Trace metal‐chelator interactions and phytoplankton growth in seawater media: Theoretical analysis and comparison with reported observations 1

Abstract

Effects of trace metal chelators in seawater are examined theoretically in terms of equilibrium chemical speciation in seawater; of chemical interactions between all metals, naturally occurring ligands, and added organic chelating agents of various binding strengths and total concentrations; and of transfer of trace metals to the phytoplankton cell surface. An equilibrium model involving 18 metals and 8 ligands is applied to find the metal species in natural seawater, chelator‐amended seawater, and synthetic seawater media. Three mechanisms for enhanced supply of iron via chelation arc examined: transport through the membrane, ligand exchange at the cell surface, and increased supply of iron to the cell surface by dissociation of a chelate. None account for the observed effects of chelator variations on growth rate. Detoxification of toxic metals via chelation shows a strong correlation between growth rate and free Cu 2+ computed at equilibrium in solution.