Stable Carbon Isotope Ratio of Polycyclic Aromatic Hydrocarbons (PAHs) in the Environment: Validation of Isolation and Stable Isotope Analysis Methods

PAHs are an ever increasing concern as a stressor of marine ecosystems and an agent of degradation of the condition and health of marine resources. In an effort to more clearly identify and apportion sources of PAHs in the environment, new isolation and purification methods for compound specific isotope analysis were developed to more accurately measure the stable carbon isotope ratio of individual PAH compounds. Sample extracts were purified by various chromatographic and high performance liquid chromatographic (HPLC) techniques. These involve alumina/silica column chromatography, size exclusion column chromatography, and thin layer chromatography (TLC). Preservation of compositional and isotopic integrity through the isolation and purification procedures was confirmed. The developed isolation and isotope analysis methods were then applied to environmental samples to validate the methods. The isolates were analyzed for PAH content and stable carbon isotope ratios. The stable carbon isotope ratio was measured by GC/C/IRMS (Gas Chromatography / Combustion / Isotope Ratio Mass Spectrometry) and the results, along with quantitative compound distributions, were used to trace and apportion the sources of contaminants in actual samples.

Sediment samples from the Lake Union in Seattle and Antarctic Winter Quarters Bay (WQB) were analyzed for molecular and stable carbon isotopic compositions of PAHs to characterize their possible sources. PAH concentrations were measured by GC/MS. Analysis of PAH concentration data and molecular ratios indicated that the PAHs were mostly pyrogenic in the Lake Union and petrogenic in the WQB. Comparison of the data with that from reference sites demonstrated that the PAHs in the Lake Union sediments had quite different sources from that of the reference sites. Compound specific isotope analysis using GC/C/IRMS provided clear evidences for the unique source of the PAHs and suggested that the PAHs in the Lake Union were likely produced during the coal gasification processes, which lasted for 50 years until 1956.

This study confirmed the usefulness of the compound specific isotope analysis of pollutant extracts by GC/C/IRMS for source identification in the natural systems. GC/C/IRMS measurement of stable isotopic compositions for the purpose of tracing contaminants can be an effective alternative to traditional molecular methods.

More information is available at http://www-ocean.tamu.edu/~moonkoo/resume.html

Email: moonkoo@ocean.tamu.edu or mkkim@hanmail.net

Currently working on dioxin (PCDDs & PCDFs) analysis using HRGC/MS (High Resolution Gas Chromatography / Mass Spectrometry) at GERG, Texas A&M University.