Microbial transformation of intracellular dissolved organic matter from Microcystis aeruginosa and its effect on the binding of pyrene under oxic and anoxic conditions.

The environmental behaviour and the bioavailability of polycyclic aromatic hydrocarbons (PAHs) are strongly affected by dissolved organic matter (DOM) in aquatic environments. In this study, we investigated the dynamics of the bioavailability and character of the intracellular DOM (IDOM) from Microcystis aeruginosa (M. aeruginosa-IDOM) during 10 days oxic and anoxic incubations by spectroscopy. Subsequently, the binding affinity of pyrene with the initial/altered M. aeruginosa-IDOM was estimated by fluorescence quenching method. The incubation results indicated that changes in dissolved organic carbon (DOC) concentration and selected spectral descriptors of the M. aeruginosa-IDOM under oxic condition were different from those of anoxic condition. The microbial transformation of the M. aeruginosa-IDOM resulted in an enhancement of the organic carbon-normalized binding coefficient (K DOC) of pyrene in both oxic and anoxic treatments. Moreover, only for the oxic condition, Pearson correlation analysis demonstrated that aromaticity (specific UV absorbance at 254 nm, SUVA254), humification degree (humification index, HIX) and the percent distribution of humic-like component 2 (%C2) presented significantly positive correlations with the pyrene K DOC, while the percent distribution of protein-like component 1 (%C1) exhibited a negative correlation with the K DOC. However, no significant correlation was observed between any spectral descriptor and the K DOC under anoxic condition. This result suggested that the binding affinity of pyrene may be primarily influenced by the altered M. aeruginosa-IDOM characteristics associated with the biological transformation. Hence, our results provided potential evidence for resolving the inconsistency in the relationships between DOM characteristics and the binding affinities of PAHs.