Ice and aqueous photochemistry of high-ring chlorinated polycyclic aromatic hydrocarbons : A systematic assessment of persistence and risk in cold regions

Ge, Linke and Xu, Rongyan and Garnett, Jack and Zhang, Peng and Bai, Dongxiao and Wang, Siyuan (2026) Ice and aqueous photochemistry of high-ring chlorinated polycyclic aromatic hydrocarbons : A systematic assessment of persistence and risk in cold regions. Journal of Hazardous Materials, 513: 142447. ISSN 0304-3894

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Abstract

Chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) are toxic contaminants that are widely detected in cold aquatic environments, highlighting a need to understand their aqueous and glacial fate. We systematically investigated the photochemistry of three high-ring Cl-PAHs (≥ 3 rings), 2-chlorofluorene (2-ClFL), 9-chlorophenanthrene (9-ClPHE) and 1-chloropyrene (1-ClPY) in ice and aqueous matrices. Under simulated solar irradiation (λ > 290nm), all three compounds underwent photodegradation that followed first-order kinetics, but with different rate constants and quantum yields. Overall, photodegradation in ice was up to 6-fold faster than in water, a difference attributed primarily to physical enrichment processes during freezing. HPLC-MS/MS analysis of intermediates indicated that photo-induced hydroxylation and dechlorination were the dominant primary reactions for these Cl-PAHs, and several secondary pathways differed between the two phases. The generation and participation of ·OH in the apparent photolysis were confirmed by EPR and quenching radical experiments. Furthermore, 9-ClPHE photodegraded more rapidly in seawater ice than in freshwater or pure-water ice, whereas its aqueous photodegradation was fastest in pure water. This pattern likely reflects that Cl− enhances photodegradation more in ice than in water, and that the inhibition effects of other major constituents (Fe(III), HASS and NO3 −) are more pronounced in ice. Environmentally relevant photolytic half-lives (t 1/2,E) extrapolated from laboratory data for the three Cl-PAHs ranged from several hours to tens of days in selected cold regions. Although ECOSAR predictions indicated that many individual transformation products had comparable or lower toxicity, bioluminescence assays with Vibrio fischeri revealed substantial photo-enhanced combined toxicities of the parent Cl-PAHs and their intermediates. These results clarify both the similarities and key differences between the ice and aqueous photochemistry, improving evaluation of the environmental fate and risks posed by PAH analogues and derivatives in seasonally ice-covered regions.