Polycyclic aromatic hydrocarbons released from Laohugou Glacier No. 12 in the Qilian Mountains: temporal dynamics, transport mechanisms and fluxes

Accelerated glacier retreat on the Tibetan Plateau is transforming high-altitude glaciers from pollutant sinks into secondary emission sources of polycyclic aromatic hydrocarbons (PAHs). This study investigated the release characteristics, fluxes, and potential ecological risks of PAHs during the whole ablation season of Laohugou Glacier No. 12. The results show that the total PAHs load ranged from 51.2 to 388.2 ng/L, with dissolved PAHs (DPAHs) dominating the total load. Concentrations of DPAHs and particulate-bound PAHs (PPAHs) peaked during the early ablation season (May) and the intensive ablation period (late July), respectively. Three-ring PAHs were the most abundant, and the average molecular weight of DPAHs was significantly lower than that of PPAHs. DPAHs exhibited no significant diurnal variation pattern, whereas PPAHs concentrations exhibited a distinct diurnal pattern with daytime increases and nighttime decreases. Low-molecular-weight PAHs tended to be released predominantly at night, while high-molecular-weight PAHs showed preferential daytime release. DPAHs release was influenced by fewer environmental factors, while PPAHs release was primarily controlled by runoff and suspended particulate matter. The annual release flux of PAHs from Laohugou Glacier No. 12 reached 6.32 kg/year, with significantly elevated fluxes in July–August due to peak PAHs concentrations and runoff. Meanwhile, PPAHs could adversely affect the survival of benthic organisms. This study provides the first assessment of PAHs release fluxes from the TP glaciers, offering critical baseline data for predicting the downstream ecological impacts of accelerated glacier retreat across High Mountain Asia under climate change.