Degradation of Aqueous Atrazine and Metazachlor Solutions by UV and UV/H₂O₂ — Influence of pH and Herbicide Concentration Abbau von Atrazin und Metazachlor in wäßriger Lösung durch UV und UV/H₂O₂ — Einfluß von pH und Herbizid‐Konzentration

Abstract

Summary: The degradation of two pesticides: atrazine and metazachlor was investigated in aqueous solution under UV-irradiation with and without H202. Rate constants of the photochemical degradation were determined applying a first order kinetics and quantum yields of the processes were calculated. This approach leads to an apparent decrease of the quantum yield with increasing initial pesticide concentration. At low H202 initial concentrations, the pesticide degradation was shown to be much more efficient than the degradation under UV-irradiation only. However, at high H202 concentrations ( > 2 mmol L-'), the efficiency of the UV/H202 system dropped down and the quantum yields of degradation were lower than for the direct photolysis. In the absence of H202, no influence of the pH value on the photodegradation of the pesticides could be noticed in a range between pH 3 and pH 11. At low H202 initial concentrations, the photochemical degradation of the pesticides was much faster at pH 3 and pH 7 compared with the degradation at pH l l . The results emphasize the potential of optimized reaction conditions in advanced oxidation.

Determining wavelength-dependent quantum yields of photodegradation: importance of experimental setup and reference values for actinometers

“…One discrepancy that was noted when reviewing the literature was the previously reported concentration dependence of the atrazine F 254 . 44 On examination of the data, we found that the observed behavior could be explained by light screening at higher atrazine concentrations. When the F 254 for each atrazine concentration determined in that study was recalculated by correcting for light screening, a consistent F 254 value with an 8% relative standard deviation was obtained (Table S8 †).…”

“…For example, F 254 values for the chemical actinometers atrazine and uridine varied by 33% and 34%, respectively. 23,[43][44][45]51,52,[56][57][58][59] Discrepancies in literature values have also prompted studies to revise F values for already established actinometers. 42,60 Based on previous studies, a Petri dish was chosen as the sample container to determine F when using a spectroradiometer to quantify the photon irradiance.…”

“…23 Similarly, a high concentration of a radical scavenger is recommended when using hydrogen peroxide as an actinometer to produce a more consistent F. 23 For uridine, the reaction kinetic order and F were reported to be concentration-dependent and affected by photoproduct absorbance, which are undesired characteristics of an actinometer; nonetheless, an established protocol for uridine actinometry is available in the literature that addresses these constraints. 43 The atrazine F has been primarily established at 254 nm within the UVC region, 44,45 whereas reported F for PNA are limited to the UVB and UVA regions. 42 Sulfamethoxazole and diclofenac have also been used as actinometers in recent studies because (1) they can be used with high UV irradiances that limit the applicability of standard actinometers, and (2) their suitability for eld studies due to their presence in natural water bodies.…”

Removal of triclosan from water by adsorption on activated carbons and photodegradation

“…Where: kTCS2 is the second-order photodegradation kinetic constant (L mg -1 s -1 ), ΦATRZ is 0.046 mol Einstein -1 , ɛATRZ is 386 m 2 mol -1 for λ = 254 nm (Hessler et al 1993) and kATRZ is 1.82 x 10 -3 s -1 .…”

Photodegradation of pesticides using compound-specific isotope analysis (CSIA): a review

“…Thus, it would be particularly useful for contaminant accumulation, 125 source detection, 126 and the development of regulatory and monitoring strategies. 127 As additional elements, such as 2 H, 37,128 37 Cl, 129 and 34 S, 130 are included in the isotopic analysis of atrazine and its metabolite desethylatrazine in a given transformation process, the opportunity to assess the underlying reaction mechanism(s) increases. 131 This is particularly important for the phototransformation processes of agrochemicals, where different functional groups or bonds of a molecule might be involved.…”