The effects of EDTA on metal solubilization in river sediment/water systems

Ethylenediaminetetraacetic acid (EDTA), widely used in chelant formulations for applications to sequester metal ions in solution, has been detected in some environmental waters. Concern has arisen that EDTA, because of its high binding constants with metals, may solubilize metals from sediments in river systems. To address this issue, the effects of EDTA on metal solubilization were examined in a river sediment/water system. Microcosms prepared with authentic Rouge River, Detroit, MI, sediment and water were amended with a range of EDTA concentrations and shaken in the dark at 23 degrees C for 28 d. Metal concentrations were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS). In the presence of EDTA, 28 d were required for equilibration of dissolved metal species with sediments. Higher levels of trace metals were solubilized by EDTA under oxidizing vs. reducing conditions. Statistically determined (alpha = 0.05) no observed effects levels (NOELs) for metal solubilization by EDTA were generated for the trace metals Ni, Co, Cu, Zn, Cd, Fe, and Pb. These NOELs were 0.4, 0.6, 1.0, 1.0, 3.0, 3.0, and 8.0 mu M EDTA, respectively. On a stoichiometric basis, these NOELs were at least fivefold higher than the background level of EDTA present in the river water sample used in this study, indicating that EDTA did not contribute to trace metal solubilization in this system. These results suggest that environmental concentrations of EDTA typically found in river systems for which the subject river is representative, are unlikely to contribute to trace metal solubilization from sediments.