The influence of pH on the liquid-phase transformation of phenolic compounds driven by nitrite photolysis: Implications for characteristics, products and cytotoxicity

Yiran Wang; Min Cai; Yuchen Wang; Weicheng Zhao; Boxuan Wang; Gehui Wang; Xingru Li

doi:10.1016/j.scitotenv.2024.177704

The influence of pH on the liquid-phase transformation of phenolic compounds driven by nitrite photolysis: Implications for characteristics, products and cytotoxicity

Sci Total Environ. 2024 Nov 20:177704. doi: 10.1016/j.scitotenv.2024.177704. Online ahead of print.

Authors

Yiran Wang¹, Min Cai², Yuchen Wang³, Weicheng Zhao¹, Boxuan Wang¹, Gehui Wang⁴, Xingru Li⁵

Affiliations

¹ Department of Chemistry, Capital Normal University, Beijing 100048, China.
² College of Resource Environment and Tourism, Capital Normal University, Beijing 100048, China.
³ Department of Chemistry, Capital Normal University, Beijing 100048, China. Electronic address: 1170701053@cnu.edu.cn.
⁴ Key Laboratory of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, China. Electronic address: ghwang@geo.ecnu.edu.cn.
⁵ Department of Chemistry, Capital Normal University, Beijing 100048, China. Electronic address: lixr@cnu.edu.cn.

PMID: 39577595
DOI: 10.1016/j.scitotenv.2024.177704

Abstract

The aqueous-phase conversion of phenolic compounds (PhCs) driven by nitrite photolysis has been recognized as a significant source of secondary brown carbon (BrC). However, the influence of pH on the conversion kinetics and product distribution of PhCs remains unclear. In this study, three representative PhCs with varying functional groups were selected to examine their aqueous-phase conversion kinetics in the presence of nitrite under different pH conditions and simulated sunlight conditions. The results indicate that as the pH increases, the decay rates of PhCs decrease, following first-order reaction kinetics. These varying decay rates also suggest that different substituents on the benzene ring significantly impact the reactivity of PhCs. The molecular composition of the products is pH-dependent, with 4-nitrocatechol (4NC) emerging as the primary reaction product. A range of conversion products were detected across different pH values: nitrification dominated at low pH, while hydroxylation products increased with rising pH, and polymerization products appeared prominently at high pH. Due to the electron-withdrawing effect of the nitro group on the benzene ring, fewer products formed from 4-nitrophenol were observed, and the visible absorption spectrum also showed a decreasing trend as the reaction progressed across various pH conditions. Toxicity assays on human non-small cell lung cancer cells (A549) revealed that the toxicity of the reaction products decreased with increasing pH. Correspondingly, the accumulation of reactive oxygen species (ROS) and apoptosis rates in cells also declined. This may be due to the fact that at lower pH levels, nitrophenols (NPs), which tend to promote ROS accumulation and cell death, dominate the product mix. This study provides valuable insights into the toxicological properties of secondary organic aerosols (SOA) formed from the photo-oxidation products of PhCs under different pH conditions. These findings contribute to a deeper understanding of the environmental and health impacts of SOA in atmospheric chemistry.

Keywords: Acidity dominant; Aqueous-phase SOA; Hydroxylate; Nitration; Polymerization.