BER Research Highlights

Search Date: August 18, 2019

10 Records match the search term(s):


October 29, 2018

Influence of Hydrological Perturbations and Riverbed Sediment Characteristics on Hyporheic Zone Respiration of CO2 and N2

Hyporheic Controls on Greenhouse Gas Production.

The Science
In this work we advanced modeling capabilities to assess the functioning of a hyporheic zone under various climatic conditions, impacted by surface-water groundwater interactions, and feedbacks with microbial biomass.

The Impact
Our results show that while highly losing rivers have greater hyporheic CO2 and N2 production, gaining rivers allowed the greatest fraction of CO2 and N2 production to return to the river.

Summary
River systems are important components of our landscape that help to degrade contaminants, support food webs, and transform organic matter. In this study, we developed and tested a model that could help reveal the role of the riverbed for these ecosystem services. We used the model to explore how different riverbed conditions eventually control the fate of carbon and nitrogen. Our results show that carbon and nitrogen transformations and the potential suite of microbial behaviors are dependent on the riverbed sediment structure and the water table conditions in the local groundwater system. The implications of this are that the riverbed sediments and the cumulative effect of water table conditions can control hyporheic processing. Under future river discharge conditions, assuming reduced river flows and siltation of riverbeds, reductions in total hyporheic processing may be observed.

Contacts (BER PM)
David Lesmes, SC-23.1
David.Lesmes@science.doe.gov

(PI Contact)
Dr. Michelle Newcomer
Lawrence Berkeley National Laboratory
mnewcomer@lbl.gov

Funding
This research was supported by the Sonoma County Water Agency (SCWA), the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under award DE-AC02-05CH11231 as well as the associated Student Research Fellowship Program and the UFZ-Helmholtz Centre for Environmental Research, Leipzig, Germany.

Publications
Newcomer, M. E., Hubbard, S. S., Fleckenstein, J. H., Maier, U., Schmidt, C., Thullner, M., et al. Influence of hydrological perturbations and riverbed sediment characteristics on hyporheic zone respiration of CO2 and N2JGR Biogeosciences 123(3), 902-922 (2018). [DOI:10.1002/2017JG004090]

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 01, 2018

Geochemical Exports to River from the Intra-Meander Hyporheic Zone under Transient Hydrologic Conditions: East River Mountainous Watershed, Colorado

Meanders of the East River act as a sink of nutrients and metals during high-water and extended base flow conditions thus sustaining river water quality.

The Science
Hyporheic exchange within the intra-meander region results in the interaction of nutrient-rich groundwater and oxygen-rich river water, which leads to the formation of distinct redox gradients. These redox gradients can significantly impact the export of metals and nutrients at the local, reach, and watershed scales. Further, transient hydrologic conditions, such as groundwater flow dynamics, river-stage fluctuations, and rainfall/snowmelt events, can impact redox processes in the hyporheic zone and ultimately the geochemical exports to the river thereby affecting river water quality.  Here we have used high-resolution hydrodynamic assessments of the hyporheic zone combined with detailed pore-water sampling to focus on the hyporheic exchange at the meander scale for the purpose of quantifying the subsurface exports from a single meander to the river under transient hydrological conditions.

The Impact
This study is a first of its kind that examines the influence of transient hydrological conditions on the hyporheic biogeochemistry using field observations.  Simulation results demonstrated that intra-meander hyporheic zones display distinct anoxic and suboxic regions, suboxic regions being localized along sides of the meander bend. Permeability within the meander has a more significant impact on biogeochemical zonation compared to the reaction pathways for transient hydrologic conditions. Here we have also demonstrated the outsized implications of micro-topographic features such as gullies on redox processes using the high-resolution LiDar data.

Summary
Hyporheic zones perform important ecological functions by linking terrestrial and aquatic systems within watersheds. Hyporheic zones can act as a source or sink for various metals and nutrients. Transient hydrologic conditions alter redox conditions within an intra-meander hyporheic zone thus affecting the behavior of redox-sensitive species. Here we investigated how transient hydrological conditions control the lateral redox zonation within an intra-meander region of the East River and examined the contribution of a single meander on subsurface exports of carbon, iron, and other geochemical species to the river. The simulation results demonstrated that the reductive potential of the lateral redox zonation was controlled by groundwater velocities resulting from river-stage fluctuations, with low-water conditions promoting reducing conditions. The sensitivity analysis results showed that permeability had a more significant impact on biogeochemical zonation compared to the reaction pathways under transient hydrologic conditions. The simulation results further indicated that the meander acted as a sink for organic and inorganic carbon as well as iron during the extended baseflow and high-water conditions; however, these geochemical species were released into the river during the falling limb of the hydrograph. This study demonstrates the importance of including hydrologic transients, using a modern reactive transport approach, to quantify exports within the intra-meander hyporheic zone at the riverine scale.

