The Toxics Geography Exercise was developed as an application-oriented exercise to develop skills in critical analysis in groups of undergraduate students from widely diverse academic backgrounds. Students use publicly available data on industrial activities, history of toxic material disposal, basic chemistry, regulatory approaches of federal and state agencies, and environmental policy theory to critique and evaluate public policy decisions and assess problems experienced by communities in our modern world where toxic substances are ubiquitous but very unevenly distributed across the United States. Developed after a collaboration of natural science, social science, and education faculty, it demonstrates the educational value of inquiry in science classes. The series of activities designed for this were developed to create a flow that involved students in analyzing their preconceptions, exploring data and expert literature, and finally synthesizing their learning. The entire process was structured using an instructional model known as Mental Model Building. (Contains 8 tables and 2 figures.)