Determination of per- and polyfluorinated alkyl substances (PFAS) in municipal wastewater in Vietnam

Abstract

Per- and polyfluorinated alkyl substances (PFAS) are well-known for their unique characteristics. PFAS are extremely chemically and thermally stable in the environment, making them resistant to any natural processes. With current wastewater treatment design, PFAS have not been removed properly from wastewater and released into the environment at an alarming level. That could cause potential risks to human health, plants, and ecosystem. This study was performed to investigate the PFAS concentrations in wastewater from three WWTPs in Southern Vietnam. PFHxA, PFOA, PFBS and PFOS were four targeted compounds. The analysis was done using solid phase extraction (SPE) method and LC MS/MS instrument. The results showed high recovery percentages (70%< %R <150%) including acceptable relative standard deviations (<30%). Four interest PFAS substances were detected in all samples from three WWTPs over four sampling days in a week. The highest median concentrations in influent and effluent were detected in WWTP2 at 14.74 3 ng/L and 14.16 ng/L, respectively. WWTP3 had the median concentration of total PFAS at 9.26 ng/L in the influent and 7.76 ng/L in the effluent. Long-chain compounds (PFOA+PFOS) were identified as dominant constituents at these two facilities. Even though PFOA and PFOS have been restricted, they are not totally phased out yet. Meanwhile, in WWTP1, the median concentration of four PFAS in influent and effluent were 5.68 ng/L and 7.99 ng/L, respectively with short-chain compounds (PFBS+PFHxA) as dominant compositions. The removal/degradation rates varied differently among three plants. The effluent concentration of PFAS in WWTP1 increased notably after chlorination while the PFAS loads in effluent from WWTP3 were slightly reduced by UV radiation. At WWTP2, the PFAS was rarely removed by the aeration ponds and lagoons. It was observed that higher PFAS concentrations were detected during the weekend when people stay at home more than weekdays. Compared to EPA and ECHA advisory limits and the levels detected in some studies around the world, PFAS concentrations in municipal wastewater in Vietnam were at very low levels. It is recommended that longer studies of PFAS in sludge and during treatment process should be done to understand the variations over time as well as the impact of wastewater treatment technologies on PFAS transformation.