Superfund Research Program Trainee Webinar Series
Superfund Research Program
This webinar series features the outstanding work being conducted by graduate and postdoctoral students conducting SRP-funded research. Specifically, this year's series consists of presentations from Poster Award Winners from the previous SRP Annual Meeting. This is an excellent opportunity for peers, SRP researchers, SRP alumni, and SRP's partners (NIEHS, U.S Environmental Protection Agency, and Agency for Toxic Substances and Disease Registry, etc.) to hear the poster winners describe their current research/activities. This will also be a chance for others to learn more about the research/activities being conducted by SRP trainees (i.e., graduate students/post-docs) and for those who were not able to view their posters at the Annual Meeting. Most importantly, the intent of the series is to increase collaboration and exchange of ideas among young investigators conducting SRP-funded research/activities and to hear about their award-winning work.
2013 Trainee Webinar Series
Session II: Erika Fritsch (University of California, Davis) and Chase Williams (University of Washington)
May 23rd, 2013 2:00 – 3:00 pm EDT, Register via the gotowebinar registration page .
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.