The major barrier of uptake for a toxicant is the cell membrane or cell wall at the site of uptake, for example; cell membrane of gastrointestinal tract or skin, epithelial cell of gill and tracheae, or cell wall of plant root. .
There are four principal processes involved in the movement of toxicants across the cell membrane. These include: passive diffusion, facilitated transport, active transport and pinocytosis. During passive diffusion small molecules of the toxicant move along a concentration gradient. The transport into the cell will then be enhanced by carriers during the facilitated transport process. Active transport occurs when the toxicant's molecule is actively combined with a carrier. During the step of Pinocytosis the cell membrane will fold around the toxicant molecule when it enters the cell and the toxicant will move to the process of biotransformation, (University of Phoenix, 2009).
The development between exposure to a toxin and the initiation of an harmful result can be divided into two facets, toxicokinetics or the transport of the toxin to its site of action and toxicodynamics or the reaction at the location of action. Toxicokinetics is the study of the movement of chemicals around the body. It includes absorption from the location of exposure into the overall circulation, distribution by circulation both into and out of the tissues, and elimination from the l circulation by biotransformation (metabolism) or elimination, (Thrush, 2008). Toxicodynamics correlates to the processes and transformations that occur in the target tissue of the toxin, such as metabolic bio-activation and covalent bonding resulting in an harmful effect.
Biotransformation is the process in which a toxicant is altered from one form of chemical to another by a chemical reaction within the body. The main objective of biotransformation is to detoxify a toxic substance, increase the substance water solubility to facilitate elimination, (Thrush, 2008).
