BIOTRANSFORMATION, BIOACCUMULATION, AND ELIMINATION OF TOXICANTS

Xenobiotic substances are those that do not naturally occur in an organism. They may be other naturally occurring substances or they may be synthetic molecules. When a person is exposed to some xenobiotic substance, what happens This question will be answered at greater length in Section 4.3.2 (Biotransformation, Bioaccumulation, and Elimination of Toxicants), but let s take a quick look at the application of some general chemistry principles to this topic first. 

BIOTRANSFORMATION, BIOACCUMULATION, AND ELIMINATION OF TOXICANTS TABLE 4.3.2.1 Potential Phase I Biotransformation Products of Various Organic Functional Groups... 

Preview This section discusses the fate of toxicants in the body, including their biotransformation, bioaccumulation, and elimination. 

Uptake of TNT in fish and invertebrates resulted in substantial bioaccumulation of nonidentified extractable and nonextractable compounds. Contrasting to the parent compound, metabolically formed transformation products of TNT appear to be eliminated at much slower rates. Neither the biological half-life nor the chemical nature of nonextractable transformation products of TNT in organisms has been investigated to date. Investigations on the biotransformation of explosives other than TNT in aquatic animals were not found in the available literature and are therefore warranted. Further studies of the fate of explosives in aquatic animals are necessary to reveal the identity of their transformation products present in the tissues of exposed organisms, to further characterize species-specific differences in the bioconcentration of transformation products, and to elucidate the mechanism of toxic action. 

Most chemical toxicants are biotransformed and eliminated from the body in urine or bile however, some xenobiotics are not amenable to these transformations—that is, the body s enzyme systems are ineffective in transforming these compounds to more polar forms. Since these compounds are often very lipid soluble and cannot be quickly eliminated, the body stores them in our fat tissues throughout the body—a process known as bioaccumulation. In order for bioaccumulation to occur, a chemical toxicant must be absorbed faster than it is eliminated. These chemical toxicants are stored in the body s fat or lipids until a dynamic state is reached where the rates of absorption and elimination become about the same. The concentrations of these xenobiotics in fat tissues can be estimated from concentrations in blood that normally carries a small amount of circulating lipid, as reported in Incident 4.3.2.I. (See also in Section 4.2.1, Chemical Connection 4.2.1.1 Solubility, Storage, and Elimination.)... 

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