Contact (BER PM)
David Lesmes, SC-23.1
david.lesmes@science.doe.gov

(PI Contact)
Susan S. Hubbard, LBNL
sshubbard@lbl.gov

Funding
DE-AC02-05CH11231, as part of the Genomes to Watershed Scientific Focus Area project and DE-SC0009732, as part of the Small Business Innovation Research.

Publications
Dwivedi, D., C.I. Steefel, B. Arora, M. Newcomer, J.D. Moulton, B. Dafflon, B. Faybishenko, P. Fox, P. Nico, N. Spycher, R. Carroll, and K.H. Williams (2018), Geochemical Exports to River from the Intra-Meander Hyporheic Zone under Transient Hydrologic Conditions: East River Mountainous Watershed, Colorado, Water Resources Research, [DOI:10.1002/2017WR022346]

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 25, 2018

Rarely Studied Microbes Associated With Production of Toxic Methylmercury in Great Lakes Estuary

New paper lays foundation for future studies of the role of understudied microorganisms in methylmercury production.

The Science
The bioaccumulation of mercury in plant and animal tissue is strongly linked to mercury methylation in sediments, and poses a significant environmental and human health concern in freshwater wetlands of the Great Lakes region. A study led by Emily Graham, a research scientist at Pacific Northwest National Laboratory, shows the influence of wetland vegetation in regulating mercury toxicity in a Great Lakes estuary. It also provides evidence that enhanced production of methylmercury in vegetated areas of the estuary is associated with degradation of dissolved organic matter, a shift in the microbial community towards fermentative microbes, and changes in the microbiome structure toward Clostridia species.

The Impact
This study shows the potential for methylmercury (MeHg) generation by understudied fermenting microorganisms that have not been historically considered to influence mercury toxicity. It also shows that dissolved organic matter (DOM) may influence microbiome structure and activity in vegetated areas of the estuary. Together, these findings provide scientists with a greater understanding of environmental conditions that lead to methylmercury production and offers a way to improve monitoring for mercury contamination in estuaries within the Great Lakes.

Summary
Inorganic mercury in wetlands becomes toxic methylmercury (MeHg) due to a primarily microbial process known as mercury methylation. Dissolved organic matter (DOM) is a strong regulator of MeHg production because its chemical interactions change the bioavailability of mercury and support the growth of specific types of microbial communities.

In this study, the team used anoxic microcosms with sediments from geochemically disparate vegetated and non-vegetated wetland environments. Sediments were from nearshore areas of Lake Superior’s St. Louis River Estuary, where sediments contain a legacy of mercury contamination from shipping and industry. The team’s research revealed a greater relative capacity for mercury methylation in vegetated sediments compared to non-vegetated ones. However, they also showed that mercury cycling in nutrient-poor non-vegetated sediments is susceptible to DOM inputs in the form of plant leachate. With leachate added, these non-vegetated microcosms produced substantially more MeHg than un-amended microcosms and also showed a marked increase in species of bacterial Clostridia.

Clostridia have the genetic potential to methylate mercury but have not been considered among the primary microbes responsible for mercury toxicity. These microbes ferment recalcitrant organic matter, and in addition to their increased abundance, an analysis of their metabolism suggested an increase in fermentation related to MeHg production. Metagenomic analysis supported both an increase in Clostridia and fermentation.
In total, the study’s observations provide a foundation for future work on the involvement of these understudied microorganisms in mercury methylation in estuaries of the Great Lakes. They also highlight the need to further study the microbial ecology of mercury methylation.

Contacts (BER PM)
David Lesmes and Paul Bayer
U.S. DOE
David.Lesmes@science.doe.gov, Paul.Bayer@science.doe.gov

(PI Contact)
Emily B. Graham
Research Scientist, Pacific Northwest National Laboratory
emily.graham@pnnl.gov

Funding
This work was supported by EPA STAR and NOAA NERRS fellowships to Emily B. Graham and a JGI CSP grant to Diana R. Nemergut. The first author also was supported in part by DOE, Office of Biological and Environmental Research (BER), as part of Subsurface Biogeochemical Research Program’s Scientific Focus Area (SFA) at PNNL.

