Elizabeth B. Kujawinski

Fate of Dispersants Associated with the Deepwater Horizon Oil Spill

Response actions to the Deepwater Horizon oil spill included the injection of ∼771,000 gallons (2,900,000 L) of chemical dispersant into the flow of oil near the seafloor. Prior to this incident, no deepwater applications of dispersant had been conducted, and thus no data exist on the environmental fate of dispersants in deepwater. We used ultrahigh resolution mass spectrometry and liquid chromatography with tandem mass spectrometry (LC/MS/MS) to identify and quantify one key ingredient of the dispersant, the anionic surfactant DOSS (dioctyl sodium sulfosuccinate), in the Gulf of Mexico deepwater during active flow and again after flow had ceased. Here we show that DOSS was sequestered in deepwater hydrocarbon plumes at 1000-1200 m water depth and did not intermingle with surface dispersant applications. Further, its concentration distribution was consistent with conservative transport and dilution at depth and it persisted up to 300 km from the well, 64 days after deepwater dispersant applications ceased. We conclude that DOSS was selectively associated with the oil and gas phases in the deepwater plume, yet underwent negligible, or slow, rates of biodegradation in the affected waters. These results provide important constraints on accurate modeling of the deepwater plume and critical geochemical contexts for future toxicological studies.

Chemical data quantify Deepwater Horizon hydrocarbon flow rate and environmental distribution

Detailed airborne, surface, and subsurface chemical measurements, primarily obtained in May and June 2010, are used to quantify initial hydrocarbon compositions along different transport pathways (i.e., in deep subsurface plumes, in the initial surface slick, and in the atmosphere) during the Deepwater Horizon oil spill. Atmospheric measurements are consistent with a limited area of surfacing oil, with implications for leaked hydrocarbon mass transport and oil drop size distributions. The chemical data further suggest relatively little variation in leaking hydrocarbon composition over time. Although readily soluble hydrocarbons made up ∼25% of the leaking mixture by mass, subsurface chemical data show these compounds made up ∼69% of the deep plume mass; only ∼31% of the deep plume mass was initially transported in the form of trapped oil droplets. Mass flows along individual transport pathways are also derived from atmospheric and subsurface chemical data. Subsurface hydrocarbon composition, dissolved oxygen, and dispersant data are used to assess release of hydrocarbons from the leaking well. We use the chemical measurements to estimate that (7.8 ± 1.9) × 106 kg of hydrocarbons leaked on June 10, 2010, directly accounting for roughly three-quarters of the total leaked mass on that day. The average environmental release rate of (10.1 ± 2.0) × 106 kg/d derived using atmospheric and subsurface chemical data agrees within uncertainties with the official average leak rate of (10.2 ± 1.0) × 106 kg/d derived using physical and optical methods.

The application of electrospray ionization mass spectrometry (ESI MS) to the structural characterization of natural organic matter

Abstract This report describes the application of electrospray ionization (ESI) mass spectrometry to the structural characterization of soil organic material, a critical component of environmental processes and the global carbon cycle. Quadrupole time-of-flight (QqTOF) mass spectrometry provided a routine screening of aqueous ions in humic and fulvic acid mixtures and MS/MS capabilities for selected ions. Fourier transform ion cyclotron resonance (FT–ICR) mass spectrometry required longer analysis time but achieved resolving powers >80,000 and mass accuracies of

High resolution electrospray ionization mass spectrometry and 2D solution NMR for the analysis of DOM extracted by C18 solid phase disk

Abstract We propose and demonstrate an approach involving use of C18 solid phase disk extraction coupled with high resolution mass spectrometry for obtaining non-invasive molecular level information on dissolved organic matter (DOM) from river water. With this approach, DOM extraction from acidified natural water can be achieved rapidly with a simple filtration setup at a remote field site. From total organic carbon and UV-Vis absorbance measurements, we show that a large portion (over 60%) of the original DOM in water is recovered without the interference of salts. NMR analysis indicates that the C18-isolated material has a similar distribution of functional groups as the original DOM but 2-D NMR details are greatly enhanced. Electrospray ionization mass spectrometry and high resolution mass spectrometry were employed to study DOM at molecular level. Highly resolved mass spectra of DOM (resolving power δ m m 50% > 80,000 at m/z

