The need to develop a capability to evaluate the environmental effects of chemicals has arisen principally from these situations. The source of the chemical is identified and quantified, as are the distribution, transport and transformation processes whereby the response of individuals in the environment can be evaluated. Organism response can be assessed to some extent, using toxicological data and finally the effects of population, community and ecosystem considered. As a first step in understanding these processes the environment can be simplified by considering it to be derived into separate phases or compartments within which a chemical behaves in a uniform manner. Environmental issues are now matters for widespread public concern and among these the management of chemicals is a high priority issue. The bio-accumulation of chemicals in the environment by organisms is of particular importance. In general, organisms take up chemicals from two principal sources, directly from the ambient environment and from food.