Black carbon is a collection of carbon-rich nanoparticles that are ubiquitous in the environment. Black carbon plays a pivotal role in controlling the fate and transport of hydrophobic organic contaminants. The current dogma states that geosorbents such as black carbon can act as contaminant adsorption sites, and the adsorbed molecules are immobile and nonreactive. However, our data suggest that black carbon can serve as both an adsorbent and a mediator of redox reactions. We showed that molecules adsorbed to black carbon have dramatically higher reductive reaction rates. We hypothesize that this is because black carbon contains microscopic graphitic domains in its structure and thus can conduct electron and atomic hydrogen from a reductant to adsorbed contaminant molecules. This study will demonstrate the adsorptive and catalytic roles of black carbon and will attempt to elucidate the mechanism for black carbon-mediated degradation of organic contaminants. Experiments were conducted using graphite and soot as model black carbons to assess the reduction of black carbon-bound nitroaromatic and heterocyclic nitramine explosives in the presence of an environmentally relevant reducing agent, such as thiol and sulfide. Our presentation will demonstrate this previously unrecognized role of black carbon and will discuss the potential impact of natural and synthetic black carbon on the fate of organic contaminant in aquatic and terrestrial systems.