Cryptic carbon and sulfur cycling between surface ocean plankton

Significance In the surface ocean, organic matter released by phytoplankton and degraded by heterotrophic bacteria is a key step in the carbon cycle. Compounds important in this trophic link are poorly known, in part because of the thousands of chemicals making up marine dissolved organic matter. We cocultured a Roseobacter clade bacterium with the diatom Thalassiosira pseudonana and used gene expression changes to assay for compounds passed to the bacterium. A C3-sulfonate with no previously known role in the microbial food web was identified and subsequently shown to be an abundant diatom metabolite and actively cycling compound in seawater. This work identifies a missing component of the marine carbon and sulfur cycles. About half the carbon fixed by phytoplankton in the ocean is taken up and metabolized by marine bacteria, a transfer that is mediated through the seawater dissolved organic carbon (DOC) pool. The chemical complexity of marine DOC, along with a poor understanding of which compounds form the basis of trophic interactions between bacteria and phytoplankton, have impeded efforts to identify key currencies of this carbon cycle link. Here, we used transcriptional patterns in a bacterial-diatom model system based on vitamin B12 auxotrophy as a sensitive assay for metabolite exchange between marine plankton. The most highly up-regulated genes (up to 374-fold) by a marine Roseobacter clade bacterium when cocultured with the diatom Thalassiosira pseudonana were those encoding the transport and catabolism of 2,3-dihydroxypropane-1-sulfonate (DHPS). This compound has no currently recognized role in the marine microbial food web. As the genes for DHPS catabolism have limited distribution among bacterial taxa, T. pseudonana may use this sulfonate for targeted feeding of beneficial associates. Indeed, DHPS was both a major component of the T. pseudonana cytosol and an abundant microbial metabolite in a diatom bloom in the eastern North Pacific Ocean. Moreover, transcript analysis of the North Pacific samples provided evidence of DHPS catabolism by Roseobacter populations. Other such biogeochemically important metabolites may be common in the ocean but difficult to discriminate against the complex chemical background of seawater. Bacterial transformation of this diatom-derived sulfonate represents a previously unidentified and likely sizeable link in both the marine carbon and sulfur cycles.

Deciphering ocean carbon in a changing world

Dissolved organic matter (DOM) in the oceans is one of the largest pools of reduced carbon on Earth, comparable in size to the atmospheric CO2 reservoir. A vast number of compounds are present in DOM, and they play important roles in all major element cycles, contribute to the storage of atmospheric CO2 in the ocean, support marine ecosystems, and facilitate interactions between organisms. At the heart of the DOM cycle lie molecular-level relationships between the individual compounds in DOM and the members of the ocean microbiome that produce and consume them. In the past, these connections have eluded clear definition because of the sheer numerical complexity of both DOM molecules and microorganisms. Emerging tools in analytical chemistry, microbiology, and informatics are breaking down the barriers to a fuller appreciation of these connections. Here we highlight questions being addressed using recent methodological and technological developments in those fields and consider how these advances are transforming our understanding of some of the most important reactions of the marine carbon cycle.

Evidence for grazing-mediated production of dissolved surface-active material by marine protists

Abstract Surface-active organic compounds or surfactants play important roles in a variety of upper ocean processes, including surface microlayer physics and gas exchange and the aggregation of colloidal material. Although surfactants are presumed to be produced primarily by phytoplankton, production by protozoan grazers has not been investigated. In general, the processes controlling surfactant abundance in the field are poorly understood. In this study, a two-phase laboratory system containing protists and prey was used to examine the possibility of surfactant production during protozoan grazing. Three protist species were examined, a scuticociliate, Uronema sp. (10–15 μm), and two flagellates, Cafeteria sp. (2–4 μm), and Paraphysomonas imperforata (4–8 μm). For all experimental cultures, protozoan inocula were added to rinsed bacterial suspensions ( Halomonas halodurans ) in sterile seawater. Surfactants, dissolved organic carbon (DOC) and population dynamics were monitored until protists had reached stationary growth. Surfactant activities increased during protozoan exponential growth. Surfactant production in the ciliate cultures was significantly higher than in either of the flagellate cultures. Bacterial controls maintained low DOC concentrations and surfactant activities. Estimates of protozoan surfactant production rates range from 10 −8 to 10 −9 mg protist −1 h −1 (Triton X-100 equivalents). Under non-bloom conditions (10 3 protozoan cells ml −1 ), we estimated a surfactant production rate of 10 −5 –10 −6 mg h −1 (within 1 ml of seawater), which is comparable to estimates of phytoplankton production of surface-active material during blooms. Thus, protozoan grazers constitute a potentially significant source of surface-active material in areas where protists are abundant, such as the sediment–water interface and microbial loop-dominated oligotrophic regimes.

