Plutonium Immobilization and Mobilization by Soil Organic Matter

The human and environmental risks associated with Pu disposal, remediation, and nuclear accidents scenarios stems mainly from the very long half-lives of several of its isotopes. The SRS, holding one-third of the nation’s Pu inventory, has a long-term stewardship commitment to investigation of Pu behavior in the groundwater and downgradient vast wetlands. Pu is believed to be essentially immobile due to its low solubility and high particle reactivity to mineral phase or natural organic matter (NOM). For example, in sediments collected from a region of SRS, close to a wetland and a groundwater plume, 239,240Pu concentrations suggest immobilization by NOM compounds, as Pu correlate with NOM contents. Micro-SXRF data indicate, however, that Pu does not correlate with Fe. However, previous studies reported Pu can be transported several kilometers in surface water systems, in the form of a colloidal organic matter carrier, through wind/water interactions. The role of NOM in both immobilizing or re-mobilizing Pu thus has been demonstrated. Our results indicate that more Pu (IV) than (V) was bound to soil colloidal organic matter (COM), amended at far-field concentrations. Contrary to expectations, the presence of NOM in the F-Area soil did not enhance Pu fixation to the organic-rich soil, when compared to the organic-poor soil or the mineral phase from the same soil source, due to the formation of COM-bound Pu. Most importantly, Pu uptake by organic-rich soil decreased with increasing pH because more NOM in the colloidal size desorbed from the particulate fraction at elevated pH, resulting in greater amounts of Pu associated with the COM fraction. This is in contrast to previous observations with low-NOM sediments or minerals, which showed increased Pu uptake with increasing pH levels. This demonstrates that despite Pu immobilization by NOM, COM can convert Pu into a more mobile form. Sediment Pu concentrations in the SRS F-Area wetland were correlated to total organic carbon and total nitrogen contents and even more strongly to hydroxamate siderophore (HS) concentrations. The HS were detected in the particulate or colloidal phases of the sediments but not in the low molecular fractions (\u3c 1000 Da). Macromolecules which scavenged the majority of the potentially mobile Pu were further separated from the bulk mobile organic matter fraction (“water extract”) via isoelectric focusing experiment (IEF). An ESI FTICR-MS spectral comparison of the IEF extract and a siderophore standard (desferrioxamine; DFO) suggested the presence of HS functionalities in the IEF extract

The Role of Microbial Exopolymers in Determining the Fate of Oil and Chemical Dispersants in the Ocean

The production of extracellular polymeric substances (EPS) by planktonic microbes can influence the fate of oil and chemical dispersants in the ocean through emulsification, degradation, dispersion, aggregation, and/or sedimentation. In turn, microbial community structure and function, including the production and character of EPS, is influenced by the concentration and chemical composition of oil and chemical dispersants. For example, the production of marine oil snow and its sedimentation and flocculent accumulation to the seafloor were observed on an expansive scale after the Deepwater Horizon oil spill in the Northern Gulf of Mexico in 2010, but little is known about the underlying control of these processes. Here, we review what we do know about microbially produced EPS, how oil and chemical dispersant can influence the production rate and chemical and physical properties of EPS, and ultimately the fate of oil in the water column. To improve our response to future oil spills, we need a better understanding of the biological and physiochemical controls of EPS production by microbes under a range of environmental conditions, and in this paper, we provide the key knowledge gaps that need to be filled to do so

Effects of Engineered Nanoparticles on the Assembly of Exopolymeric Substances from Phytoplankton

The unique properties of engineered nanoparticles (ENs) that make their industrial applications so attractive simultaneously raise questions regarding their environmental safety. ENs exhibit behaviors different from bulk materials with identical chemical compositions. Though the nanotoxicity of ENs has been studied intensively, their unintended environmental impacts remain largely unknown. Herein we report experimental results of EN interactions with exopolymeric substances (EPS) from three marine phytoplankton species: Amphora sp., Ankistrodesmus angustus and Phaeodactylum tricornutum. EPS are polysaccharide-rich anionic colloid polymers released by various microorganisms that can assemble into microgels, possibly by means of hydrophobic and ionic mechanisms. Polystyrene nanoparticles (23 nm) were used in our study as model ENs. The effects of ENs on EPS assembly were monitored with dynamic laser scattering (DLS). We found that ENs can induce significant acceleration in Amphora sp. EPS assembly; after 72 hours EN-EPS aggregation reached equilibrium, forming microscopic gels of ∼4–6 µm in size. In contrast, ENs only cause moderate assembly kinetic acceleration for A. angustus and P. tricornutum EPS samples. Our results indicate that the effects of ENs on EPS assembly kinetics mainly depend on the hydrophobic interactions of ENs with EPS polymers. The cycling mechanism of EPS is complex. Nonetheless, the change of EPS assembly kinetics induced by ENs can be considered as one potential disturbance to the marine carbon cycle

