Environmental toxicology is the study of the action of chemicals upon ecosystems. Understanding the effects of exogenous chemicals upon the inhabitants of an ecosystem may enable us to predict and possibly prevent their harmful effects. This textbook provides an insight into all the major areas of environmental toxicology, including the Introduction and Scope of Toxicology, History of Toxicology, Environmental Toxicology, Heavy Metals, Pesticides, Radioactive Substances, Nanotoxicology, Toxicogenomic, Exposure of Toxicants, Dose-Response Relationship, Translocation of Toxicants, Mechanism of Action of Toxicants, Toxic Effects, Selective Toxicity, Factors Affecting Toxicity, Bioaccumulation of Xenobiotics, Toxicity Tests, Specific Toxicity Tests, Carcinogens, Safety Evaluation of Chemicals, Antidotal Therapy. It is written in a formal, accessible style with many environmental issues taken from the author's personal experience. It will provide students and other interested individuals with a broad overview of the science of environmental toxicology.