In Situ X-ray Absorption Study of Surface Complexes: Selenium Oxyanions on agr-FeOOH.

A novel application of x-ray absorption spectroscopy has provided structural information for ions sorbed at oxide-water interfaces. As an example, in situ extended x-ray absorption fine structure (EXAFS) measurements of adsorbed selenate and selenite ions at ah alpha-FeOOH(goethite)-water interface have been performed; these measurements show that selenate forms a weakly bonded, outer-sphere complex and that selenite forms a strongly bonded, inner-sphere complex. The selenite ion is bonded directly to the goethite surface in a bidentate fashion with two iron atoms 3.38 angstroms from the selenium atom. Adsorbed selenate has no iron atom in the second coordination shell of selenium, which indicates retention of its hydration sphere upon sorption. This method provides direct structural information for adsorbed species at solid-liquid interfaces.

Integrating harm reduction therapy and traditional substance abuse treatment.

One-size-fits-all therapy has not worked well for a majority of substance users seeking help. New approaches to substance abuse treatment are desperately needed. Traditional models of service delivery offer little, if any, help to people who may not choose abstinence as a goal. To address this concern, the Bridging the Gap Conference was sponsored by the San Francisco Department of Public Health. The overall goals of the conference were to improve standards of care, develop best practice principles for integrating harm reduction approaches into traditional substance abuse services, and increase the accessibility of quality services to people in need of alcohol and drug treatment. G. Alan Marlatt gave a keynote address on the integration of harm reduction therapy into traditional treatment services, an expanded version of which is presented in this article. Such integration would broaden the scope of services available to a larger group of consumers of substance abuse treatment. Furthermore, harm reduction therapy would infuse traditional treatment practices with scientifically-based pragmatism that pays close attention to individual and community public health needs. Because of its tolerance of treatment goals other than abstinence, harm reduction therapy offers the greatest hope to expand the availability of substance abuse services to people who have not benefited from traditional abstinence-based treatment models.

Anticipated reward and time estimation in young Navajo children.

Time estimations of 1-min. intervals using the method of reproduction by 112 Navajo children were measured under neutral and reward conditions in a repeated-measures design. Anticipated reward (a piece of candy) significantly reduced the accuracy of time estimations. In contrast to previous research the girls were more accurate than the boys; however, the effect of reward was more pronounced for girls than for boys. These data suggest that motivating factors play an important role in the reproduction of time by Navajo children.

Evidence for multinuclear metal-ion complexes at solid/water interfaces from X-ray absorption spectroscopy.

Metals dissolved in natural waters often become sorbed onto oxide or clay minerals, so that prediction of their chemical behaviour and transport properties requires knowledge of the structure and bonding of metal species at the solid/water interface. For many sorption systems, X-ray absorption spectroscopy (XAS) can be used to determine the identity and number of nearest-neighbour atoms and interatomic distances in aqueous complexes on solid surfaces, and thus to identify the dominant type of surface complex and the partitioning mechanism. Here we describe an XAS study of divalent cobalt (Co(II)) complexes sorbed on three different solids, gamma-Al2O3, rutile (TiO2) and kaolinite (Al2Si2O5(OH)4). We find direct evidence for the presence of multinuclear sorption complexes at surface coverages below one monolayer of Co(II) atoms. Our spectroscopic data reveal distinct differences in the number of coordinating atoms and interatomic distances in the surface complexes formed on each of the solids at the same sorption density. These results suggest that different oxide and clay surfaces influence the structure and properties of aqueous surface complexes, and therefore must be accounted for in models of metal-ion sorption.