SRP Annual Meeting Poster Winners Webinar Series
Superfund Research Program
This webinar series features the outstanding SRP-funded work being conducted by graduate students and postdocs. Specifically, this series consists of presentations from SRP Annual Meeting Poster Award Winners. This is an excellent opportunity for those who were not able to view their posters at the Annual Meeting – as well as for peers, SRP researchers, SRP alumni, and SRP's partners (NIEHS, the U.S Environmental Protection Agency, the Agency for Toxic Substances and Disease Registry, etc.) – to hear the winners describe their current research/activities.
2017 Trainee Webinar Series
Session I: Environmental Sciences and Engineering Poster Winners
March 6, 2017 • 2:00 - 3:00 p.m. EST
Breathable Vapor Toxicant Barriers Based on Multilayer Graphene Oxide
Ruben Spitz, Brown University (firstname.lastname@example.org)
There is tremendous interest in the development of ultrathin graphene and graphene oxide films as molecular transport barriers or as selective membranes that use molecular sieving properties for small molecular separation or recovery technologies. Graphene oxide films in particular have been shown to be excellent barriers to the transport of small-molecule gases in the dry state but expand in the presence of water vapor to allow rapid permeation of H2O.
The interlayer channels in GO films are sufficiently small to exclude larger toxicants, but some toxicants can fit in the < 1nm transport channels and are known to be co-transported with water. We have developed a theoretical model and experimental facility suitable for studying vapor permeation in both directions simultaneously and show results for two model vapors. Ethanol and trichloroethylene (TCE) were chosen due to their widely varying solubility in water. The results point to design parameters that allow both outward water transport, and the results suggest that GO can be used to create breathable toxicant barriers as components in wearable devices for chemical and biochemical detection.
Development of a Novel Passive Sampling Strategy for Methylmercury in Sediments and Soils
James Sanders, University of Maryland, Baltimore County (email@example.com)
Aquatic mercury can pose a significant risk to ecological and human health when it is converted to the more toxic and bioaccumulative methylmercury by anaerobic microorganisms near the sediment-water interface. Benthic invertebrates exposed in this zone represent an important link in the accumulation of methylmercury in aquatic food webs. As such, measurement of methylmercury's availability to these organisms is critical for risk assessment of contaminated sites. To date, no sampling strategy has achieved wide acceptance for this purpose. We are developing a novel passive sampling technology to mimic the pseudo-equilibrium mode of accumulation by benthic organisms. Custom polymers containing either thiolated sorbents or activated carbon were prepared and evaluated in increasingly environmentally realistic experiments, with positive results. In contaminated soil slurries, water concentrations estimated by samplers agreed within a factor of one to four with direct measurements of centrifuged pore water. Sampler partitioning was within half an order of magnitude of soil. Ongoing work is aimed at correlating sampler measurements with accumulation by a benthic test organism in sediment microcosms with or without activated carbon amendment. Sampler data will be used as input for a bioaccumulation model to validate the predictive capability of the device. Ultimately, our sampler will enable more accurate measuring and modeling of bioavailability under multiple amendment scenarios.
The Effect of Metal Speciation in Fly Ash on Environmentally Persistent Free Radical (EPFR) Formation
Elisabeth Feld-Cook, Louisiana State University (firstname.lastname@example.org)
EPFRs are surface bound radicals with lifetimes on the order of hours to weeks. They originate typically from combustion processes and are associated with emitted solids such as fly ash. EPFRs are intermediates to PCDD/F formation in the combustion exhaust but also induce oxidative stress in biological and environmental systems. This study aims at determining the relationship of fly ash composition and EPFR formation. Real world fly ash (RWFA) and synthetically composed fly ash (SFA) were studied to evaluate the relationship between metal oxides, sulfur compounds, and EFPR formation. Thorough characterization of RWFA from China and the U.S. EPA revealed large differences in the content of EPFRs. SFA were made to model the RWFA composition and determine a driving element in the EPFR formation or inhibition. Sulfur was determined to be an essential element in controlling EPFR inhibition. Low energy X-ray beam studies performed at LSU CAMD provided detailed information on sulfur speciation. For the SFA containing calcium and sulfur, CaSO4 was the most prominent sulfate, but FeSO4 and ZnSO4 were present; however, for the sulfur-only containing SFA, ZnSO4 and FeSO4 were the dominant species. We hypothesize that sulfur rich waste releases sulfur dioxides during combustion, which block the metal active sites for the EPFR formation. The mechanisms explored here can potentially be applied to prevent EPFR formation at Superfund sites.
