Target Organ An organ in which a xenobiotic exerts a toxic effect. Threshold Dose The dose at which a toxic effect is first encountered. Total Dose The sum of all individual doses, which may be received over a period of time. Toxicant An agent that produces adverse effects when absorbed into the body. Toxicokinetics The study of the time-dependent processes related to toxicants as the interact with living organism.  It encompasses absorption, distribution, storage, biotransformation and elimination. Toxicology The study of the harmful interactions of chemicals on living organisms and biological systems. Toxin A specific protein produced by certain plants, animals and microorganisms that is highly toxic to other organisms (snake venom).