Evaporative deposition from a sessile drop is a simple and appealing way to deposit materials on a surface. In this work, we deposit living, motile colloidal particles (bacteria) on mica from drops of aqueous solution. We show for the first time that it is possible to produce a continuous variation in the deposition pattern from ring deposits to cellular pattern deposits by incremental changes in surface wettability which we achieve by timed exposure of the mica surface to the atmosphere. We show that it is possible to change the contact angle of the drop from less than 5 degrees to near 20 degrees by choice of atmospheric exposure time. This controls the extent of drop spreading, which in turn determines the architecture of the deposition pattern.
The Amish and Hutterites are U.S. agricultural populations whose lifestyles are remarkably similar in many respects but whose farming practices, in particular, are distinct; the former follow traditional farming practices whereas the latter use industrialized farming practices. The populations also show striking disparities in the prevalence of asthma, and little is known about the immune responses underlying these disparities.
Phytostabilization is a cost-effective long-term bioremediation technique for immobilization of metalliferous mine tailings. However the biogeochemical processes affecting metal(loid) molecular stabilization and mobility in the root zone remain poorly resolved. Roots of Prosopis juliflora grown for up to 36 months in compost-amended pyritic mine tailings from a federal Superfund site were investigated by micro-scale and bulk synchrotron X-ray absorption spectroscopy (XAS) and multiple energy micro X-ray fluorescence (ME-μXRF) imaging to determine iron, arsenic, sulfur speciation, abundance, and spatial distribution. Whereas ferrihydrite-bound As(V) species predominated in the initial bulk mine tailings, rhizosphere speciation of arsenic was distinctly different. Root associated As(V) was immobilized on the root epidermis bound to ferric sulfate precipitates and within root vacuoles as trivalent As(III)-SH3 complexes. Molar Fe:As ratios of root epidermis tissue was 2x times higher than the 15% compost-amended bulk tailings growth medium. Rhizoplane associated ferric sulfate phases that showed a high capacity to scavenge As(V) were dissimilar from the bulk tailings mineralogy as shown by XAS and XRD, indicating a root surface mechanism for their formation or accumulation.
