This study aimed to investigate the contamination characteristics, sources, and ecological risks of polycyclic aromatic hydrocarbons （PAHs） in the Third Drain of Ningxia. Water samples were collected in November 2021, March 2022, and July 2022, respectively. A total of 16 priority PAHs were quantitatively detected using gas chromatography-mass spectrometry （GC-MS）. The results showed that ρ(∑PAHs) in the drain ranged from 324.11 to 530.77 ng·L-1, with an average value of 414.73 ng·L-1. The detection rate of each monomer was greater than 90%, and DaA had the highest concentration, with average values of 48.53 ng·L-1, followed by IcdP. Compared with those in other rivers in China, the PAH concentrations in the Third Drain of Ningxia showed a medium pollution level. The concentration of ∑PAHs and the high ring monomers were significantly higher in summer than that in spring and winter. On a spatial scale, the average concentration of ∑PAHs in the drain decreased in the order of upstream Helan section > midstream Pingluo section > downstream Huinong section. The proportion of PAHs was in the order of high rings （5-6 rings） > low rings （2-3 rings） > middle rings （4 rings）, with 5 rings being dominant. Probabilistic matrix factorization （PMF） was used to quantitatively assess the source apportionment of PAHs. The results showed that coal chemical emissions, automobile exhaust emissions, coal combustion, and petrochemical emissions contributed 27.36%, 27.64%, 26.85%, and 18.15%, respectively. Ecological risk assessment showed that BaA, BbF, BghiP DaA, and IcdP had high risk, whereas other monomers exhibited moderate risk. Therefore, control measures should be taken as soon as possible. This study can provide a scientific basis for the prevention and control of PAH pollution in the drains flowing into the Yellow River of Ningxia．.
Keywords: contamination characteristics; ecological risk; polycyclic aromatic hydrocarbons （PAHs）; source analysis; the Third Drain.