Associations of polycyclic aromatic hydrocarbons (PAHs) with urban stream sediments

Polycyclic aromatic hydrocarbons (PAHs) in urban runoff can occur both in soluble and particulate-associated forms. Because of their low volatility (low Henry's Law constant), high octonal-water partition coefficients (K OW), and high soil organic coefficients (KOC), many of the PAHs are preferentially adsorbed to particulate matter. As part of this research, fugacity based partition calculations were performed to identify the percentage of associations of selected PAHs with different phases in the aquatic environment under equilibrium conditions. The partition prediction calculations showed higher associations of PAHs with sediments than in the liquid portion or in the air, especially for high molecular weight PAHs.;PAH analyses in environmental samples are challenging because of the relatively low concentrations and the complexity of the mixtures in the samples. Most of the available standard procedures are time-consuming, manual-work-oriented, and require large amounts of organic solvents. As one of the objectives of this research, the researcher developed a faster and less labor-intensive analysis procedure by using a thermal desorption techniques for analyses of selected PAHs in environmental sediment samples.;Understanding the association of contaminants with different particle sizes is important for determining the most effective treatment of runoff. The composition of the sediment (organic matter and other litter vs. inert soil) may effect the association of PAHs with the sediment. The sediment material composition is likely affected by contributing source areas. One of the goals of this research work was to quantify the material compositions, associated chemical oxygen demand, and associated PAH concentrations in size-fractionated sediment samples collected from three different creeks. The sediments at these creeks were affected by runoff from different major land use source areas. Overall, the PAH concentrations were found to be affected by sediment particle sizes and sampling location. The large organic material component of the sediments was found to have higher concentrations of PAHs when compared to other sediment sizes. Contamination by hydrocarbons at one of the sampling sites also affected the observed PAH concentrations, especially for small particles.