Metal oxide nanoparticles are finding increasing application in various commercial products, leading to concerns for their environmental fate and potential toxicity. It is generally assumed that nanoparticles will persist as small particles in aquatic systems and that their bioavailability could be significantly greater than that of larger particles. The current study using nanoparticulate ZnO (ca. 30 nm) has shown that this is not always so. Particle characterization using transmission electron microscopy and dynamic light scattering techniques showed that particle aggregation is significant in a freshwater system, resulting in flocs ranging from several hundred nanometers to several microns. Chemical investigations using equilibrium dialysis demonstrated rapid dissolution of ZnO nanoparticles in a freshwater medium (pH 7.6), with a saturation solubility in the milligram per liter range, similar to that of bulk ZnO. Toxicity experiments using the freshwater alga Pseudokirchneriella subcapitata revealed comparable toxicity for nanoparticulate ZnO, bulk ZnO, and ZnCl2, with a 72-h IC50 value near 60 microg Zn/ L, attributable solely to dissolved zinc. Care therefore needs to be taken in toxicity testing in ascribing toxicity to nanoparticles per se when the effects may be related, at least in part, to simple solubility.

Currently there are few ideal methods for the characterization of nanoparticles in complex, environmental samples, leading to significant gaps in toxicity and exposure assessments of nanomaterials. Single particle-inductively coupled plasma-mass spectrometry (spICP-MS) is an emerging technique that can both size and count metal-containing nanoparticles. A major benefit of the spICP-MS method is its ability to characterize nanoparticles at concentrations relevant to the environment. This paper presents a practical guide on how to count and size nanoparticles using spICP-MS. Different methods are investigated for measuring transport efficiency (i.e. nebulization efficiency), an important term in the spICP-MS calculations. In addition, an alternative protocol is provided for determining particle size that broadens the applicability of the technique to all types of inorganic nanoparticles. Initial comparison, using well-characterized, monodisperse silver nanoparticles, showed the importance of having an accurate transport efficiency value when determining particle number concentration and, if using the newly presented protocol, particle size. Ultimately, the goal of this paper is to provide improvements to nanometrology by further developing this technique for the characterization of metal-containing nanoparticles.

Sizing engineered nanoparticles in simple, laboratory systems is now a robust field of science; however, application of available techniques to more complex, natural systems is hindered by numerous challenges including low nanoparticle number concentrations, polydispersity from aggregation and/or dissolution, and interference from other incidental particulates. A new emerging technique, single particle inductively coupled plasma-mass spectrometry (spICPMS), has the potential to address many of these analytical challenges when sizing inorganic nanoparticles in environmental matrices. However, to date, there is little beyond the initial feasibility studies that investigates the performance characteristics and validation of spICPMS as a nanoparticle sizing technique. This study compares sizing of four silver nanoparticle dispersions (nominal diameters of 40, 60, 80, and 100 nm) by spICPMS to four established sizing techniques: dynamic light scattering, differential centrifugal sedimentation, nanoparticle tracking analysis, and TEM. Results show that spICPMS is able to size silver nanoparticles, across different sizes and particle number concentrations, with accuracy similar to the other commercially available techniques. Furthermore, a novel approach to evaluating particle coincidence is presented. In addition, spICPMS size measurements were successfully performed on nanoparticles suspended in algal growth media at low concentrations. Overall, while further development of the technique is needed, spICPMS yields important advantages over other techniques when sizing nanoparticles in environmentally relevant media.

Environmental context. It cannot be assumed that nanomaterials entering aquatic environments will have the same impacts on aquatic biota as their macroscopic particle equivalents. If their toxicities are different, this will have implications for the way in which nanomaterial usage is regulated. Algae, at the bottom of the food chain, are likely to be a sensitive indicator of toxic effects. Understanding the physical and chemical factors controlling nanoparticle toxicity to algae will assist in evaluating their ecological risk. Abstract. In assessing the risks posed by nanomaterials in the environment, the overriding research challenges are to determine if nanomaterials are more toxic than the bulk forms of the same material, and the extent to which toxicity is governed by particle size and reactivity. In this study, the toxicity of nanoparticulate CeO2 (nominally 10–20 nm) to the freshwater alga Pseudokirchneriella subcapitata was compared to the same material at the micron size (nominally <5 μm). Growth inhibition experiments revealed inhibitory concentration values, giving 50% reduction in algal growth rate after 72 h (IC50), of 10.3 ± 1.7 and 66 ± 22 mg L–1 for the nanoparticles and bulk materials respectively. Cells exposed to CeO2 particles were permeable to the DNA-binding dye SYTOX® Green in a concentration-dependent manner indicating damage to the cell membrane. Screening assays to assess the oxidative activity of the particles showed that the light illumination conditions used during standard algal bioassays are sufficient to stimulate photocatalytic activity of CeO2 particles, causing the generation of hydroxyl radicals and peroxidation of a model plant fatty acid. No oxidative activity or lipid peroxidation was observed in the dark. These findings indicate that inhibitory mode of action of CeO2 to P. subcapitata is mediated by a cell-particle interaction causing membrane damage. The effect is most likely photochemically induced and is enhanced for the nanoparticulate form of the CeO2.

