Any agent capable of producing a deleterious effect in a biological system. As per Paracelsus axiom, all substances are potentially poisonous, it is the dosage that determines the toxicity
Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Gail Todd, Neil White (Major contributors), University of Cape Town, Faculty of Siences, School of Public Health and Family Medicine, Postgraduate Diploma in Occupational Health (DOH), Glossary, Modules 3: Occupational Medicine & Toxicology (Basic) (Acknowledgment to the University of Natal, Nelson R Mandela School of Medicine, Center for Occupational and Enviornmental Health), Cape Town, South Africa 2007. http://www.oerafrica.org/ftpfolder/website%20mater ials/health/OccHealth-Module3/OccHealth-Module3/to xom1/Glossary.htm, (Occupn Med and Tox - Brit) {767}