Publications
Graham, E. B., R.S. Gabor, S. Schooler, D.M. McKnight, D.R. Nemergut, and J.E. Knelman. “Oligotrophic wetland sediments susceptible to shifts in microbiomes and mercury cycling with dissolved organic matter addition.” PeerJ. 6:e4575. (2018). [DOI:10.7717/peerj.4575]

Related Links
Rarely Studied Microbes Associated With Mercury Toxicity in the Great Lakes

Topic Areas:

Division: SC-23 BER


September 18, 2018

Representing Microtopography Effects in Hydrology Models

A novel subgrid model improves the representation of hydrologic processes.

The Science
Microtopography is known to be an important control on surface water retention, evaporation, infiltration, and runoff generation.   Unfortunately, direct representation of microtopography effects in models of those processes is typically not feasible because of the high spatial and temporal resolution required. A subgrid model was developed to include microtopography effects in lower-resolution models, thus improving the representation of key hydrologic processes.

The Impact
The newly developed subgrid model is broadly applicable to disparate landscapes and significantly improves the representation of runoff generation and inundation compared with neglecting small-scale topography. The subgrid model enables process-resolving models of permafrost thermal hydrology to expand to catchment scales and decadal timeframes. 

Summary
Fine-scale simulations using high-resolution digital elevation models highlight the importance of microtopography and its effects on integrated hydrology in polygonal tundra, hummocky bogs, and hillslopes with incised rills. A subgrid model that modifies the flow and accumulation terms in lower-resolution models replicates the microtopography-resolving simulations at orders-of-magnitude smaller computation cost. The subgrid model makes it possible to incorporate thaw-induced dynamic topography in simulations addressing the evolution of carbon-rich Arctic tundra in a warming climate.

Contacts (BER PM)
David Lesmes and Daniel Stover
SC-23.1
David.Lesmes@science.doe.gov and Daniel.Stover@science.doe.gov

(PI Contact)
Ahmad Jan
Climate Change Science Institute, Oak Ridge National Laboratory
jana@ornl.gov

Funding
This work was supported by Interoperable Design of Extreme-scale Application Software (IDEAS) project and by the Next Generation Ecosystem Experiment (NGEE-Arctic) project.

Publications
Jan, A., E.T. Coon, J.D. Graham, and S.L. Painter, “A subgrid approach for modeling microtopography effects on overland flow.” Water Resources Research, 54(9), 6153-6167 (2018). [DOI:10.1029/2017WR021898]

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 04, 2018

Unexpected High Carbon Fluxes from the Deep Unsaturated Zone in a Semi-Arid Region

The Science
Understanding of terrestrial carbon cycling has relied primarily on studies of top soils that are typically characterized to depths shallower than 0.5 m. We found and quantified 30% of CO2 annual efflux to atmosphere (60% in winter) originates from below 1 m, contrary to prediction of <1% by the ESM land models.

The Impact
We contend that ESM land models need to incorporate these deeper soil processes to improve CO2 flux predictions in semi-arid climate regions.

Summary
Understanding of terrestrial carbon cycling has relied primarily on studies of topsoils that are typically characterized to depths shallower than 0.5 m. At a semi-arid site, instrumented down to 7 meters, we measured seasonal- and depth-resolved carbon inventories and fluxes, and groundwater and unsaturated zone flow rates. We identified an unexpected high dissolved organic carbon (DOC) flux from the rhizosphere into the underlying unsaturated zone. We measured that ~30% of the CO2 efflux to atmosphere (60% in winter) originates from below 1 m, contrary to prediction of <1% by Earth System Model land models. The seasonal DOC influx and favorable temperatures, moisture and oxygen availability in deeper unsaturated zone sustained the respirations of deeper microbial communities and roots. These conditions are common characteristics of many subsurface environments; thus we contend that ESM land models need to incorporate these deeper soil processes to improve CO2 flux predictions in semi-arid climate regions.

Contacts (BER PM)
David Lesmes, SC-23.1
david.lesmes@science.doe.gov

(PI Contact)
Jiamin Wan, Lawrence Berkeley National Laboratory
jwan@lbl.gov

Funding
U.S. Department of Energy (DOE) Subsurface Biogeochemical Research Program, DOE Office of Science, Office of Biological and Environmental Research, under contract DE-AC02- 05CH11231.

