Occurrence, distribution characteristics, and potential ecological risks of perfluorinated compounds in major estuaries and adjacent offshore areas in Hainan Island.

Per- and polyfluoroalkyl substances (PFASs) have gained attention due to their chemical stability, bioaccumulation potential, and toxicity. The ocean serves as the ultimate sink for these compounds in the global environment. With the rapid development of the Hainan Free Trade Port, environmental pollution on Hainan Island has consequently become more pronounced. However, information on PFAS contamination in the island's coastal areas remains limited. This study collected water samples from nine river estuaries and adjacent marine areas around Hainan Island during both rainy and dry seasons, analyzing 18 target PFAS compounds to determine their concentration levels, spatial distribution, and associated regional risks. The results showed that the ΣPFASs concentrations were 0.212-11.963 ng/L in the rainy season and 0.263-20.330 ng/L in the dry season, with significantly higher levels in the dry season. In the rainy season, PFOA exhibited the highest detection frequency (DF = 97.5%) and contributed 28.3% to ΣPFASs. During the dry season, PFHpA accounted for the largest proportion (25.5%) of ΣPFASs. The emerging perfluorinated compound HFPO-DA was also widely detected, accounting for 2.4% of total PFASs in the dry season. Perfluorinated compounds with 7-8 carbon atoms (PFOA, PFHpA, and PFOS) showed higher DFs and concentrations than other PFASs. The estuarine areas showed higher ΣPFASs concentrations than the offshore areas. The SY sampling site, influenced by intensive tourism activities, recorded the highest pollution levels in both seasons, whereas agricultural regions (WJ and BM) exhibited relatively low contamination. Hainan Island's coastal waters demonstrated lower PFAS concentrations than other global coastal areas. The preliminary environmental risk assessment indicated that individual PFASs at 98% of the sampling sites did not pose significant risks to aquatic organisms. However, PFAS mixtures in the dry season posed low risks at 6.93% of sites. This study offers essential insights into PFAS contamination in the coastal waters surrounding tropical islands.