Session II: Health Sciences Poster Winners
March 27, 2017 • 2:00 - 3:00 p.m. EDT
Effects of the Trichloroethylene Metabolite S-(1,2-dichlorovinyl)-L-cysteine on Mitochondrial Function in Human Cytotrophoblasts
Elana Elkin, University of Michigan (email@example.com)
Trichloroethylene (TCE) is a widespread environmental contaminant that was recently classified as a "known human carcinogen." Despite this classification, the specific effects of TCE on pregnancy and adverse birth outcomes remain elusive. TCE causes toxicity through its active metabolites such as S-(1,2-dichlorovinyl)-L-cysteine (DCVC). This study assessed the effects of DCVC exposure on mitochondrial function in human placental cells. First-trimester human extravillous trophoblast cells, HTR-8/SVneo, were exposed to 10-50µM DCVC for 12 hours. Following exposure, the cellular oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were measured in real time using a Seahorse XF24 analyzer. Following measurement of the basal OCR/ECAR, mitochondrial complex inhibitors oligomycin and antimycin A and uncoupler FCCP were serially injected into the media to target specific elements of the electron transport chain in order to measure key parameters of mitochondrial function. The study revealed that exposure to DCVC for 12 hours significantly decreased multiple key parameters of mitochondrial function in HTR-8/SVneo cells, including basal respiration, oxygen-linked ATP production, maximum and spare respiratory capacity, and coupling efficiency. These decreases occurred in a concentration-dependent manner. The TCE metabolite DCVC induces substantial deficits in aerobic mitochondrial respiration in trophoblasts.
Understanding Tributyltin, an Environmental Obesogen, in Its Engagement of Nuclear Receptor Pathways and Molecular Gene Targets Using Transcriptomics
Stephanie Kim, Boston University (firstname.lastname@example.org)
Obesogens are environmental chemicals that perturb adipogenesis and have been linked to endocrine disruption and obesity.Tributyltin (TBT) has been shown to interact with peroxisome proliferator-activated receptor gamma (PPARγ) and retinoid X receptor (RXR) to induce white adipocyte differentiation and to negatively regulate bone formation. Given TBT's ability to regulate multiple nuclear receptor pathways, we evaluated the molecular consequences of TBT exposure during bone marrow multipotent mesenchymal stromal cell (BM-MSC) differentiation by examining the expression of nuclear receptors and enriched molecular pathways in comparison to rosiglitazone (PPARγ agonist) and LG100268 (RXR agonist). Transcriptomic analyses were performed using Affymetrix Mouse Gene 2.0ST Array. Using Gene Set Enrichment Analysis for pathway analyses, pathways related to mitochondrial biogenesis and brown adipocyte differentiation were more significantly upregulated in rosiglitazone-exposed cells than in TBT-exposed cells. Pathways related to osteogenesis were downregulated by all ligands. The differential expression of selected brown adipogenesis-related genes induced by rosiglitazone and TBT in BM-MSCs, 3T3-L1 cells, and OP9 cells was validated by qPCR. In summary, we show that TBT does not act specifically as a PPARγ or as a RXR ligand and acts distinctly from rosiglitazone, which has a greater efficacy in activating the expression of genes involved in mitochondrial biogenesis and brown adipogenesis.
Cadmium Impairs Adult Neurogenesis, Hippocampus-Dependent Memory, and Olfactory Memory in Mice
Hao Wang, University of Washington (email@example.com)
Cadmium (Cd) is a heavy metal with a long biological half-life in humans and is common to Superfund hazardous waste sites. Cd is a potential neurotoxicant, and its exposure is associated with impairments of cognition and olfaction in humans. However, little is known regarding the mechanisms of Cd neurotoxicity. Adult neurogenesis occurs in the subgranular zone (SGZ) of the dentate gyrus in the hippocampus and subventricular zone (SVZ) along the lateral ventricles in adult mammalian brains. It plays an important role for hippocampus-dependent memory and olfaction. The effect of neurotoxicants on adult neurogenesis is just beginning to be elucidated. The goal of our study is to investigate the effects of Cd on cognition and olfaction with a focus on its effects on adult neurogenesis. We found that exposure of low-level Cd can affect adult neurogenesis in vivo. Furthermore, Cd exposure impairs spatial working memory, contextual fear memory, and short-term olfactory memory in adult mice. These results provide new insights concerning the underlying mechanisms of Cd neurotoxicity and partially fulfill the UW SRP's mission of mechanistic-based toxicology studies on neurotoxic heavy metals.
