Microscale Location, Characterization, and Association of Polycyclic Aromatic Hydrocarbons on Harbor Sediment Particles

Complementary mass spectrometric and spectroscopic techniques were employed to provide direct information at the microscale on the sequestration of polycyclic aromatic hydrocarbon (PAH) contaminants in Milwaukee Harbor sediment particles. Microprobe two-step laser desorption/laser ionization mass spectrometry was used for PAH measurements, infrared microspectroscopy was used for organic carbon measurement, and scanning electron microscopy with wavelength dispersive X-ray spectroscopy was used for elemental microanalysis. PAH concentrations on coal- and wood-derived particles were found to be several orders of magnitude higher than on silica particles. A cryomicrotome sectioning procedure was employed for particle cross-sectional investigations, and it was found that most PAHs are concentrated on external surface regions indicating near surface sorption mechanisms. The coal/wood-derived particles constitute only 5% of the sediment by weight but contain 62% of the total PAHs. The remaining 38% are mainly in a clay and silt fraction. PAH desorption kinetic studies on these separated fractions revealed a relatively low availability of PAHs from the coal/wood fractions and a high availability from the clay/silt fraction. Additionally, these PAH-bearing coal/wood-derived particles may be removed by density separation from heavier clay, silt, and sand.