Toxicology may be defined as the study of interaction of physical and chemical agents with a biological system and depiction of adverse response. The ever increasing human population, industrialization, technological advancement and urbanization have resulted in the degradation of environment through the release of large quantum of a variety of toxicants become a global phenomenon. In recent past the scope of toxicology has been widely expanded by the amalgamation of all biological system. The field of toxicology is supported by various disciplines such as physiology, pathology, biochemistry, analytical chemistry, organic chemistry, cell biology and molecular sciences. The text has been compiled to deals with the effects of heavy metals exclusively on consumers, aquatic animals and the environment. The study of heavy metals their routes of entry, absorption, distribution, elimination, transformation and their dynamics with in aquatic crustaceans and fishes have been clearly dealt with in this text. The author expresses his deep sense of gratitude and indebtedness to Lambert Academic Publishers for publishing his research work in form of monograph.