Fugacity and bioavailability can be used to facilitate students' understanding of potential environmental risks associated with toxic chemicals and, therefore, should be incorporated in environmental chemistry and science laboratories. Although the concept of concentration is easy to grasp, fugacity and bioavailability can be challenging topics to communicate effectively in the timeframe of an academic laboratory course setting. In the experiment reported here, students observed the partitioning of chemical residues over time from soil into an artificial biological matrix. The two compounds utilized here as examples are commonly found in historically contaminated agricultural sites: 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane (DDT) and 1,1-bis-(4-chlorophenyl)-2,2-dichloroethane (DDE). A known quantity of the compounds was spiked and mixed into soil, which was then placed in replicate glass vials coated with a thin layer of polymer to mimic contact between soil and an organism. The polymer was then extracted and analyzed by standard gas chromatography-mass spectrometry (GC-MS). The fugacity gradient across the soil-polymer interface and the hydrophobic nature of the compounds drive the residues into the polymer, illustrating the concept of fugacity. A number of variations of this experiment, such as the comparison of different soils or the use of different contaminants could also be utilized for more advanced laboratory courses. (Contains 4 figures.)