No abstract

The origins of the breakdown of Bleaney's theory of magnetic anisotropy are described, based on an analysis of eleven different complexes of the second half of the 4f elements that form isostructural series.

Until recently, the vigorous T-cell response via the direct pathway has overshadowed studies involving the indirect pathway. Thus, while the direct pathway has previously been considered to be the main driving force in alloimmune responses, there is an increasing body of data to support a prominent role of the indirect pathway in transplant rejection. Most importantly, the direct antidonor alloresponse diminishes with time after transplantation, possibly due to the tolerogenic effects of alloantigen presentation by the parenchymal cells of the transplant. In contrast, the indirect alloresponse is likely to be permanently active, due to traffic of recipient dendritic cells (DCs) through the graft. The challenge that this poses in the pursuit of clinical transplant tolerance is how to induce tolerance in T cells with indirect allospecificity.

With the aim of developing an appropriate in vitro model of the sequestration of developing Plasmodium falciparum sexual-stage parasites, we have investigated the cytoadherence of gametocytes to human bone marrow cells of stromal and endothelial origin. Developing stage III and IV gametocytes, but not mature stage V gametocytes, adhere to bone marrow cells in significantly higher densities than do asexual-stage parasites, although these adhesion densities are severalfold lower than those encountered in classical CD36-dependent assays of P. falciparum cytoadherence. This implies that developing gametocytes undergo a transition from high-avidity, CD36-mediated adhesion during stages I and II to a lower-avidity adhesion during stages III and IV. We show that this adhesion is CD36 independent, fixation sensitive, stimulated by tumor necrosis factor alpha, and dependent on divalent cations and serum components. These data suggest that gametocytes and asexual parasites utilize distinct sets of receptors for adhesion during development in their respective sequestered niches. To identify receptors for gametocyte-specific adhesion of infected erythrocytes to bone marrow cells, we tested a large panel of antibodies for the ability to inhibit cytoadherence. Our results implicate ICAM-1, CD49c, CD166, and CD164 as candidate bone marrow cell receptors for gametocyte adhesion.Human malaria is caused by several species of protozoan parasites within the genus Plasmodium. The majority of malaria-related mortality is due to infection with the species Plasmodium falciparum. Microscopic examination of the peripheral blood of people infected with this species commonly reveals only two developmental forms: early trophozoite stages, termed "rings," and mature (stage V) gametocytes. Trophozoites are asexual forms that rapidly multiply, often causing disease, whereas gametocytes have no known association with disease but are the only form of the parasite that is infective to mosquitoes. All other stages of the parasite's development are sequestered in the deep vasculature among various host organs.Early stage V gametocytes of P. falciparum appear during in vitro culture 8 to 10 days after emergence from the parent schizont (14,22), suggesting that, in vivo, stage I to IV gametocytes spend a minimum of 7 days sequestered in host tissues. Recent observations of gametocyte emergence following antimalarial treatment of clinical malaria cases are consistent with this estimate of the duration of gametocyte sequestration (G. A. T. Targett and C. J. Drakeley, unpublished data). This is in marked contrast to the sequestration of asexual parasites, which is assumed to be in the order of 22 to 26 h in duration (9, 21). Furthermore, existing evidence from limited in vivo studies indicates that the distribution of sequestered gametocytes is measurably different from that of sequestered asexual parasites within the host. In a study of 22 Gambian children, Smalley et al. (23) found that immature gametocytes (stages II, III, and IV) had a 5-fold-highe...