Anthropogenic chemicals like pharmaceuticals, hormones, and personal care products have been widely used for decades and trace amounts of these compounds have been detected in different environmental compartments partially as traditional municipal wastewater treatment plants (WWTPs) are not designed to remove these specialized molecules. The appearance of these contaminants of emerging concern (CECs) in the environment has drawn increased attention due to the potential impacts on both human and ecological health. However, limited data are available on the environmental fate and ecotoxicity assessment of these CECs mainly attributed to the lack of effective and efficient analytical methods applied to complex environmental matrices. Moreover, considering the fact that over 4,000 pharmaceuticals, and even more personal care products, are currently being used, experimental risk assessment of all CECs in a timely manner is a tremendous task. Therefore, this dissertation focused on identification of priority CECs in complex environmental sample matrices and investigation of their associated ecotoxicological impacts through both field- and laboratory-based exposure studies. Antibiotics, estrogenic hormones, and organic UV-filters were proposed as priority CECs due to their biological impacts with respect to antimicrobial resistance and endocrine disruption, and several advanced analytical methods and effective bioassay protocols were developed for their determination in different environmental samples. The concentrations of over 50 target CECs were measured in both engineering (WWTPs) and natural (Chesapeake Bay) environmental systems including wastewater, wastewater-impacted surface water, estuary water, sediment, and invertebrate organisms. The bioaccumulation and effects of CECs was also investigated via a laboratory-scale chronic exposure study in red swamp crayfish (Procambarus clarkii) at two environmentally-relevant concentrations. Results from this dissertation highlighted the ubiquitous presence of CECs in the environment, the first identification of fleroxacin and moxifloxacin antibiotics in United States wastewater, the first UV-filters in crayfish (Orconectes virilis) and oysters (Crassostrea virginica), and the urgent need for integrated chemical and biological protocols to better understand the toxicity of complex mixtures of CECs at environmentally-relevant conditions. Overall, the comprehensive findings resulting from the interdisciplinary approaches employed in this dissertation provided a deeper understanding of the occurrence, fate, and impact of some of the most important CECs in the environment.
Ultraviolet filters (UVFs) are used in a variety of personal care products, including sunscreens and cosmetics, to protect against ultraviolet (UV) radiation. Three of the most commonly employed UVFs are oxybenzone (OXY), octocrylene (OC), and octinoxate (OMC). While these compounds provide protection against harmful UV radiation, they also represent a unique human and ecological health risk. To address these concerns, ozone application to UVFs in water and wastewater matrices was carried out and transformation efficiency was calculated. Transformation efficiency varied with water/wastewater quality. For example, an applied ozone dose of 6 mol O3/mol OXY transformed approximately 62, 44, 23, and 13% of OXY in DI water, surface water, wastewater effluent, and raw wastewater, respectively. Second order rate constants were measured for UVF reaction with ozone; reactivity with ozone varied. Second-order rate constants for OXY (k"app,o3,OXY ) ranged from 3.65×102 to 1.68×10 6 M-1s-1; for OMC, k"o 3, OMC was 22(±2.14)×104 M -1s-1; and for OC, k"o3, OC was 1.56 (±0.18) M-1s-1. The characteristic UV absorbance of solutions containing UVFs was measured as a function of wavelength, pH, and treatment level providing innovative insight into ozone attack mechanisms and identification of transformation products. Several transformation products were identified for ozonation of OXY, OMC, and OC and the corresponding structures represent similar environmental concerns as the parent UVFs.
