TABLE 1-1 Definitions of “Bioavailability” and Related Terms

Definition

Source

Bioavailability

A chemical element is bioavailable if it is present as, or can be transformed readily to, the free-ion species, if it can move to plant roots on a time scale that is relevant to plant growth and development, and if, once absorbed by the root, it affects the life cycle of the plant.

Sposito, 1989

Generally used to describe the extent and rate of absorption for a xenobiotic which enters the systemic circulation in the unaltered (parent) form from the applied (exposure) site.

Hrudy et al., 1996

The availability of a chemical to an animal, plant, or microorganism. It may be assayed by measurement of uptake, toxicity or biodegradability.

Linz and Nakles, 1997

A concept that describes the ability of a chemical to interact with living organisms.

NEPI, 1997

The accessibility of contaminants to microbes from the standpoint of their metabolism, their ability to grow on these chemicals, to change cellular physiology, and perhaps modulation of genetic response.

Sayler et al., 1998

A measure of the fraction of the chemical(s) of concern in environmental media that is accessible to an organism for absorption.

ASTM, 1998

A measure of the potential for entry into ecological or human receptors. It is specific to the receptor, the route of entry, time of exposure, and the matrix containing the contaminant.

Anderson et al., 1999

The extent to which a substance can be absorbed by a living organism and can cause an adverse physiological or toxicological response.

Battelle and Exponent, 2000

Bioavailable: For chemicals, the state of being potentially available for biological uptake by an aquatic organism when that organism is processing or encountering a given environmental medium (e.g., the chemicals that can be extracted by the gills from water as it passes through the respiratory cavity or the chemicals that are absorbed by internal membranes as the organism moves through or ingests sediment). In water, a chemical can exist in three different forms that affect availability to organisms: (1) dissolved, (2) sorbed to biotic or abiotic components and suspended in the water column or deposited on the bottom, and (3) incorporated (accumulated) into the organisms.

EPA, 2000a

The fraction of an administered dose that reaches the central (blood) compartment, whether from gastrointestinal tract, skin, or lungs. Bioavailability defined in this manner is commonly referred to as “absolute bioavailability.”

NEPI, 2000a



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