Publications
Wan, J., Tokunaga, T.K., Dong, W., Williams, K.H., Kim, Y., Conrad, M.E., Bill, M., Riley, W.J., Susan S.H., “Deep unsaturated zone contributions to carbon cycling in semiarid environments.” Journal of Geophysical Research: Biogeosciences 123(9), 3045-3054 (2018). [DOI:10.1029/2018JG004669]

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 14, 2018

A Simplified Way to Predict the Function of Microbial Communities

A pioneering study offers an easier approach to studying microbial functioning and could help scientists advance models of biogeochemical cycling.

The Science
In areas that flood frequently, microbial communities must adapt to repeated wet-dry cycles. Metabolic strategies help them survive, but these strategies can also influence nutrient cycling and atmospheric emissions from soils and sediments. An international team of scientists examined soils from rice paddies to understand how microbial communities function during floods. Their work suggests analyzing carbon that microbes extracted from water may prove critical to understanding and modeling these important communities.

The Impact
How microbes function in often-flooded soils has profound impacts on crop production, in part because they can deliver nutrients to plants and stabilize or release atmospheric emissions from soils. Understanding how microbial communities function in soils—before, during, and after flooding—can help scientists improve modeling and promote beneficial changes in those communities.

Summary
To understand how microbial activity varied in response to flooding, scientists studied three types of organic matter that are commonly found in three types of rice paddy soils: dried rice straw, charred rice straw, and cattle manure. Team members came from the SLAC National Accelerator Laboratory; Stanford University; Swedish University of Agricultural Sciences; University of California, Riverside; and EMSL, the Environmental Molecular Sciences Laboratory, a U.S. Department of Energy Office of Science user facility. While other studies used a similar approach to look at well-aerated, upland soil and simple carbon compounds, or single micro-organisms, none examined the full complexity of natural soil and carbon substrates during the transition from dry to flooded conditions. The team used EMSL’s Fourier-transform ion cyclotron resonance mass spectrometer to analyze dissolved carbon and then observed how microbial functioning changed. These pioneering experiments produced surprising results. Not only were researchers able to better understand how microbes breathed and obtained energy during flooded conditions, but they discovered that a focus on water-extractable carbon was sufficient to predict microbial respiration rates from diverse metabolic strategies. Though more in-depth studies will be important to reveal underlying functions, the insights gained from this study give scientists a proxy to begin modeling these complex interactions.

BER PM Contact
Paul Bayer, SC-23.1

PI Contact
Kristin Boye
Stanford University
kboye@slac.stanford.edu

Funding
This work was supported by the U.S. Department of Energy’s Office of Science (Office of Biological and Environmental Research), including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility; SLAC National Accelerator Laboratory and the BER Subsurface Biogeochemical Research program; Swedish Foundation for International Cooperation in Research and Higher Education; Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning; and U.S. National Science Foundation.

Publication
Boye, K., A.H. Hermann, M.V. Schaefer, M.M. Tfaily, and S. Fendorf. “Discerning Microbially Mediated Processes During Redox Transitions in Flooded Soils Using Carbon and Energy Balances.” Frontiers in Environmental Science 6 Article 15 (2018). [DOI:10.3389/fenvs.2018.00015]

Related Links
A Simplified Way to Predict the Function of Microbial Communities EMSL science highlight

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 11, 2018

Using Strontium Isotopes to Evaluate How Local Topography Affects Groundwater Recharge

The Science
A key component of understanding the connection between groundwater quality and the vadose zone (the water unsaturated region above the water table) is the movement of water from the surface to the aquifer (recharge). Measurements of the natural isotopic composition of strontium (Sr) were used to assess the effect of local topography on groundwater recharge across a semi-dry riparian floodplain in the Upper Colorado River Basin.

The Impact
This work demonstrates the use of 87Sr/86Sr (Sr isotopes) to measure groundwater recharge through analysis of porewater and groundwater samples from the vadose zone. The study resulted in an understanding how the microtopography of the Rifle Site affects the hyper-local variation in the downward movement of vadose-zone porewater that may carry nutrients and contaminants to groundwater.

Summary
Over time, loose sand, clay, silt, gravel or similar unconsolidated, or "alluvial” material is deposited by water into alluvial aquifers. Recharge of alluvial aquifers is a key component in understanding the interaction between floodplain vadose zone biogeochemistry and groundwater quality. The Rifle Site (a former U-mill tailings site) adjacent to the Colorado River is a well-established field laboratory that has been used for over a decade for the study of biogeochemical processes in the vadose zone and aquifer.  This site is exemplary of both a riparian floodplain in a semiarid region and a post-remediation U-tailings site. The authors use Sr isotopic data for groundwater and vadose zone porewater samples to build a mixing model for the fractional contribution of vadose zone porewater (i.e., recharge) to the aquifer and to assess its distribution across the site.  The vadose zone porewater contribution to the aquifer ranged systematically from 0% to 38% and appears to be controlled largely by the microtopography of the site.  The area-weighted average contribution across the site was 8%, corresponding to a net recharge of 7.5 cm. Given a groundwater transport time across the site of ~1.5 to 3 years, this translates to a recharge rate between 5 and 2.5 cm/yr, and with the average precipitation to the site, implies a loss from the vadose zone due to evapotranspiration of 83% to 92%.

