or adsorption onto the smallest particles is proposed to account for the trace element concentration dependence on particle size. The environmental significance of the results is discussed.

The toxic trace elements arsenic, antimony, cadmium, lead, selenium, and thallium were found to be most concentrated in the smallest respirable particles emitted from coal-fired power plants. These elements, or their compounds, are probably volatilized during combustion and preferentially adsorb or condense onto the small particles which can most easily pass through conventional control equipment.

Assembling structures to divide space controllably and spontaneously into subunits at the nanometer scale is a significant challenge, although one that biology has solved in two distinct ways: prokaryotes and eukaryotes. Prokaryotes have a single compartment delimited by one or more lipid-protein membranes. Eukaryotes have nested-membrane structures that provide internal compartments--such as the cell nucleus and cell organelles in which specialized functions are carried out. We have developed a simple method of creating nested bilayer compartments in vitro via the "interdigitated" bilayer phase formed by adding ethanol to a variety of saturated phospholipids. At temperatures below the gel-liquid crystalline transition, T(m), the interdigitated lipid-ethanol sheets are rigid and flat; when the temperature is raised above T(m), the sheets become flexible and close on themselves and the surrounding solution to form closed compartments. During this closure, the sheets can entrap other vesicles, biological macromolecules, or colloidal particles. The result is efficient and spontaneous encapsulation without disruption of even fragile materials to form biomimetic nano-environments for possible use in drug delivery, colloidal stabilization, or as microreactors. The vesosome structure can take full advantage of the 40 years of progress in liposome development including steric stabilization, pH loading of drugs, and intrinsic biocompatibility. However, the multiple compartments of the vesosome give better protection to the interior contents in serum, leading to extended release of model compounds in comparison to unilamellar liposomes.

A number of minor and trace elements including Be, C, Ca, Cr, K, Li, Mn, Na, P, Pb, S, Tl, V, and Zn present in coal fly ash are found to be preferentially concentrated on the particle surfaces. Environmentally effective concentrations of these elements are thus much higher than indicated by conventional bulk analyses.

Quantization of ion microprobe mass spectrometric analyses has been complicated by the variation in the ion yield of an element contained in different matrices. This work demonstrates that, for O− and Cs+ bombardment, these ion-yield variations are solely attributable to variations in the matrix sputtering yield. It is argued that the matrix sputtering yield determines the near-surface concentration of the ion-yield-enhancing species O and Cs.