Strong organic ligands in marine organisms

The interaction between thorium and marine organisms (cultured bacterium, natural phytoplankton and zooplankton) was experimentally examined by using chemical equilibrium techniques. Thorium quantitatively reacts with the binding sires of bacterium (Shewanella algae), phytoplankton (mainly diatoms) and zooplankton (mainly copepods) in 0.1 M HCl solution. According to mass balance analysis of experimental adsorption data, thorium forms an 1:1 complex with the binding site in all marine organisms studied. Their stability constants are in the range of 10(6.59) and 10(6.74) M-1 in an 0.1 M HCl solution. The mole ratio of ligand to organic carbon in the marine organisms ranged from 0.23 to 4.2 mmol/mol C; the ligand:carbon ratio in bacteria was more than one order of magnitude higher than that in phytoplankton and zooplankton. This result leads to the hypothesis that the strong organic ligand specified by Th is one of the essential functional groups in oceanic microorganisms.