Photodegradation of the azole fungicide climbazole by ultraviolet irradiation under different conditions: Kinetics, mechanism and toxicity evaluation

Abstract

h i g h l i g h t s• Climbazole (CZ) could be effectively degraded under UV-254 irradiation.• CZ underwent direct and selfsensitized photolysis involving ROS.• The main photodegradation byproducts of CZ were identified and semi-quantitated.• Pathway includes hydroxylative dechlorination, dechlorination, and de-pinacolone.• The toxicity of the photodegradation system reduced after UV-254 irradiation. Keywords: Climbazole Photodegradation Reactive oxygen species By-products Toxicity a b s t r a c t Climbazole (CZ) has been known to persist in various environmental media, and may cause potential risks to aquatic organisms. This study investigated the photodegradation of CZ by ultraviolet (UV, 254 nm) under different conditions. The results revealed that CZ could be effectively degraded in aqueous solutions under UV-254 irradiation with a half-life of 9.78 min (pH = 7.5), and the photodegradation followed pseudo-first-order kinetics. pH had almost no effect on its rate constants and quantum yields; but the water quality of natural waters could affect the photolysis of CZ, and the coexisting constituents such as Fe 3+ , NO 3 − , and HA obviously inhibited its photolysis. The addition of different radical scavengers also inhibited the photodegradation of CZ due to the reduction of reactive oxygen species (ROS). CZ underwent direct and self-sensitized photolysis involving ROS. Based on the identified photodegradation by-products, the proposed pathways included hydroxylative dechlorination, dechlorination and de-pinacolone. Moreover, toxicity evaluation using duckweed found significant toxicity reduction in the photodegradation system of CZ after the irradiation of UV-254, and the remaining by-products did not pose extra toxicity compared with CZ itself. These findings from present study suggest that CZ in effluent could be further reduced by applying UV photolysis treatment.

Biocides in wastewater treatment plants: Mass balance analysis and pollution load estimation

“…4(a)), which indicates that these biocides removed in liquid phase had been transferred into the excess sludge instead of being really degraded or transformed (Table S16). In summary, most biocides are hard to be biodegraded, so it is necessary to develop more effective technologies for their removal, such as the advanced oxidation technologies [44][45][46].…”

Aqueous photodegradation of the benzophenone fungicide metrafenone: Carbon-bromine bond cleavage mechanism

“…Direct photolysis of fungicides is caused by direct absorption of photons, while indirect photolysis is triggered by the absorption of light by photosensitizers. Active components in water (such as dissolved organic matter and ions) can interact with organic pollutants through energy transfer of excited substances or through photoproduction of reactive transient species, which affects the persistence and fate of fungicides in the environment (Avetta et al, 2014;Fréneau et al, 2019;Jennifer et al, 2019;Liu et al, 2016). As shown in Fig.…”

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

“…Chemicals that have been used as optically transparent actinometers to measure irradiance across the UV spectrum include nitrate, 23,[25][26][27] nitrite, 16,25,26 hydrogen peroxide, 23,[28][29][30][31][32][33] uridine, 23,34,35 atrazine, 33,[36][37][38][39][40][41] and p-nitroanisole (PNA). 7,42 However, there are known limitations in the application of most of these actinometers.…”