2014 Trainee Webinar Series
Session I: Featuring Minghui Gui (University of Kentucky) and Fabian Grimm (University of Iowa)April 15, 2014; 1:00 – 2:00 pm, EDT
Minghui Gui: Chloro-Organic Detoxification by Membrane Supported Iron/Iron Oxide System
Presentation Abstract: Chlorinated organic compounds such as trichloroethylene (TCE) and polychlorinated biphenyls (PCBs) have always been a threat to human health. The existing remediation techniques remove the chlorine atoms by either reduction or oxidation. The reductive pathway (such as, with Fe, Fe/Pd, Fe/Ni nanoparticles [NPs]) degrade TCE and PCBs based on electron transfer and the hydrodechlorination mechanism. The bimetallic NPs enhance the reaction rate through hydrodechlorination, and are needed for PCB dechlorination. The oxidative pathway (advanced oxidation processes) generates free radicals like OH•, which attack the model compounds and cause the chain scission.
Tunable supports such as polyelectrolyte functionalized membranes provide added benefits of eliminating NP agglomeration and leaching. Gui developed iron-functionalized membrane system in both bench-scale and large-scale. Iron and iron oxide NPs (less than 80 nm) were in-situ synthesized in polyacrylic acid (PAA) functionalized polyvinylidene fluoride (PVDF) microfiltration membranes. The large-scale functionalized membranes developed in collaboration with Sepro Membrane Inc. include the flat sheet and spiral wound modules, which have the potential to be used for dechlorination (reduction followed by oxidation) as well as toxic inorganic (e.g. selenate/selenite) capture in real life. Selenium was efficiently removed from coal-fired plant process water (Southern Co.) by iron functionalized membrane.
Fabian Grimm: High-affinity Interactions Between Human Transthyretin and Polychlorinated Biphenyl Sulfates – Implications for Thyroid Disruption and the Development of Anti-amyloid Therapeutics
Presentation Abstract: Human transthyretin (TTR) is a major transporter and potential transplacental carrier for thyroid hormones. The displacement of L-thyroxine (T4) from binding sites on TTR by metabolites of polychlorinated biphenyls (PCBs) is thought to be a major contributing mechanism in PCB-induced thyroid disruption. Structural similarities between sulfated metabolites of PCBs and T4 led Grimm to hypothesize that these metabolites are high-affinity ligands for TTR that are capable of competing with the hormone. To test this hypothesis, Grimm initially examined the ability of five lower-chlorinated PCB sulfates to bind to human TTR. All five PCB sulfates were able to bind to the high-affinity binding site with equilibrium dissociation constants (Kd) in the low nanomolar range (4.8 – 16.8 nM), similar to that determined for T4 (4.7 nM). Moreover, he was able to model their lowest energy binding conformations and molecular interactions within the T4 binding site by molecular docking simulations. Corroborating evidence for the binding of PCB sulfates stems from their ability to inhibit the formation of TTR amyloid fibrils in vitro. Small molecules that bind with high affinity to T4 binding sites on TTR are known to kinetically stabilize its tetrameric structure and prevent its disassembly into monomeric subunits, the rate-limiting step in TTR amyloid fibril formation. Aggregation of TTR fibrils causes amyloidosis like senile systemic amyloidosis , familial amyloid polyneuropathy and familial amyloid cardiomyopathy . At an equimolar concentration, all PCB sulfates examined were effective inhibitors of TTR amyloid fibril formation, and some were equally or more effective (up to 94% inhibition) than some of the most potent inhibitors described in the literature. Thus, Grimm’s current results on the binding of PCB‐sulfates to TTR are consistent with a potential role for these metabolites in thyroid disruption and/or inter-tissue transport, and they may also provide structural information for improved design of drugs to inhibit TTR amyloidosis.
