Document Type : Original Article
Authors
1
Central agricultural Pesticide Laboratory - Pesticide Analysis Research Department
2
Head of researcher in Pesticides analyses Department, CAPL, Agriculture Research Centre, Dokki, Giza, Egypt
3
Chemistry Depart, Faculty of Science, Helwan University, Ain Helwan, Cairo, 11795 Egypt.
Abstract
In the present study, the stability of hexythiazox in the formulation of Efdal hekzarun 5% EC after accelerated hot storage for 14 weeks at 35, 40, 45, and 54 °C, forced acidic and alkaline hydrolysis for 7 days in 1.0, 0.1, and 0.01N in HCl and NaOH, and photolysis in clay soil of Egypt for 14 days was investigated. The results showed that the active ingredient decreased by 18.15% after 14 weeks of storage at 54 °C. However, the decline within the same time period ranged between 5-10% at 35, 40, and 45 °C, respectively. Thus, hexythiazox storage complied with FAO specification after more than 14 weeks at 35°C and not after more than 9, 8, and 4 weeks at 40, 45, and 54°C, respectively. The data showed that the degradation rate of hexythiazox was dependent on its initial concentration and increased progressively as temperature increased. Furthermore, the shelf life of hexythiazox after storage at 54°C was found to be approximately 1/5 that of its shelf life after storage at 35°C. The kinetics of hexythiazox degradation under the studied conditions followed the first-order model, being dependent upon its initial concentration. The shelf life (t0.95) and half-life (t1/2) of hexythiazox in forced alkaline solutions were less than those in acidic solutions. The results revealed that hexythiazox is a non-persistent pesticide in soil; it decomposed rapidly in Egyptian clay-loam soil, with an 80.53% reduction in 14 days at ambient conditions and a half-life (t1/2) of 5.75 days. This is due to soil pH (8.59), organic matter (1.92), and the molecular structure of hexythiazox, which contains chromophores such as ethylene and carbonyl groups; it may be sensitive to direct photolysis by sunlight because it absorbs wavelengths longer than 290 nm. According to the GC/MS analysis, hexythiazox was degraded to different byproducts after specified conditions. The benzene and cyclohexane rings remain stable under different applied conditions; however, the thiazolidine ring is cleaved and opened during thermal and forced acidic hydrolysis and remains stable after alkaline hydrolysis and soil photolysis. The contraction reaction is unique to the forced alkaline hydrolysis and photolysis of hexythiazox in clay-loam soil; thus, two products were identified: 4-chloro-2-(cyclohexanecarboxamido) benzoic acid and 3-cyclohexyl-1-methyl-1-(2-phenylethyl) urea; the latter one and 4-methyl-5-phenylthiazolidine-2-one were identified in the forced alkaline hydrolysis of hexythiazox.
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