ABSTRACT
Modern technology has brought a dramatic increase in the production and consumption of chemicals. In order to estimate the environmental exposure of a chemical it is necessary to understand how materials are transported and transformed as they move from their point of entry to their final resting place. For example, the segment depicted by the pelican and the fish represents the food chain and indicates how chemicals may move from the source to the water to the fish and ultimately to the top of the chain symbolized by the pelican. However, for most environmental questions it suffices to assume that the fish is a single homogeneous compartment and to ignore the complex physiological events that are taking place within the organism. The system is constructed from seven base units plus two supplementary units from which all other quantities may be derived. The chapter also presents an overview of the key concepts discussed in the subsequent chapters of this book.
