Occurrence, sources, and ecological risks of polycyclic aromatic hydrocarbons in the surface water of Qilu Lake, a low-latitude plateau lake

To investigate the pollution status, sources, and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in surface waters of low-latitude plateau lakes in China, monthly sampling and analysis of surface water 16 PAHs mass concentrations, composition characteristics, and spatiotemporal distribution were conducted in Qilu Lake in the central region of Yunnan Province from January to December 2024. This study analyzes the pollution sources of PAHs were analyzed, the relative contribution of each source was quantified, and the ecological risk of PAHs was preliminarily assessed. The findings revealed that during both the rainy season and dry season, 13 PAHs were detected in varying degrees in the surface water of Qilu Lake, with detection frequency ranging from 11.1% to 100%, and mainly dominated by low ring structure (≤3 rings).During the rainy season, the total mass concentrations of Σ16PAHs ranged from 21.49 ng·L−1 to 113.19 ng·L−1 (average 43.73 ng·L−1), while during the dry season, it ranged from 12.67 ng·L−1 to 132.79 ng·L−1 (average 55.39 ng·L−1). The highest individual mass concentrations were found for phenylalanine (49.94 ng·L−1) and acenaphthene (43.63 ng·L−1). From a temporal perspective, the mean mass concentration of ΣPAHs was higher during the dry season (56.71 ng·L−1) compared to the rainy season (43.73 ng·L−1).Spatial distribution showed that during the rainy season, the highest mean ΣPAHs mass concentration (55.39 ng·L−1) was observed in the southwestern region of Qilu Lake, followed by the northeastern region (41.19 ng·L−1), while the central region had the lowest mean ΣPAHs mass concentration (34.60 ng·L−1). In contrast, during the dry season, the highest mean ΣPAHs mass concentration (61.00 ng·L−1) was recorded in the northeastern region, followed by the southwestern region (57.26 ng·L−1), with the central region again having the lowest mean ΣPAHs mass concentration (51.85 ng·L−1). The results of Positive Matrix Factorization (PMF) indicate that during the rainy season, the surface water PAHs in Qilu Lake mainly originate from coking and petroleum sources (contribution rate 31.9%) and crude oil product volatilization leakage and combustion emissions (contribution rate 29.5%). In contrast, during the dry season, the primary sources are a mixture of coal and biomass combustion (contribution rate 55.0%) and biomass combustion (contribution rate 25.2%). Additionally, based on ecological risk assessment using the Risk Quotient (RQ), the PAHs risk level in the surface water of Qilu Lake ranges from low risk to moderate ecological risk, with no high-risk areas identified. Meanwhile, under the national emphasis on new pollutant governance, traditional organic pollutants such as PAHs still require continuous monitoring.