A Sensitive Determination of Iodide Species in Fresh or Saline Matrixes Using High Performance Chromatography and UV/Visible Detection

The objective of this study is to develop an analytical method that uses readily available instrumentation and minimal sample preparation for the determination of stable lodine species at nanomolar concentration levels in a range of environmental water matrixes

A Sensitive Determination of Iodide Species in Fresh or Saline Matrixes Using High Performance Chromatography and UV/Visible Detection

The objective of this study is to develop an analytical method that uses readily available instrumentation and minimal sample preparation for the determination of stable lodine species at nanomolar concentration levels in a range of environmental water matrixes

Comparative Evaluation of Sediment Trap and Th-234-derived POC Fluxes From the Upper Oligotrophic Waters of the Gulf of Mexico and the Subtropical Northwestern Pacific Ocean

To better understand the inter-relationships between particulate organic carbon (POC) fluxes and phytoplankton and bacteria biomass and production, we compared POC fluxes determined in sediment traps and approaches based on size-fractionated (1-10, 10-50, 50-150 and \u3e150 mu m) suspended particulate Th-234 and POC concentrations in oligotrophic sections of the Gulf of Mexico during August 2005 and May 2006 and in the oligotrophic northwestern Pacific Ocean during 2009. In 2005, the sediment trap POC flux near the bottom of the euphotic zone (120 m) ranged from 71 to 94 mg C m(-2) day(-1), while Th-234-derived POC fluxes using POC/Th-234 ratios in the 10-50 mu m and 50-150 mu m varied from 71 to 150 mg C m-2 day-1. In 2006, the sediment trap POC flux at 120 m ranged from 24 to 67 mg C m(-2) day(-1), while the 234Th-derived POC fluxes in the 10-50 mu m fraction were comparable or somewhat higher, ranging from 71 to 119 mg C m(-2) day-1. The POC fluxes in 2006, calculated by using POC/234Th ratios in the 1-10 mu m and the 50-150 mu m fractions were much higher, ranging from 847 to 1369 mg C m(-2) day(-1). Correlations with biological and chemical parameters support a likely mechanism of sinking aggregates of haptophytes (0.2-20 mu m) of higher density held together by Th-complexing and uronic acid containing exopolymeric substances. The observations that 234Th (and POC) is mainly associated with medium-sized (10-15 mu m) suspended particles rather than larger (50-150 mu m) ones may be caused by the use of a one-filter method and standard filtration and processing procedures that were applied here for collecting suspended particles. This then raises the question of what constitutes representative material from the ocean that settles on the characteristic time scale of 234Th. As a comparison, size-fractionated trap-collected particles in the oligotrophic northwestern Pacific Ocean showed that the 10-50 mu m fraction contained the largest proportion of POC (22-41%), followed by the 50-150 mu m (22-37%). the \u3e150 mu m (15-27%), and the 1-10 mu m (17-23%) fraction. The partitioning of 234Th in trap-collected particles was slightly different from that of POC, with the 1-10 mu m fraction representing the largest proportion (27-48%) of Th-234 flux. Together, the \u3c50 mu m particles contributed, on average, 52 +/- 6% of POC, which suggests that the POC/Th-234 ratios traditionally derived from large (\u3e50 mu m) pump-collected particles may not accurately reflect the majority of sinking particles. Therefore, estimated POC fluxes may be significantly biased using a conventional 234Th based approach, i.e., using POC/Th-234 ratios from a single filter obtained from large (\u3e50 mu m) pump-collected particles. (C) 2010 Elsevier B.V. All rights reserved

Extracellular polymeric substances (EPS) producing and oil degrading bacteria isolated from the northern Gulf of Mexico.