BER PM Contact
David Lesmes, SC-23.1
david.lesmes@science.doe.gov

Contact
Susan Hubbard, LBNL
sshubbard@lbl.gov

Funding
This work was conducted as part of the Genomes to Watershed Scientific Focus Area at Lawrence Berkeley National Laboratory and was supported by the U.S. Department of Energy (DOE) Subsurface Biogeochemical Research Program, DOE Office of Science, Office of Biological and Environmental Research, under Contract Number DE-ACO2-05CH11231.

Publication
Christensen, J. N., et al. “Using strontium isotopes to evaluate the spatial variation of groundwater recharge.” Sci Total Environ 637-638, 672-685 (2018).  [DOI:10.1016/j.scitotenv.2018.05.019]

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 07, 2018

Machine Learning to Upscale Nanoscale Chemical Heterogeneity of Shale Materials

The Science
Scientists used machine learning to interpret the microscale heterogeneity of shale materials that influence water quality, based on their nanoscale properties.

The Impact
Scientists have identified a way to use machine learning to integrate fine- and large-scale infrared characterizations of shale—sedimentary rocks composed of minerals and organic matter. The flow of fluids through shale’s nanoporous networks is fundamental to hydraulic fracturing and enhanced geothermal heating as well as to carbon sequestration and water storage. Thus, understanding shale chemistry at both the nano- and meso-scale is relevant to energy production, climate-change mitigation, and sustainable water and land use.

Summary
The organic and mineralogical heterogeneity in shale at micrometer and nanometer spatial scales contributes to the quality of gas reserves, gas flow mechanisms and gas production. In this work, we demonstrate two molecular imaging approaches based on infrared spectroscopy to obtain mineral and kerogen information at these mesoscale spatial resolutions in large-sized shale rock samples. The first method is a modified microscopic attenuated total reflectance measurement that utilizes a large germanium hemisphere combined with a focal plane array detector to rapidly capture chemical images of shale rock surfaces spanning hundreds of micrometers with micrometer spatial resolution. The second method, synchrotron infrared nano-spectroscopy, utilizes a metallic atomic force microscope tip to obtain chemical images of micrometer dimensions but with nanometer spatial resolution. This chemically “deconvoluted” imaging at the nano-pore scale is then used to build a machine learning model to generate a molecular distribution map across scales with a spatial span of 1000 times, which enables high-throughput geochemical characterization in greater details across the nano-pore and micro-grain scales and allows us to identify co-localization of mineral phases with chemically distinct organics and even with gas phase sorbents. This characterization is fundamental to understand mineral and organic compositions affecting the behavior of shales.

Contacts (BER PM)
David Lesmes,
SC-23.1
david.lesmes@science.doe.gov

(PI Contact)
Zhao Hao, LBNL
zhao@lbl.gov

Publications
Hao, Z., Bechtel, H. A., Kneafsey, T., Gilbert, B., Nico, P. S. “Cross-Scale Molecular Analysis of Chemical Heterogeneity in Shale Rocks.” Scientific Reports 8(Article 2552) (2018). [DOI:10.1038/s41598-018-20365-6]

Related Links
EESA Scientists Leverage Machine Learning
Scientists Use Machine Learning to Span Scales in Shale

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 27, 2018

Clarifying Rates of Methylmercury Production

New model provides more accurate rate constant estimates for mercury methylation and demethylation.

The Science
Using new experiments and re-analyses of previous experiments, a new two-site reversible sorption model was developed to describe the production of methylmercury over time. The new model takes into account competing processes and results in faster rates of production than previously estimated.

The Impact
Simulations of methylmercury production and transport demonstrate that methylmercury production is likely significantly larger than estimated by currently used models.

