Toxicants that at low concentrations modify or inhibit some biological process by binding at a specific site or molecule have a specific acting mode of toxic action. However, at high enough concentrations, toxicants with specific acting modes of toxic actions can produce narcosis that may or may not be reversible. Nevertheless, the specific action of the toxicant is always shown first because it requires lower concentrations.
There are several specific acting modes of toxic action:
* Uncouplers of oxidative phosphorylation. Involves toxicants that uncouple the two processes that occur in oxidative phosphorylation: electron transfer and adenosine triphosphate (ATP) production.
* Acetylcholinesterase (AChE) inhibitors. AChE is an enzyme associated with nerve synapses that it’s designed to regulate nerve impulses by breaking down the neurotransmitter Acetylcholine (ACh). When toxicants bind to AChE, they inhibit the breakdown of ACh. This results in continued nerve impulses across the synapses, which eventually cause nerve system damage. Examples of AChE inhibitors are organophosphates and carbamates, which are components found in pesticides (see Acetylcholinesterase inhibitors).
* Irritants. These are chemicals that cause an inflammatory effect on living tissue by chemical action at the site of contact. The resulting effect of irritants is an increase in the volume of cells due to a change in size (hypertrophy) or an increase in the number of cells (hyperplasia). Examples of irritants are benzaldehyde, acrolein, zinc sulphate and chlorine.
* Central nervous system (CNS) seizure agents. CNS seizure agents inhibit cellular signaling by acting as receptor antagonists. They result in the inhibition of biological responses. Examples of CNS seizure agents are organochlorine pesticides.
* Respiratory blockers. These are toxicants that affect respiration by interfering with the electron transport chain in the mitochondria. Examples of respiratory blockers are rotenone and cyanide.