The large volume of crude oil released into the Gulf of Mexico by the Deepwater Horizon (DHW) accident has raised considerable concerns over potential ecosystem impacts. The dispersion of harmful oil components into the ocean waters could pose long term risks to flora and fauna. One of the main concerns focuses on polycyclic aromatic hydrocarbons (PAHs). Since several PAHs are toxic and a subset exhibit carcinogenic activity, the exposure of human populations to hazardous concentration levels may lead to unreasonable health risks. Particular attention has been paid to the sixteen PAHs currently listed as priority pollutants by the Environmental Protection Agency (EPA). Their chemical structures consist of two or more un-substituted benzene rings with molecular weights (MW) ranging from approximately 128 to 278 g mol-1. Since their toxicity varies widely depending upon the isomer, data on total PAH levels is not particularly useful in determining human health risks. It is important to determine the most toxic PAHs unambiguously, even if they are present at much lower concentrations than their less toxic isomer
This proposal tackles a different aspect of PAHs analysis as it focuses on detection and characterization of higher-molecular weight PAHs (HMW-PAHs), i.e. PAHs with MW equal or higher than 302 g mol-1. The HMW-PAHs isolated from environmental and combustion-related samples exhibit mutagenic activity and petroleum transformation products from HMW-PAHs persist in the environment longer than their lighter counterparts. Studies have shown significant sedimentation of HMW-PAHs that may be increased with the addition of dispersants in a coastal setting. Their continued monitoring will ensure that HMW-PAHs present in sediments are not being redistributed and accumulating through the food chain.
Individual isomers of HMW-PAHs are not routinely identified or quantified. Difficulties in the determination of HMW-PAHs arise from their low concentration levels in environmental samples compared to those of the priority pollutant PAHs. The number of isomers increases dramatically with each additional aromatic ring, which makes separation and identification difficult by gas chromatography-mass spectrometry and liquid chromatography. Finally, there are still only a limited number of commercially available reference standards for HMW-PAHs, which hinders their identification and quantification. Since their carcinogenic properties can vary by orders of magnitude from one isomer to another, conclusions drawn from risks assessment studies could be seriously in error if the analytical characterization techniques cannot distinguish isomers.
The development of a robust approach with the ability to efficiently and reliably detect and quantify specific isomers of HMW-PAHs would be a significant analytical breakthrough. The goal of this proposal, then, is to fulfill this gap. The specific research goals are the following: (a) unambiguously determine HMW-PAHs with MW 302 in complex environmental extracts from the Gulf of Mexico using the multidimensional laser excited time-resolved Shpol’skii spectroscopy (LETRSS) technique; (b) synthetize pure standards of MW 302 currently unavailable from commercial sources; and (c) extend the developed approach to the analysis of specific isomers of HMW-PAHs with MW > 302 including alkylated PAHs (APAHs) and sulfur containing PAHs (PASHs). When compared to un-substituted PAHs, APAHs comprise a relatively large fraction of the total number and mass of PAHs found in crude oil and crude-contaminated seafood samples. Sulfur is the principal heteroatom in coal, crude oil, tar and their by-products. Thus, to fully understand the environmental implications of the DWH accident, the ideal technique should be able to determine isomers of APAHs and PASHs
Through collaborations with other scientists involved in the Gulf of Mexico Research Initiative, this proposal will provide environmental scientists will the ability to track down specific PAH isomers and fully understand their environmental fate in the Gulf of Mexico.
Project Research Overview (2016):
An overview of the proposed research activities from the GoMRI 2016 Meeting in Tampa.
Direct link to the Research Overview presentation.