Activated charcoal impregnated into each Scienceware® Disposable Charcoal Disks absorbs the volatile 35S radioactive component before it can escape from the Petri dish during metabolic labeling experiments. The sterile filter paper disks are saturated with activated charcoal. Prior to metabolic labeling, the disk is set in the top half of the 100mm Petri dish lid. Following the addition of the 35S - labeled compounds to the cell culture fluid, the Petri lid with the activated charcoal disk is placed over the bottom half of the Petri dish.