Abiotic transformation processes

No published data were located referencing biotic transformation of thorium in soil. Abiotic transformation processes that can convert immobile thorium in soil into mobile forms through the formation of complexes were discussed in Section 5.3.13. 

Chlorinated Pesticides. The major metabolic degradation pathways for toxaphene in all organisms are probably reductive dechlorination and reductive dehydrochlorination. In some cases, oxidative dechlorination has been observed to result in hydroxy derivatives, acids and ketones.76 Aldrin is transformed into dieldrin in biotic as well as abiotic transformation processes. 

Abiotic mechanisms for degradation of herbicides in soil, discussion, 15 Abiotic transformation processes of pesticide dissipation in soil hydrolytic reactions, 5 role in pesticide degradation, 4-5... 

The transport and transformation of chemicals provide valuable information on their exposure concentration used in risk analysis. The chemical on entry into the environment will be influenced by its physico-chemical properties and the transport processes to concentrate in a particular compartment (Figure 11.4). Biotic and abiotic transformation processes could degrade the chemical. 

Abiotic transformation of contaminants in subsurface natural waters result mainly from hydrolysis or redox reactions and, to lesser extent, from photolysis reactions. Complexation with natnral or anthropogenic ligands, as well as differential volatilization of organic compounds from multicomponent hquids or mixing with toxic electrolyte aqueous solutions, may also lead to changes in contaminant properties and their environmental effects. Before presenting an overview of the reactions involved in contaminant transformations, we discuss the main chemical and environmental factors that control these processes. 

Wolfe, N. L., Mingelgrin, U. Miller, G. C. (1990). Abiotic transformations in water, sediments, and soil. In Pesticides in the Soil Environment Processes, Impacts, and Modeling, ed. H. H. Cheng, pp. 103-68. Madison, WI Soil Science Society of America. 

Zepp, R.G. and N.L. Wolfe. 1987. Abiotic transformation of organic chemicals at the particle-water interface. In W. Stumm, ed., Aquatic Surface Chemistry Chemical Processes at the Particle-Water Interface, pp. 423-455. Wiley, New York. 

Research to date has focused primarily on azo and anthraquinone dyes, due to their commercial importance. Environmental processes including biodegradation, photolysis, sorption to soils and sediment, and abiotic transformation in sediment /water systems have been studied. The quantity of dyes apparently entering and potentially passing through wastewater treatment systems unaltered has prompted research on the behavior of these chemicals in biological and other types of wastewater treatment systems. 

The tests were conducted in an open, mixed and aerated reactor to maintain constant values of pH, DO, and temperature. Thus the difference in COD drop may not be related to pH, temperature. Aeration and mixing maintained DO around saturation in all tests, thus the effect of oxygen production at the anode is minimized. The only other process (other than microbial activity) that may relate to COD drop is abiotic transformation by electrolysis reactions at the electrodes. If abiotic redox of the organic content occurs in this study, then increasing the current density should increase the... 

Abiotic degradation transforms organic compounds by chemical reactions such as oxidation, reduction, hydrolysis, and photodegradation. Abiotic degradation processes do not usually achieve a complete breakdown of the chemical (mineralization). 

The fundamentals and background of QSAR modeling and predictions have been detailed previously (e.g., Nendza, 1998). Regarding the different physicochemical bases of transformation processes, different approaches to their estimation have been taken. The intention should always be to use process-related models. Thermodynamic principles underlie the relationships between abiotic one-step reaction rates and physicochemical descriptors of the structures. Mechanistic modeling is much more intricate for multistep biodegradations, where the (varying) rate-limiting... 

Photolysis of 2-bromo-4,4-dimethyl-2-cyclohexenone only affords reduction, even in a nucleophilic medium343,344. Apparently, this substrate is structurally not suitable to form a vinyl cation. Formation of vinyl radical-derived products is also the main process for all vinylic halides, if their irradiation is performed in an apolar medium. Such photochemical reductive dehalogenation and especially dechlorination reactions have been extensively studied in the past, not in the least because of their importance as abiotic transformation of persistent polychlorinated environmental pollutants. Examples are the cyclodiene insecticides aldrin and dieldrin, which contain a vicinal dichloroethene chromophore. In recent... 

We have chosen to follow Watts [24] and discuss chemical and biological transformation processes in the same section. Watts notes that, although this approach is somewhat nontraditional, it is advantageous in that understanding of the abiotic chemical reactions serves as a conceptual basis for understanding the biochemical reactions (which are essentially the same except for the fact that the biochemical reactions are mediated by microorganisms). Where a reaction is predominantly abiotic or biotic, it will be noted in the discussion. In this section, the fundamentals of each chemical or biological reaction will be discussed, and model formulations for the reaction kinetics presented. 

The enantiomers of a chiral compound have identical physical and chemical properties. Accordingly, abiotic processes such as air-water exchange, sorption, and abiotic transformation are generally identical for both enantiomers. However, biochemical processes may differ among stereoisomers because they can interact differentially with other chiral molecules such as enzymes and biological receptors. Thus, enantiomers may have different biological and toxicological effects. 

Arsenic speciation in anaerobic sediments is controlled by both microbially mediated transformations of species and by abiotic chemical processes including adsorption. The two... 

Examples of relevant chemical transformation processes in aqueous environment are hydrolysis, nucleophilic substitution, elimination, oxidation and reduction reactions (Schwarzenbach et al, 1993). Of these, hydrolysis is often considered the most important and it is the only chemical transformation process for which international test guidelines are generally available. The tests for abiotic degradation of chemicals are generally in the form of determination of transformation rates under standardized conditions. 

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