UV filters are added to a number of personal care products to mitigate damage to underlying surfaces and several studies have identified their presence of in a variety of water compartments in the environment. UV filters have demonstrated endocrine disrupting potential in vertebrate models, but few studies have addressed their effects on resident aquatic invertebrates. The acute and chronic effects of the UV filters avobenzone, dioxybenzone, homosalate, octyl methoxycinnamate, octisalate, and oxybenzone on Daphnia magna were assessed. Only avobenzone was acutely toxicity at LC50 0.74 (0.41, 0.94) mg/L. Chronic effects of inhibited reproductive occurred in the upper test concentrations for all UV filters. A potential hormetic effect on reproduction was noted in dioxybenzone, homoslate, octisalate, and oxybenzone (LOEC 0.75, 0.075, 0.0019, 0.7 mg/L). Male neonates, a potential indication of endocrine disruption, were identified in avobenzone, homosalate, and oxybenzone tests (LOEC 0.004, 0.6, and 5 mg/L). Environmental monitoring of UV filters is limited, especially in high use recreational lake areas. The current work identified the presence octisalate, homosalate, oxybenzone, and OMCN in selected US lakes using GC/MS. A seasonal (July-October) and spatial (beach versus offsite) effect on UV filter concentration was noted for the detected UV filters, but only octisalte, homosalate, and oxybenzone were found to be significant. Hazard quotients (HQ) were calculated using the maximum environmental concentration from this study and LOEC from our toxicological study and previous studies. HQ’s for detected UV filter were well below 1, indicating the tested UV filters are not likely occurring in concentrations high enough to produce toxicological effects. Many anthropogenic compounds such as pharmaceuticals and insecticides have demonstrated potential for endocrine disruption. Despite this knowledge, teaching this concept in undergraduate labs is not common most likely due to complexity, expense, and difficulty in observation. A research system using the invertebrate D. magna and the pesticide fenoxycarb is presented that demonstrates endocrine disruption, alleviates the complications of vertebrate models, and engages students in an authentic research experience. The system has been implemented in a small class containing a variety of declared major with 90% of the students showing proficiency in procedures and conceptual knowledge.
Ultraviolet filters (UVFs) are used in a variety of personal care products, including sunscreens and cosmetics, to protect against ultraviolet (UV) radiation. Three of the most commonly employed UVFs are oxybenzone (OXY), octocrylene (OC), and octinoxate (OMC). While these compounds provide protection against harmful UV radiation, they also represent a unique human and ecological health risk. To address these concerns, ozone application to UVFs in water and wastewater matrices was carried out and transformation efficiency was calculated. Transformation efficiency varied with water/wastewater quality. For example, an applied ozone dose of 6 mol O3/mol OXY transformed approximately 62, 44, 23, and 13% of OXY in DI water, surface water, wastewater effluent, and raw wastewater, respectively. Second order rate constants were measured for UVF reaction with ozone; reactivity with ozone varied. Second-order rate constants for OXY (k"app,o3,OXY ) ranged from 3.65x102 to 1.68x10 6 M-1s-1; for OMC, k"o 3, OMC was 22(+/-2.14)x104 M -1s-1; and for OC, k"o3, OC was 1.56 (+/-0.18) M-1s-1. The characteristic UV absorbance of solutions containing UVFs was measured as a function of wavelength, pH, and treatment level providing innovative insight into ozone attack mechanisms and identification of transformation products. Several transformation products were identified for ozonation of OXY, OMC, and OC and the corresponding structures represent similar environmental concerns as the parent UVFs.
Advanced reduction processes (ARP) are a class of chemical treatment processes that target oxidized contaminants in water/wastewater. ARPs operate through the generation of reducing radical species such as the hydrated/aqueous electron (eaq-). UV irradiation of sulfite (SO 32-) in solution is an effective generation method for eaq-. The photochemistry of sulfite in solution renders the UV/ SO32- ARP advantageous for application to water/wastewater treatment. UV/SO32- ARP was successfully tested for application to disinfection byproduct removal and perfluorooctanoic acid (PFOA) defluorination. Batch experiments were conducted to develop kinetic data for defluorination of PFOA. A pseudo component kinetic model for stepwise defluorination of PFOA was applied to experimental observations of inorganic fluoride to obtain two rate constants for PFOA defluorination. The effectiveness of UV/SO3 2- ARP was tested under UV-L and excimer lamps. Quantum yields for the process were calculated to be in the range of 0.002 to 0.004 mol/Ein. Presence of radical scavengers such as alkalinity lowered the kinetics and quantum yields for the process. Excimer lamp offered improvement in kinetics but required greater energy input, due to low UV conversion efficiency. Photolytic removal of chlorite (ClO2-) was investigated under UV-L lamp. Aqueous chlorite photolysis resulted in a reduced form (Cl-) and an undesirable oxidized form (chlorate, ClO 3-). The effect of background water constituents, natural organic matter (NOM) and alkalinity, on photo degradation of chlorite was studied. Results indicate that NOM significantly reduces chlorate formation by scavenging oxidizing radicals and hindering chlorine dioxide production. The problem of chlorate formation due to high DO in water could be eliminated by applying UV/SO32- ARP with high sulfite doses. Batch kinetic experiments for reduction of bromate (BrO3 -) with UV/SO32- ARP were conducted. A generic kinetic model for functioning of ARPs was applied to understand the effects of process variables on bromate reduction kinetics. Low wavelength excimer lamp improved BrO3- reduction kinetics significantly, but required an order of magnitude higher electrical energy as compared to the UV-L lamp. The dual effect of NOM is to scavenge reducing radicals and to filter UV irradiance and these effects were examined to determine if they would be significant limitations for application of UV/SO3 2- ARP to natural waters with high NOM concentrations.
