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Title:Fate of polycyclic aromatic hydrocarbons associated with coal-tar pitch, asphalt, charcoal, and soot in urban lake sediments
Author(s):Boyd, Victoria H
Director of Research:Werth, Charles J.
Doctoral Committee Chair(s):Nguyen, Thanh H.
Doctoral Committee Member(s):Mahler, Barbara J.; Plewa, Michael J.; Van Metre, Peter C.
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Polycyclic aromatic hydrocarbons (PAHs)
Fate and transport
Carbonaceous materials
Abstract:The concentrations of polycyclic aromatic hydrocarbons (PAHs) in urban lake sediments have increased significantly over the past several decades. Increased PAH loadings have been correlated with urbanization, and carbonaceous materials (CMs) such as coal tar and asphalt sealcoat and soot. PAH concentrations in urban lakes are often above sediment quality guidelines which have been identified as harmful to aquatic life. A better understanding of the fate of PAHs bound to these CMs in lake sediment is needed in order to assess the risks to aquatic life in urban lakes sediment. The objectives of this work were to 1) Determine whether PAHs associated with CMs redistribute to more strongly sorbing CMs in sediment or are lost to the water column. 2) Determine the rates at which PAHs are redistributed to CMs and sediments or are lost to the water column. 3) Determine the relative importance of kinetic compared to equilibrium sorption on PAH redistribution in CMs and sediment. To address these objectives, the redistribution of PAHs between CMs and sediment was measured in a series of controlled, well-mixed laboratory experiments as well as a two year in situ field study. In both studies particles of coal-tar pitch, asphalt, charcoal, and soot were created and loaded with deuterated PAHs as tracers (dPAHs). Each type of particle was loaded with a unique series of dPAHs of varying molecular weight and Kow. The particles were then mixed with sediment and the redistribution among materials was measured over time. In the well-mixed laboratory experiments, samples were loaded into serum bottles and rotated on a bottle roller at 5 rpm for up to 90 days. Samples were taken at designated time intervals in order to measure changes in redistribution with time. The in situ field studies involved loading sediment and CMs into sample cores, pushing the sample cores into the top layer of lake sediment, and retrieving cores from the lake over a 2 year period. A PAH redistribution model was created incorporating mass transfer kinetics and thermodynamic equilibrium sorption. The model was fit with the results from the well-mixed laboratory experiments and apparent mass transfer coefficients for materials were determined. The modeling results were used to help interpret both laboratory and field data. The results of both the laboratory and field studies show dPAHs associated with coal-tar pitch, asphalt, charcoal, and soot are mobile in the sediment, moving in significant amounts to other CMs and sediment. Low molecular weight dPAHs associated with coal-tar pitch and asphalt sealcoat were found to account for the majority of dPAH transport between materials. These low molecular weight dPAHs are also more toxic. Therefore, the findings from this work indicate lakes with large runoff from seal-coated pavement may be at elevated risk to aquatic life. These findings also indicate that a significant portion of the risk associated with CM bound PAHs in sediment can be mitigated by reducing sealcoat use. The results of the laboratory study show that the kinetics of sorption can result in different trends at early times compared to those at equilibrium. Materials that are considered less strongly sorbing, such as asphalt and sediment, had a large effect on sorption trends at early times. More strongly sorbing materials, like charcoal, started to account for the majority of sorption at later times. These findings show the importance of considering both kinetic and thermodynamic distribution when determining PAH mobility and associated risks. Results from the redistribution model show redistribution to strongly sorbing CMs does occur, but can take decades or more. Therefore, natural attenuation may not mitigate PAHs in sediment on an adequate time scale and active remediation may be needed. Although this project is focused on one lake, studies have shown coal-tar pitch, asphalt, and soot significantly contribute to PAH loading in many urban lakes across the U.S., thereby making the results of this work applicable to other locations.
Issue Date:2017-06-30
Rights Information:Copyright 2017 Victoria Boyd
Date Available in IDEALS:2017-09-29
Date Deposited:2017-08

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