Chapter OverviewStocks and flows become harder to track once they enter into living organisms, especially humans where severe restrictions exist on experimentation. What we don't know, and what we assume, become as important in understanding the risks environmental toxins pose to human health as what we are certain of. Humans have manipulated lead for centuries, although the amount of lead that humans mobilized increased dramatically with the addition of lead to paints and gasoline in the early to mid 20th century. Lead has been widely distributed in our environment; fascinating stories exist about the roles scientists played in assessing the wisdom of widely using lead.Today lead is banned from paints and gasoline (in some countries). In the U.S. the average levels of lead in the blood of children has declined dramatically. Still, in many urban areas, elevated levels of lead pose threats to the health of children. Questions of social justice abound. Asking students to learn about urban lead provides a good opportunity to introduce students to some of the basic factors that control the flow of materials. The chemical form in which lead appears is critical for predicting the extent to which it will be distributed in various compartments, including biological compartments where neurological and developmental damage is thought to occur. We also ask our students to return again to the notion of uncertainty as we talk to them about the basic approaches used in the developed world to assess risk. For this discussion, one of us (Austin) is deeply endebted to Professor Douglas Crawford-Brown whose approach to thinking about environmental risk is far more insightful than standard treatments of the subject. References to his work, as well as to other work on risk assessment, is provided in a sidebar |