Poly- and Perfluoroalkyl Substances: A first glimpse of the “forever chemicals” in water samples from Red River, Vietnam

The Red River is one of the most important watercourses in northern Vietnam, providing water for agriculture, industries and domestic uses. Given the proximity of metropolitan areas, agricultural and industrial zones, the Red River is under strong anthropogenic influence and susceptible to contamination by persistent substances, such as Poly- and Perfluoroalkyl Substances (PFAS). Being highly resistant to extreme heat and repellent to both water and oil, PFAS have been widely used in aqueous firefighting foam and in various consumer goods, e.g. cooking wares, food packaging, textile[1], [2]. However, epidemiological studies have suggested that PFAS can induce cancers, toxic effects, and other health problems [3], [4]. Hence, PFAS have been listed as priority substances by several regulatory agencies and added as Persistent Organic Pollutants (POPs) by the Stockholm Convention.

Being a member state of the Stockholm Convention, Vietnam has restricted the usage of Perfluorooctanoic acid (PFOA) and Perfluorohexane sulfonic acid (PFHxS) in the industrial sector (Decree 82/2022/ND-CP). However, PFAS are until now not included in the national environmental quality standards and a deficit of PFAS research effort makes their occurrence in the Red River unknown. Therefore, the aim of this research is to apply a targeted approach (54 PFAS) along with the Total Oxidizable Precursor Assay (TOPA) in water samples collected in the Red River in June and September 2023 and estimate their flux towards the ocean. After the solid phase extraction on mixed mode Weak Anion Exchange cartridges, samples were analyzed by Ultra-High Performance Liquid Chromatography coupled with Mass Spectrometry Orbitrap Exploris^TM 120.

While twenty-one PFAS were detected in samples from June (from 3.0 to 109 ng.L^-1), it was only twelve for September samples (from < limit of quantification to 9.2 ng.L^-1). Perfluorobutanoic acid (PFBA) was the most predominant PFAS in samples from both sampling campaigns. An exception was reported in one sample in June where the 6:2-Fluorotelomersulfonic acid (6:2-FTS) concentration reached up to 99.9 ng.L^-1. The concentrations of PFOA and Perfluorooctane sulfonic acid (PFOS), the two most extensively targeted PFAS, were well below the European and American standard limits, contributing to less than 10% of the PFAS burden. Besides the legacy perfluoroalkyl acids (PFAAs), emerging PFAS analogs could also be quantified in water samples namely the fluorotelomer sulfonic acids and the ether sulfonic acids. The occurrence of emerging PFAS suggests they are being used as substitutes for the regulated PFOA and PFOS in industrial and commercial applications. TOPA consistently demonstrated significantly higher PFAS concentrations, up to one order of magnitude, implying the presence of non-targeted or unknown PFAS besides the 54 selected ones. Positive correlations (p < 0.05) between certain PFAAs and dissolved organic carbon (DOC) suggest either common sources for both DOC and PFAAs or the preferential binding of PFAAs to DOC. The estimated average riverine flux of PFAS varied from several kg to ton.yr^-1, depending on the flow variability and estimation approach (targeted or TOPA). 

References 

[1] Schmidt et al. (2019), doi: 10.1016/J.MARPOLBUL.2019.110491

[2] Evich et al. (2022), doi: 10.1126/science.abg9065

[3] Fenton et al. (2021), doi: 10.1002/ETC.4890

[4] Kim et al. (2021), doi: 10.1016/J.ENVPOL.2021.116929