The report is an initial effort in the development of a program that allows the Public Health Service to maintain an active overview of chemical contaminants that are now, or are likely to be, present in the environment. To illustrate the methods of applying the approach, as well as to develop the base for considering eventually all possible hazards, five specific contaminant classes are selected for individual treatment in separate sections following the general discussions. These sections summarize the contamination potentials of mercury, vanadium, nickel, fluorocarbons, and pulp and paper production, respectively. (Author)