Degradation of Thiabendazole and Its Transformation Products by Two Photo-Assisted Iron-Based Processes in a Raceway Pond Reactor

For the first time, the fungicide thiabendazole (TBZ) and its transformation products (TPs) were monitored under outdoor conditions, using natural sunlight (NSL) as a photon source, and the Magnetic Fraction of a low-grade titanium ore (MFTO) as an iron catalyst, in a raceway pond reactor. The TBZ degradation (TBZ(D)) was performed by two systems: solar photo-Fenton-like (MFTO-H2O2-NSL) and solar photo Fe/NaOCl (MFTO-NaOCl-NSL), both treatments were carried out using distilled water spiked with 1 mg/L TBZ under natural sunlight. The TPs were determined by a highly sensitive method based on liquid chromatography (LC) coupled to hybrid quadrupole time-of-flight mass spectrometry (QTOF-MS). The TBZ(D) results of four TPs were detected throughout the MFTO-NaOCl-NSL operation, and only two of them remained after t = 75 min. While, twelve TPs were formed during the TBZ(D) in the MFTO-H2O2-NSL system, and all reached stable concentrations after t = 180 min. That might be related with a faster degradation when NaOCl was used as an oxidant instead of H2O2. Thus, 80% of TBZ(D) was achieved at t = 40 and 240 min by the MFTO-NaOCl-NSL and MFTO-H2O2-NSL systems, respectively. Consequently, the pseudo-first-order kinetic constant of MFTO-NaOCl-NSL (0.059 min(-1)) was almost tenfold higher than the value obtained by MFTO-H2O2-NSL (0.006 min(-1)). The results obtained emphasize that the use of NaOCl as an alternative oxidant to H2O2, not only improves the reaction kinetics but also reduces the number of TPs at the end of the degradation process.

Automated summary

This study monitored the degradation of the fungicide thiabendazole and its transformation products under outdoor conditions. The results showed that the use of NaOCl as an oxidant improved the reaction kinetics and reduced the number of transformation products formed during the degradation process.