Session II: Featuring Jing Sun (Columbia University) and Peter Wagner (Harvard University)April 30, 2014; 1:00 – 2:00 pm EDT
Jing Sun: Arsenic In-Situ Immobilization by Magnetite Formation within Contaminated Aquifer Sediments
Presentation Abstract: One approach for remediating arsenic-contaminated aquifers involves stimulating iron mineral transformations that immobilize arsenic in the solid phase through sorption or precipitation. Despite much research, the immobilization strategies are often ineffective, in part because iron host minerals are often sensitive to redox changes. Since magnetite (Fe3O4) is stable under most redox conditions at Superfund sites, Sun has been performing laboratory-scale experiments to examine its potential as a long-term arsenic sink. The study presented here focused on a series of flow-through columns, loaded with reduced aquifer sediments from the Dover Landfill Superfund site. This study was designed to stimulate the formation of magnetite which successfully sequestered arsenic from solution, to test its ability of maintaining arsenic retention under changing conditions, and then to evaluate its potential to immobilize additional arsenic flowing into the system. Sun’s data demonstrate that the adsorption capacity and the stability of solid-phase arsenic greatly increased in amended sediments. These findings suggest that magnetite, produced via simultaneous addition of ferrous iron and nitrate, is a promising target mineral for long-term arsenic remediation.
Peter Wagner: RNA-seq Gives Insights into Lead Neurotoxicity in Neural Stem Cells
Presentation Abstract: Lead (Pb) is a ubiquitous and canonical neurotoxicant that poses a significant public health threat. Despite myriad studies of Pb neurotoxicity, the specific genes and pathways involved in the associated adverse neurocognitive outcomes remain poorly understood. As Pb freely crosses the placenta, pre-natal Pb exposure is of critical concern. To address some of the changes that may occur early in the developing brain, Wagner performed next-generation RNA sequencing (RNASeq) on human neural stem cells (hNSCs). The high sensitivity afforded by RNASeq enabled the use of a physiologically relevant dose of Pb (1μM). hNSCs were sequenced in triplicate unexposed-exposed pairs revealing 19 statistically significant differentially expressed genes. Reported genes include all those with greater than ±0.3 log2 fold change and FDR-adjusted q-values below 0.05. Among the up-regulated genes are several canonical NRF2 target genes, indicating NRF2 activation. Two of the top hits not previously annotated as NRF2 targets, F2RL2 and SPP1, were also up-regulated upon exposure to a canonical NRF2 inducer DL-Sulforaphane and their up-regulation when exposed to Pb was attenuated by siRNA-mediated knockdown of NRF2. These results indicate F2RL2 and SPP1 are likely novel NRF2-target genes. Relatively little is known of SPP1’s function in the brain and there are no known functions of F2RL2. Dysregulation of these genes in these early developmental windows may lead to adverse changes in normal brain development.
Session III: Leslie Knecht (University of Miami) and Daniel Gusenleitner (Boston University)May 13, 2014; 1:00 – 2:00 pm EDT
Leslie Knecht: Sensing Environmental Contaminants with Paper-Based Platforms
Presentation Abstract: Detection of environmental contaminants on-site is important in areas where resources are limited. Remote site detection requires that the sensors employed are selective, sensitive, rugged, and amenable for use by untrained personnel. To this end, Knecht has developed cell-based sensors for environmental contaminants encapsulated within Bacillus subtilis spores. These spores are robust and able to withstand harsh environmental conditions which make them ideal whole-cell biosensors for field work. To enhance the portability of the spores, she has employed filter paper-based platforms on which detection of a target contaminant in environmental samples can be performed. The paper-based platform is inexpensive and simple to design, making it amendable for a variety of applications. Specifically, she has utilized E. coli and B. subtilis cells for the detection of quorum sensing molecules as well as arsenic and organoarsenicals on paper-based platforms. The assay times and detection limits for the microtiter plate and for the newly designed paper-based platform were comparable. Advantages of the spores include their ability to survive in extreme, diverse environmental conditions, be transported without a loss of activity, and their long-term storage capabilities. Colorimetric biosensing systems for use in field analysis of a variety of contaminants have been developed by combining both the spores and the paper-based platform.
Daniel Gusenleitner: Rodent-based Toxicogenomic Models of Hepatocarcinogenicity
Presentation Abstract: Despite an overall decrease in incidence and mortality, about 40% of Americans will be diagnosed with cancer in their lifetime, and around 20% will die of it. Current approaches to test carcinogenic chemicals adopt the 2-year rodent bioassay as the de-facto "gold-standard". This assay is costly and time-consuming and, as a result, fewer than 2% of the chemicals on the market have actually been tested for carcinogenicity. However, evidence accumulated to date suggests that gene expression profiles of model organisms exposed to chemical compounds reflect underlying mechanisms of action, and these toxicogenomic models could be used in the prediction of chemical carcinogenicity of individual chemicals or mixtures.
