) system. Results show that the interaction of HA and cations is the primary factor in the variations of the partition coefficient. It is believed that, as cations reacting with specific binding sites on HA, the molecules' configuration of HA is changed and the binding mechanism of PAHs and HA is altered. A "four-stage variation model" is then proposed to explain the relationship between the ionic strength and partition coefficient. Therefore, a non-constant trend of ionic strength effect is resulted and is used to explain the controversial findings in the literature. Furthermore, Mg++ is found to cause stronger effect than K+ owing to higher charge density. The introduction of Br- would complicate the fluorescence quenching mechanism of phenanthrene-HA system because it's a fluorescence quencher. However, effects of anions on the variation of Kdom are not as significant as cations in our system. The effects of ionic strength on the variation of Kdom for four humic acids are LHA¡ÖPHA¡]Peat humic acid¡^¡ÖSHHA¡]Summit Hill humic acid¡^¡ÖSRHA. Results from different humic acids indicate that the Suwannee River humic acid (SRHA) is not as sensitive as Leonardite humic acid (LHA) on the ionic strength effect because of lower hydrophobicity. The influence of ionic strength on the variation of Kdom for pyrene-HA system is also amplified because of pyrene's higher hydrophobicity compared with phenanthrene.

The toxicity of alkyl-chrysenes and benz[a]anthracenes to embryonic fish

Lin, HONGKANG 13 January 2014 (has links)
Alkylated polycyclic aromatic hydrocarbons (alkyl-PAHs) are major constituents of crude oil, and the 3-5 ringed alkyl-PAHs have been identified as the main components chronically toxic to fish. While chysene homologues have higher cytochrome P4501A (CYP1A) induction potencies than alkyl-phenanthrenes, there is little characterization of toxicity for 4-ringed alkyl PAHs. This study measured the chronic toxicity of chrysene, benz[α]anthracene, and some alkylated congeners to the embryos of Japanese medaka (Oryzias latipes) using the partition-controlled delivery method (PCD) of exposure. This exposure method relies on the partitioning of chemicals from polydimethylsiloxane (PDMS) films, loaded with various concentrations of test chemical, to embryo rearing solutions. The objectives of this thesis were: (1) to further characterize the PCD method with a series of 4-ringed PAHs; (2) to evaluate the effects of different chemical structures on the toxicity of test compounds; and (3) to extend structure toxicity relationships from alkyl-phenanthrenes. The PCD method generated a gradient of aqueous concentrations for test compounds, and these exposure concentrations were maintained constant for the 17-day period. Benz[α]anthracene showed higher toxicity than chrysene. Toxicity increased with the degree of alkylation on the ring structures, except that 2-methylbenz[α]anthracene was less toxic than the unsubstituted benz[α]anthracene. Substitutions at the middle region contributed to a higher toxicity than substitutions at the distal region. While actual mechanisms for these compounds to cause toxicity are unknown, the narcotic mode of action seems to be not involved due to the lack of mortality. Within the range of test concentrations, the chronic sublethal toxicity was limited by the low solubility of the test compounds. A structure toxicity relationship was illustrated by the regression between log EC50s and log Kow values. In addition to hydrophobicity represented by log Kow, structural dissimilarities between compounds and physical characteristics such as aqueous solubility limits should be taken into account in toxicity assessments with alkyl-PAHs. This research is the first toxicological assessment of alkyl-chrysenes and benz[α]anthracenes which is essential for a better understanding of structure toxicity relationships of alkyl-PAHs, and will contribute to more accurate ecological risk assessments of PAH contamination. / Thesis (Master, Biology) -- Queen's University, 2014-01-10 16:35:00.232

Page generated in 0.0223 seconds