Photolytic Degradation of Florasulam on Soil and in Water

Abstract

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 degrees 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 degrees N latitude, indicating that indirect photolytic processes will be important contributors to photodegradation of florasulam in aqueous environments.

The role of indirect photolysis in limiting the persistence of crop protection products in surface waters

“…Some studies report increased degradation rates [17][18][19] and others a decrease in degradation due to the attenuation of incident light by components of the natural water and sorption [4,11,[20][21][22]. Comparison of data from published work is further complicated by variations in the test systems used.…”

Chemistry and Fate of Triazolopyrimidine Sulfonamide Herbicides

“…In studies using radiolabeled florasulam in fl aqueous buffer, only one product (triazolopyrimidine sulfonic acid, TPSA; Fig. 3) was found at greater than 10% of the applied radioactivity (it attained 18% after 32 d; Krieger et al 2000c). Analogous TPSA degradates were also found as products of aqueous photolysis for diclosulam (Concha et al 1994) and penoxsulam (Fig.…”

“…Photolytic processes are considered important contributors to the degradation of TSA herbicides, both on soil and, particularly, in water (USEPA 1997;van Weesenbeeck et al 1997;Krieger et al 2000c;Zabik et al 2001;USEPA 2004b;Jabusch and Tjeerdema 2006b). Photodegradation studies with fl orasulam yielded a fl t 1/2 of 3.3 d in a natural water system in summer at 51.5°N latitude compared to an estimated t 1/2 of 36 d based on photolysis experiments in sterile buffered solution.…”

“…Photodegradation studies with fl orasulam yielded a fl t 1/2 of 3.3 d in a natural water system in summer at 51.5°N latitude compared to an estimated t 1/2 of 36 d based on photolysis experiments in sterile buffered solution. The much faster rate in the natural system suggests an important role for indirect photolytic processes in the overall photodegradation of fl orasulam (Krieger et al 2000c). In contrast, fl degradation studies for penoxsulam in summer sunlight at 39°N yielded no significant differences between the rates determined in sterile buffered fi solution and rice fi eld water.…”

“…Proposed photodegradation pathways have been published for flora-fl sulam (Krieger et al 2000c; Fig. 3) and penoxsulam (Jabusch and Tjeerdema 2006b;Fig.…”