Degradation of carbendazim in water via photo-Fenton in Raceway Pond Reactor: assessment of acute toxicity and transformation products

Abstract

This study aimed at investigating the degradation of fungicide carbendazim (CBZ) via photo-Fenton reactions in artificially and solar irradiated photoreactors at laboratory scale and in a semi-pilot scale Raceway Pond Reactor (RPR), respectively. Acute toxicity was monitored by assessing the sensibility of bioluminescent bacteria (Aliivibrio fischeri) to samples taken during reactions. In addition, by-products formed during solar photo-Fenton were identified by liquid chromatography coupled to mass spectrometry (UFLC-MS). For tests performed in lab-scale, two artificial irradiation sources were compared (UV and UV-Vis). A complete design of experiments was performed in the semi-pilot scale RPR in order to optimize reaction conditions (Fe and HO concentrations, and water depth). Efficient degradation of carbendazim (> 96%) and toxicity removal were achieved via artificially irradiated photo-Fenton under both irradiation sources. Control experiments (UV photolysis and UV-Vis peroxidation) were also efficient but led to increased acute toxicity. In addition, HO/UV required longer reaction time (60 minutes) when compared to the photo-Fenton process (less than 1 min). While Fenton's reagent achieved high CBZ and acute toxicity removal, its efficiency demands higher concentration of reagents in comparison to irradiated processes. Solar photo-Fenton removed carbendazim within 15 min of reaction (96%, 0.75 kJ L), and monocarbomethoxyguanidine, benzimidazole isocyanate, and 2-aminobenzimidazole were identified as transformation products. Results suggest that both solar photo-Fenton and artificially irradiated systems are promising routes for carbendazim degradation.

Intensification of UV-C treatment to remove emerging contaminants by UV-C/H2O2 and UV-C/S2O82−: Susceptibility to photolysis and investigation of acute toxicity

“…As confirmed by the results shown in Figure 3, CBZ is known to be toxic to Allivibrio fischeri [80]. Similarly to what was observed for CAF, UV-C photolysis alone was not able to remove CBZ due to its low molar absorptivity and quantum yield.…”

“…Consequently, UV-C photolysis had a negligible effect on the acute toxicity of CBZ. Meanwhile, both UV-C/H2O2 and UV-C/S2O8 2eliminated the toxic effect of CBZ; as it was also observed by other irradiated AOPs under artificial and solar irradiation in another study [80]. During UV-C/H2O2, CBZ degradation occurred alongside the reduction in acute toxicity (Figure 3).…”

“…However, considering the exact mass obtained here, the product proposed in the referred paper was not realistic in our case. Species of m/z 128.02 (III) and146.03 (IV) would be formed from the further oxidation of II, leading to an isocyanate structure[80] and the formation of carboxylic acid moieties. Then, compound VI would later accumulate in the system as a product of oxidation of the intermediate compounds.…”

Novel and versatile TiO2 thin films on PET for photocatalytic removal of contaminants of emerging concern from water

“…For example, da Costa et al [72] found a similar value for a.T.U. toxicity for their nontreated CBZ water solution and the authors observed an increase of toxicity for UV photolysis and UV-H2O2 processes, due to the by-products formed.…”

The Effects of Carbendazim on Acute Toxicity, Development, and Reproduction in Caenorhabditis elegans

“…Although the toxic effect of carbendazim has been reported since the 1980s, the toxicity of carbendazim becomes a hot topic because of the increasing concern about environmental endocrine disruptors [4]. Carbendazim has been banned in several countries because of its negative impacts on the environment and health such as development and reproductive disturbances, toxicity, and mutagenicity [8].…”