Seasonal evolution of water contributions to discharge from a Greenland outlet glacier: insight from a new isotope-mixing model

The Greenland ice sheet (GrIS) subglacial hydrological system may undergo a seasonal evolution, with significant geophysical and biogeochemical implications. We present results from a new isotope-mixing model to quantify the relative contributions of surface snow, glacial ice and delayed flow to the bulk meltwater discharge from a small (� 5k m 2 ) land-terminating GrIS outlet glacier during melt onset (May) and at peak melt (July). We use radioactive ( 222 Rn) and stable isotopes ( 18 O, deuterium) to differentiate the water source contributions. Atmospherically derived 7 Be further constrains meltwater transit time from the glacier surface to the ice margin. We show that (1) 222 Rn is a promising tracer for glacial waters stored at the bed and (2) a quantitative chemical mixing model can be constructed by combining 222 Rn and the stable water isotopes. Applying this model to the bulk subglacial outflow from our study area, we find a constant delayed-flow (stored) component from melt onset through peak melt. This component is diluted first by snowmelt and then by increasing glacial ice melt as the season progresses. Results from this pilot study are consistent with the hypothesis that subglacial drainage beneath land-terminating sections of the GrIS undergoes a seasonal evolution from a distributed to a channelized system.

Evidence for quorum sensing and differential metabolite production by a marine bacterium in response to DMSP

Microbes, the foundation of the marine foodweb, do not function in isolation, but rather rely on molecular level interactions among species to thrive. Although certain types of interactions between autotrophic and heterotrophic microorganisms have been well documented, the role of specific organic molecules in regulating inter-species relationships and supporting growth are only beginning to be understood. Here, we examine one such interaction by characterizing the metabolic response of a heterotrophic marine bacterium, Ruegeria pomeroyi DSS-3, to growth on dimethylsulfoniopropionate (DMSP), an abundant organosulfur metabolite produced by phytoplankton. When cultivated on DMSP, R. pomeroyi synthesized a quorum-sensing molecule, N-(3-oxotetradecanoyl)-l-homoserine lactone, at significantly higher levels than during growth on propionate. Concomitant with the production of a quorum-sensing molecule, we observed differential production of intra- and extracellular metabolites including glutamine, vitamin B2 and biosynthetic intermediates of cyclic amino acids. Our metabolomics data indicate that R. pomeroyi changes regulation of its biochemical pathways in a manner that is adaptive for a cooperative lifestyle in the presence of DMSP, in anticipation of phytoplankton-derived nutrients and higher microbial density. This behavior is likely to occur on sinking marine particles, indicating that this response may impact the fate of organic matter.

Chemical Composition and Potential Environmental Impacts of Water-Soluble Polar Crude Oil Components Inferred from ESI FT-ICR MS.

Polar petroleum components enter marine environments through oil spills and natural seepages each year. Lately, they are receiving increased attention due to their potential toxicity to marine organisms and persistence in the environment. We conducted a laboratory experiment and employed state-of-the-art Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to characterize the polar petroleum components within two operationally-defined seawater fractions: the water-soluble fraction (WSF), which includes only water-soluble molecules, and the water-accommodated fraction (WAF), which includes WSF and microscopic oil droplets. Our results show that compounds with higher heteroatom (N, S, O) to carbon ratios (NSO:C) than the parent oil were selectively partitioned into seawater in both fractions, reflecting the influence of polarity on aqueous solubility. WAF and WSF were compositionally distinct, with unique distributions of compounds across a range of hydrophobicity. These compositional differences will likely result in disparate impacts on environmental health and organismal toxicity, and thus highlight the need to distinguish between these often-interchangeable terminologies in toxicology studies. We use an empirical model to estimate hydrophobicity character for individual molecules within these complex mixtures and provide an estimate of the potential environmental impacts of different crude oil components.