Iron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions.

Iron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy, The sediment examined in this study was collected from a waterway receiving acid-sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 micromol g(-1)), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an 02 partial pressure of approximately 0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 +/- 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S8(0)) was a key intermediate S oxidation product Transmission electron microscopy showed the S8(0) to be amorphous nanoglobules, 100-200 nm in diameter. The quantitative importance of S8(0) was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S8(0) particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S8(0) to SO4(2-) was mediated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here.

Divorce versus intact parental marriage and perceived risk and dyadic trust in present heterosexual relationships.

The relationship between parental divorce and intimate relationships in late adolescence was estimated for 60 undergraduates (17 men, 43 women). Subjects from divorced families were assessed to address whether they perceived their present heterosexual relationship to be risky and if they were less trusting of their partners than were subjects from intact families. Divorce appears to be transmitted through generations in a family. Dyadic Trust and Perceived Risk were investigated as two learned components passed down within families, thereby contributing to a cycle of divorce. A correlation was found between parents' marital status and children's trust in their dating partners. An inverse relationship was indicated; when ratings of trust are low, ratings of perceived risk are high. A possible order of this relationship was discussed, i.e., low dyadic trust preceded perceived risk. One implication of these findings was that children of divorced parents may benefit from being shown how failures in relationships may result from negative expectations.