Which environmental processes control oil degradation and the fate of other water contaminants? That’s a question to ask Charles Sharpless, professor of chemistry at the University of Mary Washington.
Dr. Sharpless teamed up with scientists from the Woods Hole Oceanographic Institution and University of California in the summer of 2015 for a research cruise that aimed to collect oil samples in the Gulf of Mexico. The results of the cruise will clarify the role of solar degradation in the fate of oil in marine systems.
The whole project focuses on gaining a better understanding of what environmental processes control oil weathering rates, the aging of oil from crude to tar in the environment.
Dr. Sharpless’ research interests include photochemistry in natural and engineered systems, the chemistry of humic substances, environmental analysis, and fate and remediation of anthropogenic pollutants, particularly pharmaceuticals and other organic contaminants in streams and rivers, and spilled oil and biofuels in marine ecosystems.
His research has been supported by grants from the National Science Foundation, the U.S. Environmental Protection Agency, Research Corporation, and the Virginia Academy of Sciences. His work has been published in several peer-reviewed publications including Environmental Science Technology, Aquatic Sciences, Water Research, and the Journal of Environmental Engineering and Science.
Areas of Expertise (8)
Duke University: Ph.D., Post-Graduate Studies
The Johns Hopkins University: B.A., Undergraduate Studies
Media Appearances (1)
As Virginia Considers Offshore Drilling, UMW Professor Examines Petroleum in Gulf of Mexico
As Virginia considers allowing drilling for oil off its coast, scientists at the University of Mary Washington are doing basic research that could prove valuable in the event of a spill. Sandy Hausman reports on what they hope to learn after two weeks of trolling for oil in the Gulf of Mexico.
Research Grants (3)
Collaborative Research: Oxygenation of Hydrocarbons in the Ocean
National Science Foundation $106763
More than 400,000 tons of petroleum hydrocarbons are released annually into the ocean, where they are subject to physical, chemical and biological processes, known as weathering, that are known to remove select hydrocarbons from the ocean. However, little attention has been given to the residues left by the weathering of oil, and studies indicate that oxygenation of these hydrocarbons can play a part in the formation of recalcitrant tar and toxic compounds. To address this gap, researchers from Woods Hole Oceanographic Institution, University of Mary Washington, and University of California Santa Barbara will conduct research to lay a scientific foundation for understanding 1) which processes control the formation of oxygenated hydrocarbons, 2) the rates of these processes, 3) the identity of the major products, 4) the rates at which they are formed and destroyed, and 5) for distinguishing photochemical oxygenation from biological oxygenation. The results from these experiments will contribute to a better understanding of the petroleum oxygenation processes and the environmental fate of understudied oxygenation products.
Broader Impacts: This study will provide for several undergraduates and two postdoctoral scholars to be trained in innovative analytical and experimental techniques. The results of this effort will help regulatory agencies to define new analytical methods and target compounds for oil spill research, and will add to our understanding regarding the fate and impacts of hydrocarbons released into the ocean.
Collaborative Research: Role of Organic Matter Source in the Photodegradation of Pharmaceutical Compounds
National Science Foundation, $26892
Evaluating the impacts of human pharmaceutical compounds in the environment is a daunting task, given the wide variety of chemicals administered for medical conditions and the various wastewater management schemes that facilitate their release to aquatic systems. Prior studies suggest photodegradation reactions to be important attenuation processes for pharmaceutical compounds in the environment. The susceptibility of pharmaceuticals to photochemical reactions will be impacted by the co-release of these compounds with effluent organic matter (EfOM). EfOM is expected to have differing photoreactivity, relative to well-studied natural organic matter (NOM) sources, presumably because of its anticipated lower aromatic content and lower color, compared to NOM.
The PIs hypothesize that pharmaceutical compound photodegradation will be altered with increasing proportion of wastewater effluent in natural channel flow because of the increased presence of EfOM, relative to NOM. The ultimate goal of the proposed research is to identify key environmental system characteristics that are associated with enhanced environmental photodegradation rates of pharmaceutical compounds.
