Utilizing polymer-coated vials to illustrate the fugacity and bioavailability of chlorinated pesticide residues in contaminated soils

Authors: ANDRADE, NATASHA - University Of Maryland; McConnell, Laura; TORRENTS, ALBA - University Of Maryland; Hapeman, Cathleen

Submitted to: Journal of Chemical Education
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2013
Publication Date: 3/1/2013
Citation: Andrade, N.A., Mcconnell, L.L., Torrents, A., Hapeman, C.J. 2013. Utilizing polymer-coated vials to illustrate the fugacity and bioavailability of chlorinated pesticide residues in contaminated soils. Journal of Chemical Education. 90:479-482.

Interpretive Summary: This work describes a laboratory experiment that can be used in environmental chemistry courses to illustrate key concepts related to the study of contaminant behavior in the environment. It describes a method recently utilized in our laboratory to examine the fate of pesticides in a historically contaminated orchard. The method uses small glass vials coated on the inside with a thin film of polymer. The polymer has properties similar to a biological matrix or organism. The contaminated soil is placed inside the vials and left to incubate over time. The contaminant migrates from the soil into the film such as an organism may become contaminated in soil that contains pollutants. The soil is removed and the pesticides are extracted from the film and analyzed. The results can be used to carry out calculations related to a concept called fugacity whereby a contaminant is distributed among different environmental compartments like air, water and soil according to the properties of the compartments and the contaminant. Results can also be used to compare the potential for different contaminants to be bioaccumulated into organisms. This work may be useful for instructors to connect students with a real world environmental problem and important environmental chemistry concepts.

Technical Abstract: Fugacity and bioavailability concepts can be challenging topics to communicate effectively in the timeframe of an academic laboratory course setting. In this experiment, students observe partitioning of the residues over time into an artificial biological matrix. The three compounds utilized are ones commonly found in historically contaminated sites: 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane, commonly known as DDT, 1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethyl]benzene (DDD), a contaminant present in the DDT formulation, and 1,1-bis-(4-chlorophenyl)-2,2-dichloroethane (DDE), the primary degradation product of DDT. A known quantity of the three compounds is spiked and mixed into soil to simulate environmental pollution. The soil is then placed in replicate glass vials coated on the inside with a thin layer of polymer to mimic contact between the soil and an organism such as an earthworm. Over different time points, the soil is removed from the vial and the polymer film is extracted with solvent and analyzed by gas-chromatography-mass spectrometry (GC-MS). The concentration gradient across the soil/polymer interface and the hydrophobic nature of the compounds drives the residues into the polymer film to achieve equilibrium, illustrating the concept of fugacity. The accumulation of the pesticides into the polymer layer also provides an example of how contaminants can be accumulated into soil-borne organisms. This experiment provides experience to basic analytical chemistry techniques such as the proper handling of solvents, the use of syringes and rollers, as well as the handling of a common analyzed environmental matrix (soil) and quantitative analysis of contaminants using GC-MS. This experiment demonstrates a direct application of a current research project experiment to the teaching of fugacity and bioavailability, and a number of variations on this experiment such as the comparison of soils with differing properties or the use of additional contaminants can also be utilized for more advanced laboratory courses.