Yuefei Ji

2-Acetyl-6-methoxynaphthalene (2A6MN) is an important environmental transformation product of the anti-inflammatory drug naproxen (NPX), and causes accumulating concerns because of its undesired toxicity. Understanding the persistence and environmental fate of 2A6MN in natural and engineered systems is crucial for the ecological risk assessment of NPX transformation products. In this study, we systematically investigated the photochemical reactivity and behavior of 2A6MN under 254 nm ultraviolet (UV₂₅₄) and natural sunlight irradiation. Our results indicated that 2A6MN exhibited strong absorption due to the conjugation between its carbonyl functionality and the naphthalene ring. Photolysis of 2A6MN was primarily driven by its triplet state, with quantum yields of 8.09 × 10⁻⁴ and 5.04 × 10⁻⁴ mol E⁻¹ under UV₂₅₄ and sunlight irradiation, respectively. The presence of dissolved oxygen significantly inhibited photolysis by quenching the triplet state. The photolysis pathways involved α-cleavage, dimerization, O-demethylation, and ring-opening. Some products generated by the photolysis of 2A6MN exhibited high ecotoxicity to aquatic organisms, potentially threatening the aquatic environment and public health. Dissolved organic matter (DOM) exhibited inhibitory effects on 2A6MN photolysis, possibly by screening light and quenching its triplet. GCSOLAR predicted that the direct photolysis of 2A6MN in natural surface water diminished remarkably with increasing water depth due to the attenuation of incident radiation. The photolysis half-lives of 2A6MN at a depth of 5 m were approximately 20-times higher than those of the near surface. Results of this study fulfills the knowledge gaps in the photochemical reactivity and environmental fate of NPX transformation products in UV-irradiated wastewater and sunlit surface waters. Graphical abstract

Ambroxol (AMB), a widely used expectorant drug, has been ubiquitously detected in aquatic environments due to its limited metabolism in the human body. Herein, we systematically investigated the photodegradation of AMB in waters upon natural sunlight irradiation. AMB has a pK_a value of 8.42, as determined by spectroscopic titration. A dibromoaniline moiety was identified as the primary chromophore responsible for its light absorption. AMB underwent relatively fast photodegradation, with a near-surface half-life (t_1/2) of 2.1–3.0 h at noon on a clear midsummer day at 32°N. The quantum yield (Φ) of direct sunlight photolysis was actinometrically determined to be 0.015 in a neutral aqueous solution. Natural organic matter (NOM) played dual roles in the sunlight-induced photolysis of AMB, serving as a light screener and photosensitizer. Product analysis suggested that the direct photolysis of AMB proceeded mainly through photoionization and photonucleophilic substitution. Kinetic modeling predicted half-lives ranging from 2 to 4 days in well-mixed lake water columns (depth = 3 m, [DOC] = 5 mg C L⁻¹). These findings highlight the significant role of direct photolysis in determining AMB's environmental fate in sunlit surface waters and provide insights into the photochemical behavior of pharmaceuticals in aquatic environments.

As an alternative to bisphenol A, bisphenol S (BPS) is considered an emerging concern. In this study, the degradation of BPS by persulfate (PS), ultraviolet (UV), and UV/PS was comprehensively examined in ultra-pure and saline waters. UV/PS effectively degraded BPS, and the observed first-order rate constant, k_obs, increased from 0.021 to 0.382 min⁻¹ with an increasing PS concentration from 100 to 1000 μΜ. The addition of humic acid (HA) inhibited the degradation of BPS, and 1/k_obs was directly proportional to the concentration of HA. In salty water containing 540 mM Cl⁻ or 0.8 mM Br⁻, UV/PS possessed a higher degradation ability for BPS: the corresponding k_obs values were 1.45 and 1.66 times that of the control sample, respectively. Eighteen degradation products, including β-scission, sulfate addition, quinone type, ring-opening, and cross-coupling, were identified using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Two possible pathways were proposed: (i) the initial step was considered to be an electron transfer reaction from BPS to SO₄^•−, leading to the formation of a phenyl radical cation R1, and then phenol radical R4, 4-hydroxybenzenesulfonate cation R5, phenoxyl radical R3, resonant-type carbon-centered radical R2, and their secondary products; (ii) another pathway was the sulfate addition and hydroxylation. These primary reaction sites were further verified by theoretical calculation. This study highlights the effectiveness of UV/PS as a promising strategy for the remediation of BPS and other endocrine-disrupting chemicals in ultra-pure and saline waters (540 mM NaCl or/and 0.8 mM NaBr).

Dissolved natural organic matter (NOM) significantly influences the performance of water treatment processes. It is generally recognized that NOM acts as a radical scavenger, thus inhibiting the degradation of organic pollutants in advanced oxidation processes (AOPs). This study examined the impacts of 8 different NOM isolates on the degradation of 4-chlorophenol (CP), a representative phenolic pollutant, in sulfate radical (SO₄^•-)-based AOPs. We developed an improved probe method to measure the steady-state concentration of SO₄^•- ([SO₄^•-]_ss) in both the absence and presence of NOM. Results show that adding 1.00 mg_C L^-1 NOM resulted in only a 1.3-3.4% decrease in [SO₄^•-]_ss. However, the apparent rate constants of CP degradation decreased by 76-88%. This discrepancy indicates that radical scavenging cannot be the primary mechanism for observed inhibition. We proposed NOM primarily acts as a reducing agent, reacting with the phenoxy radical intermediates generated from the single-electron oxidation of CP by SO₄^•-. Based on this hypothesis, we developed and validated a kinetic model using experimental data. The reductive capacity of NOM, as determined by the kinetic model, correlates positively with its electron-donating capacity. These findings enhance the understanding of NOM's role in SO₄^•--based AOPs and provide a foundation for developing strategies to mitigate its adverse effects.