This study will be the first to examine the fate of pharmaceutical compounds in New England and Midwestern rivers, expanding on prior fate studies from arid systems. They will establish an important body of knowledge about environmental system drivers of pharmaceutical compound fates that will contribute to robust science-based decisions about regulation, remediation, and/or ?green? design for pharmaceutical compounds. They will work closely with the Pomperaug River Watershed Coalition and the East Fork Watershed Cooperative to engage citizens in cutting-edge science through semi-annual project progress presentations, to involve water managers and community members in water quality sampling, and to organize a cross-disciplinary Roundtable to bring together environmental scientists and engineers, regulators, with ecologists and pharmacologists to discuss environmental management of pharmaceutical compounds in the environment.
Probing the Origins of Natural Organic Matter Photochemistry Using Spectroscopic and Electrochemical Approaches
Research Corporation $25460
Two aquatic fulvic acids and one soil humic acid were irradiated to examine the resulting changes in the
redox and photochemical properties of the humic substances (HS), the relationship between these changes, and their relationship to changes in the optical properties. For all HS, irradiation caused photooxidation, as shown by decreasing electron donating capacities. Photooxidation was accompanied by decreases in specific UV absorbance and increases in the E2/E3 ratio (254 nm absorbance divided by that at 365 nm). In contrast, photooxidation had little effect on the samples’ electron accepting capacities. The coupled changes in optical and redox properties for the different HS suggest that phenols are an important determinant of aquatic HS optical properties and that quinones may play a more important role in soil HS. Apparent quantum yields of H2O2,·OH, and triplet HS decreased with photooxidation, thus demonstrating selective destruction of HS photosensitizing chromophores. In contrast, singlet oxygen (1O2) quantum yields increased, which is ascribed to either decreased1O2 quenching within the HS microenvironment or the presence of a pool of photostable sensitizers. The photochemical properties show clear trends with SUVA and E2/E3, but the trends differ substantially between aquatic and soil HS. Importantly, photooxidation produces a relationship between the1O2 quantum yield and E2/E3 that differs distinctly from that observed with untreated HS. This finding suggests that there may bewatershed-specific correlations between HS chemical and optical properties that reflect the dominant processes controlling the HS character.
Effluent organic matter (EfOM), contained in treated municipal wastewater, differs in composition from naturally occurring dissolved organic matter (DOM). The presence of EfOM may thus alter the photochemical production of reactive intermediates in rivers that receive measurable contributions of treated municipal wastewater. Quantum yield coefficients for excited triplet-state OM (3OM*) and apparent quantum yields for singlet oxygen (1O2) were measured for both whole water samples and OM isolated by solid phase extraction from whole water samples collected upstream and downstream of municipal wastewater treatment plant discharges in three rivers receiving differing effluent contributions: Hockanum R., CT (22% (v/v) effluent flow), E. Fork Little Miami R., OH (11%), and Pomperaug R., CT (6%). While only small differences in production of these reactive intermediates were observed between upstream and downstream whole water samples collected from the same river, yields of 3OM* and 1O2 varied by 30-50% between the rivers. Apparent quantum yields of 1O2 followed similar trends to those of 3OM*, consistent with 3OM* as a precursor to 1O2 formation. Higher 3OM* reactivity was observed for whole water samples than for OM isolates of the same water, suggesting differential recoveries of photoreactive moieties by solid phase extraction. 3OM* and 1O2 yields increased with increasing E2/E3 ratio (A254 nm divided by A365 nm) and decreased with increasing electron donating capacities of the samples, thus exhibiting trends also observed for reference humic and fulvic acid isolates. Mixing experiments with EfOM and DOM isolates showed evidence of quenching of triplet DOM by EfOM when measured yields were compared to theoretical yields. Together, the results suggest that effluent contributions of up to 25% (v/v) to river systems have a negligible influence on photochemical production of 3OM* and 1O2 apparently because of quenching of triplet DOM by EfOM. Furthermore, the results highlight the importance of whole water studies for quantifying in situ photoreactivity, particularly for 3OM*.
