DESORPTION OF COPPER FROM ILLITE CLAY USING A CHELATING RESIN ENCAPSULATED BETWEEN POROUS MEMBRANES

Toxicity studies have established the need for information concerning species distribution of heavy metals in the environment. In aquatic environments, the nature of trace metals, whether free, adsorbed, or complexed controls impact on biota. Often, major portions of the trace metals present in an aquatic system are immobilized on suspended particulates. Changes in environmental conditions such as pH, soluble ligand concentration and type, and concentration of suspended particulate material in the water column, can affect speciation of a metal. Filter feeding organisms are especially susceptable to these environmental changes. High bioconcentrations of trace metal species which are available to organisms can retard growth or cause mortality as well as posing a hazard to human ingestion. In an attempt to investigate the bioavailability of particulate-bound metals under varying environmental conditions, we have developed a syringe drive system employing a membrane sandwiched chelating resin. The device consists of a cassette containing 100 mg of Chelex-100 sandwiched between two 0.40 um Polycarbonate membranes. While the device is similar to the one described by Kerfoot and Vaccaro (1975), it has been modified from a passive system dependent upon diffusional processes to an active mode in which a syringe draws solution through the cassette and then expels it to the bulk solution. Free metal ions, metal complexes in solution, and some particulates which are smaller than 0.40 um pass the membrane and are retained in the cassette. The construction allows a great deal of versatility in choice of membranes, their porosity, and the chelating resin used. The exchange rate with the primary solution may also be varied within a large range by appropriate selection of the step-function speed reducer connected to the drive motor. This versatility enables the experimenter to match the performance of the device to his needs. Early experiments with pure copper nitrate solutions established the reproducibility and effectiveness of the method as a trace metal scavenging technique. Mathematical simulation results were matched closely by experimental data obtained with atomic absorption spectrometry. To study the release characteristics of trace metals, illite clay was contaminated with known amounts of trace metals and suspended in aqueous solutions. Continuous agitation was provided. As the cassette removes metal from solution, the clay is driven by equilibrium considerations to desorb more metal ions to the system. In numerous trials, it has been possible to achieve mass balance for metal collected in the cassette compared to metal lost by the clay. The desorption curves generated at various pH levels show features which can be interpreted to yield speciation characteristics of the solutions. Ion selective electrode work in conjunction with atomic absorption spectrometry has aided in elucidating the ratio of free to total trace metal content of the solutions. Results from this research may be utilized in predicting the impact of the changes in environmental variables such as pH and the disposal of metal-rich wastes

Sorption of metals by extracellular polymers from the cyanobacterium Microcystis aeruginosa fo. flos-aquae strain C3-40

The sorption of cadmium (II), copper (II), lead (II),manganese (II), and zinc (II) by purified capsularpolysaccharide from the cyanobacterium Microcystis aeruginosafo. flos-aquae strainC3-40 was examined by four methods: equilibriumdialysis, metal removal from solution as detected byvoltammetry, metal accumulation by capsule-containingalginate beads, and calorimetry. The polysaccharide's saturation binding capacities for these metals rangedfrom 1.2 to 4 mmol of metal g-1 of capsule, whichcorresponds to 1 metal equivalent per 2 to 4saccharide subunits of the polymer. Competitionbetween paired metals was tested with simultaneous andsequential additions of metal. Cadmium (II) andlead (II), as well as lead (II) and zinc (II), competedrelatively equally and reciprocally for polymerbinding sites. In contrast, manganese (II) stronglyinhibited the binding of cadmium (II) and lead (II), butitself was not substantially inhibited by either theprior or simultaneous adsorption of cadmium (II) or lead (II).The data are interpreted with respect to overlap ofbinding sites and possibilities of altered polymerconformation or solvation. Calorimetric studies oflead (II) and cadmium (II) association reactions withthe polysaccharide suggest that the enthalpies aresmall and that the reactions may be driven by entropy

Effects of aging on biological motion discrimination

Peer reviewedPreprin

Aging and consumer decision making

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90138/1/j.1749-6632.2011.06390.x.pd

Sex differences in the Simon task help to interpret sex differences in selective attention.

In the last decade, a number of studies have reported sex differences in selective attention, but a unified explanation for these effects is still missing. This study aims to better understand these differences and put them in an evolutionary psychological context. 418 adult participants performed a computer-based Simon task, in which they responded to the direction of a left or right pointing arrow appearing left or right from a fixation point. Women were more strongly influenced by task-irrelevant spatial information than men (i.e., the Simon effect was larger in women, Cohen's d = 0.39). Further, the analysis of sex differences in behavioral adjustment to errors revealed that women slow down more than men following mistakes (d = 0.53). Based on the combined results of previous studies and the current data, it is proposed that sex differences in selective attention are caused by underlying sex differences in core abilities, such as spatial or verbal cognition

Age-related differences in selection by visual saliency

We examined the ability of older adults to select local and global stimuli varying in perceptual saliency – a task requiring non-spatial visual selection. Participants were asked to identify in separate blocks a target at either the global or local level of a hierarchical stimulus, while the saliency of each level was varied (across different conditions either the local or the global form was the more salient and relatively easier to identify). Older adults were less efficient than young adults in ignoring distractors that were higher in saliency than targets, and this occurred across both the global and local levels of form. The increased effects of distractor saliency on older adults occurred even when the effects were scaled by overall differences in task performance. The data provide evidence for an age-related decline in non spatial attentional selection of low-salient hierarchical stimuli, not determined by the (global or local) level at which selection was required. We discuss the implications of these results for understanding both the interaction between saliency and hierarchical processing and the effects of aging on non-spatial visual attention