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(598) "GOOD" AND "BAD" PAHS: A MATTER OF ASSOCIATION?
Hickey, Christopher*,1, Ahrens, Michael1, Depree, Craig1, 1 National Institute of Water and Atmospheric Research (NIWA), Hamilton, New Zealand
ABSTRACT- Sediment concentrations of polycyclic aromatic hydrocarbons (PAHs) in urban estuaries and harbours are expected to increase with continuing urban development. Presently, sediment PAH concentrations already exceed existing sediment quality guidelines in many locations. Nevertheless, PAH accumulation in benthic macrofauna (as observed in shellfish ('musselwatch') biomonitoring, for example) can often be several orders of magnitudes less than predictions based on equilibrium partitioning between pore waters and the fraction of sedimentary organic carbon (SOC). Recent evidence has shown that bioavailability of combustion-derived (pyrogenic) PAHs can be significantly lower than that of petroleum-derived PAHs. Furthermore, it has been suggested that extractability of PAHs strongly depends on the type of organic matter that they are sorbed to. We compared extractability of PAHs from a variety of natural and man-made organic carbon matrices, including bulk sediment organic carbon, peat moss, power plant fly ash, diesel soot, petroleum soot, carbon black and tire rubber. Artificial sediments were prepared from glass beads amended with equal weight percentages of different types of organic matter, and subsequently spiked and equilibrated with 14C-fluoranthene. Ensuing extraction with dichloromethane and sodium dodecylsulfate (SDS, used to mimic conditions of the digestive tracts of deposit feeding macrofauna) showed PAH extractability to differ by nearly two orders of magnitude depending on organic carbon matrix. Sediments from Auckland Harbor, New Zealand, had a PAH signature typical of pyrogenic origin (i.e. predominance of fluoranthene and pyrene, and a relatively low ratio of methyl-naphthalenes and methyl-phenanthrenes to non-alkylated PAHs) and a large fraction of 'black carbon' organic matter. Only 15% of the PAHs in these field-collected sediments were extractable by mild SDS solutions, suggestive of poor bioavailability to digestive uptake by benthic biota. Furthermore, density fractionation revealed over 75% of the total PAHs to be associated with the 'light' (<2.15 g/ml), organic matter fraction. These findings have significant implications for biomonitoring and the implementation of urban storm water mitigation programs.
Key words: PAH, sediment, bioavailability, digestion
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