Biodegradation in the Hydrosphere

Detoxification (or detoxication) is of particular importance with respect to environmental toxicological chemistry. Reaction 3.53 shows the conversion of insecticidal paraoxon, a potent neurotoxin (see insecticidal organophosphates in Chapter 4, Section 4.11), to p-nitrophenol, which is only about 0.005 X as toxic. In some cases, microorganisms actually produce more toxic materials. This occurs 

Highly biodegradable compound with a straight hydrocarbon chain and a functional group amenable to biological attack 

Highly branched, poorly hiodegradahle compound. The presence of a quaternary carhon atom hound with four other carbons, as denoted hy the asterisk above, makes a compound especially resistant to biodegradation 

Phenol, a biocidal compound and the first commonly used disinfectant, is an example of a normally nonbiodegradable substance that can be degraded under appropriate conditions. Acclimated bacteria will break down phenol in dilute water solution. When bacteria are used in waste treatment processes to break down substances such as phenol that are normally biorefractory, acclimated microorganisms are often gathered from sites where the substances in question have been present for some time. For example, sites of crude oil spills serve as sources of bacteria that can biodegrade petroleum wastes. 

FIGURE 3.17 Surfactants that have been used in household detergent formulations the aUcyl benzene sulfonate surfactant (ABS) originally used did not undergo biodegradation very well and caused problems due to its persistence, which is the result of its branched-chain structure. The ABS was replaced by Unear alkyl sulfonate (LAS), which is biodegradable because of its straight-chain structure. 

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