Dissimilatory metal reducing bacteria (DMRB) catalyze the reduction of Fe(III) to Fe(II) in anoxic soils, sediments, and groundwater. Two-line ferrihydrite is a bioavailable Fe(III) oxide form that is exploited by DMRB as a terminal electron acceptor. A wide variety of biomineralization products result from the interaction of DMRB with 2-line ferrihydrite. Here we describe the state of knowledge on the biotransformation of synthetic 2-line ferrihydrite by laboratory cultures of DMRB using select published data and new experimental results. A facultative DMRB is emphasized (Shewanella putrefaciens) upon which most of this work has been performed. Key factors controlling the identity of the secondary mineral suite are evaluated including medium composition, electron donor and acceptor concentrations, ferrihydrite aging/recrystallization status, sorbed ions, and co-associated crystalline Fe(III) oxides. It is shown that crystalline ferric (goethite, hematite, lepidocrocite), ferrous (siderite, vivianite), and mixed valence (magnetite, green rust) iron solids are formed in anoxic, circumneutral DMRB incubations. Some products are well rationalized based on thermodynamic considerations, but others appear to result from kinetic pathways driven by ions that inhibit interfacial electron transfer or the precipitation of select phases. The primary factor controlling the nature of the secondary mineral suite appears to be the Fe(II) supply rate and magnitude, and its surface reaction with the residual oxide and other sorbed ions. The common observation of end-product mineral mixtures that are not at global equilibrium indicates that microenvironments surrounding respiring DMRB cells or the reaction-path trajectory (over Eh-pH space) may in uence the identity of the nal biomineralization suite.

The sorption of three hydrophobic organic compounds (HOC) was investigated on hematite and kaolinite that had been coated with natural humic substances over a mass percent carbon range of 0.01-O.5%. Increasing quantities of sorbed humic substances increased the sorption of HOC. Anthracene, the most hydrophobic HOC, showed the greatest sorption enhancement, while the most aromatic coating, peat humic acid, was the strongest sorbent. Depending on the type of humic acid coating and the mineral substrate, the experimental K , values were either higher or lower than those predicted by the Kow The sorptivity of a given humic acid for HOC was not the same on kaolinite and hematite, suggesting that the orientation and structure of the humic substance on the mineral may affect the surface area of the organic phase and the accessibility of hydrophobic domains that control HOC sorptivity. Sorption isotherms for HOC on the humic-coated mineral substrates were nonlinear, implying that the sorption phenomenon was adsorption onto rather than partitioning into the surface organic phase.

The sorption of Cs ϩ was investigated over a large concentration range (10 Ϫ9 -10 Ϫ2 mol/L) on subsurface sediments from a United States nuclear materials site (Hanford) where high-level nuclear wastes (HLW) have been accidentally released to the vadose zone. The sediment sorbs large amounts of radiocesium, but expedited migration has been observed when HLW (a NaNO 3 brine) is the carrier. Cs ϩ sorption was measured on homoionic sediments (Na ϩ , K ϩ , Ca 2ϩ ) with electrolyte concentrations ranging from 0.01 to 1.0 mol/L. In Na ϩ electrolyte, concentrations were extended to near saturation with NaNO 3(s) (7.0 mol/L). The sediment contained nonexpansible (biotite, muscovite) and expansible (vermiculite, smectite) phyllosilicates. The sorption data were interpreted according to the frayed edge-planar site conceptual model. A fourparameter, two-site (high-and low-affinity) numeric ion exchange model was effective in describing the sorption data. The high-affinity sites were ascribed to wedge zones on the micas where particle edges have partially expanded due to the removal of interlayer cations during weathering, and the low-affinity ones to planar sites on the expansible clays. The electrolyte cations competed with Cs ϩ for both high-and low-affinity sites according to the trend K ϩ ϾϾ Na ϩ Ն Ca 2ϩ . At high salt concentration, Cs ϩ adsorption occurred only on high-affinity sites. Na ϩ was an effective competitor for the high-affinity sites at high salt concentrations.In select experiments, silver-thiourea (AgTU) was used as a blocking agent to further isolate and characterize the high-affinity sites, but the method was found to be problematic. Mica particles were handpicked from the sediment, contacted with Cs ϩ (aq) , and analyzed by electron microprobe to identify phases and features important to Cs ϩ sorption. The microprobe study implied that biotite was the primary contributor of high-affinity sites because of its weathered periphery. The poly-phase sediment exhibited close similarity in ion selectivity to illite, which has been well studied, although its proportion of high-affinity sites relative to the cation exchange capacity (CEC) was lower than that of illite. Important insights are provided on how Na ϩ in HLW and indigenous K ϩ displaced from the sediments may act to expedite the migration of strongly sorbing Cs ϩ in subsurface environments.

500 "c overnight prior to the sorption experiments. The BET surface areas determined by triple-point Nz(g) adsorption were 12.5 and 5.4 m2/g for kaolinite and hematite, respectively (Table 1). Peat humic acid (PHA), a well-characterized terrestrial humic substance from the International Humic Substances

Patients with germline mutation of succinate dehydrogenase (SDH) subunit genes are prone to develop paraganglioma, gastrointestinal stromal tumor, and rarely renal cell carcinoma (RCC). However, SDH-deficient RCC is not yet widely recognized. We identified such tumors by distinctive morphology and confirmed absence of immunohistochemical staining for SDHB. Immunohistochemical features were evaluated using a panel of antibodies to renal tumor antigens. Targeted next-generation sequencing was performed on DNA extracted from paraffin-embedded tissue. Eleven tumors were identified from 10 patients, 22-72 years of age (median 40). Two patients had paragangliomas, 1 bilateral SDH-deficient RCC, and 1 contralateral oncocytoma. Grossly, tumors were tan or red-brown, 2-20 cm in diameter (median 4.25 cm). Fuhrman grade was 2 (n ¼ 10) or 3 (n ¼ 1). Stage was pT1a-pT2b. One patient developed widespread metastases 16 years after nephrectomy and died of disease 6 years later. All tumors were composed of uniform eosinophilic cells containing vacuoles or flocculent cytoplasmic inclusions. Architecture was primarily solid; entrapped renal tubules and intratumoral mast cells were common. By immunohistochemistry, tumor cells were negative for SDHB (11/11) and rarely SDHA (1/11). Labeling was uniformly positive for PAX8 and kidney-specific cadherin and absent for KIT, RCC, and carbonic anhydrase IX. Staining for broad-spectrum epithelial markers was often negative or focal (positive staining for AE1/AE3 in 4/10, CAM5.2 3/7, CK7 1/11, EMA 10/10). By sequencing, SDHB mutation and loss of the second allele were present in 5/6 tumors; the SDHA-deficient tumor showed no SDHB abnormality. SDH-deficient RCC is a unique neoplasm that is capable of progression, often harboring SDHB mutation. A monomorphic oncocytic renal tumor with solid architecture, cytoplasmic inclusions of flocculent material, and intratumoral mast cells should prompt evaluation of SDH status, as it may have implications for screening the patient and relatives. Negative immunohistochemistry for KIT and heterogeneous labeling for epithelial antigens are other supportive features.