Metal Speciation and Sequestering in Wetland SystemsEPA Grant Number: U915398
Title: Metal Speciation and Sequestering in Wetland Systems
Investigators: Peltier, Edward F.
Institution: Northwestern University
EPA Project Officer: Lee, Sonja
Project Period: September 23, 1998 through January 1, 2001
Project Amount: $95,620
RFA: STAR Graduate Fellowships (1998) RFA Text | Recipients Lists
Research Category: Fellowship - Environmental Engineering , Engineering and Environmental Chemistry , Academic Fellowships
The objective of this research project is to design and create a wetlands system on a contaminated site in South Chicago that has been impacted by a number of metal and organic contaminants, particularly chromium, manganese, arsenic, and polycyclic aromatic hydrocarbon (PAH) compounds.
The use of wetlands, either natural or created, as treatment systems for a wide range of contaminants has gained acceptance in recent years. One area where wetlands could potentially be beneficial is in the remediation of brownfield and former waste disposal sites, which often contain a mix of organic and inorganic contaminants. For those sites that cannot be economically redeveloped and sold, wetlands could provide a low-cost and low-effort treatment method that could alleviate the danger from the site and remove the potential for contaminant transport to the surrounding community. While wetlands have been shown to be remarkably effective in degrading organic contaminants, the presence of toxic metal compounds is a more problematic issue, because these compounds cannot be destroyed. The major concern with respect to these compounds is their potential for bioaccumulation in the flora and fauna of the system. In particular, the possibility of these contaminants impacting the wildlife that will likely use the area must be considered. The hypothesis behind this project is that sequestration of metal compounds in the sediment will make them essentially bio-unavailable, and thus reduce the overall ecological hazard of the site. To prove this hypothesis; however, it is necessary to gain a better picture of the speciation of metal compounds in a wetland system.
This wetland system will help to remediate the site and remove the danger of contaminant migration offsite. Before this is complete, sampling experiments will be conducted in existing wetlands surrounding the site that have been impacted by similar pollutants. This sampling will determine the speciation and associations of trace metals, and will assess their bioavailability to establish the validity of the above hypothesis. An important feature of this research is to further the use of nondestructive analytical methods that allow the determination of oxidation states, mineral phases, and contaminant associations of metal contaminants in natural samples without chemical extraction. Sampling will include the use of three state-of-the-art techniques to examine particulate-associated contaminants and metal complexing in the aqueous phase: transmission electron microscopy/energy dispersive x-ray spectrometry, x-ray absorption fine structure, and voltammetry. In addition, kinetic experiments will be conducted to determine the long-term stability of trace metal precipitate phases.
The results of this research project will be used to assess the potential for the system to sequester trace metal contaminants from accumulating in the biota. Preliminary work is in progress to assess the distribution of contaminants at the proposed wetland site and to design the wetland system. Kinetic studies are being carried out on a laboratory scale using a flow through reactor system designed for this project. Samples from other similarly contaminated sites have been used to assess and modify the sampling procedure and methods. The first sampling trip is planned for April 1999, at two sites bordering the proposed wetland site.