Polycyclic aromatic compounds (PACs), encompassing polycyclic aromatic hydrocarbons (PAHs) and their heteroatom-containing analogues, are well-known environmental contaminants. The 16 priority PAHs proposed by the U.S. Environmental Protection Agency (U.S. EPA) have long been the targets of environmental screening and toxicity studies, but there is growing awareness of the potential for thousands of additional PACs to be found within the environment and advanced analytical methods are required. A study of a River Thames estuary sediment core has offered an opportunity to investigate the local history with respect to anthropogenic contamination.
Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) offers the very highest levels of resolving power and mass accuracy, which makes it well-suited to the characterization of highly complex mixtures. In the present study, a Chiswick Eyot sediment core (River Thames, London) was collected and 8 organic extracts were produced, representing a period of approximately 80-90 years. The organic extracts were analyzed using atmospheric pressure photoionization (APPI) coupled to a 12 T solariX FTICR mass spectrometer, where APPI affords the ability to ionize non-polar components. The approach represents untargeted screening of both anthropogenic and natural organic matter in the sediment core. Following APPI FTICR MS experiments, complex data sets were analyzed using DataAnalysis (Bruker Daltonik GmbH), Composer (Sierra Analytics) for molecular formula assignments, and KairosMS, which is in-house software used for data visualization and comparison.
Plots of double bond equivalents (DBE) versus carbon number, as well as calculations of aromaticity indices, revealed insights into the PACs in the Chiswick Eyot sediment core. In addition to PAHs, PACs with heteroatoms such as oxygen, sulfur, nitrogen, and chlorine were detected, the latter of which represents an emerging contaminant class. The findings have been examined in combination with complementary analytical methods and within the context of historic energy usage.
Approximately 1600 PAC molecular components were detected at the core depth corresponding to the 1950s, a decade notable for the coal-induced Great Smog of London event. There was a steady decline in numbers of PAC molecular components when moving up through the decades to modern times. Finally, the trends for the U.S. EPA priority PAHs were also considered in comparison to the numbers of PAC molecular components detected via APPI FTICR MS.
