Food Toxicology 2(2+0)

Lesson 3 : General Principles of Toxicology

Toxicokinetic phase

All of the physiological processes and factors involved in absorption, distribution, biotransformation, and excretion of a toxicant comprise the toxicokinetic phase. For the concentration of toxicant that is ingested by an organism, a fraction of the dose reaches the general circulation or becomes available systemically. The remaining dose is eliminated as waste in the feces. If the toxicant is ingested only once, availability will depend on the dose, rate of absorption, and rate of elimination. In a chronic exposure, the plasma concentration eventually reaches a steady-state level, i.e., the quantity absorbed is equal to the quantity eliminated per unit of time. Usually, elimination increases as plasma concentration increases. The amount of toxicant that reaches the target or receptor sites is designated as toxicologically available or bioavailable. However, the situation is complicated by the fact that toxicants may be converted to other products or metabolites that results in bioactivation or biotoxification. Bioactivation occurs when the metabolite is bioactive and biotoxification occurs when the metabolite is biologically inactive.