An Introduction to Environmental Chemistry

128 Chapter Four

Box 4.16 Mechanisms of microbial degradation and transformation of

organic contaminants

Mineralization

eqn. 1

Complete biodegradation of an organic contaminant into its inorganic components for

example CO 2 and H 2 O.

Polymerization

eqn. 2

A metabolic transformation that involves the coupling or bonding of small molecules to form

polymers. In equation 2, two pentachlorophenol molecules polymerize to form para-

pentachlorophenoxy-tetrachlorophenol.

Detoxification

eqn. 3

Detoxification involves a chemical change to a molecule. In equation 3, pentachlorophenol

(PCP), a powerful biocide used in wood preservative, undergoes O-methylation. This

transforms PCP to a far less toxic compound pentachloroanisole. Detoxification by one group

of microorganisms often allows other organisms to continue biodegradation.

OH

Cl

Cl

Cl

Cl

Cl Cl

detoxification

OCH 3

Cl

Cl

Cl

Cl

Pentachlorophenol Pentachloroanisole

Cl

O

Cl

Cl

Cl

Cl

Cl

OH

Cl

Cl

Cl

Cl

OH

Cl

Cl

Cl

Cl

Cl

OH

Cl

Cl

Cl

Cl

polymerization

Pentachlorophenol Para-pentachlorophenoxy-tetrachlorophenol

OH

CO 2 + H 2 O

mineralization

Phenol

(continued)