Abiotic chemical degradation process

The objective of this chapter is to follow the process of abiotic chemical degradation as it takes place within a piece of wood by examination of a series of tissues taken at increasing distances from the wood surface. Chemical analysis of the tissues under investigation is indispensable for interpretation of the optical evidence. Standard analyses for the main wood constituents were made of the respective tissues to supplement the micro-... 

A plethora of environmental forces compromise the structural integrity of chemicals in the environment. Many prominent abiotic degradative processes occur due to the influences of light (photolysis) and water (hydrolysis). 

Several processes may play a role in the environmental dissipation of -triazine herbicides. Dissipation processes can include microbial or chemical degradation in soil metabolism or conjugation in plants photodegradation in air, water, and on soil and plant surfaces and volatilization and transport mechanisms. This chapter will address photolytic degradation and abiotic hydrolysis of the currently used triazine herbicides, the triazinone herbicides (metribuzin and metamitron), and the triazinedione herbicide hexazinone. 

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). 

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. 

Fukui functions support the understanding of biotic and abiotic reactions and degradation processes for small molecules. In conjunction with (bio-)chemical expertise and experience, Fukui functions can also be used to predict reactive behavior. In contrast to other quantum chemical approaches to reactivity, the calculation of Fukui functions does not directly depend on energies for open shell systems, which require a higher level of theory to be of acceptable quality. 

The disappearance of a solvent fi om solution can also be the result of a number of abiotic and biotic processes that transform or degrade the compound into daughter compounds that may have different physicochemical properties from the parent solvent. Hydrolysis, a chemical reaction where an organic solvent reacts with water, is not one reaction, but a family of reactions that can be the most important processes that determine the fate of many organic compounds. Photodegradation is another family of chemical reactions where the solvent in solution may react directly under solar radiation, or with dissolved constituents that have been made reactive by solar radiation. For example, the photolysis of water yields a hydroxyl radical ... 

This chapter is focused on the natural attenuation behavior of CS at the field scale. The first part of the chapter reviews many of the physical, chemical and abiotic natural attenuation processes that attenuate CS concentrations in ground water. Some of these processes have been described in more detail in previous chapters in the handbook and are therefore only reviewed in brief In the second part of this chapter, we will review the biological processes that bring about the degradation of the most common chlorinated solvents, present conceptual models of chlorinated solvent plumes, and summarize data from field studies with chlorinated solvent contamination. 

The disappearance of a plasticizer from water can be the result of a number of abiotic and biotic processes that can transform or degrade the compound into daughter compounds that have different physicochemical properties from the parent compound. Hydrolysis is a family of chemical reactions where a plasticizer reacts with water. Phthalate esters may hydrolyze to form monoesters and then dicarboxylic acid. It has been predicted that di-(2-ethylhexyl) sebacate will form 2-ethylhexanol and decanedioic acid. Wolfe et al experimentally measured second-order alkaline hydrolysis rate constants for dimethyl, diethyl, di-n-butyl, and di-(2-ethylhexyl) phthalates, and it appears that hydrolysis may be too slow to have a major impact on the fate of most dissolved plasticizers. The estimated hydrolysis half-lives at pH 7 for 20 plasticizers were longer than 100 days. No information was located for diallyl, ditridecyl and diundecyl phthalates. Under alkaline conditions, hydrolysis may be important for tricresyl phosphate and tri-(2-ethylhexyl) trimellitate at pH 8 their predicted half-lives are 3.2 and 12 days respectively. 

---