Summary
Mercury (Hg) is a toxic element that occurs naturally and as an anthropogenic pollutant in the environment. The neurotoxin monomethylmercury (MMHg) is a particular concern because it biomagnifies in aquatic environments and has adverse development effects on young children and developing embryos. MMHg is formed in the environment from inorganic Hg through the action of microorganisms in a process called Hg methylation. Because of its toxicity, there have been many attempts to measure Hg methylation and MMHg demethylation rates in various environmental settings with differing results. Even in laboratory experiments, rates for the methylation of Hg to MMHg often exhibit kinetics that are inconsistent with first-order kinetic models. In a new study, scientists from Oak Ridge National Laboratory used time-resolved measurements of filter-passing Hg and MMHg during methylation/demethylation assays, and they re-analyzed previous assays. Then they used a multi-site kinetic sorption model to show that competing kinetic sorption reactions can lead to apparent non-first-order kinetics in Hg methylation and MMHg demethylation. The new model can describe the range of behaviors for time-resolved methylation/demethylation data reported in the literature including those that exhibit non first-order kinetics. Additionally, the team showed that neglecting competing sorption processes can confound analyses of methylation/demethylation assays, resulting in rate constant estimates that are systematically biased low. Simulations of MMHg production and transport in a hypothetical periphyton biofilm bed illustrate the implications of the new model and demonstrate that methylmercury production may be significantly different than projected by single-rate first-order models.

Contacts (BER PM)
Paul Bayer
Paul.Bayer@science.doe.gov; 301-903-5324

(PI Contact)
Scott Brooks
brookssc@ornl.gov/ 865-574-6398

Funding
This work was funded by the U.S. Department of Energy, Office of Science, Biological and Environmental Research, Subsurface Biogeochemical Research Program and is a product of the Science Focus Area (SFA) at ORNL. The isotopes used in this research were supplied by the United States Department of Energy Office of Science by the Isotope Program in the Office of Nuclear Physics.

Publications Olsen, T.A., K. A. Muller, S. L. Painter, and S. C. Brooks. "Kinetics of Mercury Methylation Revisited" Environmental Science & Technology 52(4), 2063-2070 (2018). [DOI:10.1021/acs.est.7b05152]

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 25, 2018

Fundamental Understanding of Engineered Nanoparticle Stability in Aquatic Environments

The Science
It is commonly true that a diluted colloidal suspension is more stable over time than a concentrated one, because dilution reduces collision rates, so delays formation of aggregates. However, we observed the opposite relationship between stability and concentration for some engineered ligand-coated nanoparticles.

The Impact
Because the stability of nanoparticles determines their physicochemical and kinetic behavior including toxicity, dilution induced instability needs to be understood to realistically predict the behavior of engineered ligand-coated nanoparticles in aqueous systems.

Summary
It is commonly true that a diluted colloidal suspension is more stable over time than a concentrated one, because dilution reduces collision rates of the particles, therefore delays formation of aggregates. However, this generalization does not apply for some engineered ligand-coated nanoparticles (NPs). We observed the opposite relationship between stability and concentration of NPs. We tested four different types of NPs; CdSe-11-mercaptoundecanoic acid, CdTe-polyelectrolytes, Ag-citrate, and Ag- polyvinylpirrolidone. The results showed that dilution alone induced aggregation and subsequent sedimentation of the NPs that were originally monodispersed at very high concentrations. Increased dilution caused NPs to progressively become unstable in the suspensions. The extent of the dilution impact on the stability of NPs is different for different types of NPs. We hypothesize that the unavoidable decrease in free ligand concentration in the aqueous phase following dilution causes detachment of ligands from the suspended NP cores. The ligands attached to NP core surfaces must generally approach exchange equilibrium with free ligands in the aqueous phase, therefore ligand detachment and destabilization are expected consequences of dilution. More studies are necessary to test this hypothesis. Because the stability of NPs determines their physicochemical and kinetic behavior including toxicity, dilution induced instability needs to be understood to realistically predict the behavior of engineered ligand-coated nanoparticles in aqueous systems.

Contacts (BER PM)
David Lesmes, SC-23.1
david.lesmes@science.doe.gov

(PI Contact)
Jiamin Wan, Lawrence Berkeley National Laboratory
jwan@lbl.gov

Funding
U.S. Department of Energy (DOE) Subsurface Biogeochemical Research Program, DOE Office of Science, Office of Biological and Environmental Research, under contract DE-AC02- 05CH11231.

Publications
Wan, J., Y. Kim, M.J. Mulvihill, and T. K. Tokunaga. “Dilution destabilizes engineered ligand-coated nanoparticles in aqueous suspensions.” Environmental Toxicology and Chemistry 37(5), 1301-1308 (2018).[DOI:10.1002/etc.4103]

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER