Environmental Forensics: Employing 2-Dimensional Gas Chromatography/Mass Spectrometry (GCXGC/MS) to Predict Environmental Weathering of Oil and Tar

Poster Presentation

Prepared by N. Wilton, A. Robbat, Jr. , P. Antle
Tufts University, 62 Talbot Ave, Chemistry Department, Medford, MA, 02155, United States

Contact Information: [email protected]; 617-584-5041


Pollution from petroleum sources and coal tar is the result of naturally occurring and unintended seepages; collection, transport, storage and manufacturing activities; and from incomplete combustion sources. When these products are released into the environment, they are subject to a number of weathering factors. These process include physical (evaporation, adsorption, dissolution, and emulsification), biological (microbial degradation), and chemical (photo- and oxidative degradation), all of which can significantly change the chemical composition of the source material over time. Understanding how local environments impact weathering is critical to determining whether local ecosystems are capable of remediation, i.e., the natural attenuation of pollution effects. Because site-specific weathering processes dramatically change the chemical composition of these complex mixtures, even at the isomer level, it is important to assess these changes as a function of each component’s physical and chemical properties. Once known, this information can be used to determine if natural attenuation is sufficient to reduce pollutant impact on the environment or if active remediation is required. To make this determination, the compositional effects of dissolution, organic phase partitioning, and evaporation must be known; each of which can be examined by studying the aqueous solubility (SW), octanol-water partition coefficient (KOW), and vapor pressure (VP) of sample components, respectively.

A novel approach for estimating these physical properties from comprehensive 2-dimensional gas chromatography/mass spectrometry (GC×GC/MS) retention data is presented. A polyparameter linear free energy relationship (LFER) model was developed to correlate each compound’s retention index with the aforementioned physical properties. The model employs isovolatility curves to generate accurate and precise retention indices for families of homologous compounds, leading to better estimates of their physical properties. Findings indicate that the physical property estimates produced by this approach have the same error on a logarithmic-linear scale as previous researchers’ log-log estimates, yielding marked improvement in their property estimates.. A new software program was developed that automates the determination of these properties for each compound in the sample from a single GC×GC analysis of that sample. This process produces component maps that we use to discern the mechanism and progression of how a particular site weathers due to dissolution, organic phase partitioning, and evaporation resulting from local conditions. Outcomes support hazardous waste site investigation and cleanup projects by providing quantitative data of pollutants by GC×GC/MS. This approach can be used by researchers in a wide range of disciplines, including toxicology (bioaccumulation and toxicity studies) and restoration (ecological and urban planning studies).