Fig. 1.

Biological fate of organophosphorus compounds in humans.

Routes of penetration of OPs are absorption through the skin, eyes, and/or respiratory tract (nerve agents, pesticides), or ingestion (self-poisoning). OP molecules distribute from the blood compartment into tissues, including depot sites, biophase (physiological targets), and sites of elimination (liver and kidneys). ChEs of cholinergic synapses are the primary targets; their inhibition is responsible for the acute toxicity of OPs; reaction with secondary targets (carboxylesterases, serine-amidases, peptidases and other serine/tyrosine proteins) may be responsible for the non-cholinergic sub-lethal effects of OPs and chronic toxicity at low-dose exposure (Casida and Quistad, 2004; Costa, 2006).