Chemical products pervade modern society, and furnish unprecedented wealth and comfort to citizens of countries with industrialized economies. Demand for products such as pesticides, industrial chemicals, flame-retardants and additives for consumer products requires large scale production and distribution of these chemicals, and they are inevitably released into the environment. Responsible management of chemicals therefore requires a quantitative understanding of amounts released, how the chemicals partition and travel in the environment, and how they might expose and thus adversely affect human and ecological populations. This seminar will present modeling tools that confront this challenge by improving our ability to understand and predict the sources and fate of chemical substances in the environment and their potential impacts on human and ecological populations. Case studies will be presented of exposure and impact assessment on local, regional, continental and global scales, including 1) A model of mercury sources and fate in the San Francisco Bay area, 2) An examination of the relationship between residence time in the environment and potential for population level exposure expressed as Intake Fraction (iF), 3) Continental-scale assessment of contaminant fate and human exposure in North America using the BETR North America model, and 4) A new global-scale multimedia contaminant fate model that utilizes data from a climate model.--The seminar will be presented by Matt MacLeod, who is concluding a two-year appointment at the Lawrence Berkeley National Lab as a visiting post-doctoral fellow under the supervision of Dr. Thomas E. McKone.