Sediments anoxic

In the context of diagenesis in recent anoxic sediments, reduced carotenoids, steroids, and hopanoids have been identified, and it has been suggested that reduction by sulhde, produced for example, by the reduction of sulfate could play an important part (Hebting et al. 2006). The partial reduction of carotenoids by sulfide has been observed as a result of the addition of sulfide to selected allylic double bonds, followed by reductive desulfurization. This is supported by the finding that the thiol in allylic thiols could be reductively removed by sulhde to produce unsaturated products from free-radical reactions (Hebting et al. 2003). 

Peijnenburg WJGM, MJ t Hart, HA den Hollander, D van de Meent, HH Verboom, NL Wolfe (1992) QSARs for predicting reductive transformation constants of halogenated aromatic hydrocarbons in anoxic sediment systems. Environ Toxicol Chem 11 301-314. 

Oremland RS, JP Zehr (1986) Formation of methane and carbon dioxide from dimethylselenide in anoxic sediments and by a methanogenic bacterium. Appl Environ Microbiol 52 1031-1036. 

Environmental Fate. Hydrogen sulfide is known to easily evaporate into the air (EPA 1993 Layton and Cederwall 1986 Leahey and Schroeder 1986), although its solubility in water may also cause it to persist in unperturbed, anoxic sediments. Additional information on the transport, transformation, and persistence of the compound in soils and groundwater, particularly at hazardous waste sites, would be useful in identifying the most important routes of human exposure to hydrogen sulfide. 

Dunnette DA, Chynoweth DP, Mancy KH. 1985. The source of hydrogen sulfide in anoxic sediment. Water Res 19 875-884. 

Baughman GL, Weber E (1994) Transformation of dyes and related compounds in anoxic sediment Kinetics and products. J Environ Sci Technol 28 267-276... 

Copper concentrations in sediment interstitial pore waters correlate positively with concentrations of dissolved copper in the overlying water column and are now used to predict the toxicity of test sediments to freshwater amphipods (Ankley et al. 1993). Sediment-bound copper is available to deposit-feeding clams, especially from relatively uncontaminated anoxic sediments of low pH (Bryan and Langston 1992). The bioavailability of copper from marine sediments, as judged by increased copper in sediment interstitial waters, is altered by increased acid volatile sulfide (AYS)... 

Hudson-Raritan estuary and Long Island Sound 1984-89 total PCBs Upper Hudson River anoxic sediments PCB 1 PCB 4 PCBs 6/19 PCB 8... 

Bisphenol A Production of resins (polycarbonate and epoxy resins). Component in flame retardant production Antioxidant, preservative - River water mean values 0.016 pg L 1 (Europe) and 0.5 pg L"1 (US) [66]. -SW <0.001-1 pg U1 [9] - WW effluents mean values 1.5 pg L-1 [67] Not persistent in surface water. Rapidly biodegraded in aquatic environments [68] and removed in WWTP. Half-life 1-4 days [69] in water. Accumulated in anoxic sediments [9]... 

Although the abundance of silver in the Earth s crust is comparatively low (0.07 pgg-1), it is considered an environmental contaminant and is toxic at the nanomolar level. As an environmental pollutant it is derived from mining and smelting wastes and, because of its use in the electrical and photographic industries, there are considerable discharges into the aquatic environment. Consequently, there have been studies on the geochemistry and structure of silver-sulfur compounds [31]. Silver, either bound to large molecules or adsorbed on to particles, is found in the colloidal phase in freshwater. In anoxic sediments Ag(I) can bind to amorphous FeS, but dissolved silver compounds are not uncommon. A more detailed study of silver speciation in wastewater effluent, surface and pore waters concluded that 33-35% was colloidal and ca. 15-20% was in the dissolved phases [32]. 

Iron sulphides are ubiquitous in marine and freshwater sediments. They are usually present either as pyrite or as monosulphides, which can be liberated by hydrochloric acid. These acid volatile sulphides give rise to an intense black colour that is characteristic of anoxic sediments. They play an important role in recent diagenetic processes in sediments and the ratio of pyrite to acid volatile sulphides has been used as an historical indicator to determine whether sediments were formed in marine or freshwater conditions. They can be present over a wide range of... 

Anoxic Sediments, Water-Logged Soils, and Aquifers... 

Phelps TJ, Zeikus JG. 1984. Influence of pH on terminal carbon metabolism in anoxic sediments from a mildly acidic lake. Appl Environ Microbiol 48 1088-95. 

A particularly important consequence of bioirrigation and bioturbation is the introduction of relatively 02-rich bottom water into the sediments. This enhancement in O2 supply is analogous to the aeration of soil by earthworms. Bioturbation can occur as deeply as 1 m below the sediment surface, but is most intense in the top 10 cm. The depth of O2 penetration is also strongly influenced by the flux of sedimenting POM. High accumulation rates of organic-rich particles can fuel bacterially mediated aerobic respiration supporting rates of O2 removal that exceed the benthic animals abilities to reaerate the sediments. In this case, anoxic conditions result. Since animals require O2, bioturbation does not occur in anoxic sediments. Thus, the effects of bioturbation are limited to the oxic portion of the sediments. 

Demonstrating that Mn(lll,lV) is reduced microbially is complicated by the rapid abiotic reduction of Mn(lll,lV) by Fe + and other reductants. Lovley and Goodwin (1987) obtained indirect evidence for microbial mediation of Mn(III,IV) reduction in experiments in which they follows the consumption of H2 by anoxic sediment. Addition of Mn02 caused H2 to decrease to smaller concentrations than possible under Fe reducing conditions, suggesting that Mn reduction was out competing Fe reduction for H2 in the same way that Fe reduction out competes S04 reduction and methanogenesis. 

Biological. Under aerobic conditions or in experimental systems containing mixed cultures, hexachloroethane was reported to degrade to tetrachloroethane (Vogel et al, 1987). In an uninhibited anoxic-sediment water suspension, hexachloroethane degraded to tetrachloroethylene. The reported half-life for this transformation was 19.7 min (Jafvert and Wolfe, 1987). When hexachloroethane (5 and 10 mg/L) was statically incubated in the dark at 25 °C with yeast extract and settled domestic wastewater inoculum for 7 d, 100% biodegradation with rapid adaptation was observed (Tabak et al, 1981). 

Jafvert, C.T. and Wolfe, N.L. Degradation of selected halogenated ethanes in anoxic sediment-water systems. Environ. Toxicol C/je/n,.6(ll) 827-837. 1987. 

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