Incorporation of weathering in PAH source apportionment

Forensic Chemistry
Oral Presentation

Prepared by C. Tuit, J. Rominger
Gradient, 20 University Road, Cambridge, MA, 02138, United States


Contact Information: ctuit@gradientcorp.com; 617-395-5575


ABSTRACT

At urban sediment sites, urban run-off, a highly weathered mixture of both petrogenic and pyrogenic material, as well as fresher sources of petrogenic (e.g. fuel oil, motor oil, diesel) or pyrogenic (e.g. creosote, MGP tar) PAHs can all be significant sources of PAHs to sediments. It can be extremely difficult using standard fingerprinting techniques to distinguish the relative contributions of these sources in weathered sediments. Principal Component Analysis (PCA) and receptor modeling of various types are typically used at these sites for PAH source apportionment. Unequivocally attributing contamination to sources requires an understanding of both the site-specific source compositions and how those compositions may have been altered in the environment by mixing or weathering processes. PCA and receptor modeling assist in identifying source compositions and relative source proportions in samples with mixed sources; however, weathering processes can alter PAH source compositions in ways that can obscure mixing trends. To incorporate the effects of weathering into PAH source apportionment, we have developed a PAH weathering model to help predict how PAH source fingerprints will change during weathering at sediment sites. The model assumes that water washing is the dominant weathering process in sediments and equilibrium partitioning of PAHs based on individual octanol-water partition coefficients. The model can be used to identify weathered source signatures that may be more appropriate source compositions for PAH apportionment than fresh or literature source fingerprints. This technique has been applied to both petrogenic and pyrogenic dominated urban water way case studies.