Effective photodegradation of perfluorooctane sulfonate (PFOS), an environmentally-ubiquitous persistent organic pollutant, in simple aqueous solution has been previously demonstrated. However, photocatalyst usually needs to be added and its application in complicated aquatic environment has not been reported so far. Here, we investigated the photodegradation of PFOS in environmental matrices, including municipal wastewater treatment plant (WWTP) effluent and lake water, and without adding any photocatalyst. A moderate PFOS degradation in the WWTP effluent and lake water was observed, with pseudo-first-order decomposition rate constants of 0.10 +/- 0.02 h(-1) and 0.16 +/- 0.01 h(-1) respectively. A further investigation using artificial water solution suggest that the weak alkaline pH and the presence of some dissolved organic matters (e.g., phenol and ammonia) might be important factor accounting for the efficient PFOS decomposition in environmental matrices, while humic acid and the relatively low ionic strength posed negative impacts. This study demonstrates the feasibility of eliminating PFOS pollution by photodegradation approach and may have implications for wastewater deep treatment and environmental remediation. (C) 2015 Elsevier B.V. All rights reserved.