Determination of Degradation Products and Pathways of Mancozeb and Ethylenethiourea (ETU) in Solutions Due to Ozone and Chlorine Dioxide Treatments

Abstract

The objective of the present study was to determine the degradation products of mancozeb and ethylenethiourea (ETU) and elucidate the possible degradation pathways in solution as a result of chemical oxidation using ozone and chlorine dioxide. This study was developed in a solution at 100 ppm of mancozeb and ETU concentration over the course of 60 min. Two different oxidizing agents used in this study were (1) ozone at 3 ppm and (2) chlorine dioxide at 20 ppm. Ozone was continuously provided throughout the course of the reaction. Degradation products were detected with high-resolution GC-MS. The total analysis time was 4 min per sample combined with rapid GC separation and time-of-flight mass spectrometry (TOFMS). Hydrolysis of mancozeb led to m/z 144 ion fragmentation, which is 5-imidazoledithiocarboxylic acid, as a major degradation product. ETU showed M⁺ 102, which corresponds to its mass, indicating this compound was stable in distilled water and did not undergo hydrolysis during 60 min. The average retention times of mancozeb and ETU were approximately 181−189 and 210−230 s, respectively. Ozonation of mancozeb produced ETU as a major product. Treatment of ETU with ozone produced several degradation compounds. From prolonged ozonation, the CS₂ or CS group was removed. Overall, several byproducts identified were M⁺ 60, M⁺ 84, M⁺ 163, M⁺ 117, and M⁺ 267 by ozone and M⁺ 117, M⁺ 86, and M⁺ 163 by chlorine dioxide treatment. Several of these have been reported, but others have never been reported previously. Keywords: Mancozeb; ETU; ozone; chlorine dioxide; degradation