Longevity of granular iron in groundwater treatment processes: solution composition effects on reduction of organohalides and nitroaromatic compounds

Although granular iron permeable reactive barriers (PRBs) are increasingly employed to contain subsurface contaminants, information pertaining to system longevity is sparse. The present investigation redresses this situation by examining the long-term effects of carbonate, silica, chloride, and natural organic matter (NOM) on reactivity of Master Builders iron toward organohalides and nitroaromatic contaminants. Six columns were operated for 1100 days (approximately 4500 pore volumes) and five others for 407 days (approximately 1800 pore volumes). Nine were continuously exposed to mixtures of contaminant species, while the other two were only intermittently exposed in order to differentiate deactivation induced by water (and inorganic cosolutes) from that resulting from contaminant reduction. Contaminants investigated were trichloroethylene, 1,2,3-trichloropropane, 1,1-dichloroethane, 2-nitrotoluene, 4-nitroacetophenone, and 4-nitroanisole. Column reactivity declined substantially over the first 300 days and was dependent on the feed solution chemistry. High carbonate concentrations enhanced reactivity slightly within the first 90 days but produced poorer performance over the long term. Both silica and NOM adversely affected reactivity, while chloride evinced a somewhat mixed effect. Observed contrasts in relative reactivities suggest that trichloroethylene, 1,2,3-trichloropropane, and nitroaromatic compounds all react at different types of reactive sites. Our results indicate that differences in groundwater chemistry should be considered in the PRB design process.     

Methanogens: principal methylators of mercury in lake periphyton

Mercury methylation and demethylation rates were measured in periphyton biofilms growing on submerged plants from a shallow fluvial lake located along the St. Lawrence River (Quebec, Canada). Incubations were performed in situ within macrophytes beds using low-level spikes of (199)HgO and Me(200)Hg stable isotopes as tracers. To determine which microbial guilds are playing a role in these processes, methylation/demethylation experiments were performed in the absence and presence of different metabolic inhibitors: chloramphenicol (general bacteriostatic inhibitor), molybdate (sodium molybdate, a sulfate reduction inhibitor), BESA (2-bromoethane sulfonic acid, a methanogenesis inhibitor), and DCMU (3-(3,4-dichlorophenyl)-1,1 dimethyl urea, a photosynthesis inhibitor). Active microbes of the periphytic consortium were also characterized using 16S rRNA gene sequencing. Methylation rates in the absence of inhibitors varied from 0.0015 to 0.0180 d(-1) while demethylation rates ranged from 0.083 to 0.217 d(-1), which corresponds to a net methylmercury balance of -0.51 to 1.28 ng gDW periphyton(-1) d(-1). Methylation rates were significantly decreased by half by DCMU and chloramphenicol, totally inhibited by BESA, and were highly stimulated by molybdate. This suggests that methanogens rather than sulfate reducing bacteria were likely the primary methylators in the periphyton of a temperate fluvial lake, a conclusion supported by the detection of 16S rRNA gene sequences that were closely related to those of methanogens. This first clear demonstration of methanogens' role in mercury methylation in environmental periphyton samples expands the known diversity of microbial guilds that contribute to the formation of the neurotoxic substance methylmercury.     

The Role of Charge Localization in Current-Driven Dynamics

We explore the role of charge localization in current-triggered, resonance-mediated, dynamical events in molecular junctions. To that end we use a simple model for a molecular rattle, a Li⁺C₉H⁻₉ zwitterion attached between two metal clusters. By varying the size of the metal clusters we systematically vary the degree of delocalization of the electronic orbitals underlying the resonant current, and thus can draw general conclusions regarding the effect of delocalization on dynamical processes induced by resonance inelastic current in molecular electronics. In the small cluster limit, we find interesting quantum dynamics in the nuclear subspace, corresponding to coherent tunneling of the wave packet through the barrier of an asymmetric double-well potential. These dynamics are rapidly damped with increasing charge delocalization in extended systems.     

