Light regime, riboflavin, and pH effects on 2,4-D photodegradation in water.
A laboratory study was conducted to determine the effects of light regime, riboflavin, and pH on photodegradation of 2,4-D in aqueous solution. In controlled-environment chamber experiments, riboflavin sensitized 2,4-D photolysis in a concentration-dependent manner under both attenuated UV (-UV) and enhanced UV (+UV) light regimes. The photolysis half-life of 2,4-D in solutions containing 10 mg L-1 riboflavin was 9.7 and 12.5 h when exposed to +UV and -UV, respectively, compared to no photolysis in the absence of riboflavin. In contrast, the extrapolated half-life of 2,4-D in solutions containing 2.5 mg L-1 riboflavin was 46 h under +UV and 72 h under -UV. The rate of 2,4-D photolysis in the presence of riboflavin increased under both light regimes as initial pH of the solution was decreased from 7.5 to 4.5. The half-life of 2,4-D in the presence of 10 mg L-1 riboflavin at pH 4.5 and exposed to +UV was 1.6 h. Lumichrome, a principal photoproduct of riboflavin, did not photosensitize 2,4-D. Concentrations of 2,4-dichlorophenol formed as a result of riboflavin-sensitized 2,4-D photolysis were higher under the -UV than the +UV regime. These results indicate that riboflavin concentration, solution pH, and light regime are interacting factors that may be manipulated to enhance rates of aqueous 2,4-D photolysis.
Harrison
S K
SK
Department of Horticulture and Crop Science, College of Food, Agricultural and Environmental Sciences, Ohio State University, Columbus 43210, USA.
Venkatesh
R
R
D015084:2,4-Dichlorophenoxyacetic Acid / Q000737:chemistry*; D006540:Herbicides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008027:Light; D010782:Photolysis; D012256:Riboflavin / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
D006540:Herbicides; D014874:Water Pollutants, Chemical; D015084:2,4-Dichlorophenoxyacetic Acid; D012256:Riboflavin