Acceptable levels for ingestion of dimethylsilanediol in water on the International Space Station.

INTRODUCTION: Water is recovered aboard the International Space Station (ISS) from humidity condensate and treated urine. The product water is monitored for total organic carbon (TOC). In 2010 the TOC readings indicated that a new contaminant had entered the potable water and was steadily increasing toward the TOC screening limit of 3 mg x L(-1). In a ground-based laboratory, chemists discovered that dimethylsilanediol (DMSD) was the principal new contaminant. As no standard existed for safe levels of DMSD in water, the Toxicology Office at Johnson Space Center was asked to set such a standard. METHODS: The Toxicology Office used methods developed over the past decade, in collaboration with the National Research Council Committee on Toxicology, for setting Spacecraft Water Exposure Guidelines (SWEGs). These methods require a thorough literature search and development of an acceptable concentration (AC) for each potential toxic effect, keeping in mind that the adverse effects that accompany spaceflight could increase toxicity for certain end points. Benchmark dose modeling was encouraged if sufficient data were available. The most sensitive AC becomes the driver for the SWEG. RESULTS: Hematotoxicity, hepatotoxicity, and possibly neurotoxicity were the most sensitive toxicological endpoints for DMSD. CONCLUSIONS: The SWEG for DMSD for 100 d of ingestion was set at 35 mg x L(-1), which is equivalent to 9 mg x L(-1) as TOC. This is well above the TOC SWEG of 3 mg x L(-1) and the peak DMSD level of processed water observed on orbit, which was 2.2 mg x L(-1) asTOC (8.5 mg x L(-10 of DMSD).

Organic-inorganic hybrid mesoporous silicas: functionalization, pore size, and morphology control.

Topological design of mesoporous silica materials, pore architecture, pore size, and morphology are currently major issues in areas such as catalytic conversion of bulky molecules, adsorption, host-guest chemistry, etc. In this sense, we discuss the pore size-controlled mesostructure, framework functionalization, and morphology control of organic-inorganic hybrid mesoporous silicas by which we can improve the applicability of mesoporous materials. First, we explain that the sizes of hexagonal- and cubic-type pores in organic-inorganic hybrid mesoporous silicas are well controlled from 24.3 to 98.0 A by the direct micelle-control method using an organosilica precursor and surfactants with different alkyl chain lengths or triblock copolymers as templates and swelling agents incorporated in the formed micelles. Second, we describe that organic-inorganic hybrid mesoporous materials with various functional groups form various external morphologies such as rod, cauliflower, film, rope, spheroid, monolith, and fiber shapes. Third, we discuss that transition metals (Ti and Ru) and rare-earth ions (Eu(3+) and Tb(3+)) are used to modify organic-inorganic hybrid mesoporous silica materials. Such hybrid mesoporous silica materials are expected to be applied as excellent catalysts for organic reactions, photocatalysis, optical devices, etc.