Punched membranes as fine pore diffuser material have become available in the last ten years because they are more efficient. Heat, moisture and UV light are three main factors causing degradation of plastics and rubber membranes. In order to better understand the impact of sunlight on membranes, a series of outdoor tests were conducted on actual membranes. Results of this experiment showed that heat decreased hardness values; existence of UV light resulted in decreased modulus values; heat only had very slight effect on thickness and weight. To prevent membranes from degradation, it is suggested that they are stored in water as deep as at least 24 cm and they are covered with UV filter, especially when the weather is hot and UV light is strong.
Solar radiation impacts many aspects of the Earth's atmosphere and biosphere. The total solar radiation impacts the atmospheric temperature profile and the Earth's surface radiative energy budget. The solar visible (VIS) radiation is the energy source of photosynthesis. The solar ultraviolet (UV) radiation impacts plant's physiology, microbial activities, and human and animal health. Recent studies found that solar UV significantly shifts the mass loss and nitrogen patterns of plant litter decomposition in semi-arid and arid ecosystems. The potential mechanisms include the production of labile materials from direct and indirect photolysis of complex organic matters, the facilitation of microbial decomposition with more labile materials, and the UV inhibition of microbes' population. However, the mechanisms behind UV decomposition and its ecological impacts are still uncertain. Accurate and reliable ground solar radiation measurements help us better retrieve the atmosphere composition, validate satellite radiation products, and simulate ecosystem processes. Incorporating the UV decomposition into the DayCent biogeochemical model helps to better understand long-term ecological impacts. Improving the accuracy of UV irradiance data is the goal of the first part of this research and examining the importance of UV radiation in the biogeochemical model DayCent is the goal of the second part of the work. Thus, although the dissertation is separated into two parts, accurate UV irradiance measurement links them in what follows. In part one of this work the accuracy and reliability of the current operational calibration method for the (UV-) Multi-Filter Rotating Shadowband Radiometer (MFRSR), which is used by the U.S. Department of Agriculture UV-B Monitoring and Research Program (UVMRP), is improved. The UVMRP has monitored solar radiation in the 14 narrowband UV and VIS spectral channels at 37 sites across U.S. since 1992. The improvements in the quality of the data result from an improved cloud screening algorithm that utilizes an iterative rejection of cloudy points based on a decreasing tolerance of unstable optical depth behavior when calibration information is unknown. A MODTRAN radiative transfer model simulation showed the new cloud screening algorithm was capable of screening cloudy points while retaining clear-sky points. The comparison results showed that the cloud-free points determined by the new cloud screening algorithm generated significantly (56%) more and unbiased Langley offset voltages (VLOs) for both partly cloudy days and sunny days at two testing sites, Hawaii and Florida. The V¬LOs are proportional to the radiometric sensitivity. The stability of the calibration is also improved by the development of a two-stage reference channel calibration method for collocated UV-MFRSR and MFRSR instruments. Special channels where aerosol is the only contributor to total optical depth (TOD) variation (e.g. 368-nm channel) were selected and the radiative transfer model (MODTRAN) used to calculate direct normal and diffuse horizontal ratios which were used to evaluate the stability of TOD in cloud-free points. The spectral dependence of atmospheric constituents' optical properties and previously calibrated channels were used to find stable TOD points and perform Langley calibration at spectrally adjacent channels. The test of this method on the UV-B program site at Homestead, Florida (FL02) showed that the new method generated more clustered and abundant VLOs at all (UV-) MFRSR channels and potentially improved the accuracy by 2-4% at most channels and over 10% at 300-nm and 305-nm channels. In the second major part of this work, I calibrated the DayCent-UV model with ecosystem variables (e.g. soil water, live biomass), allowed maximum photodecay rate to vary with litter's initial lignin fraction in the model, and validated the optimized model with LIDET observation of remaining carbon and nitrogen at three semi-arid sites. I also explored the ecological impacts of UV decomposition with the optimized DayCent-UV model. The DayCent-UV model showed significant better performance compared to models without UV decomposition in simulating the observed linear carbon loss pattern and the persistent net nitrogen mineralization in the 10-year LIDET experiment at the three sites. The DayCent-UV equilibrium model runs showed that UV decomposition increased aboveground and belowground plant production, surface net nitrogen mineralization, and surface litter nitrogen pool, while decreased surface litter carbon, soil net nitrogen mineralization and mineral soil carbon and nitrogen. In addition, UV decomposition showed minimal impacts (i.e. less than 1% change) on trace gases emission and biotic decomposition rates. Overall, my dissertation provided a comprehensive solution to improve the calibration accuracy and reliability of MFRSR and therefore the quality of radiation products. My dissertation also improved the understanding of UV decomposition and its long-term ecological impacts.
