The reactions of Ni, Zn and Cd with goethite were studied over a range of initial metal concentrations to pH values (4 to 8), reaction times (2h to 42d) and temperatures (5 to 35°C). The adsorption of metals increased with pH, reaction time and temperature. Adsorption of Ni increased relative to Zn and Cd with increasing time and temperature. The initially rapid adsorption of metals within a few hours was followed by a much slower reaction linearly related to time''2, interpreted as diffusion-controlled penetration of goethite. The pH-dependent relative diffusion rates (Ni > Zn > Cd) were
Polysaccharide-based aerogels in the form of microspheres were investigated as carriers of poorly water soluble drugs for oral administration. These bio-based carriers may combine the biocompatibility of polysaccharides and the enhanced drug loading capacity of dry aerogels. Aerogel microspheres from starch, pectin and alginate were loaded with ketoprofen (anti-inflammatory drug) and benzoic acid (used in the management of urea cycle disorders) via supercritical CO2-assisted adsorption. Amount of drug loaded depended on the aerogel matrix structure and composition and reached values up to 1.0×10-3 and 1.7×10-3 g/m2 for ketoprofen and benzoic acid in starch microspheres. After impregnation, drugs were in the amorphous state in the aerogel microspheres. Release behavior was evaluated in different pH media (pH 1.2 and 6.8). Controlled drug release from pectin and alginate aerogel microspheres fitted Gallagher-Corrigan release model (R2>0.99 in both cases), with different relative contribution of erosion and diffusion mechanisms depending on the matrix composition. Release from starch aerogel microspheres was driven by dissolution, fitting the first-order kinetics due to the rigid starch aerogel structure, and showed different release rate constant (k1) depending on the drug (0.075 and 0.160 min-1 for ketoprofen and benzoic acid, respectively). Overall, the results point out the possibilities of tuning drug loading and release by carefully choosing the polysaccharide used to prepare the aerogels. HIGHLIGHTS-Polysaccharide aerogel microspheres are investigated as carriers of drugs for oral administration -Aerogels were loaded with ketoprofen and benzoic acid, poorly water soluble model drugs -Starch, with the lowest specific surface area, was more prone to adsorb drug molecules -Release of ketoprofen from alginate and pectin aerogel particles was sensitive to pH of the medium -Results point out the possibilities of polysaccharide aerogels of tuning drug loading and release Polysaccharide-based aerogels in the form of microspheres were investigated as carriers of poorly 19 water soluble drugs for oral administration. These bio-based carriers may combine the 20 biocompatibility of polysaccharides and the enhanced drug loading capacity of dry aerogels. Aerogel 21 microspheres from starch, pectin and alginate were loaded with ketoprofen (anti-inflammatory drug) 22and benzoic acid (used in the management of urea cycle disorders) via supercritical CO 2 -assisted 23 adsorption. Amount of drug loaded depended on the aerogel matrix structure and composition and 24 reached values up to 1.0×10 -3 and 1.7×10 -3 g/m 2 for ketoprofen and benzoic acid in starch 25 microspheres. After impregnation, drugs were in the amorphous state in the aerogel microspheres. 26Release behavior was evaluated in different pH media (pH 1.2 and 6.8). Controlled drug release from 27 pectin and alginate aerogel microspheres fitted Gallagher-Corrigan release model (R 2 >0.99 in both 28 cases), with different relative contribution of erosion and...
The ecological effects of heavy metals in soils are closely related to their content and species distribution in the solid and liquid phases of soils. Methods for the determination of metal species in both phases are described and critically evaluated. In connection with the possible binding mechanisms of heavy metals in soils the concept of specific and nonspecific adsorption is discussed. Recent results indicate that the adsorption of heavy metals on soil particles is not only restricted to the formation of surface complexes but can also take place in the structure of minerals. Diffusion processes of heavy metals into soil minerals are described for goethite. In order to assess metal mobility and availability in soils, the concentration of the species in the soil solution or in comparable aqueous equilibrium solutions of soil samples, and the transfer of metals from solid pools to the liquid phase, and vice versa, have to be assessed. Methods for the determination of the amount of plant-available heavy metals are described and the associated problems discussed.
The ecological effects of heavy metals in soils are closely related to the content and speciation of the elements in the solid and liquid phases of soils. Methods for the determination of metal species in both phases are described and critically evaluated. In connection with the possible binding mechanisms of heavy metals in soils the concept of specific and non-specific adsorption is discussed. Recent results indicate that the adsorption of heavy metals on soil particles is not only restricted to the formation of surface complexes but can also take place in the interior of minerals. Diffusion processes of heavy metals into soil minerals are described for goethite. In order to assess metal mobility and availability in soils, the concentration and speciation of metals in the soil solution or in comparable aeqeous equilibrium solutions of soil samples and the transfer of metals from solid pools to the liquid phase and vice versa have to be assessed. Methods for the determination of the amount of plant available heavy metals are described and the associated problems discussed.Die okologische Wirksamkeit von Schwermetallen in Boden ist eng verknupft mit dem Gehalt und der Art der Schwermetallspezies in der Feststoff-und Lasungsphase der Boden. Es werden Methoden fur die Bestimmung der Schwermetallspezies in beiden Phasen beschrieben und kritisch bewertet . Als wichtigster Mechanismus der Schwermetallbindung in Boden wird die spezifische und unspezifische Schwermetalladsorption diskutiert. Neuere Ergebnisse zeigen, daS die Adsorption von Schwermetallen dabei nicht nur auf Mineraloberflachen, sondern auch im Innern von Mineralpartikeln stattfinden kann. Mechanismus und Art der Diffusionsprozesse von Schwermetallen in das Innere mineralkcher Partikel werden exemplarisch fur die Diffusion von Ni, Zn und Cd in Goethitpartikel beschrieben. Zur Erfassung der Mobilitat und Verfugbarkeit von Schwermetallen in Boden ist die Bestimmung der Konzentration und Art der SchwermetaIlspezies in der Bodenlosung oder in vergleichbaren Gleichgewichtslosungen, z.B. dem Bodensattigungsextrakt, sowie des Metalltransfers von den Feststoffen in die Losungsphase und vice versa erforderlich. Methoden fiir die Bestimmung des Gehaltes an pflanzenverfugbaren Schwermetallen werden beschrieben und die rnit diesen Methoden verknupften Probleme diskutiert. 00463263/86/040~382 $ M.SO/O 0 VCH Verlagsgesellschah mbH, D-6940 Weinheim, 1986 149, 382-398 (1986) Heavy metal species 383
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