Photodegradation of 3,5,6-trichloro-2-pyridinol in aqueous solution

A medium-pressure mercury lamp, emitting strongly in the 200–400 nm range was applied for the degradation of 3,5,6-trichloro-2-pyridinol (TCP), a hydrolysis product of chlorpyrifos. Photodegradation of TCP in aqueous solution exhibited pseudo-first order kinetics with a rate constant that was wavelength dependent and increased below 300 nm. The TCP degradation rate and quantum yield increased with solution pH up to a constant maximum value of (6.40 ± 0.046) × 10^?3 cm² mJ^{? 1} and 0.178 ± 0.002 mol E^?1 respectively, at pH 5 and above. Addition of 5 mg L^{? 1} H₂O₂ to generate OH radicals led to an increase in removal rates by a factor of 1.5. Addition of phosphate buffer resulted in decreased photolysis at 3 < pH < 6.