Equilibria between Chelex 100" and manganese, zinc and cadmium ions were used
to determine the complexation of these trace metals in 36 %o Gulf Stream seawater
at 25Oc and pH 8.2. The method utilized radiotracers (S4Mn, 6SZn, and l°gCd) to quantify
trace metal adsorption from trace metal-amended seawater and from seawater containing
a series of ethylenediaminetetracetate (EDTA)--metal ion buffers. Results were consistent
with Chelex adsorption of both trace metal ions and trace metal--EDTA chelates. Equilibrium models fitted to the data were used to establish conditional stability constants for
Chelex adsorption of manganese, zinc and cadmium ions and for adsorption of EDTAchelates. These models also yielded ratios of free metal ions to total dissolved trace metal
concentrations in seawater: 10 -°"1 for manganese, 10 -0.2 for zinc, and 10-1.s for cadmium.
Independent measurements with a cadmium ion-selective electrode also yielded a free:
total cadmium ratio of 10 -1"5.