On the chelation of toxic trace metals by humic acid of marine origin

The interaction of ⁶⁵Zn, ¹⁰⁹Cd and ²¹⁰Pb−²¹⁰Bi with humic acid isolated from marine sediment was investigated by high voltage paper electrophoresis in sea water and 0·55 m NaCl solutions. The experiments were performed in 100, 30 and 10% seawater to simulate also the estuarine conditions. The concentration of humic acid was varied from 3 to 300 mg l⁻¹. The electrophoretic mobility of the radionuclides was measured as function of the concentration of humic acid in the various systems and on aging of these systems from 0 to 7 days. Without addition of humic acid to seawater ¹⁰⁹Cd behaves as a cation, ⁶⁵Zn and ²¹⁰Pb give one cationic and a second nonmobile zone. In 0·55 m NaCl both ⁶⁵Zn and ²¹⁰Pb, give only one cationic zone. By addition of humic acid the radionuclides partly changed their electrophoretic mobility to anionic values and the zone at the starting point became more pronounced than in seawater without addition of humic acid. In general the results obtained confirm that the amounts of humic material dissolved in the open sea are too small to contribute significantly to the chelation of the investigated trace metals while in estuarine waters their contribution to trace metal chelation can play a role.