Discussion Comment on ‘‘The environmental photolysis of perfluorooctanesulfonate, perfluorooctanoate, and related fluorochemicals’’ Zhanyun Wang a,⇑ , Ian T. Cousins b , Martin Scheringer a a Institute for Chemical and Bioengineering, ETH Zurich, CH-8093 Zurich, Switzerland b Department of Applied Environmental Science, Stockholm University, SE-10691 Stockholm, Sweden Previous studies have shown that perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkane sulfonic acids (PFSAs) are extremely persistent in the environment with almost no natural degradation pathways (as summarized in risk assessment profiles published by UNEP (2006) and ECHA (2013)), with the exception that PFCAs may react with OH radicals (Hurley et al., 2004). In con- tradiction to this understanding, Taniyasu et al. (2013) proposed that long-chain PFSA and PFCA homologues can undergo relatively rapid photodegradation and form shorter-chain homologues under natural conditions, based on findings from a combination of field and laboratory experiments. We have concerns about the strong conclusions drawn in the paper by Taniyasu et al. given the absence of essential experimen- tal details (notably the UV light spectrum used in the laboratory experiments), internal inconsistencies in the experimental results, and the lack of a mechanism for photolytic degradation. We be- lieve that the observations in the Taniyasu et al. study can be attributed to experimental artifacts. Our three main points of con- cern are outlined below. For a better illustration of our concerns and to help the readers understand them, we compiled the reported percentage reduction of PFSA and PFCA homologues from Taniyasu et al. after irradiation in the field and laboratory experiments in Table 1. [i] A plausible transformation mechanism is essential to understand the environmental relevance of their results, but is not provided (the authors stated, ‘‘Our study was not designed to address the mechanism of photolysis’’). When discussing the results of the field experiments, the authors concluded, ‘‘We be- lieve that both direct and indirect photolysis have played a role in the photolytic transformation of PFASs in this study’’. However, based on the following reasons, we believe that direct and indirect photolysis under natural light conditions should not have occurred for (at least) perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA). For the laboratory experiments, the authors did not report the light conditions used, particularly the UV light spectrum and, therefore, a rational judgment on the environmental relevance of these experiments cannot be made. Taniyasu et al. observed signif- icant losses of PFOS, PFOA and PFDA in the experiments using quartz glass tubes after a short time of irradiation (216 h), whereas no actual losses of these acids were observed in the experiments using Pyrex glass tubes after the same irradiation time (Table 1). Considering the lower wavelength cut-off for quartz glass (170 nm) compared to Pyrex glass (275 nm) (http://www2. chemistry.msu.edu/faculty/reusch/virttxtjml/photchem.htm), the photolysis of PFOS, PFOA and PFDA in the laboratory experiments with quartz glass was very likely induced by light with a wavelength between 170 and 275 nm, which is clearly in the UV- C range. This implication is supported by a further analysis that takes the settings of the field experiments into account. Regarding direct photolysis: The absorption spectrum of perflu- orooctanoic acid (PFOA) in water has been measured; PFOA shows strong absorption from the deep UV-region to 220 nm and a weak, broad absorption from 220 to 270 nm (Hori et al., 2004), which is below the natural light spectrum at the surface of the Earth (>280 nm). The experimental conditions in the Taniyasu et al. study were different from those in the Hori et al. study, but we do not believe that the addition of small amounts of methanol to the water would significantly change the UV absorption spectrum of PFOA. Adding organic solvents such as methanol may change the polarity of the solution and thus influence the spectra of the target compound (Kosower, 1958). However, the very low levels of meth- anol (<2%) in the solutions will have negligible influence on the polarity of the solutions used in Taniyasu et al. (Kosower, 1958). In addition, it is unlikely that adding less than 2% of methanol has any effect on the dissociation of PFOA (Sager et al., 1964). Therefore, the low levels of methanol (<2%) in the solutions are un- likely to have changed the absorption spectrum of PFOA compared to the spectrum that was measured in pure water (Hori et al., 2004). Regarding indirect photolysis: The UV cut-off of methanol is in the far UV region (<220 nm), i.e. methanol has no absorption of light with wavelengths above 220 nm (Cheng et al., 2002). There- fore, it is very unlikely that methanol, under the conditions used by Taniyasu et al. (wavelength above 280 nm, with reduced inten- sity of light from 280 to 315 nm due to Pyrex glass), absorbs and transfers energy to PFCA and PFSA homologues. [ii] Reported reductions of long-chain PFCAs and PFSAs after irradiation are not internally consistent between experiments (see Table 1). First, much lower degradation (or no degradation at all) of PFOS, PFOA and PFDA was observed in laboratory exper- iments using the same Pyrex tubes as in the field measurements, http://dx.doi.org/10.1016/j.chemosphere.2014.03.066 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +41 446334437. E-mail address: zhanyun.wang@chem.ethz.ch (Z. Wang). Chemosphere 122 (2015) 301–303 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere