Treatment of Aqueous Solutions Containing Four Commercial Pesticides by Means of TiO2 Solar Photocatalysis

Abstract

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.

The effect of inorganic anions and organic matter on mesotrione (Callisto®) removal from environmental waters

“…Namely, this formulated compound contains important amounts of the mentioned organic excipients, which are responsible for an important proportion of the organic matter and could interfere in the photo-oxidative process. 13 These results are in agreement with those obtained in study of the photocatalytic degradation of sulcotrione as standard and as the active ingredient in Tangenta ® . 8 Bearing in mind that the presence of inorganic ions in the water matrix has been shown to greatly influence the removal efficiency of target pollutants, 4 after investigations of mesotrione removal from Callisto ® in DDW, its stability in ground, as well as in the river water was performed with/without catalyst and under UVA/simulated sunlight irradiation ( Fig.…”

Facile destruction of formulated chlorpyrifos through green oxidation catalysis

“…2 In resource poor circumstances, any real-world degradation system must be safe, inexpensive, simple to use, and adaptable for formulations as well as for the free active ingredients and the toxic byproducts that form upon aging or leaking into water or soil. Excellent noncombustion studies of formulated OPI destruction involve photolytic, 3,4 photo-Fenton, 5 enzymatic, 6 and electrochemical 7 approaches, but the process details of each are not suitable for concentrated obsolete formulations or for the infrastructural conditions typically found in underdeveloped areas.…”

Comparison of different TiO2 samples as photocatalyst for the degradation of a mixture of four commercial pesticides

“…It is also notable that COD and TOC mainly decreased during the early stages of the reaction and remained fairly constant thereafter; this implies that COD and TOC reduction may partly be due to adsorption onto the catalyst surface and/or evaporation of some volatile components of the mixture of the commercial products rather than to oxidative degradation. The presence of organics might also have some influence on the degradation rate as shown in a previous paper, where results obtained for individual photodegradation in the presence of P25 of pure and commercial products were compared; in all cases, reduction up to 50% of the k values were observed …”