In this study Gusenleitner used a rat-based microarray dataset from the NTP DrugMatrix Database, to test the ability of toxicogenomics to model carcinogenicity. He analyzed 4442 gene-expression profiles treated with 255 well-characterized compounds, including genotoxic and non-genotoxic carcinogens. He applied machine-learning approaches to build a classifier that predicts (AUC: 0.78) the carcinogenic potential of compounds within the dataset. The classification models were validated on an independent, dataset from the Japanese Toxicogenomics Project and achieved comparable prediction accuracy. Furthermore, comparison of the prediction results with pathological items showed a sensitivity of up to 95.8%.
In conclusion, Gusenleitner substantially validated the toxicogenomic approach to predict carcinogenicity, and provided strong evidence that with a larger set of compounds and cellular contexts he should be able to improve the sensitivity and specificity of the predictions. He found that the prediction of carcinogenicity is tissue-dependent and the results also confirm and expand upon previous studies implicating DNA damage, peroxisome proliferator-activated receptor (PPAR) and aryl hydrocarbon receptor (AhR) signaling and regenerative pathology in the response to exposure.
2013 Trainee Webinar Series
Session III: Daniel Brown (Duke University) and Caitlin Howe (Columbia University)
May 30th, 2013 1:00 – 2:00 pm EDT
Daniel Brown: Sublethal embryonic exposure to complex PAH mixtures alters later life behavior and swimming performance in Fundulus heteroclitus
Polycyclic aromatic hydrocarbons (PAHs) are important environmental contaminants in many aquatic systems. Acute embryonic exposure to PAHs is known to cause cardiac teratogenesis in fish, and research has shown that early life exposure to some types of hydrocarbons causes heart alterations and decreased swimming capacity in fish. A population of Atlantic killifish inhabits a Superfund site (Atlantic Wood Industries, Norfolk, VA—AW) that is heavily contaminated with a mixture of PAHs from former creosote operations. This population has developed resistance to the acute toxicity and teratogenic effects caused by the chemical mixture in sediment from the site. While studies have examined heart alterations and decreased swimming capacity in fish following exposure to PAHs, little is known about the impacts of more subtle, early life exposures, which are arguably more broadly applicable to environmental contamination scenarios. This study examined the later life consequences of early life exposure to sublethal concentrations of PAH mixtures in both the adapted and unadapted Atlantic killifish.
Caitlin Howe: Interplay between S-adenosylmethionine, folate, cobalamin, and arsenic methylation in Bangladesh
Chronic exposure to inorganic arsenic (InAs) through contaminated drinking water is a major problem worldwide. InAs undergoes hepatic methylation to form mono- (MMA) and di- methyl (DMA) arsenical species thereby facilitating As elimination. Both reactions are catalyzed by arsenic methyltransferase (AS3MT) using S-adenosylmethionine (SAM) as the methyl donor. SAM biosynthesis depends on folate-dependent one-carbon metabolism. The objective of this project was to test the hypothesis that blood SAM is associated with increased As methylation in Bangladeshi adults. Howe additionally wished to test the hypothesis that the associations between SAM and methylated As metabolites are dependent on folate and cobalamin levels.
