Aquatic sediments are a repository and a long-term source to water and biota of hydrophobic organic contaminants. Insights on the management and treatment of persistent organic contaminants, such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons, and DDT began with particle and sub-particle-scale views of sediments from urban sites. We learned that most hydrophobic organic contaminants are concentrated on a small fraction of the sediment comprising coal and char-like particles and are not readily available to biota or the aqueous phase. This led to the new idea that adding activated carbon to the biologically-active sediment layer may achieve contaminant repartitioning and in-situ stabilization of persistent hydrophobic organic contaminants. We evaluated this concept in the laboratory using physicochemical measurements and biological uptake assessments with different organisms. Our laboratory tests with three different sediments show as much as 95% reduction in PCB bioaccumulation by clams and more than 99% reduction in aqueous PCBs depending on PCB homolog distribution and sediment composition. We are conducting field tests at a tidal mudflat adjacent to a former shipyard in San Francisco in which activated carbon will be mixed into the upper sediment layer to stabilize PCBs. Activated carbon addition may be appropriate for in-situ stabilization of low-level contamination, or as a follow-up in conjunction with dredging to manage residuals. This research demonstrates that modern analytical techniques and collaborations among engineers, chemists, and biologists can lead to important observations from nature, resulting in new approaches for sediment contaminant risk reduction and treating sediments in place without costly and controversial dredging.