Photodegradation of Sulfamethoxypyridazine in UV/Co(II)/Peroxymonosulfate System: Kinetics, Influencing Factors, Degradation Pathways, and Toxicity Assessment

Sulfonamides (SAs) including sulfamethoxypyridazine (SMP) are regarded as a new type of persistent pollutant at present due to their abuse. In this work, the direct photodegradation behavior of 11 SAs under simulated sunlight was first investigated, and the results indicated that the direct photolysis of SMP is the slowest among these SAs. Then the oxidation degradation of SMP in UV/Co(II)/peroxymonosulfate (PMS) system was systematically explored. Up to 95.2% removal of 0.071 mM SMP was observed after 20 min of reaction under the optimal condition with a molar ratio of 1:150:5 between SMP, PMS, and Co(II). The effects of some coexisting anions on degradation of SMP were investigated. It was found that Cl(−) and high concentrations of CO(3)(2−) and HCO(3)(−) have a significant inhibitory effect, while HPO(4)(2−) has only a slight positive effect. Radical scavenger experiments indicated that hydroxyl radicals (HO(•)) are prevailing active species responsible for SMP removal in UV/Co(II)/PMS system. The degradation of SMP in UV/Co(II)/PMS system was accomplished mainly by hydroxylation of the aromatic ring, extrusion of SO(2), oxidation of NH(2) group, and N − S bond cleavage. Eight intermediates for SMP degradation were identified, and their toxicities to aquatic organisms were predicted by using the ECOSAR program based on the structure − activity relationships (SARs), which suggested that the chronic toxicities of SMP and its degradation intermediates are more significant than their acute toxicities. The present research indicates that UV/Co(II)/PMS system is applicable for SMP degradation in aqueous solutions and may be helpful to understand the transformation behavior of SAs. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11270-021-05351-5.