Rock varnish occurs in virtually all environments, most commonly in arid and semi‐arid climates, including Antarctica. Rock varnish consists of thin layers of intimately mixed aeolian and chemical sediments often showing botryoidal and more rarely stromatolite‐like morphologies. Typical rock varnish samples collected at Twin Peak Mountain Park, near Phoenix, Arizona, consist of abundant quartz, with plagioclase, illite and a mixed layer, Fe‐clay mineral, probably corrensite. EDS, SEM (BSE) and TEM analyses revealed that the typical Mn, Fe minerals occur as minute particles; some of these particles and other mineral grains are attached to filaments. XRD and electron diffraction showed that the Mn.Fe‐bearing particles are poorly crystalline. The filaments, based on morphological criteria, are virtually indistinguishable from fungal filaments. Most filaments are fragments, probably broken by scraping during sample collection. Coccoid and rod‐shaped forms, resembling cyanobacteria and other bacteria, respectively, are also present. Unlike definitive minerals, these filaments disintegrated in the concentrated energy of the SEM electron beam at the instrumental and experimental conditions used. In addition, no filamentous, rod‐shaped or coccoid forms were observed in samples hydrolysed with 6 N HCl for 24 h at 100°C. Bacteria and fungi in powdered rock varnish were cultured on four media, incubated aerobically in the dark at 25°C. The culture media yielded dense growths of spore‐forming bacteria and filamentous fungi. One fungus and two Bacillus isolates oxidized and concentrated manganese. Control experiments revealed that fungi and bacteria are present on and below the surfaces of rock varnish. Free and hydrolysed, peptide/protein‐bound amino acids were identified in the rock varnish. Amino acids showed virtually no racemization with the exception of D/L asp = 0.1. Relatively high molecular weight humic matter was also separated from the rock varnish. High‐resolution mass spectrometry revealed non‐hydrocarbon moieties, similar to a Suwannee River (FL) humic acid standard. Micro‐organisms and their original biochemical compounds do not seem to be preserved for long in the accreting varnish layer. The studies showed that the filaments helped to trap mineral particles of rock varnish, and that bacteria and fungi abetted Mn concentration. Some structures in the layers of rock varnish resemble stromatolites and present definitions would allow them to be termed as such.
Radioiodine (129I) poses a risk to the environment due to its long half-life,
toxicity, and mobility. It is found at the U.S. Department of Energy
Hanford Site due to legacy releases of nuclear wastes to the subsurface
where 129I is predominantly present as iodate (IO3
–). To date, a cost-effective and scalable cleanup
technology for 129I has not been identified, with hydraulic
containment implemented as the remedial approach. Here, novel high-performing
sorbents for 129I remediation with the capacity to reduce 129I concentrations to or below the US Environmental Protection
Agency (EPA) drinking water standard and procedures to deploy them
in an ex-situ pump and treat (P&T) system are introduced. This
includes implementation of hybridized polyacrylonitrile (PAN) beads
for ex-situ remediation of IO3
–-contaminated
groundwater for the first time. Iron (Fe) oxyhydroxide and bismuth
(Bi) oxyhydroxide sorbents were deployed on silica substrates or encapsulated
in porous PAN beads. In addition, Fe–, cerium (Ce)–,
and Bi–oxyhydroxides were encapsulated with anion-exchange
resins. The PAN–bismuth oxyhydroxide and PAN–ferrihydrite
composites along with Fe- and Ce-based hybrid anion-exchange resins
performed well in batch sorption experiments with distribution coefficients
for IO3
– of >1000 mL/g and rapid removal
kinetics. Of the tested materials, the Ce-based hybrid anion-exchange
resin was the most efficient for removal of IO3
– from Hanford groundwater in a column system, with 50% breakthrough
occurring at 324 pore volumes. The functional amine groups on the
parent resin and amount of active sorbent in the resin can be customized
to improve the iodine loading capacity. These results highlight the
potential for IO3
– remediation by hybrid
sorbents and represent a benchmark for the implementation of commercially
available materials to meet EPA standards for cleanup of 129I in a large-scale P&T system.
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