The accelerating and inhibiting effects ofdissolved organic matter (DOM) on the sunlight-induced transformation ofanilines and sulfonamide antibiotics, which occur as contaminants in surfacewaters, will be studied in detail. The molecular basis of the inhibiting effectwill be investigated using laser flash photolysis and phenolic antioxidants asmodel inhibitors.
The recently characterized inhibitioneffect of DOM on triplet-induced oxidation of relevant aquatic organiccontaminants is likely to play an important role for the fate of suchcontaminants in sunlit surface waters. The effect was attributed to antioxidantmoieties present in DOM, a conclusion that was supported by the positivecorrelation between the magnitude of the inhibition of oxidation and theelectron donating capacity of DOM, and by the observation of an analogouseffect in the presence of phenols, used as model antioxidants. The proposedkinetic model, supported to date by data obtained from steady-state irradiationexperiments, implies a redox reaction between oxidation intermediates of thecontaminants and antioxidant moieties of DOM, leading to partial reformation ofthe parent contaminant. In the present proposal we address some central openquestions that concern on the one hand the mechanism of the inhibition ofoxidation and on the other hand the application of the concept of DOM-inducedinhibition of oxidation to characterize and quantify the transformation ofcontaminants, such as anilines and sulfonamides, induced by sunlight in surfacewaters.
Objectives and methods
Detection, bynanosecond laser flash photolysis, of the oxidation intermediates of a fewselected anilines and sulfonamides antibiotics and investigation of their decaykinetics in the presence of DOM and model antioxidants. Verification of the proposedmodel for the mechanism of inhibition of oxidation. 1.
Quantification ofthe sunlight-induced transformation rates of the selected contaminants undersurface water-like conditions. Determination of the variability of such ratesupon type and concentration of DOM. 2.
The expected practical result is thequantification of the sunlight-induced transformation rates of the selectedclasses of contaminants under realistic surface water conditions. Themethodology will serve to characterize the photochemical fate of furtherclasses of aquatic contaminants.