Determination of the Reaction Quantum Yield for the Photochemical Degradation of Fe(III)-EDTA: Implications for the Environmental Fate of EDTA in Surface Waters

The photochemical reaction quantum yield θ of the Fe(III)-EDTA complex at concentrations <1 μM was determined as a function of wavelength, pH, and temperature. The reaction quantum yield is independent of pH but clearly dependent on wavelength. At wavelengths of 313, 366, and 405 nm the reaction quantum yields (average values at 25 °C) are 0.082, 0.034, and 0.018, respectively. The temperature dependence (5-40 °C) of Φ is characterized by a small activation energy of ≈9 kJ mol⁻¹. The impact of the presence of oxygen on the reaction quantum yield of Fe(III)-EDTA was also investigated. The determined O values were used to predict typical photochemical half-lives of this substance in the Glatt River. The validity of this prediction was confirmed by comparison of computed and measured kinetic data for the photochemical conversion of Fe(III)-EDTA in Glatt River water. From the predicted half-lives of the Fe(III)-EDTA complex, it can be derived that Fe(III)-EDTA is quickly degraded in typical rivers and that EDTA concentrations found in the North Sea or the Black Sea consist of EDTA species that are not degradable by sunlight.