Modelling Bioaccumulation and Toxicity of Metal Mixtures

ABSTRACT

Bioaccumulation of metals in mixtures may demonstrate competitive, anticompetitive, or non-competitive inhibition, as well as various combinations of these and/or enhancement of metal uptake. These can be distinguished by plotting (metal in water)/(metal in tissue) against metal in water and comparison to equivalent plots for single-metal exposure. For the special case of pure competitive inhibition where only one site of uptake is involved, inhibition of metal accumulation in any metal mixture can be predicted from bioaccumulation of the metals when present singly. This is consistent with the commonly used Biotic Ligand Model (BLM) but does not explain bioaccumulation of metals in Hyalella azteca. Options for modelling toxicity of metal mixtures include concentration or response addition based on metal concentrations in either water or tissues. If the site of toxic action is on the surface of the organism, if this is the same as the site of metal interaction for bioaccumulation, if there is only one such type of site, and if metal bioaccumulation interactions are purely competitive (as in the BLM), then metal toxicity should be concentration additive and predictable from metal concentrations in either water or tissues. This is the simplest toxicity interaction to model but represents only one of many possibilities. The BLM should, therefore, be used with caution when attempting to model metal interactions, and other possibilities must also be considered.

Key Words:

• metals
• mixtures
• bioaccumulation
• toxicity
• models

ACKNOWLEDGMENT

This study is a contribution to the Metals in the Human Environment Research Network (MITHE-RN). A full list of sponsors is available at http://www.mithe-rn.org. The insightful comments of Joe Meyer and an anonymous referee are gratefully acknowledged. We thank the Aquatic Ecosystems Protection Research Division of Environment Canada and the University of Waterloo for their support.

Notes

^aPredicted change in uptake = (1 + K_M• M) / (1 + sum of K_M• M values for all metals in mixture).

^bNot available. No saturation of uptake detected (i.e., 1/K_0.5 = 0).