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 po lycyclic aromatic hydrocarbon (PAH) contaminants in Milwaukee Harbor sedime nt particles. Microprobe two-step laser desorption/ laser ionization mass s pectrometry was used for PAH measurements, infrared microspectroscopy was u sed for organic carbon measurement, and scanning electron microscopy with w avelength dispersive X-ray spectroscopy was used for elemental microanalysi s. PAH concentrations on coal- and wood-derived particles were found to be several orders of magnitude higher than on silica particles. A cryomicrotom e sectioning procedure was employed for particle cross-sectional investigat ions, 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 t he total PAHs. The remaining 38% are mainly in a clay and silt fraction. PA H desorption kinetic studies on these separated fractions revealed a relati vely low availability of PAHs from the coal/ wood fractions and a high avai lability from the clay/silt fraction. Additionally, these PAH-bearing coal/ wood-derived particles may be removed by density separation from heavier cl ay, silt, and sand.