Hydroxyl radical alteration of HPLC fractionated lignin: Formation of new compounds from terrestrial organic matter

Reactive oxygen species (ROS) are thought to play an important, although poorly understood, role in modifying the composition of terrigenous-derived dissolved organic matter (tDOM) upon export to aquatic systems. Of the dominant ROS in natural systems, OH has been shown to substantially modify lignin under laboratory conditions, simulating processes responsible for transformation of DOM in natural waters. Utilizing high performance liquid chromatography (HPLC) in conjunction with ultrahigh resolution mass spectrometry, we examined HPLC fractionated lignin extracts in an effort to establish which fractionated components of the lignin extract were (i) most susceptible to attack by OH and (ii) most likely to be responsible for compounds observed in the DOM. The results indicate that the most polar components of the lignin extract, representing tDOM, could be responsible for a large portion of newly generated formulas observed within DOM in natural waters. This suggests that partially oxidized lignin may be readily altered to compounds observed in DOM which are not typically associated with terrigenous OM, such as alicyclic and condensed aromatic-like compounds.