Oxic environment

Atmosphere—Water Interaction. Although water is a very minor component of the atmosphere, less than 10 vol % of the atmosphere consisting of water, many important reactions occur ki the water droplets of cloud, fog, and rain. The atmosphere is an oxic environment ki its water phase, gigantic quantities of reductants, such as organic substances, Fe(II), SO2, CH SCH (dimethyl sulfide), and nitrogen oxides, are oxidized by oxidants such as oxygen, OH radicals, H2O2, and Fe(III). 

By analogy to higher animals, we might expect that respiring microbes would use reduced carbon compounds as electron donors and O2 as the electron acceptor indeed, aerobic bacteria that do just this are common in oxic environments. Microbes, however, are notably versatile, employing H2, H2S, NHj", CH4, Fe++, and many other species as electron donors. They can similarly use SO4-, NO3, NO2, HCOJ, and so on as electron acceptors. The microbes can even use ferric... 

Clastic sediments from oxic environments (loess, turbidites, grey shales) 1 ... 

Based on the pE value, redox environments are classified as follows (a) pE > 7 indicates an oxic environment, (b) at pE values between 2 and 7, the environment is considered suboxic, and (c) pE < 2 indicates an environment considered anoxic. The occurrence of redox reactions in the subsurface environment is limited by the decomposition and reduction of water ... 

Figure 3.9 Degradation pathway for the analgesic ibuprofen under anoxic and oxic environments.

We can start with vertebrates. Vertebrates are speciabzed to oxic environments, because their mitochondria are specialized to oxic environments. Vertebrates go back maybe 500 Myr in the fossil record (Benton and Donoghue 2007), so this makes sense. Vertebrates arose after the oceans were oxic and moved onto land at a time when they had evolved lungs and were able to crawl. 

Oxidations Involving Electrophilic Oxygen-Containing Bioreactants Illustrative Example 17.4 What Products Do You Expect from the Microbial Degradation of Vinyl Chloride in an Oxic Environment ... 

Generally Even Electron Density Oxic Environment... 

Vinyl chloride (VC) is the monomer from which the common polymer, polyvinyl chloride, is produced. Hence, VC is produced on a very large scale. Not surprisingly, occasional releases of the rather toxic VC to the environment occur. What initial biodegradation product would you expect from VC if it were released into an oxic environment ... 

But noting the presence of the TT-cloud of electrons, an initial metabolic attack using an electrophilic bioreagent might be expected. Thus, microbial attack in oxic environments likely starts with use of an oxidase on this part of the structure ... 

Tessier, A. (1992) Sorption of trace elements on natural particles in oxic environments. In Environmental Particles (eds Buffle, J. and van Leeuwen, H.R), Vol. 1. Lewis Publishers, Chelsea, MI, pp. 425M53. 

Figure 5 Time courses for CH4 production (left) and CH4 oxidation (right) in selected 5 cm core sections (site LB2 in Lemeta Bog) that were alternately made anoxic and oxic in an attempt to mimic response to changing water table levels. Methane production hy anoxic core sections was measured for 54 h. Core sections were drained for 20 h in an oxic environment and then amended with 20 pJ L CH4, after which the time course for CH4 oxidation (right) was determined. No CH4 was produced over 48 h hy core sections rewetted and made anoxic at 120 h (source Whalen...

Most direct CH4 oxidation rate measurements have focused on anoxic sediments and waters, so there have been very few direct oxidation rate measurements in oxic environments. The study of... 

Fe, common in surhcial oxic environments, forms hydroxides, complexes formerly called hmonite (a collection of mst-Uke precipitates, chemically designated as Fe(OH)3). The aggregate has now been shown to contain several oxyhydroxide species, FeOOH, and the oxides, hematite, Fe203, and magnetite, Fe304, and some new minerals have been identified (Schwertmann and Fitzpatrick, 1992, tables 1-3, pp. 10-11). 

Both direct cleavage of DMSP to DMS/acrylate and DMSP demethylation pathways have been observed in anoxic sediments and oceanic waters (Kiene and Taylor, 1988b Yoch, 2002). However, unlike oxic environments, the demethylation of DMSP in anoxic sediments appears to require two organisms, one to demethylate DMSP to 3-methiolpropionate, followed by another to form... 

Tessier, A. (1993) Sorption of Trace Elements on Neutral Particles in Oxic Environments. In Environmental Particles, Vol. 2, J. Ruffle and H. P. Van Leeuwen, Eds., Lewis, Boca Raton, FL. 

The efficiency of detachment is a key parameter in the overall photochemical reductive dissolution kinetics, because in oxic environments detachment of reduced surface metal centers may be in competition with their oxidation (9, 10). 

The relative constancy of pH in subaqueous sediments (usually 6 to 8, most often 6.5 to 7.5) and the difficulty of measuring a thermodynamically meaningful Eh, led Berner (1981b) to propose a simplified redox classification scheme. The scheme is broadly based on the presence or absence of dissolved oxygen or dissolved sulfide (Table 11.5). Measureable dissolved oxygen indicates an oxic environment, its absence an anoxic environment. More recently others have suggested that Berner s... 

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