Search

Browse

• Communities
• Authors
• Year
• Titles
• Subjects

My Space

• Login

Advanced studies on the detection and fate of organic pollutants in water

Solomou Nikolitsa

Full record

---

Summary

The present doctoral thesis is orientated towards the investigation of the broad topic of advanced studies of detection and monitoring of the fate of organic pollutants in the aquatic environment. Τhe achievement of this objective is implemented using various scientific means, ranging from the establishment of novel microextraction techniques under atmospheric pressure as well as vacuum conditions regarding the presence of aromatic hydrocarbons in water and tobacco product leachates, to the UVC-induced degradation of a prominent pharmaceutical substance (cilastatin) and nicotine in natural water and treated waste water, where the photodegradation kinetics are studied thoroughly.In Chapter 1 introductory themes are being presented. A comprehensive review on sample preparation and classification of the most popular extraction techniques is demonstrated. The main focus is placed on solvent – free sample preparation techniques and more specifically on SPME and SBSE principles, their two sampling modes (direct and headspace) and the optimization parameters implemented to effectuate optimum extraction yields in each technique. Emphasis is then steered towards the effect of vacuum in headspace microextraction sampling as an alternative way of accelerating the kinetics of an extraction procedure and attaining therefore faster equilibration times. The development of the theoretical model is being presented along with principles regarding the pressure (in)dependence at equilibrium and pressure dependence at pre-equilibrium conditions of headspace sampling from water samples and the KH criterion. HiSorb Sorptive Extraction as a solid phase microextraction technique is also being reported here. On a final note, the subject of photodegradation is examined on a theoretical basis covering degradation mechanisms and photolysis processes as well as basic principles of photolysis, the kinetics of degradation processes and the reaction mechanisms inspected during photolytic procedures.Chapter 2 presents the published report titled: Vacuum-assisted headspace sorptive extraction: Theoretical considerations and proof-of-concept extraction of polycyclic aromatic hydrocarbons from water samples. In this work we propose HSSE sampling under vacuum conditions to reduce equilibration times. A theoretical model is presented that describes the pressure dependence of the so-called vacuum-assisted HSSE (Vac-HSSE) method, and predicts the reduction in equilibration times when lowering the sampling pressure. We take advantage of the theoretical formulation to reach some general conclusions for HSSE on the relationship between the physical characteristics of the stir bar, uptake rates and equilibration times. The theoretical predictions were experimentally verified using water solutions spiked with naphthalene, acenaphthene and fluoranthene as model compounds. The effects of sampling temperature and extraction time under vacuum and regular pressure conditions were thoroughly investigated. The positive combined effect of heating the sample under low sampling pressure pointed that high humidity did not affect the performance of the extraction phase; an effect commonly recorded in headspace solid-phase microextraction. The extraction time profiles built at 25 and 55oC visualized the substantial improvement in extraction kinetics with Vac-HSSE compared to the regular HSSE method. The results on naphthalene (assumed to evaporate relatively fast from the water sample) provided evidence that at 1 atm gas-sided resistance limited analyte uptake by the stir-bar and that this limitation could be effectively reduced by adopting the vacuum sampling approach. The accelerations of acenaphthene and fluoranthene suggested that gasphase constraints limited both the evaporation and analyte uptake processes. Independent method optimization of HSSE under each pressure condition yielded a shorter sampling time for Vac-HSSE compared to the regular HSSE procedure (30 min vs. 60 min respectively). The analytical performances of the two optimized methods were evaluated and it was concluded that Vac-HSSE was performing similar (naphthalene and acenaphthene) or better (fluoranthene) than regular HSSE in half the sampling time needed.Chapter 3 presents the published report titled: Total and bioavailable polycyclic aromatic hydrocarbons in unused and operated heat-not-burn tobacco products and conventional cigarettes. The present studies report, for the first time, the total and bioavailable polycyclic aromatic hydrocarbons (PAHs) concentrations in unused and operated heat-not-burn (HnBs) tobacco products. To enable direct comparisons, identical sets of studies were conducted using conventional cigarettes (CCs). Five low-molecular PAHs were determined in HnBs at total concentrations that were of the same order before and after operation (Σ5PAH = 47.37 ± 3.44 ng unit−1 and Σ5PAH = 69.36 ± 5.78 ng unit−1 in unused and used HnBs, respectively). The incomplete combustion of organics during smoking of CCs, yielded substantially higher amounts of PAHs with their sum (Σ10PAHs = 1449 ± 113 ng unit−1) being >20 times larger than those in HnBs. The tobacco and filter were the most contaminated parts in HnBs. In unused CCs, tobacco had the highest PAHs load and after smoking, the spent filter was the most contaminated part, containing ∼80% of the total amount of PAHs. Naphthalene was the most abundant PAH detected in all tobacco products. Despite the high total PAH concentrations found in smoked CCs, the sums of the bioavailable PAH concentrations were of the same order in all tested tobacco products (Σ5PAH = 61.38 ± 1.79 ng unit−1 in unused HnBs, Σ5PAH = 70.87 ± 7.67 ng unit−1 in used HnBs, Σ4PAH = 66.92 ± 5.95 ng unit−1 in unused CCs, and Σ6PAH = 47.94 ± 1.26 ng unit−1 in smoked CCs). This finding was related to smoking affecting PAHs’ leachability from CCs and delaying their desorption from the solid matrix. Adjusting the pH, salt and humic acids content at environmentally relevant values did not affect PAHs leaching at 24 h of soaking. Finally, the leaching behavior of PAHs in natural waters (river water, rainwater, and seawater) was found similar to that in ultrapure water, experimentally verifying the ability of tobacco product waste to leach PAHs into the aquatic environment.Chapter 4 presents the published report titled: UV-254 degradation of nicotine in natural waters and leachates produced from cigarette butts and heat-not-burn tobacco products. In this study, the UV254 photolytical fate of nicotine in natural water and leachates produced from conventional cigarettes (CCs) and the new generation heat-not-burn (HnBs) tobacco products is examined for the first time. The effect of UV254 irradiation on nicotine depletion in ultrapure water was initially studied. The reaction was pseudo first-order with respect to nicotine concentration at low concentrations and shifted to lower order at higher concentrations, an effect associated to absorption saturation. Although nicotine removal was fast, only 9.5% of the total organic carbon was removed after irradiation due to the formation of by-products. The chemical structures of six photo-products were derived by means of liquid and gas chromatography coupled to mass spectrometry. The photodegradation kinetics was found to depend on pH and faster kinetics were recorded when the monoprotonated form of nicotine was dominant (pH = 5–8). The presence of humic acids was found to slightly delay kinetics as they competed with nicotine for lamp irradiance, whereas the presence of salt had no effect on the direct photolysis of nicotine. Direct photolysis studies were also performed using natural waters. Compared to ultra-pure water, photodegradation was found to proceed slightly slower in river water, in similar kinetics in seawater, and relatively faster in rain water. The later was assumed to be due to the lower pH compared to the rest of the natural water tested. Leachates from used HnBs and smoked CCs were also submitted to UV254 irradiation and direct pho

Available Files

Services