WA1 Biorestoration Strategies for Contaminated Sediments
256 Portland Ballroom
8:00 AM - 12:00 PM, Wednesday
() Assessing the Availability of Select Hydrophobic Organic Compounds from Geosorbents and Sediments using Thermal Programmed Desorption Mass Spectrometry.
Talley, J1, Nicholl, S1, 1 Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN, USA
ABSTRACT- There is widespread contamination of soils and sediments by various hydrophobic organic contaminants (HOCs) and remediation of these compounds often results in residual contamination that exceeds clean up standards. This has lead to an interest in determining if these residual contaminants are available for uptake by plants and organisms and pose a threat to human health and the environment (Kraaij et al., 2002; Tang et al., 1998). Research has established that HOC concentrations in soils and sediments found by exhaustive extraction methods may not be indicative of the concentrations available to microorganisms (Alexander, 2000, Kelsey et al., 1997) and that the availability tends to decrease with aging and treatment (Hatzinger and Alexander, 1995, Tang et al., 1998). This indicates that an understanding of the relevant sorption and desorption behavior of the solid-bound contaminant is essential. _CR__LF_ _CR__LF_In general, the strength or degree of the total sorption determines the physical availability of HOCs, their associated partitioning into the aqueous phase and subsequent uptake by microorganisms. Although bioavailability is often defined differently in various disciplines, it is generally agreed that one necessary component of the process is the release of a solid-bound contaminant (Ehlers, 2003). This release or physical availability can be linked to the energy required to release the compound from its sorbent matrix, with a higher energy value indicating a more tightly bound compound. In surface science and catalysis literature, this energy is called desorption activation energy and is often found using thermal program desorption mass spectrometry (TPD-MS) techniques. For this work, the term release energy is defined as the total energy required to release the compound from its sorbent matrix. Thus, it includes the energy required for desorption from and diffusion through the sorbent matrix. _CR__LF__CR__LF_This work focused on developing an analytical protocol and valid mathematical models that would make it possible to use TPD-MS as a stand alone tool to qualify and quantify the physical availability of PAHs on mineral geosorbents. Release energy values were calculated from TPD-MS thermograms using four desorption kinetics models: the non-linear fit method, the Arrhenius plot method, the Long and Yang method, and the Mingelgrin method. The TPD-MS techniques was also applied to several contaminated sediments to determine if the technique could be used as a tool for the initial qualitative analysis of the physical availability of PAHs in real sediment systems. It was found that the TPD-MS technique provided a qualitative assessment of the physical availability of PAHs on mineral geosorbents as well as contaminated sediments. The modeling methods resulted in different release energy values indicating the need for further study.
Key words: thermal desorption, availability, PAHs, PCBs