The organophosphorus (OP) pesticides are synthetic esters, amides, or thiol derivatives of the phosphoric, phosphonic, phosphorothioic, or phosphonothioic acids (Corbett et al., 1984; Eto, 1974; Gupta, 2006; Hassall, 1982; Quin, 2000). The structural diversity of this family of compounds is reflected in their physicochemical and biological properties: vapour pressure, solubility in water, chemical stability and toxicity (Corbett et al., 1984; Hassall, 1982; WHO, 1986), which determine their specific application (Hassal, 1982). Compared to the mostly banned in U.S. and Europe organochlorine pesticides, the OP ones are less persistent in the environment, are not subject of bioaccumulation and biomagnification, and do not release toxic break down products (Krieger, 2001). These features justify their application in the agricultural and veterinary practices of the modern world. In 1999 the OP insecticides represented ≈37% of the pesticides in use at a global scale (Table 1) and 72% of the insecticides used in U.S. (Kiely et al., 2004). The top ten OP insecticides active ingredients include malathion, chlorpyrifos, terbufos, diazinon, methyl-parathion, phorate, acephate, phosmet, azinphos-methyl, and dimethoate (Kiely et al., 2004).