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Fate and behavior of pharmaceuticals and nanoparticles in the subsurface

Fountouli Theodosia

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Summary

Soil, along with aquatic ecosystems, is the main recipient of anthropogenic environmental pollution. The variety and amount of pollutants deposited in the soil is large, so it is difficult to assess their effects, which are often not limited to the disposal site, but are likely to extend to the wider area. For this reason it is necessary to know the chemical, physical and biological processes that are responsible for the fate, transport and degradation of these pollutants. Specifically, knowledge the fate of these pollutants in soils or sediments is important for environmental exposure assessment and risk assessment. The results of the present study are expected to contribute to the assessment of the resilience of the examined substances to the environment and the possibility of their accumulation in natural resources and environmental recipients (groundwater and surface water, soil). The aim of this dissertation was to evaluate the behavior of various types of pollutants, pharmaceuticals (pharmaceuticals and pesticides) and nanoparticles (or colloids) in the subsurface. More specifically, substances belonging to 3 pollutant categories were studied: the pharmaceuticals acyclovir and fluconazole, the disinfectant formaldeyde and the nanoparticle titanium dioxide, (TiO2). These pollutants were selected due to their widespread consumption and the frequency with which they are found in the aquatic environment and the subsurface.Initially, the interaction of two pharmaceuticals (acyclovir and fluconazole) with quartz sand was investigated. More specifically, the adsorption behavior of acyclovir and fluconazole onto quartz sand at three different temperatures (40C, 100C and 220C) under static and dynamic conditions was examined. Kinetic adsorption data were described successfully by a pseudo-second order model. Furthermore, adsorption equilibrium data were quantified with a linear adsorption isotherm. Based on the experimental results of this study, it can be presumed that acyclovir and fluconazole are weakly adsorbed onto quartz sand. Consequently, it is anticipated that these pharmaceuticals will be considerably mobile in sandy subsurface formations and can be potentially transported to the aquatic environment with potentially negative effects on living organisms and human health.The interaction of formaldehyde with quartz sand and colloidal kaolinite particles under static and dynamic conditions was studied and the results indicated that formaldehyde has a weak affinity for quartz sand but a relatively strong affinity for kaolinite colloid particles. The transport of formaldehyde through columns packed with quartz sand under different salinity concentrations was also investigated. Experimental results showed that salinity had minimum effect on formaldehyde sorption onto quartz sand, but somewhat more significant effect on formaldehyde sorption onto kaolinite (KGa-1b). Therefore, formaldehyde could be relatively mobile in natural soil and sediments and could potentially pollute the aquatic environment with possible undesirable effects on living organisms and human health.The effect of two representative colloid-sized clay particles (kaolinite, KGa-1b and montmorillonite, STx-1b) on the transport of formaldehyde in unsaturated porous media was examined. More specifically, the transport of formaldehyde in the absence or the presence of clay particles under various flow rates and various levels of saturation in columns packed with quartz sand, under unsaturated conditions was examined. Τhe classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to calculate the total interaction energy, at air-water interfaces (AWI) and the solid-water interfaces (SWI). The experimental results of this study showed that the presence of kaolinite and montmorillonite colloids significantly inhibited the transport of formaldehyde under unsaturated conditions.Furthermore, laboratory-scale experiments were conducted to investigate the simultaneous transport of titanium dioxide (TiO2) nanoparticles and formaldehyde (FA) in columns packed with quartz sand under water saturated and unsaturated flow conditions. The effects of interstitial velocity and solution ionic strength on the TiO2 and FA cotransport were examined. Also, the DLVO interaction energies between TiO2 nanoparticles and quartz sand, the solid-water interface (SWI), and the air-water interface (AWI) were calculated. The experimental results indicated that substantial retention of TiO2 nanoparticles occurs in both saturated and unsaturated porous media. The solution ionic strength was found to have a noticeable effect on the retention of TiO2 nanoparticles in the packed columns. Moreover, the results from the TiO2 nanoparticle transport experiments in water-saturated packed columns showed that the TiO2 nanoparticle mass recoveries increased with increasing flow rate. The results from the TiO2 nanoparticles and FA cotransport experiments in both water saturated and unsaturated packed columns did not reveal a distinct relationship between mass recoveries and flow rate. The transport of FA in both saturated and unsaturated packed columns was hindered in the presence of TiO2 nanoparticles, especially at high ionic strength.

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