A MECHANISTIC MODEL OF COPPER ACCUMULATION IN HYALELLA-AZTECA

A mechanistic model is proposed for describing the accumulation of cop per in Hyalella azteca. The metal is assumed to diffuse passively into and out of the animal. Once inside, it binds primarily to a ligand (X ), the function of which is probably to supply copper to copper-requir ing essential macromolecules. Once X is saturated, no further copper i s accumulated. The rate of approach to the steady-state is much faster during uptake than during depuration because the number of binding si tes (X-t) is limited. Diffusion across the animal's body surface does not seem to be rate-limiting. The binding strength of copper to X (KCu -x) is stronger than the binding of copper to fish gills, but this is not necessarily a valid comparison because KCu-x is the product of sev eral constants, including the equilibrium for diffusion across the ani mal's surface and the strength of the internal binding site. Prolonged exposure to elevated copper in the water gradually reduces the concen tration of X-t, primarily through growth dilution. Regulation of body copper appears to be through control of the concentration of X-t, rath er than through control of copper influx or efflux rates, and chronic mortality is not affected by changes in X-t. (C) 1998 Elsevier Science B.V. All rights reserved.