Photolytic Degradation of Florasulam on Soil and in Water

The rate and pathway of degradation in the presence of light for the triazolopyrimidine herbicide florasulam was determined on soil and in aqueous systems. Florasulam was exposed to natural sunlight for up to 32 days; solar irradiance was measured with either chemical actinometers or by radiometry. The quantum yield for direct photodegradation in a sterile, buffered aqueous solution was determined to be 0.096; an analogous quantum yield for the sum of direct and indirect photodegradation on soil was 0.245. The quantum yields were used to estimate half-lives due to photodegradation as a function of season and temperature. Estimated half-lives due to photodegradation in summer at 40° N latitude were 14 days on soil and 36 days in sterile, buffered water. Photodegradation was much faster in a natural water system, with a measured half-life of 3.3 days in summer at 51.5° N latitude, indicating that indirect photolytic processes will be important contributors to photodegradation of florasulam in aqueous environments. Keywords: Florasulam; 5-OH-florasulam; aqueous photolysis; natural water photolysis