Absorption of sunlight by chromophoric dissolved natural organic matter (CDOM) is environmentally significant because it controls photic zone depth and causes photochemistry that affects elemental cycling and contaminant fate. Both the optics (absorbance and fluorescence) and photochemistry of CDOM display unusual properties that cannot easily be ascribed to a superposition of individual chromophores. These include (i) broad, unstructured absorbance that decreases monotonically well into the visible and near IR, (ii) fluorescence emission spectra that all fall into a single envelope regardless of the excitation wavelength, and (iii) photobleaching and photochemical quantum yields that decrease monotonically with increasing wavelength. In contrast to a simple superposition model, these phenomena and others can be reasonably well explained by a physical model in which charge-transfer interactions between electron donating and accepting chromophores within the CDOM control the optical and photophysical properties. This review summarizes current understanding of the processes underlying CDOM photophysics and photochemistry as well as their physical basis.
Two aquatic fulvic acids and one soil humic acid were irradiated to examine the resulting changes in the redox and photochemical properties of the humic substances (HS), the relationship between these changes, and their relationship to changes in the optical properties. For all HS, irradiation caused photooxidation, as shown by decreasing electron donating capacities. Photooxidation was accompanied by decreases in specific UV absorbance and increases in the E2/E3 ratio (254 nm absorbance divided by that at 365 nm). In contrast, photooxidation had little effect on the samples’ electron accepting capacities. The coupled changes in optical and redox properties for the different HS suggest that phenols are an important determinant of aquatic HS optical properties and that quinones may play a more important role in soil HS. Apparent quantum yields of H2O2, ·OH, and triplet HS decreased with photooxidation, thus demonstrating selective destruction of HS photosensitizing chromophores. In contrast, singlet oxygen (1O2) quantum yields increased, which is ascribed to either decreased 1O2 quenching within the HS microenvironment or the presence of a pool of photostable sensitizers. The photochemical properties show clear trends with SUVA and E2/E3, but the trends differ substantially between aquatic and soil HS. Importantly, photooxidation produces a relationship between the 1O2 quantum yield and E2/E3 that differs distinctly from that observed with untreated HS. This finding suggests that there may be watershed-specific correlations between HS chemical and optical properties that reflect the dominant processes controlling the HS character.
Dissolved organic matter (DOM) irradiated by sunlight generates photo-oxidants that can accelerate organic contaminant degradation in surface waters. However, the significance of this process to contaminant removal during engineered UV water treatment has not been demonstrated, partly due to a lack of suitable methods in the deep UV range. This work expands methods previously established to detect 1O2, HO•, H2O2, and DOM triplet states (3DOM*) at solar wavelengths to irradiation at 254 nm, typical of UV water treatment. For transient intermediates, the methods include a photostable probe combined with selective scavengers. Quantum yields for 1O2, 3DOM* and H2O2 were in the same range as for solar-driven reactions but were an order of magnitude higher for HO•, which other experiments indicate is due to H2O2 reduction. With the quantum yields, the degradation of metoxuron was successfully predicted in a DOM solution irradiated at 254 nm. Further modeling showed that the contribution of DOM sensitization to organic contaminant removal during UV treatment should be significant only at high UV fluence, characteristic of advanced oxidation processes. Of the reactive species studied, 3DOM* is predicted to have the greatest general influence on UV degradation of contaminants.
Various aquatic dissolved organic matter (DOM) samples produce singlet oxygen (1O2) and hydrogen peroxide (H2O2) with quantum yields of 0.59 to 4.5% (1O2 at 365 nm) and 0.017 to 0.053% (H2O2, 300−400 nm integrated). The two species’ yields have opposite pH dependencies and strong, but opposite, correlations with the E2/E3 ratio (A254 divided by A365). Linear regressions allow prediction of both quantum yields from E2/E3 in natural water samples with errors ranging from −3% to 60%. Experimental evidence and kinetic calculations indicate that less than six percent of the H2O2 is produced by reaction between 1O2 and DOM. The inverse relationship between the 1O2 and H2O2 yields is thus best explained by a model in which precursors to these species are populated competitively. A model is presented, which proposes that important precursors to H2O2 may be either charge-transfer or triplet states of DOM.