Session II: Erika Fritsch (University of California, Davis) and Chase Williams (University of Washington)
May 23rd, 2013 2:00 – 3:00 pm EDT
Erika Fritsch: Non-coplanar PCBs and Ca2+ Signaling in Teleost Species: Addressing Comparative Mechanisms of Toxicity and Developed Resistance in New Bedford Harbor
To date risk assessment practices for polychlorinated biphenyls (PCBs) primarily focus on the impact of dioxin-like or so called coplanar congeners, especially in non-mammalian species. Non-coplanar PCBs (ncPCBs) lack dioxin like toxicity but have been found to enhance the activity of the ryanodine receptor (RyR) a Ca2+ release channel necessary for excitation-contraction coupling in cardiac and skeletal muscle. Thus far, these effects have only been addressed in mammals even though ncPCBs account for more than 50% of the documented PCB burdens in aquatic organism, namely fish species. Fritsch utilized in vitro assays to investigate the impact of commonly detected ncPCBs on RyR activity in rainbow trout (Oncorhynchus mykiss). Additionally, she investigated whether Atlantic killifish (Fundulus heteroclitus) inhabiting the heavily PCB contaminated New Bedford Harbor (NBH) have RyR related mechanisms of ncPCB resistance. She found that environmentally relevant ncPCBs, but not coplanar PCBs, enhance the activity of the RyR isoform 1 (RyR1) found in rainbow trout skeletal muscle. She also shows that in accordance with increased RyR1 related protein expression; RyR1 channels in NBH killifish display increased ligand binding, increased responses to Ca2+ sensitivity and increased maximal responses to channel disruption by the ncPCB congener 95. Additionally, NBH killifish had elevated protein levels of the FK-binding protein, known to play a role in ncPCB mediated toxicity at the RyR. These findings further the understanding of PCB induced altercations at the RyR by exploring common mechanisms of action across vertebrate species and describing population susceptibility in an effort to protect human and wildlife health.
Chase Williams: Effects of Cadmium on Olfactory Mediated Behaviors and Molecular Biomarkers in Coho Salmon (Oncorhynchus kisutch)
Salmon populations have declined in the western United States, with several species being listed as extinct or endangered. One factor implicated in these population declines is inhibition of olfactory processes associated with exposures to waterborne pollutants, including metals such as copper and cadmium. Cadmium (Cd) represents an EPA priority compound but remains relatively under studied in regards to olfactory toxicity in salmonids. In the current study, Williams analyzed olfactory-mediated alarm responses, epithelial injury and recovery, and a suite of olfactory molecular biomarkers encoding genes critical in maintaining olfactory function in juvenile coho salmon receiving acute exposures to Cd. The molecular biomarkers analyzed included four G-protein coupled receptors (GPCRs) representing the two major classes of odorant receptors, as well as markers of antioxidant responses to metals. Coho received acute exposures to 3.7 ppb and 347 ppb Cd, and a subset of fish was analyzed following a 16-day depuration. The results indicate that acute Cd exposures can have rapid and persistent effects on olfactory neurobehavioral function. Similar behavioral effects have been linked to impaired survival and increased susceptibility to predation in salmonids. Williams’ approach involving molecular biomarkers, histological analysis, and behavior suggested that impairment of key olfactory sensory neurons (OSNs) and GPCRs may underlie impaired alarm responses. In the context of biomonitoring for olfactory injury in the field, the molecular biomarkers of oxidative stress may be of particular relevance in reflecting metal exposures and the ability of fish olfactory tissues to mount an antioxidant response within the olfactory epithelium.
Session I: Sahar Fathordoobadi (University of Arizona) and Timothy Jobe (University of California, San Diego)
May 2, 2013; 1:00 pm - 2:00 pm EDT
Sahar Fathordoobadi: How Arsenic Fate is Coupled to Sulfur Biomineral Formation in Landfills
Currently arsenic-bearing solid residuals (ABSR) are being disposed in landfills and as a consequence arsenic is likely being released into leachate. The purpose of this study is to investigate the degree to which sulfate can prevent arsenic from leaching into landfills through biomineralization and to study ABSR biogeochemical weathering affect on arsenic sequestration. Lowering the Maximum Contaminant Level for arsenic in drinking water in the U.S., has caused a significant increase in the volume of ABSR generated by drinking water utilities. Because of their high adsorption capacity and low cost, iron sorbents are used treatment technology and, when the sorbent's capacity is spent, these ABSRs are disposed in municipal solid waste (MSW) landfills. However, a mature landfill is a biotic, reducing environment, which causes arsenic mobilization from the ABSR. It is well documented that iron and sulfur redox cycles largely control arsenic cycling and, because iron and sulfur are ubiquitous in MSW, it is suspected that they play key roles in arsenic disposition in the landfill microcosm. The primary routes of iron and sulfate reduction in landfills are microbially mediated and biomineralization is a common by-product. Biomineralization may lead to formation of minerals such as siderite (FeCO3), vivianite (Fe3(PO4)2), iron sulfide (FeS), goethite (FeOOH), and realgar (AsS). In this work, microbial reduction and biomineralization of iron, sulfur, and arsenic species are evaluated as processes that both cause arsenic release from landfilled ABSR and may possibly provide a means to re-sequester it in a recalcitrant solid state. The work uses flow-through laboratory-scale columns in which controlled conditions similar to those found in a mature landfill prevail. The feed contains lactate as the carbon source and primary electron donor, and ferric iron, arsenate, and a range of sulfate concentrations as primary electron acceptors. Our results suggest that biomineralization changes the stability of arsenic through a number of different processes including (i) release of arsenic through reductive dissolution of iron-based ABSR; (ii) readsorption/incorporation of released arsenic on secondary biominerals; and (iii) passivation of a portion of the original ABSR by deposition of secondary biominerals. Preliminary results show that the concentration of sulfate fed to the system affects the biomineral formation, and that the relative amounts and sequence of precipitation of biominerals affect the free arsenic concentration that can seemingly be engineered by the concentration of sulfate fed to the system.
