TRACE-ELEMENT TROPHIC TRANSFER IN AQUATIC ORGANISMS - A CRITIQUE OF THE KINETIC-MODEL APPROACH

The bioaccumulation of trace elements in aquatic organisms can be desc ribed with a kinetic model that includes linear expressions for uptake and elimination from dissolved and dietary sources. Within this model , trace element trophic transfer is described by four parameters: the weight-specific ingestion rate (IR); the assimilation efficiency (AE); the physiological loss rate constant (k(e)); and the weight-specific growth rate (g). These four parameters define the trace element trophi c transfer potential (TTP = IR . AE/[k(e) +g]) which is equal to the r atio of the steady-state trace element concentration in a consumer due to trophic accumulation to that in its prey. Recent work devoted to t he quantification of AE and k(e) for a variety of trace elements in aq uatic invertebrates has provided the data needed for comparative studi es of trace element trophic transfer among different species and troph ic levels and, in at least one group of aquatic consumers (marine biva lves), sensitivity analyses and field tests of kinetic bioaccumulation models. Analysis of the trophic transfer potentials of trace elements for which data are available in zooplankton, bivalves, and fish, sugg ests that slight variations in assimilation efficiency or elimination rate constant may determine whether or not some trace elements (Cd, Se , and Zn) are biomagnified. A linear, single-compartment model may not be appropriate for fish which, unlike many aquatic invertebrates, hav e a large mass of tissue in which the concentrations of most trace ele ments are subject to feedback regulation. (C) 1998 Elsevier Science B. V. All rights reserved.