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SYNOPSIS OF DISCUSSION SESSION ON THE KINETICS BEHIND ENVIRONMENTAL BIOAVAILABILITY
Citation:
Landrum, P., W. Hayton, H. II, L. McCarty, D. MacKay, AND J. McKim. SYNOPSIS OF DISCUSSION SESSION ON THE KINETICS BEHIND ENVIRONMENTAL BIOAVAILABILITY. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/A-94/235 (NTIS PB95138251).
Description:
Kinetics are involved in virtually all environmental processes. The time frame (frequency) can very from extremely brief, say, billionths of econds, to very long, on the order of billions of years. owever. only the rate which are within a few orders of agnitude of the examined biological rate are of practical importance. One of the most important determinants is the influence of body size on different metabolic rates at which organisms live.1.2 hat is to say, internal processes and interactions with the external environment occur at a faster rate for small organisms than for large organisms. ince this body-size effect can encompass several orders of magnitude, factors that influence environmental bioavailability may vary considerably between organisms of substantially different body sizes. Thus, the processes that are kinetically important for microbes will likely be different from those that are important for fish. Rather than continuing to examine fundamental influencing factors, we propose to discuss kinetics within a toxicological framework, and on a process-orientated basis within that framework. Kinetics come into play in all three of the basic areas defined in classic toxicology/pharmacology: 1. Exposure from external to the organism that control contact with the chemical; 2. Toxicokinetics-those physiological and behavioral factors controlling uptake, distribution, metabolic processing, elimination and, ultimately, delivery to the site(s) of toxic action; and 3. Toxicodynamics-those processes which constitute the biochemical and physiological sequelae resulting from the effects of the chemical at the site(s) of action. For this report, discussion will be limited to the first two categories.