Timothy Jobe: Regulation of a High Affinity Sulfate Transporter in Glutathione Biosynthesis Mutants Exposed to Cadmium and Arsenic
The transcriptional regulators of cadmium- and arsenic-induced gene expression remain largely unknown in plants. Using microarray analyses, Jobe has identified genes that are highly and rapidly induced by cadmium and arsenic exposure, including a high affinity sulfate transporte. The promoter of this gene was fused to the firefly luciferase reporter gene to create a cadmium- and arsenic-inducible reporter line. This reporter line was then used to screen for mutants impaired in cadmium- and arsenic-induced gene induction (Jobe et al. 2012). Systematic analyses of the reporter response in key sulfate assimilation and glutathione biosynthesis mutants suggest that, while arsenic and cadmium detoxification rely on similar mechanisms, the signaling components that activate these mechanisms may be distinct. The luciferase response of these mutants to cadmium and arsenic will be presented along with additional transcriptomic analyses. These findings may impact the approaches and strategies used in phytoremediation of cadmium and arsenic - two high priority Superfund toxicants.
2012 Trainee Webinar Series
Session III: Featuring Lauren Tetz (University of Michigan – Northeastern University) and Fabian Grimm (University of Iowa)
August 1, 2012; 1:00 PM - 2:00 PM, Eastern Daylight Time
Lauren Tetz: Mono-2-Ethylhexyl Phthalate-Induced Oxidative Stress in Human Placental Cells
Exposure to di-2-ethylhexyl phthalate (DEHP), an environmental contaminant used as a plasticizer, increases risk of adverse pregnancy outcomes in humans. Moreover, monoethylhexyl phthalate (MEHP), the active metabolite of DEHP, increases oxidative stress responses in vitro, which is linked to the pathogenesis of preterm birth. The researchers investigated MEHP stimulated oxidative stress in human placental cells as a mechanism by which MEHP exposure may contribute to preterm birth. They treated human placental cells with MEHP and measured reactive oxygen species (ROS) generation. They found that MEHP increased ROS generation, oxidative DNA damage, and apoptosis, and modified redox-sensitive gene expression. Notably, MEHP significantly induced mRNA expression of prostaglandin-endoperoxide synthase 2 (PTGS2), the gene for COX-2, an enzyme important for prostaglandin synthesis and labor initiation. These findings warrant future epidemiological studies of oxidative stress as a mechanism by which MEHP may contribute to preterm birth and other adverse pregnancy outcomes.
Fabian Grimm: Sulfated Metabolites of Polychlorinated Biphenyls are High-Affinity Ligands for Human Transthyretin
Exposure to polychlorinated biphenyls (PCBs), environmentally persistent hazardous chemicals, is related to pathological abnormalities of the thyroid gland and decreased serum levels of thyroid hormones. Certain hydroxylated metabolites of PCBs (OHPCBs) are capable of displacing L-thyroxine from transthyretin (TTR). Some OHPCBs are excellent substrates for cytosolic sulfotransferases that catalyze the formation of sulfate conjugates, but little is known about the fate or toxicities of these sulfate esters. PCB sulfates structurally resemble thyroxine and may represent a second class of high affinity ligands for thyroxine binding sites on TTR. To test this, the sulfate esters of five mono‐hydroxylated PCB congeners and their respective OHPCBs were examined for their ability to bind to human TTR. All five PCB sulfates were able to bind to the high-affinity binding site with Kd values similar to those determined for their respective OHPCB precursors and for L-thyroxine. In addition, the binding interactions of PCB sulfates to TTR were found to be non-covalent and fully reversible. Molecular docking simulations were utilized to calculate the lowest energy binding conformations of these PCB sulfates within the thyroxine binding site of human TTR, thereby providing corroborating evidence for their binding potential. Moreover, the corresponding OHPCBs were found to be substrates for human and rat forms of sulfotransferase 1A1. These results on the binding of PCB‐sulfates to TTR suggest a potential relevance in PCB‐mediated thyroid disruption.
