Oxidation, biotic

This chemistry has been investigated and implemented for wastewater minerahza-tion by oxidizing the organic pollutants. The process is very efficient, not selective and, as a consequence, almost all carbon matter can be removed. Topical areas also include soil and aquifer treatments, sometimes in combination with a secondary biotic process [145]. 

The ammonium dynamics showed that the initial concentrations of N were reduced after the first 3 days, and after that, a release of the mineral occurred from day 3 up to day 14. Later still, the concentration of ammonium decreased by up to < 14 mg N kg 1 dry soil for all the treatments in both the Otumba and Texcoco soils, and the ammonium concentration decreased by up to < 2 mg N kg 1 dry soil for all treatments, except for the soil treated with sterilized sludge, < 31 mg N kg 1 dry soil. The contour of the ammonium dynamics was similar in both the Otumba and Texcoco soils. Many abiotic and biotic processes might affect the concentration of NH4+ in soil, such as NH4+ fixation in the soil matrix, volatilisation of NH3, and immobilization or oxidation of NH4+. Some soil processes were occurring at too low a level to be detectable, such as NH4+ fixation and the volatilisation of NH3. The nitrate dynamics were similar in both soils. The concentration of N03 was 120 mg N kg 1 dry soil in the control treatment in both soils. The ammonium concentration was similar in both soils, > 200 mg N kg 1 dry soil, treatments with sludge reached > 255 mg N kg 1 dry soil and > 300 mg N kg 1 dry soil in the Texcoco and Otumba soils respectively, and soils treated with sterilized sludge increased the concentration... 

Exploratory experiments with dictyotene and suspensions of male gametes of E. siliculosus showed a significantly enhanced production of the 6-butylcyclohepta-2,4-dienol and its isomers. This indicates that a biological degradative pathway does exist and that this pathway follows the same oxidative sequence as the abiotic route. However, final conclusions about the biotic contribution to the pheromone transformation cannot be drawn before careful analysis of the degree of enantioselectiv-ity of the biotic reaction. 

Oxidative Burst and Related Responses in Biotic Interactions of Algae... 

Stimulated by nature and in particular by the idea of modelling biotic coupled reaction systems such as ion transport and oxidative phosphorylation, recent attention has focused on a new generation of abiotic host... 

Many of the chemical reactions that occur in sediments during diagenesis are mediated by marine organisms or are a consequence of biotic activities. Most are energy-yielding redox reactions driven by the oxidation of organic matter and, hence, represent a critical metabolic resource to benthic organisms. 

Abiotic catalysis is generally less important than biotic but may be important. Examples are Mn(lll,IV) and Fe(III) reduction by microbial metabolites, and Fe(ll) oxidation which is catalysed by sorption onto soil particles. 

Abiontic, involving free extracellular enzymes or solubilizing agents, enzymes bound to soil surfaces, enzymes within dead or non-proliferating cells, or enzymes associated with dead cell fragments. Extracellular enzymes are important in the initial stages of organic matter oxidation, in which polysaccharides and proteins are hydrolysed to soluble compounds that can be absorbed by microbial cells and further oxidized in biotic processes. 

Chromate is reduced to Cr(lll) in dissimilatory microbial reactions, but this process is inhibited at moderate concentrations of C(V1) and so is probably of limited value in detoxifying soils contaminated with Cr(Vl) (Lovley, 1993). However, Cr(VI) can also be reduced to Cr(lll) abiotically by oxidation of Fe(ll) Fe(III) in ferric oxide is reduced to Fe(ll) biotically ... 

An important factor in the response of vegetation to oxidants (primarily ozone) is the presence of biotic pathogens. Such responses have been studied from several perspectives since Yarwood and Middleton accidentally found that rust-infected bean leaves were less sensitive to photochemical oxidants (probably PAN). Several investigators have looked at the protection from ozone injury afforded to plants with active infections others have noted that ozone injury increases the sensitivity of plants to... 

The effects of ozone and other photochemical oxidants on individual species of green plants and microorganisms are discussed in detail in Chapter 11. The purpose of this chapter is to examine the effects of oxidant-pollutant stress on both simple and complex communities of organisms. The human population is an integral and dependent component of these biotic communities, or ecosystems. ... 

The response of some plants to oxidants is conditioned by the presence or absence of biotic pathogens. Depending on the plant and the pathogen, oxidants may cause more or less injuiy to a given species. Pathogens may protect their host or make it more sensitive. The pathogens themselves may be injured or may be protected by the host plant. This subject is just beginning to be understood. 

A third mechanism by which the structural bonds between Fe atoms in iron oxides may be weakened involves reduction of structural Fe to Fe". In natural environments, reductive dissolution is by far the most important dissolution mechanism. It is mediated both biotically and abiotically. The most important electron donors, particularly in near surface ecosystems result from metabolic oxidation of organic compounds under O2 deficient conditions. In anaerobic systems, therefore, the availability of Fe oxides i. e. the electron sink, may control the degradation of dead biomass and organic pollutants in the ground water zone (see chap. 21). Reductive dissolution is also often applied to the removal of corrosion products from piping in industrial equipment and the bleaching of kaolin. 

The rate of the biotic reduction of Fe oxides by a strain of Corynehacterium under 02-free conditions followed the order natural ferrihydrite > synthetic goethite > hematite (Fischer (1988) (Fig. 12.29) in accordance with the sequence in reducibility by Fe-reducing bacteria isolated from a eutrophic lake sediment (Jones et al., 1983). Iron from ferrihydrite reduced by Shewandla alga was found to be isotopically lighter than that of the ferrihydrite Fe by a 5 ( Fe/ " Fe) of 1.3 %o This difference may be used to trace the distribution of microorganisms in modern and ancient earth (Beard etal. 1999). 

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