Photodegradation of perfluorooctane sulfonate by UV irradiation in water and alkaline 2-propanol.

Perfluorooctane sulfonate (PFOS) is the environmentally concerned compound because of its persistence and bioaccumulative properties. Since photodegradation of PFOS is not yet experimentally confirmed, photodegradation study of PFOS in water and alkaline 2-propanol solution was conducted. Aqueous and alkaline 2-propanol solution of PFOS (40 microM) was irradiated with a low-pressure mercury lamp (254 nm, 32 W) by internal irradiation for 10 d, and then PFOS, fluoride and sulfate ions, and the other degradation products were analyzed. Photodegradation of PFOS was confirmed in both media. PFOS was degraded by 8% after 1 day and by 68% after 10 days irradiation compared to the initial concentration in water. In alkaline 2-propanol, 76 and 92% of PFOS was degraded after 1 and 10 days irradiation, respectively. Photodegradation of PFOS in alkaline 2-propanol was much faster and effective than in water, as the photodegradation rate constants were 0.93 days(-1) in alkaline 2-propanol and 0.13 days(-1) in water, respectively. Formation of fluoride and sulfate was also confirmed by ion chromatography and X-ray diffraction analysis. From observation of the degradation products, two major degradation pathways of PFOS were considered: via C8HF17 and C8F17OH, respectively, resulting in short-chain fluorinated compounds such as C7HF15 and C7F15OH by stepwise removal of CF2. Formation of short-chain fluorocarbons such as CF4, C2F6, and C3F8 were also confirmed. This is the first study to confirm photodegradation of PFOS in water and alkaline 2-propanol.