Effect of pH on binding of pyrene to hydrophobic fractions of dissolved organic matter (DOM) isolated from lake water

In order to better understand the compositional and structural complexity of dissolved organic matter (DOM) macromolecules and provide mechanistic information on the binding of hydrophobic organic contaminants (HOCs) to DOM, we fractionated large amounts of lake water into three hydrophobic DOM-fractions. The variation of the partitioning coefficients (K _DOC) of pyrene at different pH levels was examined by florescence quenching titration. Results show that, relative to the more polar acidic DOM-fractions, the hydrophobic neutral fraction exhibits a higher sorption ability to pyrene. Generally, the sorption of pyrene to the three hydrophobic fractions is strongly pH-dependent. The K _DOC values of pyrene generally increase with decreasing pH levels, which is especially obvious in the sorption of pyrene to the fulvic acid fractions, suggesting that the binding is controlled by hydrophobic interactions. The mechanisms underlying the binding of pyrene to the hydrophobic fractions were also discussed. Our data are beneficial to further understanding the binding of HOCs to DOM and how it has been affected, which may result in more accurate predictions of K _DOC.