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.