Nitrite-driven abiotic transformation of sulfonamide micropollutants during freezing process

The nitrite-driven transformation of a typical pharmaceutical during freezing process was investigated. Sulfamethoxazole (SMX), one of the most frequently detected pharmaceuticals and personal care products (PPCPs) in environment, was selected for this study. The transformation of SMX with the presence of nitrite under different pH and temperature conditions was compared and discussed. The results demonstrated that the nitrite-driven transformation of SMX, which was negligible at ambient temperature, can be significantly accelerated during the freezing process due to both freeze-concentration and the freeze-potential effects. It was found that apart from abiotic nitration and hydroxylation reactions, free radicals as oxidizing species were likely produced from nitrite during freezing and played an important role in the transformation of SMX. The obtained result provides new insights into the environmental transformation processes of PPCPs in the cold environment. Moreover, it provides a new prospective for researchers reconsidering the freezing method to preserve environmental liquid samples and avoid possible physical/chemical interactions among the target compounds.