Problem Formulation

The problem formulation component of the risk assessment process is, hopefully, the beginning of an iterative process. This critical step defines the question under consideration and directly affects the scientific validity and policy-making usefulness of the risk assessment. Initiation of the process can begin due to numerous causes such as a request to introduce a new material into the environment, examination of cleanup options for a previously contaminated site, or as a component of...

Biotransformation Detoxification and Biodegradation

As mentioned in the previous chapter, following the entry into a living organism and translocation, a pollutant may be stored, metabolized, or excreted. When the rate of entry is greater than the rate of metabolism and or excretion, storage of the chemical often occurs. However, storage or binding sites may not be the sites of toxic action. For example, lead is stored primarily in the bone, but acts mainly on the soft tissues of the body. If the storage site is not the site of toxic action,...

Nadh

The cytochrome P-450 monooxygenase system. P-4503+ Cytochrome P-450 with heme iron in oxidized state (Fe3+) P-4502+ cytochrome P-450 with iron in reduced state S substrate e electron. (Adapted from J. A. Trimbell, 1982. Principles of Biochemical Toxicology. Taylor & Francis, London.) by NADH via cytochrome b5 and NADH cytochrome b5 reductase. The enzyme-substrate-oxygen complex splits into water, oxidized substrate, and the oxidized form of the enzyme. The overall reaction is therefore SH +...