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The Influence of Ionic Strength on the Partition Coefficient of Polycyclic Aromatic Hydrocarbons and Dissolved Organic Matter

Hydrophobic organic pollutants (HOPs) are in general characterized by high toxicity, long environmental half-life and high bio-accumulation factors. Due to their hydrophobicity, HOPs tend to sorb onto particulates in natural aquatic environment and their degradation pathways and rates are altered with the change of the reaction media and the settlement of these particles. The influence of the dissolved organic matters (DOMs), termed as the third phase, on the sorption partition coefficient is observed because of their interactions with HOPs. This binding (between DOM and HOP) increases apparent solubility and mobility of the HOP and the sorption coefficient of HOP in aquatic system is reduced. On the purpose of obtaining data closer to the real world, many aquatic factors, such as the concentration and types of DOM, pH value and ionic strength, are studied intensively recently.
Nevertheless, it is difficult to clarify the influence of ionic strength because the relationship between binding constant of DOM-HOP and ionic strength is ambiguous in the literature. As such, by applying fluorescence quenching method, we investigate the influence of ionic strength on the partition coefficient (Kdom) of PAHs (phenanthrene¡Bpyrene)-humic acid (HA) system. Results show that the interaction of HA and cations is the primary factor in the variations of the partition coefficient. It is believed that, as cations reacting with specific binding sites on HA, the molecules' configuration of HA is changed and the binding mechanism of PAHs and HA is altered. A "four-stage variation model" is then proposed to explain the relationship between the ionic strength and partition coefficient. Therefore, a non-constant trend of ionic strength effect is resulted and is used to explain the controversial findings in the literature.
Furthermore, Mg++ is found to cause stronger effect than K+ owing to higher charge density. The introduction of Br- would complicate the fluorescence quenching mechanism of phenanthrene-HA system because it's a fluorescence quencher. However, effects of anions on the variation of Kdom are not as significant as cations in our system. The effects of ionic strength on the variation of Kdom for four humic acids are LHA¡ÖPHA¡]Peat humic acid¡^¡ÖSHHA¡]Summit Hill humic acid¡^¡ÖSRHA. Results from different humic acids indicate that the Suwannee River humic acid (SRHA) is not as sensitive as Leonardite humic acid (LHA) on the ionic strength effect because of lower hydrophobicity. The influence of ionic strength on the variation of Kdom for pyrene-HA system is also amplified because of pyrene's higher hydrophobicity compared with phenanthrene.
Date24 June 2000
CreatorsWang, Hui-Ling
ContributorsYeong-Tarng Shien, Jen-Fon Jen, Chon-Lin Lee, Wei-Hsien Wang
Source SetsNSYSU Electronic Thesis and Dissertation Archive
Detected LanguageEnglish
Rightsunrestricted, Copyright information available at source archive

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