The initial focus of this thesis is a full characterization study of the UV photodegradation of dye-sensitized solar cells (DSCs). This has been achieved by exposing cells to UV light and measuring the change in their properties with I-V measurements, EIS and UV-Vis spectrophotometry. Insights into the photodegradation mechanisms of DSCs were gained and it was found that the principle cause of cell failure is the consumption of I3- by reaction with oxidative holes that arise from direct excitation of the TiO2 semiconductor. Changes to the cell properties, particularly the change to the VOC were used to assess the effectiveness of different levels of UV filtering. It was subsequently found that filtering was required at greater than 385 nm but no more than 400 nm. The effects of filtering upon the performance of DSCs was also investigated by applying filters at various wavelength cut-offs. It was shown that the further into the visible region the cut-off moves, the greater the reduction in cell efficiency and it was estimated that a 400 nm filter should not reduce relative cell efficiency by more than 10% in a forward illuminated cell and should be much less than a 2% relative reduction in a reverse illuminated cell. Furthermore it was shown that dyes with broader photocurrent action spectra, such as N749, suffer less reduction in %n due to UV filtering than dyes with narrower action spectra, emphasising the need for sensitizers or co-sensitizers to absorb more red and near infrared radiation. Finally, during the characterization study it was found that the depleted I3- could be restored by application of a reverse bias. The consequence of this upon the long term stability of DSCs was investigated by periodic application of the reverse bias during UV exposure. The photostability of clear polymer films was also investigated. These films could be used for counter electrode materials, and/or encapsulation materials for flexible dye-sensitized solar cells (DSCs) built upon a steel substrate. This was achieved by conducting accelerated weathering experiments on various polymer films. The extent of photodegradation in these films was measured using spectroscopic techniques and it was found that the rate of photodegradation could be reduced significantly by the application of a comparatively thin layer (20 ?m) of a commercially available, polyurethane clear lacquer containing UV absorber and Hindered Amine Light Stabilizer additions. As well as preventing photodegradation in the polymer film, the application of a UV absorbing clearcoat was also considered necessary to filter UV light in order to prevent direct band gap excitation of the TiO2 semi-conductor, which is known to photocatalyse the breakdown of organic chemicals adsorbed onto, or in the vicinity of TiO2 particles. The UV cut-offs of various films, lacquers and additives were investigated and a number of possible solutions were put forward.
