Degradation Kinetics and Half-Lives of Fenitrothion and Thiobencarb in The New Reclaimed Calcareous Soil of Egypt Using GC-MS

The degradation process of pesticides is one of the mechanisms for losing sush chemical from the soil after application. The persistence, degradation kinetics and half-lives of fenitrothion (insecticide) and thiobencarb (herbicide) in the new reclaimed calcareous soil in Egypt were studied under laboratory conditions. The recovery percentages of fenitrothion and thiobencarb were 89.67 and 88.34%, respectively. The results of degradation kinetics showed that residues of fenitrothion and thiobencarb were rapidly decreased during the first five days after treatment. Residues of fenitrothion and thiobencarb remained on the second day were 72.45% and 57.63%, while on the fifth day were 37.72 and 47.18%, respectively. Both tested pesticides disappeared very rapidly from the soil following a bi-phasic pattern. According to the graphical and integral methods, the fit model to describe the degradation kinetic of fenitrothion and thiobencarb is the first order model. The rate constant (k) values for degradation of the two pesticides were 0.036 and 0.068 for fenitrothion and thiobencarb, respectively. The estimated values of half-life were 19.36 days for fenitrothion and 10.24 days for thiobencarb. In general, thiobencarb degraded in sandy clay loam soil about twice faster than fenitrothion.