The transformation of 1-naphthol in the presence of nitrite in ice

As global warming intensifies freeze-thaw cycles, the understanding of environmental chemistry processes in ice and their potential impact on global water quality becomes increasingly important. This study investigated the transformation of 1-naphthol in the presence of nitrite (NO₂^-) under slightly acidic conditions in ice, focusing on the formation of nitro-naphthol. Results demonstrated that increasing NO₂^- concentration enhanced the conversion of 1-naphthol and the formation of nitrated products. This transformation of 1-naphthol was attributed to the freeze-concentration effect, which led to the accumulation of H⁺, NO₂^-, and 1-naphthol in the liquid-like grain boundary layer amid ice crystals. In this brine, NO₂^- underwent protonation to form reactive nitrous acid (HNO₂) and nitrosonium ions (NO⁺), which facilitated the nitration, nitrosation, and oxidative coupling reactions, respectively. The pH was shown to influence nitro products formation by altering the HNO₂ to NO ⁺ ratio. Toxicity assessment revealed increased toxicity of the NO₂^-/1-naphthol solution after freezing treatment, likely due to the formation of nitrated products, whereas natural organic matter (NOM) reduced this toxicity by suppressing the generation of nitrated products. The findings of this study advance the understanding of NO₂^- chemistry and the behavior of hydroxylated polycyclic aromatic hydrocarbons in cold environments.