The study of the adverse effects of chemical and physical agents on living organisms. Toxicology has also been referred to as the science of poisons. Since about 1970, there has been a substantial increase in the understanding of biological systems and the way in which chemicals can interfere with the proper functioning of such systems. At the same time, there has been a tremendous increase in the number and volume of chemicals that are in everyday use. Therefore, despite intensive research efforts, knowledge of fundamental toxicological principles and the specific effects of many individual compounds is incomplete.