Entomopathogenic nematodes (EPNs) are obligate parasites of insects. EPNs have a broad host range, are easily mass reared, and kill insects within 48 hours. EPNs are safe for vertebrates, plants, and non-target organism. On the other hand, EPNs have disadvantages that make them less effective against foliar insect pest because they are sensitive to desiccation, ultraviolet (UV) radiation and high temperatures. The goal of this research was to improve the efficacy of aboveground application EPNs by protecting them against desiccation and UV radiation. The first objective was to determine efficacy of the desiccation protectant Barricade gel in extending the viability of EPNs. The second objective was to evaluate the effect of UV chemical protectants on EPNs viability. The third objective was to demonstrate enhanced insect control with EPNs protected from UV radiation and desiccation. Barricade® is a proprietary fire-protection product that prevents desiccation. Barricade® gel toxicity to Steinername feltiae and mealworm (Tenebrio molitor) was determined in laboratory experiments. Subsequently, the effect of Barricade® gel on IJ infectivity was determined at different (0, 1, 1.5, 2, 3, and 4%) concentration. Barricade® gel was not toxic to mealworm larvae nor the IJ of S. feltiae. IJ survival was enhanced by Barricade® gel and Barricade® gel prevented desiccation of IJs allowing for greater IJ infection and mealworm larvae mortality. In an excised leaf experiment, Barricade® application enhanced IJ infection of the mealworm larvae over time compared to application in water alone. EPNs and mealworm larvae were exposed to UV radiation protectant chemicals P-amino benzoic acid (PABA) and octyl methoxycinnamate (OMC), Congo red, titanium dioxide, and zinc oxide were not toxic to mealworm larvae and EPNs. PABA, OMC, Congo red, titanium dioxide, and zinc oxide protected IJ from exposure to UV light for 0, 4, 8 and 12 hrs. After 48 hrs exposure, PABA afforded the greatest protection to EPN compared to other chemicals. OMC provided the second greatest protection to EPN compared to other chemicals. The UV protectants PABA and OMC were individually combined with Barricade® fire gel and IJs were added. The IJs were exposed to full spectrum UV light in the laboratory for up to 12 hrs. The subsequent number of dead mealworm larvae was greatest in the combination treatments of OMC+Barricade and PABA+Barricade. These treatments afforded the greatest protection to IJs from UV radiation and desiccation in a filter paper experiment and a choy sum (Brassica chinensis var. parachinensis) leaf assay. The survival of IJ can be enhanced when applied with a desiccant protectant such as Barricade and a chemical such as PABA or OMC to protect against UV radiation. The protection afforded to the IJ by these chemicals allows for greater infection and mortality of target insect pests. The formulation of IJs with desiccant and UV radiation protection will allow the greater use of EPN for the management of foliar insect pests.
The penetration of ultraviolet-B (UV-B; 290-320 nm) into the biosphere has increased in response to decreased stratospheric ozone. As a consequence, significant attempts have been made to elucidate the effects of UV-B radiation on primary producers such as phytoplankton and plants. Considerably less effort has been devoted to describing the role played by ultraviolet-A (UV-A; 320-400 nm) radiation, which is not attenuated by stratospheric ozone. The present work details the independent and combined effects of UV-B and UV-A radiation on photosynthetic and oxidative stress responses using the unicellular green alga Dunaliella tertiolecta as a model organism. A UV-B spectral profile comparable to natural solar irradiance was produced in the laboratory by filtering UV-B lamp emissions with a novel liquid urate solution (UA) and compared against the conventionally used cellulose acetate (CA) filter. Cells growing at 100, 200 or 600 μmol photons m -2s-1 photosynthetically active radiation (PAR) were exposed to 12-hour UV-B (6 μmol photons m-2s-1), UV-A (60 μmol photons m-2s-1) or UV-B + UV-A (6 + 60 μmol photons m-2s-1) radiation treatments after which, photosynthesis, fluorescence parameters, D1 protein contents and antioxidant enzyme activities were recorded. In almost all cases, the physiology of UA cultures remained comparable to controls, white CA cultures suffered declines in photosynthesis and D1 protein content plus elevated antioxidant enzyme activities. UV-B: PAR ratios comparable to solar irradiance reduced UV-B induced photodamages, highlighting the significance of properly balanced irradiance environments within laboratory studies. Regardless of the PAR level applied, exposure to UV-A radiation resulted in acute photosynthetic and oxidative stress, which remained unchanged following the addition of UV-B flux. The findings of this study suggest that exposure to UV-A (and not UV-B) causes the direct impairment of photosynthesis and increased oxidative stress within plant cells. It is therefore recommended that laboratory based UV studies employ the use of UA filters and UV: PAR ratios that correspond to solar flux. Lastly, the discovery of least two ascorbate peroxidase (APX) isoforms suggests that like higher plants, green algae also possess APX isoenzymes. This is the first report documenting the presence of multiple APX isoforms within green algae.