Environmental pollution is caused by a wide range of chemicals released as a consequence of human activities. This book aims to identify major classes of pollutants and their environmental fate, before going on to consider the effects that they might have on individual organisms and ecosystems. The book progresses from the molecular basis of pollutant toxicity to consequent effects at higher levels of organization - cellular, whole organism, population, community and ecosystem.; The book defines ecotoxicology as the study of the harmful effects of chemicals upon ecosystems. It is an interdisciplinary subject which represents a synthesis of elements from the disciplines of chemistry, biochemistry, toxicology, physiology, population ecology and population genetics. In contrast to "classical" toxicology, the ultimate concern is for the effects at the level of populations and consequent effects at the level of populations.