Metallic nanoparticles are among the most widely used types of engineered nanomaterials; however, little is known about their environmental fate and effects. To assess potential environmental effects of engineered nanometals, it is important to determine which species are sensitive to adverse effects of various nanomaterials. In the present study, zebrafish, daphnids, and an algal species were used as models of various trophic levels and feeding strategies. To understand whether observed effects are caused by dissolution, particles were characterized before testing, and particle concentration and dissolution were determined during exposures. Organisms were exposed to silver, copper, aluminum, nickel, and cobalt as both nanoparticles and soluble salts as well as to titanium dioxide nanoparticles. Our results indicate that nanosilver and nanocopper cause toxicity in all organisms tested, with 48-h median lethal concentrations as low as 40 and 60 microg/L, respectively, in Daphnia pulex adults, whereas titanium dioxide did not cause toxicity in any of the tests. Susceptibility to nanometal toxicity differed among species, with filter-feeding invertebrates being markedly more susceptible to nanometal exposure compared with larger organisms (i.e., zebrafish). The role of dissolution in observed toxicity also varied, being minor for silver and copper but, apparently, accounting for most of the toxicity with nickel. Nanoparticulate forms of metals were less toxic than soluble forms based on mass added, but other dose metrics should be developed to accurately assess concentration-response relationships for nanoparticle exposures.

Experimental conditions that mimic likely scenarios of manufactured nanomaterials (MNs) introduction to aquatic systems were used to assessthe effect of nanoparticle dispersion/solubility and water chemical composition on MN-toxicity. Aqueous suspensions of fullerenes (C60), nanosilver (nAg), and nanocopper (nCu) were prepared in both deionized water and filtered (0.45 microm) natural river water samples collected from the Suwannee River basin, to emphasize differences in dissolved organic carbon (DOC) concentrations and solution ionic strengths (I). Two toxicity tests, the Ceriodaphnia dubia and MetPLATE bioassays were used. Results obtained from exposure studies show that water chemistry affects the suspension/solubility of MNs as well as the particle size distribution, resulting in a wide range of biological responses depending on the type of toxicity test used. Under experimental conditions used in this study, C60 exhibited no toxicity even when suspended concentrations exceeded 3 mg L(-1). MetPLATE results showed that the toxicity of aqueous suspensions of nCu tends to increase with increasing DOC concentrations, while increasing I reduces nCu toxicity. The use of the aquatic invertebrate C. dubia on the other hand showed a tendency for decreased mortality with increasing DOC and I. MetPLATE results for nAg showed decreasing trends in toxicity with increasing DOC concentrations and I. However, C. dubia exhibited contrasting biological responses, in that increasing DOC concentrations reduced toxicity, while the latter increased with increasing I. Overall, our results show that laboratory experiments that use DI-water and drastic MN-suspension methods may not be realistic as MN-dispersion and suspension in natural waters vary significantly with water chemistry and the reactivity of MNs.

SiO2/V2O5/TiO2 catalysts were synthesized for removing elemental mercury (Hg0) from simulated coal-combustion flue gas. Experiments were carried out in fixed-bed reactors using both pellet and powder catalysts. In contrast to the SiO2-TiO2 composites developed in previous studies, the V2O5 based catalysts do not need ultraviolet light activation and have higher Hg0 oxidation efficiencies. For Hg0 removal by SiO2-V2O5 catalysts, the optimal V2O5 loading was found between 5 and 8%, which may correspond to a maximum coverage of polymeric vanadates on the catalyst surface. Hg0 oxidation follows an Eley-Rideal mechanism where HCI, NO, and NO2 are first adsorbed on the V2O5 active sites and then react with gas-phase Hg0. HCI, NO, and NO2 promote Hg oxidation, while SO2 has an insignificant effect and water vapor inhibits Hgo oxidation. The SiO2-TiO2-V2O5 catalysts exhibit greater Hg0 oxidation efficiencies than SiO2-V2O5, may be because the V-O-Ti bonds are more active than the V-O-Si bonds. This superior oxidation capability is advantageous to power plants equipped with wet-scrubbers where oxidized Hg can be easily captured. The findings in this work revealed the importance of optimizing the composition and microstructures of SCR (selective catalytic reduction) catalysts for Hg0 oxidation in coal-combustion flue gas.

Selective adsorption onto agarose gels has become a powerful method to separate single-walled carbon nanotubes (SWCNTs). A better understanding of the nature of the interactive forces and specific sites responsible for adsorption should lead to significant improvements in the selectivity and yield of these separations. A combination of nonequilibrium and equilibrium studies are conducted to explore the potential role that van der Waals, ionic, hydrophobic, π-π, and ion-dipole interactions have on the selective adsorption between agarose and SWCNTs suspended with sodium dodecyl sulfate (SDS). The results demonstrate that any modification to the agarose gel surface and, consequently, the permanent dipole moments of agarose drastically reduces the retention of SWCNTs. Because these permanent dipoles are critical to retention and the fact that SDS-SWCNTs function as macro-ions, it is proposed that ion-dipole forces are the primary interaction responsible for adsorption. The selectivity of adsorption may be attributed to variations in polarizability between nanotube types, which create differences in both the structure and mobility of surfactant. These differences affect the enthalpy and entropy of adsorption, and both play an integral part in the selectivity of adsorption. The overall adsorption process shows a complex behavior that is not well represented by the Langmuir model; therefore, calorimetric data should be used to extract thermodynamic information.

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