Model development for evaluating remediation of contaminated sediments: PCBs and PBDEs as cases for halogenated hydrophobic organics

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2016
Karakaş, Filiz
Understanding fate and transport (F&T) of halogenated hydrophobic organic compounds (HOCs) in sediments is a major concern and is imperative for their sound environmental management. This study aims to model the F&T of HOCs in sediments as individual compounds, and by taking into account anaerobic dehalogenation (AD). For this purpose, F&T of hydrophobic pollutant (FTHP) model is developed. As distinct from the literature, this model predicts future concentration of HOCs both as individual compounds and as total, by taking into account AD, as well as other relevant F&T mechanisms. AD rate constants (km) of pathways are estimated by modifying a previously developed model as Anaerobic Dehalogenation Model. The range of km for PCBs and PBDEs estimated using laboratory studies of Baltimore Harbor contaminated sediments, USA, and of contaminated soil from Guangdong province, China, are between 0.0001 – 0.129 d-1 and 0.001 – 0.024 d-1, respectively. The median of estimated km are found to be comparable to the few available rate constants published in the literature. The FTHP model is applied to sediments of Lake Michigan and San Francisco Bay, USA, contaminated by PCBs and PBDEs, respectively. FTHP model calibration, validation, sensitivity and uncertainty analyses are performed for most of the congeners with satisfactory results. Goodness of fit results of model calibration is found to be comparable or better than those of similar models in the literature. For PCBs, future projection scenarios indicate reduction of toxicity – and the model is able to pinpoint which scenarios would better reduce toxicity, as individual toxic congener concentrations can be modeled. Similarly, for PBDEs, the bioaccumulation potential of sediments is found to be decreased through bioaugmentation. Total contaminant concentrations, however, can only be reduced by dredging. On the other hand, predicting bioremediation with FTHP model enables the user to evaluate toxicity changes through the time course of bioremediation, as toxic congeners are produced/reduced via individual AD reactions. Overall, systematic identification and quantification of AD pathways coupled with congener specific modeling can aid remediation efforts such that congener specific monitoring/enhancement of bioremediation could be possible for sediment-bound HOCs.

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Citation Formats
F. Karakaş, “Model development for evaluating remediation of contaminated sediments: PCBs and PBDEs as cases for halogenated hydrophobic organics,” Ph.D. - Doctoral Program, Middle East Technical University, 2016.