Photochemical processes affect the fate of spilled oil in the environment, but the relative contribution and kinetics of these degradation pathways are not fully constrained. To address this problem, we followed the weathering of No. 6 fuel oil by periodically sampling rocks covered with a film of oil from Buzzards Bay, MA after the April 2003 Bouchard 120 oil spill. Two sets of polycyclic aromatic hydrocarbon (PAH) isomers, benzo[a]pyrene (BAP) and benzo[e]pyrene (BEP), and benz[a]anthracene (BAA) and chrysene (CHR), were found to have very different disappearance rates in spite of their close structural similarity (kBAA/kCHR ∼ 2.0, kBAP/kBEP ∼ 2.2). This well-documented phenomenon is suspected to arise from differing capacity for direct photoreaction in the oil film. To investigate the validity of this assumption, we developed a model to estimate the contribution of direct photolysis to the loss of these PAHs from the oil. Newly determined PAH quantum yields demonstrate that the efficiency of phototransformation in hydrophobic media are 2 orders of magnitude lower (Φ′ ∼ 10−5) than in aqueous systems, and the thickness and light-attenuating properties of the oil film reduce the potential for photoreaction by up to 2 orders of magnitude. Given these limiting factors, direct photolysis cannot account for the complete removal of these PAHs (except BAP). Additional results suggest that singlet oxygen photodegradation pathways are not favored in hydrophobic media, as they are in some mineral-associated and aqueous systems. Our results indicate that photomediated reactions with other compounds in the oil mixture were responsible for PAH photodegradation in the oil film.
The objective of this study was to establish the relative rate constants for the reactions of selected pesticides (linuron, diuron, prometon, terbacil, diazinon, dyfonate, terbufos, and disulfoton) listed on the U.S. EPA Contaminant Candidate List with UV and hydroxyl radicals (·OH). Batch experiments were conducted in phosphate buffered solution at pH 7. All pesticides were found to be very reactive toward ·OH as indicated by rate constant values above 109 M-1 s-1. Using molinate as a reference compound, kOH ranged from 2.7 × 109 to 12.0 × 109 M-1 s-1 for the contaminants while slightly higher values from 2.9 × 109 to 14.3 × 109 M-1 s-1 were obtained using nitrobenzene as a reference compound. A method was established that accounts for direct photolysis when calculating kOH using UV/H2O2 process for compounds which degrade significantly by a direct photolysis mechanism.
One concern with UV disinfection of water is the production of nitrite when polychromatic UV sources are utilized. Based on previous work, it was hypothesized that a small addition of hydrogen peroxide (H2O2) may be useful in controlling nitrite during UV disinfection. However, it was found that H2O2 addition (5 or 10 mg/L) during polychromatic UV irradiation of drinking water at doses used for disinfection significantly increases the levels of nitrite produced relative to solutions without H2O2. Enhancement rates ranged from approximately 15% to 40% depending upon pH and H2O2 concentration; the relative increase in the NO2− yield was greater at pH 6.5 than at pH 8.3. The observed effects are tentatively ascribed to a combination of enhanced superoxide production and increased hydroxyl radical scavenging when H2O2 is added. These results indicate that H2O2 cannot be used to control nitrite production during UV disinfection and that enhanced nitrite formation will occur if H2O2 is added during UV water treatment to achieve advanced oxidation of contaminants.
Both low- and medium-pressure Hg lamps (LP and MP, respectively) were used as ultraviolet light (UV) sources to destroy N-nitrosodimethylamine in a synthetic “natural” water. The lamp performances were directly compared via the UV fluence-based rate constants, which demonstrates that LP and MP have virtually identical photonic efficiencies (fluence-based rate constants of 2.29E-3 and 2.35E-3 cm2/mJ, respectively).
Nitrite (NO2-) formation during ultraviolet (UV) photolysis of nitrate was studied as a function of pH and natural organic matter (NOM) concentration to determine water-quality effects on quantum yields and overall formation potential during UV disinfection of drinking water with polychromatic, medium-pressure (MP) Hg lamps. Quantum yields measured at 228 nm are approximately 2 times higher than at 254 nm under all conditions studied.