A study was conducted to investigate the degradation of chlorpyrifos, as well as studying the
formation of its impurity sulfotep after storage at 54 ±2 oC for 1, 3, 7, 14, 21 days, at 72 ±2 oC for 1-5
days, and at room temperature within range 1-12 weeks of three commercial chlorpyrifos Emulsifiable
Concentrate (EC) formulations (48% w/v) from the Egyptian market (manufactured from three different
companies). The obtained results showed that chlorpyrifos was more stable after storage at 54 ±2 oC and
at room temperature, whereas the rate of degradation increased after storage at 72 ±2 oC. There is no
difference on the rate of degradation for all chlorpyrifos formulations under investigation. The sulfotep
content of the three commercial formulations didn't show any correlation with storage temperature and
storage time. However, in one of the commercial formulations of chlorpyrifos, the sulfotep content was
more than the maximum permissible concentration of impurity recommended by (FAO Specifications for
chlorpyrifos 2008).