Synthesis and Cytotoxicity of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles of Various Morphologies

As the field of nanotechnology continues to grow, evaluating the cytotoxicity of nanoparticles is important in furthering their application within biomedicine. Here, we report the synthesis, characterization, and cytotoxicity of nanoparticles of different morphologies of yttrium oxide, a promising material for biological imaging applications. Nanoparticles of spherical, rod-like, and platelet morphologies were synthesized via solvothermal and hydrothermal methods and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), light scattering, surface area analysis, thermogravimetric analysis (TGA), and zeta potential measurements. Nanoparticles were then tested for cytotoxicity with human foreskin fibroblast (HFF) cells, with the goal of elucidating nanoparticle characteristics that influence cytotoxicity. Cellular response was different for the different morphologies, with spherical particles exhibiting no cytotoxicity to HFF cells, rod-like particles increasing cell proliferation, and platelet particles markedly cytotoxic. However, due to differences in the nanoparticle chemistry as determined through the characterization techniques, it is difficult to attribute the cytotoxicity responses to the particle morphology. Rather, the cytotoxicity of the platelet sample appears due to the stabilizing ligand, oleylamine, which was present at higher levels in this sample. This study demonstrates the importance of nanoparticle chemistry on in vitro cytotoxicity, and highlights the general importance of thorough nanoparticle characterization as a prerequisite to understanding nanoparticle cytotoxicity.     

Conditional probability versus spatial contiguity in causal learning: Preschoolers use new contingency evidence to overcome prior spatial assumptions.

This study examines preschoolers' causal assumptions about spatial contiguity and how these assumptions interact with new evidence in the form of conditional probabilities. Preschoolers saw a toy that activated in the presence of certain objects. Children were shown evidence for the toy's activation rule in the form of patterns of probability: The toy was more likely to activate either when objects made contact with its surface (on condition) or when objects were several inches above its surface (over condition). In Experiment 1, 61 three-year-olds saw a deterministic activation rule. In Experiments 2 and 3, 48 four-year-olds saw an activation rule that was probabilistic. In Experiment 4, 30 four-year-olds saw a screening-off pattern of activation. In all 4 experiments, children used new evidence in the form of patterns of probability to make accurate causal inferences, even in the face of conflicting prior beliefs about spatial contiguity. However, children were more likely to make correct inferences when causes were spatially contiguous, particularly when faced with ambiguous evidence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive-processing bias in chronic pain: A review and integration.

Do patients with chronic pain selectively process pain- and illness-related stimuli? The evidence with regard to attention, interpretation, and recall biases is critically reviewed. A model is proposed to account for the findings in which it is suggested that biases in information processing in chronic pain are the result of overlap between 3 schemas: pain, illness, and self. With frequent repeated or continued experience of pain, the pain schema becomes enmeshed with illness and self-schemas. The extent of the enmeshment and the salient content of the schema determine the bias. A fundamental assumption is that all patients with pain selectively process sensory-intensity information. A clinical implication of the results is that processing biases that extend beyond this healthy and adaptive process to enmesh the self-schema with pain and illness schemas could maintain and exacerbate distress and illness behavior in patients with chronic pain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Supportive versus cognitive–behavioral intervention programs in achieving adjustment to home peritoneal kidney dialysis.

Two psychological interventions given for 8 weeks, supportive and cognitive–behavioral, were compared in achieving psychosocial adjustment to home peritoneal kidney dialysis. Participants were divided into 3 groups of patients and their spouses: a supportive group (18 couples), a cognitive–behavioral group (18 couples), and a no-intervention control group (24 couples). A group of 97 healthy participants served as a baseline control group. Self-report measurements were made before treatment (T?), halfway through (T?), and after treatment (T?). Results indicated that, without treatment, the no-intervention control group demonstrated a deterioration of psychosocial adjustment going from T? to T?. Both interventions were effective in aiding patients and spouses in maintaining psychosocial adjustment in comparison with the no-intervention control group, with few differences between treatments. Most improvement was obtained in the emotional, cognitive, and interpersonal areas, with smaller gains made in the behavioral area. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Career compromises: Framings and their implications.

The authors investigated the effects of 3 framings of career compromise (I. Gati, 1993): in terms of alternatives, aspect importance, and within-aspect preferences. Three groups of Israeli young adults (ns?=?95, 108, and 154) and 71 school counselors were presented with hypothetical stories about individuals whose career decision involved a compromise. The results of 4 studies, using both between-subjects and within-subject designs, and both rating scales and forced choices, supported the hypothesis: The alternatives framing was associated with a greater extent of compromise and greater difficulty in making a career decision than were the 2 aspect framings. No differences were found between aspect importance and the within-aspect preference framings. The implications for research and counseling are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)