Karen J. Murray

Cr(III) Oxidation and Cr Toxicity in Cultures of the Manganese(II)-Oxidizing Pseudomonas putida Strain GB-1

Abstract Mn oxides have long been considered the primary environmental oxidant of Cr(III), however, since most of the reactive Mn oxides in the environment are believed to be of biological origin, microorganisms may indirectly mediate Cr(III) oxidation and accelerate the rate over that seen in purely abiotic systems. In this study, we examined the ability of the Mn(II)-oxidizing bacterium, Pseudomonas putida strain GB-1, to oxidize Cr(III). Our results show that GB-1 cannot oxidize Cr(III) directly, but that in the presence of Mn(II), Cr(III) can be rapidly and completely oxidized. Growth studies suggest that in growth medium with few organics the resulting Cr(VI) may be less toxic to P. putida GB-1 than Cr(III), which is generally considered less hazardous. In addition, Cr(III) present during the growth of P. putida GB-1 appeared to cause iron stress as determined by the production of the fluorescent siderophore pyoverdine. When stressed by Fe limitation or Cr(III) toxicity, Mn(II) oxidation by GB-1 is inhibited.

Indirect oxidation of Co(II) in the presence of the marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1

ABSTRACT Cobalt(II) oxidation in aquatic environments has been shown to be linked to Mn(II) oxidation, a process primarily mediated by bacteria. This work examines the oxidation of Co(II) by the spore-forming marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1, which enzymatically catalyzes the formation of reactive nanoparticulate Mn(IV) oxides. Preparations of these spores were incubated with radiotracers and various amounts of Co(II) and Mn(II), and the rates of Mn(II) and Co(II) oxidation were measured. Inhibition of Mn(II) oxidation by Co(II) and inhibition of Co(II) oxidation by Mn(II) were both found to be competitive. However, from both radiotracer experiments and X-ray spectroscopic measurements, no Co(II) oxidation occurred in the complete absence of Mn(II), suggesting that the Co(II) oxidation observed in these cultures is indirect and that a previous report of enzymatic Co(II) oxidation may have been due to very low levels of contaminating Mn. Our results indicate that the mechanism by which SG-1 oxidizes Co(II) is through the production of the reactive nanoparticulate Mn oxide.

Distribution and Attenuation of Polycyclic Aromatic Hydrocarbons in Gulf of Mexico Seawater from the Deepwater Horizon Oil Accident

The extended duration of the oil release from the Deepwater Horizon accident (April 20-July 15, 2010) triggered a need to characterize environmental exposures in four dimensions through sampling and tracking the changes in distributions, concentrations, and compositions of oil and total polycyclic aromatic hydrocarbons (TPAH) in the Gulf of Mexico over time and space. More than 11,000 water samples were collected offshore during more than 100 cruises and were measured for 50 parent and alkylated polycyclic aromatic hydrocarbons (PAHs). Elevated concentrations (greater than 1 ppb) of TPAH were largely limited to an area within about 20 km of the wellhead in the subsurface deepwaters at 1000-1200 m depth to the southwest of the wellhead and in the top 3 m underlying the surface oil. Concentrations decreased with distance and time, and changes in the PAH composition indicate that these changes were due to differential solubilization, photodegradation, evaporation, and/or biodegradation of individual PAH compounds. These limited areas of elevated PAH concentrations disappeared within weeks after the release was stopped.

Aromatic Hydrocarbon Concentrations in Seawater: Deepwater Horizon Oil Spill

ABSTRACT When oil is spilled or discharged into the marine environment, the chemistry and chemical concentrations of oil constituents in seawater become the target of intensive investigation as these ephemeral data are crucial to toxicity and injury assessments. The preliminary results from more than 6000 offshore water samples (>3 miles from shore) from the Deepwater Horizon (MC252) oil spill are discussed. Total Polycyclic Aromatic Hydrocarbon (TPAH) concentrations in whole, unfractionated water samples were found at concentrations ranging from not detected (ND) to 146,000 μg/L (parts per billion), with a geometric mean of 0.007 ppb. Eighty-five (85) percent of all samples were at TPAH concentrations of <0.1 ppb, essentially at or near background levels. Total Petroleum Hydrocarbons (TPH) ranged from ND to 6130 mg/L (parts per million), with a geometric mean = 1.09 ppb. Concentrations of TPAH attenuated rapidly with distance from the release point (the wellhead) and were seen to reach <1.0 ppb within 15...

Assessing the Representativeness and Sufficiency of Chemical Data from Water Samples Collected During an Oil Spill

ABSTRACT Traditionally, the representativeness and sufficiency of data in environmental monitoring efforts are judged against an external standard, such as a pre-determined statistically-based surv...

Towards an Understanding of the Evolution (Fate and Transport) of the 2010 Deepwater Horizon Oil Spill

ABSTRACT 2017-192 While examination of the question “what happened to the oil?” has been undertaken on other oil spills, the wealth of data from the 2010 Deepwater Horizon accident presents a uniqu...

Fingerprinting of Weathered Oil Residues from the Deepwater Horizon Oil Spill: The Importance of Multiple Lines of Investigation

ABSTRACT 2017-189 The crude oil released from the Macondo Well, also known for its location in Mississippi Canyon area as the MC252 well during the Deepwater Horizon Oil Spill, entered an environme...