Growth inhibition and tissue accumulation of palladium in the ubiquitous macrofungus Pleurotus ostreatus (oyster mushroom).

The growth effects and tissue accumulation of palladium (Pd) in the ubiquitous white-rot macrofungus Pleurotus ostreatus (oyster mushroom) are reported. Submerged cultures of P. ostreatus were exposed to Pd (as Na2PdCl4) at concentrations of 0, 6.25, 12.5, 25, 50 and 100 mg/L in potato dextrose broth media and incubated for 18 days at 25 °C. The growth response was measured as dried tissue biomass. Relative to controls, growth was partially inhibited at [Pd]broth = 25 and 50 mg/L. The minimum inhibitory concentration (MIC) of Pd was 100 mg Pd/L. Mean Pd concentrations of dry tissue (± standard error) ranged from 93.5 ± 17.1 mg Pd/kg to 1912.0 ± 293.9 mg Pd/kg, with bioconcentration factors (BCFs) ranging from 16.10 ± 4.17 to 40.91 ± 8.89. A linear positive log-log relationship was found between the Ctissue and [Pd]broth (R2 = 0.476), consistent with a Freundlich isotherm model of sorption. This relationship suggested that physicochemical processes may dominate tissue Pd accumulation in this system rather than biological processes.

Palladium release from catalytic converter materials induced by road de-icer components chloride and ferrocyanide.

Environmental levels of platinum group elements (PGEs) are rising due to emissions of vehicle catalytic converter (VCC) materials containing palladium, platinum and rhodium. When these PGE-containing VCC materials are exposed to soil and water, coordination complex formation with ligands present in the environment may mobilize PGEs into solution, particularly Pd. Road de-icing salt contains two ligands with high affinities for Pd2+: chloride (Cl-) from NaCl and cyanide (CN-) from ferrocyanide (Fe(CN)64-) anti-caking agents. Batch leaching studies of VCC materials were conducted with solutions representative of de-icer-contaminated road runoff at pH 8 and room temperature for 48 h. Ferrocyanide (FC) concentrations of 0 µM, 1 µM, 2 µM and 10 µM were tested with background electrolyte concentrations of 0.028 M NaCl (1000 mg/L Cl-) or 0.028 M NaClO4. Palladium release increased with FC concentration, ranging from 0.014 ± 0.002 µM Pd without FC to 5.013 ± 0.002 µM Pd at 10 µM FC. At 0 µM, 1 µM and 2 µM FC, chloride induced further Pd release, but had no effect at 10 µM FC. PHREEQC modeling predicted that the predominant species present in equilibrium with Pd(OH)2(s) were Pd(OH)20 and Pd(CN)42-, and that PdClx2-x complexes had only a minor effect on the total concentration of dissolved palladium. The effect of FC on Pd release was predicted but not the effect of Cl-, indicating possible kinetic control. Platinum was measured above limits of detection (LODs) only at 10 µM FC, and rhodium levels were below LODs, consistent with their slower complexation kinetics.

Enhanced release of palladium and platinum from catalytic converter materials exposed to ammonia and chloride bearing solutions.

The environmental levels of platinum group elements (PGEs) are steadily rising, primarily due to exhaust emissions of vehicle catalytic converter (VCC) materials containing solid PGEs. Once these VCC materials reach soil and water, the PGEs may be transported in the form of nanoparticles (dimensions 1-100 nm) or they may be mobilized by forming coordination complexes with ligands in the environment. Chloride (Cl-) and ammonia (NH3) are two ligands of particular concern due to their ubiquity as well as their potential to form the chemotherapy drug cisplatin (Pt(NH3)2Cl2) or other potentially bioactive complexes. This initial study examines the release of Pd and Pt into solutions exposed to VCC materials at pH 8 and 25 °C, using elemental analysis of metal content in post-exposure extracts. The solutions had total ammonia nitrogen concentrations (TAN, [NH4+] + [NH3]) of 0 µM, 5.56 µM, 55.6 µM and 1.13 × 105 µM (0 ppm, 0.1 ppm, 1 ppm, and 2147 ppm). The former three represent background environmental levels had a minimal effect on release. However, when combined with 1.13 × 105 µM Cl- (4000 ppm Cl-), 55.6 µM TAN induced a marked increase in metal release (∼41× for Pd). High TAN solutions induced more Pd and Pt release than equimolar NaCl solutions. Materials characterization revealed that ∼4 nm palladium-containing nanoparticles were present, spatially associated with nanoparticles of γ-Al2O3; ceria-zirconia nanoparticles were also present but did not have any metal associated with them. Platinum-containing nanoparticles were not observed.

