Toxic Metal Ion-Synthetic Chelating Agent Interactions in Aqueous MediaEPA Grant Number: R829356
Title: Toxic Metal Ion-Synthetic Chelating Agent Interactions in Aqueous Media
Investigators: Stone, Alan T.
Current Investigators: Stone, Alan T. , Ball, William P.
Institution: The Johns Hopkins University
EPA Project Officer: Louie, Nica
Project Period: October 1, 2001 through September 30, 2005 (Extended to September 30, 2006)
Project Amount: $333,057
RFA: Complex Chemical Mixtures (2000) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Our first objective is to explore chemical processes that serve as sources and sinks for toxic metal ion-synthetic chelating agent complexes. Emphasis will be placed on contaminant scenarios where chromium and synthetic chelating agents come into contact. Additional work will also be performed with NiII and AlIII. We hypothesize that toxic metal ion speciation in many aquatic environments is under kinetic, rather than thermodynamic control.
Our second objective is to measure the physicochemical properties of metal ion-chelating agent complexes that affect adsorption, partitioning, and mass transport. We hypothesize that the net charge and degree of hydration have a profound affect on partitioning in environmental media. Neutral complexes, known to elicit toxicological effects but which have received little attention in the past, are particularly noteworthy.
Our laboratory at Johns Hopkins has developed capillary electrophoresis (CE) techniques for identifying and quantifying free chelating agents and distinct metal ion-chelating agent complexes. CE will be used in a series of detailed studies of chemical processes and physicochemical properties: 1) Chelating agents will be brought into contact with particulate-bound CrIII; rates and extent of CrIII solubilization will be measured. 2) Breakdown of dissolved CrIII-chelating agent complexes by metal ion exchange and by ligand exchange will be explored. 3) CrIII-containing complexes will be brought into contact with MnOOH and MnO2, and rates of CrVI production measured. 4) CrVI will be added to solutions containing reductants and synthetic chelating agents, and rates of dissolved CrIII formation will be measured. 5) Adsorption and partitioning of metal ion-chelating agent complexes onto well-characterized subsurface materials will be examined. In all of these studies, the effects of pH and other medium characteristics on sources and sinks for dissolved toxic metal ion-chelating agent complexes will be carefully explored.
Environmental situations where concentrations of toxic metal ion complexes may reach problematic levels will be identified. By providing a more complete understanding of sources and sinks for toxic metal ion-chelating agent complexes, we hope to assist professionals in assessing the impact of existing contamination, evaluating alternative remediation strategies, and predicting potential impacts of proposed new chemicals and practices. We suspect that kinetics, rather than equilibrium, controls the speciation of CrIII and other slowly-exchanging toxic metal ions in environmental media. Hence, "total" and "free" metal ion concentrations will not be sufficient to predict environmental behavior; more complete speciation information is needed.