Degradation of PFOA Substitute: GenX (HFPO-DA Ammonium Salt): Oxidation with UV/Persulfate or Reduction with UV/Sulfite?

Hexafluoropropylene oxide dimer acid (HFPO-DA, ammonium salt with trade name: GenX) has been recently detected in river water worldwide. There are significant concerns about its persistence, and potential adverse effects to the biota. In this study, the degradability of GenX by typical advanced redox technologies (UV/persulfate and UV/sulfate) is investigated. Results demonstrate that <5% GenX is oxidized after 3 h in UV/persulfate system, which is much lower than ∼27% for PFOA. In comparison, GenX can be readily degraded and defluorinated by hydrated electron (eaq-) generated by UV/sulfite system. Specifically, GenX is not detectable after 2 h, and >90% of fluoride ion is recovered 6 h later. This is attributed to the accumulation and subsequent degradation of CF3CF2COOH and CF3COOH, which are stable intermediates of GenX degradation. Mechanistic investigations suggest that the etheric bond in the molecule is a favorable attack point for the eaq-. Such finding is corroborated by quantum chemical calculations. The side CF3- at the α-carbon probably acts as an effective barrier that prevents GenX from being cleaved by SO4-• or OH• at its most sensible point (i.e. the carboxyl group). This study illustrates that reduction by UV/sulfite might be a promising technology to remove GenX from contaminated water.

Seasonal and spatial variations of pharmaceuticals and personal care products occurrence and human health risk in drinking water - A case study of China.

A case study was implemented to investigate the seasonal and spatial variations of 43 kinds of pharmaceuticals and personal care products (PPCPs) in the water supply system of Changzhou in China. The source water, water samples in each unit along the drinking water treatment process, as well as the drinking water product in both urban and rural area in different seasons have been included. The total concentrations of detected PPCPs range from 6.37 ng/L to 809.28 ng/L, the level of which is higher than other reports in China. In summer, more kinds of PPCPs were at higher concentrations in drinking water in urban area in spite of that fewer kinds of PPCPs were detected in raw water than in winter. It mainly because some kinds of PPCPs, which can be still detected under higher temperature and stronger irradiation in summer, were hardly removed by the drinking water treatment plant (DWTP). Therefore, people are at relatively higher health risk by PPCPs exposure through the intake of drinking water during summer than winter. The advanced treatment which applied GAC (granular activated carbon) filtration improved 2% to 46% of removal efficiency on PPCPs compared with conventional process, for which advanced treatment processes should be advocated in more DWTPs in China. In rural private wells, the situation is more worrying. Twelve more kinds of PPCPs were detected in rural drinking water than in urban, of which the max concentration reached 107 ng/L. The total concentrations of PPCPs in drinking water in rural area were obviously higher than in urban area, which lead to risk quotient (RQ) values of 4-6 times higher.