Antimicrobial nanotechnology: its potential for the effective management of microbial drug resistance and implications for research needs in microbial nanotoxicology.

The development of antibiotics revolutionized human health, providing a simple cure for once dreaded diseases such as tuberculosis. However, widespread production, use, and mis-use of antibiotics have contributed to the next-generation concern for global public health: the emergence of multiple drug-resistant (MDR) infectious organisms (a.k.a. "superbugs"). Recently, nanotechnology, specifically the use of nanomaterials (NMs) with antimicrobial activity, has been presented as a new defense against MDR infectious organisms. We discuss the potential for NMs to either circumvent microbial resistance or induce its development in light of our current state of knowledge, finding that this question points to a need for fundamental research targeting the molecular mechanisms causing antimicrobial activity in NMs. In the context of current microbial nanotoxicology studies, particularly reductionist laboratory studies, we offer suggestions and considerations for future research, using an illustrative example from our work with silver nanoparticles.

Self-assembly of magnetic nanoparticles in evaporating solution.

When deposited from an evaporating solution onto a substrate, even nondescript nanoparticles can organize into intricate spatial patterns. Here we show that a simple but long-ranged anisotropy in nanoparticles' interactions can greatly enrich this scenario. In experiments with colloidal Co nanocrystals, which bear a substantial magnetic dipole, we observe assemblies quite distinct from those formed by nonmagnetic particles. Reflecting the strongly nonequilibrium nature of this process, nanocrystal aggregates also differ substantially from expected low-energy arrangements. Using coarse-grained computer simulations of dipolar nanoparticles, we have identified several dynamical mechanisms from which such unusual morphologies can arise. For particles with modest dipole moments, transient connections between growing domains frustrate phase separation into sparse and dense regions on the substrate. Characteristic length scales of the resulting cellular networks depend non-monotonically on the depth of quenches we use to mimic the effects of solvent evaporation. For particles with strong dipole moments, chain-like aggregates formed at early times serve as the agents of assembly at larger scales. Their effective interactions drive the formation of layered loop structures similar to those observed in experiments.

Influence of size and aggregation on the reactivity of an environmentally and industrially relevant nanomaterial (PbS).

Rarely observed nanoparticle dissolution rate data have been collected and explained for an environmentally and industrially relevant nanomaterial (PbS, the mineral galena) as a function of its particle size and aggregation state using high-resolution transmission electron microscopy (HRTEM) and solution analysis. Under identical anoxic acidic conditions (pH 3 HCl), it has been determined that the dissolution rate of PbS galena varies by at least 1 order of magnitude simply as a function of particle size, and also due to the aggregation state of the particles (dissolution rates measured are 4.4 x 10(-9) mol m(-2) s(-1) for dispersed 14 nm nanocrystals; 7.7 x 10(-10) mol m(-2) s(-1) for dispersed 3.1 microm microcrystals; and 4.7 x 10(-10) mol m(-2) s(-1) for aggregated 14 nm nanocrystals). The dissolution rate difference between galena microparticles and nanoparticles is due to differences in nanotopography and the crystallographic faces present. Aggregate vs. dispersed dissolution rates are related to transport inhibition in the observed highly confined spaces between densely packed, aggregated nanocrystals, where self-diffusion coefficients of water and ions decrease dramatically. This study shows that factors at the nanometer scale significantly influence the release rate of aqueous, highly toxic and bioavailable Pb in natural or industrial environments during galena dissolution.

Collective behaviour in two-dimensional cobalt nanoparticle assemblies observed by magnetic force microscopy.

The use of magnetic nanoparticles in the development of ultra-high-density recording media is the subject of intense research. Much of the attention of this research is devoted to the stability of magnetic moments, often neglecting the influence of dipolar interactions. Here, we explore the magnetic microstructure of different assemblies of monodisperse cobalt single-domain nanoparticles by magnetic force microscopy and magnetometric measurements. We observe that when the density of particles per unit area is higher than a determined threshold, the two-dimensional self-assemblies behave as a continuous ferromagnetic thin film. Correlated areas (similar to domains) of parallel magnetization roughly ten particles in diameter appear. As this magnetic percolation is mediated by dipolar interactions, the magnetic microstructure, its distribution and stability, is strongly dependent on the topological distribution of the dipoles. Thus, the magnetic structures of three-dimensional assemblies are magnetically soft, and an evolution of the magnetic microstructure is observed with consecutive scans of the microscope tip.