Photolytic and Microbial Degradation of 3,5,6-trichloro-2-pyridinol

The photolytic and microbial degradation of 3,5,6-trichloro-2-pyridinol (TCP), a metabolite of the insecticide chlorpyrifos and the herbicide triclopyr, has been investigated. TCP (80 mg/L) was decomposed to nondetectable levels within 2 h of ultraviolet irradiation. Release of CO2 and chloride ion was observed; however, approximately 60% of the initial radioactivity remained in the solution. Dichlorodihydroxypyridine isomers and reductive dechlorination products were found as intermediate products of TCP photolysis. It was proposed that both hydrolytic and reductive dechlorination occurred during photodegradation of TCP. Although TCP can be degraded via photolysis, many degradation products remained in the aqueous medium and only some of them, the reductive dechlorination products, can be mineralized by Pseudomonas sp. ATCC 700113. The degradation of the parent compound, TCP, by Pseudomonas sp. ATCC 700113 also appears to involve a reductive dechlorination mechanism. A consortium of microorganisms may be needed if a treatment process combining microbial and photolytic activity is to be used to remove TCP in industrial wastewater. Keywords—3,5,6-trichloro-2-pyridinol Photodegradation Microbial degradation Chlorpyrifos Triclopyr