SREL Reprint #1858







Chapter 1

Ligands and the Bioavailability of Metals
in Aquatic Environments

Michael C. Newman and Charles H. Jagoe


Metal bioavailability is influenced by physical, chemical, and biological factors in aquatic environments. Physical factors include temperature, phase association (solid, liquid, or gas), physical adsorption, sequestration by occlusion within a solid phase, or depositional regime as dictated by water movement. Chemical factors include those influencing speciation at thermodynamic equilibrium, complexation kinetics, lipid solubility, and phase transitions such as those associated with precipitation, coprecipitation, or chemical adsorption. Both organic and inorganic species contribute to these phenomena. A myriad of biological factors can also modify bioavailability including trophic interactions, biochemical or physiological adaptation, microhabitat utilization, animal size and age, and particular species characteristics. Physical and chemical factors can also interact with these biological factors. For example, temperature, pH, or Cl- can modify gill function and, consequently, uptake of dissolved metals.

A major class of chemicals that modify bioavailability are the ligands. Ligands are anions or molecules that form coordination compounds or complexes with metals.' Ligand influence may be direct, e.g., sequestering the metal by complexation, or indirect, e.g., influencing gill function. Most studies of ligand effects on metal bioavailability have been descriptive and the mechanism for their influence often remains speculative. Our intention here is to describe the various roles that ligands may play in determining metal bioavailability. Turner and co-workers' classification of cation-ligand interactions will be used as a central theme in our description.Ligand effects on biological processes will also be highlighted.

SREL Reprint #1858

Newman, M.C. and C.H. Jagoe. 1994. Ligands and the bioavailability of metals in aquatic environments. p. 39-61. In Bioavailability: Physical, Chemical and Biological Interactions, edited by J.L. Hamelink, P.F. Landrum, H.L. Bergman, and W.H. Benson. Lewis Publishers. Proceedings of the Thirteenth Pellston Workshop, Pellston, MI.

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