Technical Abstract: This study investigated the effects of redox-active and iron-coordinating functional groups within natural organic matter (NOM) on the electron transfer interactions between Fe(II) and 2,4-dinitrotoluene (2,4-DNT), an energetic residue often encountered in aqueous environments as a propellant component and impurities in 2,4,6-trinitrotoluene (TNT). Experiments were first conducted in homogeneous phases as a function of pH in the presence of ligands that (1) complex iron (e.g., citric acid, oxalic acid), (2) complex and reduce iron (e.g., caffeic acid, ascorbic acid), and (3) humic substances with known carboxyl content and electron transfer capacity. Then, effects of these NOM components on Fe(II) reactivity in heterogeneous media were investigated by introducing goethite. Our results indicate complex catalytic and inhibitory effects of NOM components on the reaction between Fe(II) and 2,4-DNT, depending upon the ability of NOM component to (1) reduce dissolved and particulate Fe(III) (e.g., ascorbic acid), (2) form kinetically labile dissolved Fe(II) reductants (e.g., tiron and caffeic acid), and (3) produce surface-associated Fe(II) species that are accessible to 2,4-DNT.