Susan E. Kegley and Laura J. Wise
The presence of pesticide residues in the food supply is an undeniable fact of life in our society. Pesticide use presents both risks and benefits that provide ample fodder for argument about the wisdom of our existing agricultural practices. With the evolution of technology to both detect pesticide residues and measure their effects on humans and animals, chemists have played an important role in defining the extent of the problems and some potential solutions. This three to four week laboratory module presents the practice of risk assessment in the context of pesticide use and introduces the student to the the role of the chemist in the process.
The chemical concepts covered in this module include structure/solubility relationships of organic compounds, gas chromatography, biodegredation, bioaccumulation, and organic extraction techniques. The full module can be carried out in four weeks, with the final week of the module used for a debate on pesticides in the food supply. This experience provides the student with the opportunity to grapple with the problem of balancing the risks and benefits of using organochlorine pesticides and presents an opportunity to explore the interface of science and society.
This module has been tested for seven semesters in a first semester general chemistry course at the University of California, Berkeley in special laboratory sections focusing on environmental chemistry. Student response to the module has been overwhelmingly positive, with many students commenting that the knowledge gained has had a significant impact on their day-to-day lives. The module could also be used in an organic laboratory course, since it covers traditional organic topics.
This module has also been used in an upper-level instrumental methods of analysis course. More advanced students are able to delve deeper into the theory and practice of gas chromatography, determining response ratios and retention times for different pesticides and designing an effective temperature program that permits separation of all components of a pesticide mixture. The extraction efficiency of selected pesticides can be tested by processing a spiked sample.
A detailed instructor's manual, complete with instrument parameters, supplier information, stockroom prep lists, pre-lab lecture notes, evaluation data on the debate from the UC Berkeley class, and transparency masters, is available to provide assistance to faculty in carrying out this non-traditional experiment.
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