Sinking marine oil snow was found to be a major mechanism in the transport of spilled oil from the surface to the deep sea following the Deepwater Horizon (DwH) oil spill. Marine snow formation is primarily facilitated by extracellular polymeric substances (EPS), which are mainly composed of proteins and carbohydrates secreted by microorganisms. While numerous bacteria have been identified to degrade oil, there is a paucity of knowledge on bacteria that produce EPS in response to oil and Corexit exposure in the northern Gulf of Mexico (nGoM). In this study, we isolated bacteria from surface water of the nGoM that grow on oil or Corexit dispersant. Among the 100 strains isolated, nine were identified to produce remarkable amounts of EPS. 16S rRNA gene analysis revealed that six isolates (strains C1, C5, W10, W11, W14, W20) belong to the genus Alteromonas; the others were related to Thalassospira (C8), Aestuariibacter (C12), and Escherichia (W13a). The isolates preferably degraded alkanes (17-77%), over polycyclic aromatic hydrocarbons (0.90-23%). The EPS production was determined in the presence of a water accommodated fraction (WAF) of oil, a chemical enhanced WAF (CEWAF), Corexit, and control. The highest production of visible aggregates was found in Corexit followed by CEWAF, WAF, and control; indicating that Corexit generally enhanced EPS production. The addition of WAF and Corexit did not affect the carbohydrate content, but significantly increased the protein content of the EPS. On the average, WAF and CEWAF treatments had nine to ten times more proteins, and Corexit had five times higher than the control. Our results reveal that Alteromonas and Thalassospira, among the commonly reported bacteria following the DwH spill, produce protein rich EPS that could have crucial roles in oil degradation and marine snow formation. This study highlights the link between EPS production and bacterial oil-degrading capacity that should not be overlooked during spilled oil clearance

Comparison of microgels, extracellular polymeric substances (EPS) and transparent exopolymeric particles (TEP) determined in seawater with and without oil

Extracellular polymeric substances (EPS), produced by microorganisms, are implicated for greatly influencing the fate of environmental contaminants, including oil. Transparent exopolymeric particles (TEP) are gel-like acidic polysaccharide particles that can be stained with Alcian blue, whereas Coomassie stainable particles (CSP) contain proteins and are stained with Coomassie brilliant blue. Marine microgels are reversibly formed from EPS. These terms are often used interchangeably, but they have rarely been measured simultaneously. Mesocosm and bottle experiments provided an opportunity to compare EPS, TEP, CSP and microgels in a water-accommodated fraction (WAF) of oil and seawater (control). Our results reveal that the biopolymers making up EPS, TEP and CSP consisted primarily of polysaccharides and proteins, mostly likely as proteoglycans and glycoproteins. Significant correlations were found between concentrations of TEP-C vs particulate organic carbon (POC), TEP-C vs particulate organic nitrogen (PON), TEP vs EPS, TEP vs CSP, TEP vs carbohydrates, proteins, CSP and carbohydrates, CSP vs proteins, and carbohydrates vs proteins. Chemical analysis of whole particles and colloids yielded both protein and polysaccharides concentrations higher than those in EDTA extraction, thus providing an upper limit of actual EPS contents in the particulate phase. The EPS that was electrostatically held onto particle surfaces (extractable by 1% EDTA) accounted for a minor (~4%) yet relatively constant proportion of TEP. Overall, the concentrations of the three terms ranked in the order of [gels] > [TEP] > [particulate EPS] in the water. Lastly, spectrophotometric methods have limitations in identifying complex or refractory polysaccharides, as evidenced by the comparison between NMR-quantified EPS and the total EPS determined by spectrophotometric methods. This study is the first time these terms were compared in the same sample. They provide useful information when reviewing historical TEP, CSP, EPS data collected field- and laboratory-studies, and provide linkages between them. In addition, they also demonstrate that they could provide complementary information relevant to ecosystem and flux studies

Aggregation, Dissolution, and Stability of Quantum Dots in Marine Environments: Importance of Extracellular Polymeric Substances

There is an increasing concern that a considerable fraction of engineered nanoparticles (ENs), including quantum dots (QDs), will eventually find their way into the marine environment and have negative impacts on plankton. As ENs enter the ocean, they will encounter extracellular polymeric substances (EPS) from microbial sources before directly interacting with plankton cells. In this study, EPS harvested from four phytoplankton species, <i>Amphora</i> sp., <i>Dunaliella tertiolecta</i>, <i>Phaeocystis globosa</i>, and <i>Thalassiosira pseudonana,</i> were examined for potential interactions with CdSe nonfunctionalized and functionalized (carboxyl- and amine-) QDs in artificial seawater. Our results show that EPS do not reduce the solubility of QDs but rather decrease their stability. The degradation rate of QDs was positively correlated to the protein composition of EPS (defined by the ratio of protein/carbohydrate). Two approaches showed significant inhibition to the degradation of carboxyl-functionalized QDs: (1) the presence of an antioxidant, such as <i>N</i>-acetyl cysteine, and (2) absence of light. Owing to the complexity in evaluating integrated effects of QDs intrinsic properties and the external environmental factors that control the stability of QDs, conclusions must be based on a careful consideration of all these factors when attempting to evaluate the bioavailability of QDs and other ENs in the marine environments