Microbial degradation of dissolved organic matter (DOM) and its influence on phenanthrene–DOM interactions

Microbial degradation-induced changes in the characteristics of dissolved organic matter (DOM), and the subsequent effects on phenanthrene–DOM interactions were investigated based on the microbial incubation of DOM collected from four different sources for 28 d. Partially biodegraded DOM presented higher specific UV absorbance (SUVA), lower protein-like fluorescence, higher humic-like fluorescence, lower aliphatic carbon fraction, and higher hydrophobic neutral fractions compared to the original DOM. Microbial changes in DOM led to an increase in the isotherm nonlinearity as well as the extent of phenanthrene binding. A negative relationship between SUVA and the Freundlich n values was established for the original and the biodegraded DOM, suggesting that aromatic condensed structures may play important roles in providing nonlinear strong binding sites irrespective of microbial degradation. In contrast, there were two separate slopes of the correlations between the percentage of hydrophobic acid (HoA) fraction and the n values for the original and the biodegraded DOM with a higher slope exhibited for the latter, implying that the microbial utilization of oxygen-containing structures in the HoA fractions may contribute to enhancing the associated isotherm nonlinearity.

► Microbial changes in DOM led to the increase in the isotherm nonlinearity.
► Aromatic condensed structures of DOM appear to provide strong specific binding sites.
► Microbial utilization of oxygen-containing HoA structures may contribute to enhancing the isotherm nonlinearity.