Degradation of Cylindrospermopsin Spiked in Natural Water (Paranoá Lake, Brasília, Brazil) by Fenton Process: A Bench–Scale Study

The frequency and intensity of harmful cyanobacterial blooms have increased in the last decades, posing a risk to public health since conventional water treatments do not effectively remove extracellular cyanotoxins. Consequently, advanced technologies such as the Fenton process are required to ensure water safety. The cyanotoxin cylindrospermopsin (CYN) demands special attention, as it is abundant in the extracellular fraction and has a high toxicological potential. Hence, this study aimed to assess the application of the Fenton process for the oxidation of CYN spiked in natural water from Paranoá Lake (Brasília, Brazil). The H₂O₂/Fe(II) molar ratio was evaluated from 0.2 to 3.4, with an optimum molar ratio of 0.4, achieving a CYN degradation efficiency of 97.8% when using 100 µM of H₂O₂ and 250 µM of Fe(II). The CYN degradation efficiency, using 75 µM of H₂O₂ and 187.5 µM of Fe(II), decreased by increasing the initial pH (from 96.2% at pH 2 to 23.0% at pH 9) and the initial CYN concentration (from 93.7% at 0.05 µM of CYN to 85.0% at 0.2 µM of CYN). At the optimum H₂O₂/Fe(II) molar ratio of 0.4, the hydroxy radical scavengers tested (124.3 µM C of algogenic organic matter, 5 mg L⁻¹ of humic acid, and 513.3 µM of methanol) did not considerably affect the CYN degradation, reaching a maximum CYN degradation reduction from 98.3% to 82.2%.