Session II: Featuring Dena Cologgi (Michigan State University) and Richard Meggo (University of Iowa)
July 5, 2012; 1:00 PM – 2:00 PM, Eastern Daylight Time
Dena Cologgi: Novel Mechanism of Uranium Reduction via Microbial Nanowires
The in situ stimulation of metal reduction by Geobacter bacteria shows promise for the reductive precipitation of uranium contaminants. However, the mechanism behind this reaction has remained elusive. As bacterial cells are nanostructured interfaces that employ defined components to catalyze chemical reactions, our team sought to investigate the mechanism of U reduction by Geobacter bacteria in vivo to develop biomimetic nanoplatforms for U removal. U reduction during in situ bioremediation is concomitant to the reduction of Geobacter's natural electron acceptor, Fe(III) oxides, a process that requires the production of conductive protein filaments termed pilus nanowires. Thus, we investigated a potential role for the nanowires in U reduction by testing the ability of pili-expressing and nonexpressing strains of the model organism Geobacter sulfurreducens to remove soluble hexavalent U (U(VI)) and reduce it to the less mobile tetravalent U (U(IV)).
Richard Meggo: Rhizosphere Biotransformation Products of Selected PCB Cogeners
Reductive dechlorination followed by aerobic bio-oxidation is necessary to achieve complete degradation of mixtures of higher and lower chlorinated PCBs. Plant rhizospheres are known to support large and diverse populations of microorganisms by providing an ample supply of electron donors. It is hypothesized that manipulation of soil moisture content in plant rhizosphere can produce fluctuations in redox potential which may be able facilitate both reductive dechlorination and aerobic bio-oxidation. Soil artificially contaminated with a mixture of hexa and tetra chlorinated PCB congeners is planted with switchgrass and subjected to sequential cycles of high and moisture content. The dissipation of the parent compounds in the mixture and the formation of transformation products is investigated and reported.
Session I: Featuring Bei Zhang (University of Kentucky) and Corin Hammond (University of Arizona)
February 21, 2012; 1:00 - 2:00pm, Eastern Daylight Time
Bei Zhang: Cerebrovascular Toxicity of PCBs Bound to Nanoparticles in the Experimental Stroke Model
Polychlorinated biphenyls (PCBs) are organochlorinated chemicals that are persistent in the environment due to their structural stability and high lipophilicity. Recent evidence suggests that exposure to PCBs may increase the incidence of stroke and worsen stroke outcomes. PCBs released from environmental sources are capable of binding onto nanoparticles present in the environment and being taken up by humans. However, the toxicity of PCBs assembled onto nanoparticles is unknown. In the current study, the research team hypothesizes that binding to nanoparticles can potentiate PCB-induced vascular toxicity and brain damage in an experimental stroke model through activation of toll-like receptor 4 (TLR4), stimulation of inflammatory responses, and alterations of tight junction protein expression in brain capillaries.
Corin Hammond: Biogeochemical Transformation of Metal(loid)s during Phytostabilization of Iron King Mine Tailings, Dewey-Humboldt, Arizona
The Iron King Mine-Humboldt Smelter Site, which was added to the National Priorities List in 2008, comprises a large mass of exposed un-vegetated mine tailings with high concentrations of arsenic and lead contained in relatively small particles. The tailings pose a health risk to adjacent communities from possible water- and air-borne exposure. A randomized-block field trial is currently underway to test “phytostabilization” of the tailings and associated contaminants via establishment of a vegetative cap. Since plant germination is hindered by an inhospitable geochemical environment (low organic matter, high acidity and toxic metal concentrations), composted organic matter and irrigation water are being added to promote plant growth. This research focuses on evaluation of the efficacy of phytostabilization as a bioremediation approach to the smelter site. To assess changes in contaminant lability in relation to molecular speciation over the course of tailings bio-colonization, the researchers are combining analytical wet chemistry (sequential extraction, cascade filtration) with synchrotron-based X-ray methods (XANES, EXAFS, XRD) as a function of time and specific treatment.