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Metasystox, Ultracid, Sevnol, and Laition are commercial pesticides, whose active ingredients are, respectively, oxydemethon-methyl, methidathion, carbaryl, and dimethoate. Laboratory scale experiments were carried out to treat solutions of the pure active ingredient and the commercial formulation employing a solar simulator as irradiation source. Degradation of the active ingredient followed in all cases a pseudo-first-order kinetic and rate constants, k, indicated that reaction was faster when the thiophosphate moiety was present. Additives existing in the commercial formulations resulted in an important decrease in the reaction rate, as k values were at least 50% lower than those obtained with the corresponding pure active principle (0.013min−1 for Ultracid and 0.033min−1 for methidathion, 0.011min−1 for Laition and 0.026min−1 for dimethoate, and 0.007min−1 for Sevnol and 0.016min−1 for carbaryl). Important increase in the surface tension was measured in all cases, indicating that the photocatalytic treatment is able to remove the surface active species present in the commercial formulation. Finally, assays based on the inhibition of the respiration of activated sludge indicated a decrease in the toxicity of all four commercial mixtures from initial values in the range 40–80% to achieve complete detoxification when the elimination of the active ingredient is reached.

A commercial pesticide, namely metasystox, has been chosen to study its detoxification in aqueous solution by means of solar photocatalysis employing titanium dioxide. Initial toxicity/biodegradability has been checked by means of active sludges respirometry and the Zahn–Wellens test. Laboratory scale experiments indicate that significant detoxification (by approximately one order of magnitude) of a 0.05g∕L solution of the active species can be achieved in only 3h of solar irradiation due to the nearly complete elimination of the active compound, methyloxydemeton. In this case, total organic carbon (TOC) measurements cannot be used to evaluate the process as nonactive organic excipients interfere in the measurement. The experiment has been scaled-up to 25L in a solar pilot plant; also in this case more than 75% elimination of methyloxydemeton is achieved in 5h irradiation (∼1400kJ). Besides detoxification (80% initial inhibition of the active sludges and 20% at the end of the experiments), and moderate TOC reduction (∼20%) are observed together with an increase of the surface tension of the solutions, probably due to elimination of excipients having surfactant properties.