AbstractThe photodegradation of chlorpyrifos‐methyl (1), and two of its photodegradation products, chlorpyrifos‐methyl oxon (2), and 3,5,6‐trichloro‐2‐pyridinol (3) was studied using low pressure Hg lamps irradiating at 254 nm either in pure acetonitrile (ACN) or in 10% ACN/H2O. Experiments conducted in pure ACN allowed us to identify the photoproducts in the photolysis of 1, 2, and 3 both, in air saturated samples and in the absence of oxygen as analyzed by gas chromatography–mass spectrometry (GC‐MS), high resolution mass spectrometry (HRMS), and phosphorus‐31 nuclear magnetic resonance (31P NMR).Since 2 and 3 are products in the photodegradation of 1, their degradations in 10% ACN/H2O were independently measured, and it was determined that 1 and 2 degrade at comparable rates. Instead, 3 does not interfere in the measurement since it degrades much faster, and their products do not absorb in the region of 1.Our results indicate that short wave photolysis could become a plausible detoxification mechanism.