Insights into reactive oxygen species formation induced by water-soluble organic compounds and transition metals using spectroscopic method

•The complexing ability and complexing stability of WSOCs and TMs significantly affected ROS generation.•The light absorption characteristics of WSOCs might be effected by the types and concentrations of TMs.•The aromatic acid-like component and fulvic acid-like components were major binding sites for TMs.•The π electron transfer in conjugate system played an important role for ROS generation.