Identifying sources and risks of polycyclic aromatic hydrocarbons in the Yarlung Tsangpo river: A seasonal study

The presence of polycyclic aromatic hydrocarbons (PAHs) in the Yarlung Tsangpo River (YTR) poses substantial threats to both regional ecological security and human health. While it is imperative to accurately assess and pinpoint the risks and sources of PAHs in the YTR, a comprehensive understanding of their seasonal variations in composition and distribution is currently lacking. In a thorough investigation aimed at evaluating seasonal fluctuations, sources, potential hazards, and the impact of natural and anthropogenic factors on PAHs concentrations in the YTR, enlightening findings emerged. During the dry season, concentrations of the sum of 16 PAHs (Ʃ₁₆PAHs) ranged from 18.74 to 60.01 ng/L, with low molecular weight PAHs (2-3 rings) prevailing, primarily originating from biomass combustion. Conversely, in the wet season, concentrations varied from 10.35 to 27.04 ng/L, with high molecular weight PAHs (5-6 rings) dominant, largely sourced from transportation emissions. The increased rainfall during the wet season led to a dilution of PAHs concentrations, resulting in lower levels compared to the dry season. Factors such as population density, energy consumption, and energy production exhibited positive correlations with PAHs levels, influencing their spatio-temporal distribution. The spatial distribution of PAHs concentrations was found to be associated with ecological and health risks, with risk quotient analysis indicating lower ecological risks, but heightened risks during in the dry season. Moreover, through monte carlo simulation and risk assessment, it was revealed that there were elevated carcinogenic risks for adults during the dry season. Prioritizing reductions in concentrations of specific PAHs such as DahA and BaP proved effective in mitigating the risk of carcinogenic risk. This study furnishes valuable reference data for the management and regulation of PAHs in the YTR, offering insights crucial for safeguarding the river's ecosystem and the well-being of the communities reliant on it.