Abstract
Fluorescence quenching (FQ) is extensively used for quantitative assessment of partition coefficients (KOC) of polycyclic aromatic hydrocarbons (PAHs) to natural organic materials - humic substances (HS). The presence of bound PAHs with incompletely quenched fluorescence would lead to underestimation of the KOC values measured by this technique. The goal of this work was to prove the validity of this assumption using an original experimental setup, which implied FQ measurements upon excitation into two distinct vibronically coupled electronic states. Pyrene was used as a fluorescent probe, and aquatic fulvic acid (SRFA) and leonardite humic acid (CHP) were used as the humic materials with low and high binding affinity for pyrene, respectively. Excitation of pyrene into the forbidden (S0-S1) and allowed (S0-S2) electronic states yielded two pairs of nonidentical FQ curves. This was indicative of incomplete quenching of the bound pyrene, and the divergence of the two FQ curves was much more pronounced for CHP as compared to SRFA. The two component model of fluorescence response formation was proposed to estimate the KOC values from the data obtained. The resulting pyrene KOC value for CHP (220 ± 20) g L(-1) was a factor 3 higher compared to the KOC value determined with the use of the Stern-Volmer formalism (68 ± 2) g L(-1). At the same time for aquatic FA the difference in FQ curves was almost negligible, which enables the use of the Stern-Volmer formalism for weakly interacting HS and PAHs.
Highlights
Interactions of polycyclic aromatic hydrocarbons (PAHs) with natural organic matrices, e.g. humic substances (HS), are of serious environmental concern due to the multiple adverse effects of these hydrophobic contaminants on living organisms.[1,2,3] Binding to HS causes an increase in mobility and a change in the bioavailability and toxicity of PAHs.[4,5,6] To quantify and prognosticate these effects, partition coefficients (KOC) of PAHs to HS are used for geochemical and ecotoxicological modeling
We propose an original experimental setup to acquire fluorescence quenching (FQ) measurements, which could enable observation of pyrene bound to HS
Two humic materials were used in our studies: the aquatic fulvic acid (SRFA) with a high content of oxidized polar moieties, and the leonardite humic acid (CHP) with a high content of poorly-oxidized aromatic and aliphatic moieties
Summary
Interactions of polycyclic aromatic hydrocarbons (PAHs) with natural organic matrices, e.g. humic substances (HS), are of serious environmental concern due to the multiple adverse effects of these hydrophobic contaminants on living organisms.[1,2,3] Binding to HS causes an increase in mobility and a change in the bioavailability and toxicity of PAHs.[4,5,6] To quantify and prognosticate these effects, partition coefficients (KOC) of PAHs to HS are used for geochemical and ecotoxicological modeling.
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Schedule a callMore From: Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology
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