Comment on “Unexpected Occurrence of Volatile Dimethylsiloxanes in

NILU-Norwegian Institute for Air Research, Fram Centre, P.O. Box 6606 Langnes, NO-9296 Tromsø Norway. ‡ Department of Geography, University of Leic...
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Comment on “Unexpected Occurrence of Volatile Dimethylsiloxanes in Antarctic Soils, Vegetation, Phytoplankton, and Krill” anchiś et al. (2015)1 recently reported the occurrence of volatile methyl siloxanes (VMS) in soil, vegetation, phytoplankton, and krill samples from Antarctica. As the paper’s title suggests, findings of these chemicals in such a remote region is unexpected and of significant concern. However, our experience with the analysis of these compounds at trace concentrations suggests that the observations reported may have been influenced by artifacts. Here we present our concerns based upon known emissions, physicochemical properties and on apparent quality control measures including treatment of blank samples and detection limits. Cyclic and linear VMS (cVMS and lVMS) are extensively used in personal care products and industrial applications. They display unique properties of high hydrophobicity and high volatility2 and readily volatilize, resulting in significant emissions to the atmosphere with low theoretical potential for surface deposition, even in polar areas.3,4 The dominant atmospheric removal mechanism is reaction with OH radicals5,6 to form silanols, which are then subjected to wet deposition.7 The low deposition potential of VMS themselves is supported by studies reporting concentrations below or close to detection limits in biota in Arctic fjords and Swedish lakes not receiving wastewater inputs, a known source of VMS.8,9 Sanchiś et al. (2015)1 postulate snow scavenging as a feasible mechanism for contamination of surface media in Antarctica. Unfortunately, no concentrations of VMS in Antarctic air or snow have been measured. Given the lower population and associated emissions of VMS in the southern hemisphere compared to the northern hemisphere, as well as interhemispheric exchange times well in excess of atmospheric half-lives for VMS,10 concentrations of VMS in Antarctic air are expected to be lower than in Sweden (0.3−9 ng/m3 for D511) and the Arctic ( D6> D4),25−27 which are normally mirrored in environmental samples from northern latitudes.9,13,28−31 For instance, the VMS congener profiles in the Antarctic soil samples vary greatly (Table S5a1), while one would expect these to be relatively similar if they were influenced by the same atmospheric transport and snow scavenging mechanisms. The fact that D4 displayed comparable concentrations to D5 and D6 in phytoplankton and was the dominant oligomer in >60% of krill samples is perplexing considering that its hydrolysis is significantly faster than that of D5 and D6.25−27 In previous studies, reported concentrations of D4 in zooplankton, invertebrates, and small fish have been below detection limits and/or at lower concentrations than D5 and D6.9,13,28−31 Any contamination of the Antarctic environment by synthetic organic pollutants is cause for concern, and we give credit to the authors for attempting to measure such a difficult group of compounds in such a remote region. However, we believe that the data should be interpreted with caution because of the significant difficulties posed by the analysis of trace concentrations of VMS in environmental matrices. We argue here that the concentrations reported may reflect variations in

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DOI: 10.1021/acs.est.5b01612 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

Environmental Science & Technology

Correspondence/Rebuttal

(12) Krogseth, I. S.; Kierkegaard, A.; McLachlan, M. S.; Breivik, K.; Hansen, K. M.; Schlabach, M. Occurrence and seasonality of cyclic volatile methyl siloxanes in Arctic air. Environ. Sci. Technol. 2013, 47 (1), 502−509. (13) Warner, N. A.; Nøst, T. H.; Andrade, H.; Christensen, G. Allometric relationships to liver tissue concentrations of cyclic volatile methyl siloxanes in Atlantic cod. Environ. Pollut. 2014, 190 (0), 109− 114. (14) Horii, Y.; Kannan, K. Survey of organosilicone compounds, including cyclic and linear siloxanes, in personal-care and household products. Arch. Environ. Contam. Toxicol. 2008, 55 (4), 701−710. (15) Kierkegaard, A.; McLachlan, M. S. Determination of decamethylcyclopentasiloxane in air using commercial solid phase extraction cartridges. J. Chromatogr. A 2010, 1217 (21), 3557−3560. (16) Pieri, F.; Katsoyiannis, A.; Martellini, T.; Hughes, D.; Jones, K. C.; Cincinelli, A. Occurrence of linear and cyclic volatile methyl siloxanes in indoor air samples (UK and Italy) and their isotopic characterization. Environ. Int. 2013, 59 (0), 363−371. (17) Varaprath, S.; Stutts, D.; Kozerski, G. A primer on the analytical aspects of silicones at trace levelsChallenges and artifactsA review. Silicon Chem. 2006, 3 (1−2), 79−102. (18) Kierkegaard, A.; Adolfsson-Erici, M.; McLachlan, M. S. Determination of cyclic volatile methylsiloxanes in biota with a purge and trap method. Anal. Chem. 2010, 82 (22), 9573−9578. (19) Sparham, C.; van Egmond, R.; Hastie, C.; O’Connor, S.; Gore, D.; Chowdhury, N. Determination of decamethylcyclopentasiloxane in river and estuarine sediments in the UK. J. Chromatogr. A 2011, 1218 (6), 817−823. (20) Sparham, C.; Van Egmond, R.; O’Connor, S.; Hastie, C.; Whelan, M.; Kanda, R.; Franklin, O. Determination of decamethylcyclopentasiloxane in river water and final effluent by headspace gas chromatography/mass spectrometry. J. Chromatogr. A 2008, 1212 (1− 2), 124−129. (21) Warner, N. A.; Kozerski, G.; Durham, J.; Koerner, M.; Gerhards, R.; Campbell, R.; McNett, D. A. Positive vs. false detection: A comparison of analytical methods and performance for analysis of cyclic volatile methylsiloxanes (cVMS) in environmental samples from remote regions. Chemosphere 2013, 93 (5), 749−756. (22) Glaser, J. A.; Foerst, D. L.; McKee, G. D.; Quave, S. A.; Budde, W. L. Trace analyses for wastewaters. Environ. Sci. Technol. 1981, 15 (12), 1426−1435. (23) Companioni-Damas, E. Y.; Santos, F. J.; Galceran, M. T. Analysis of linear and cyclic methylsiloxanes in sewage sludges and urban soils by concurrent solvent recondensation − large volume injection − gas chromatography−mass spectrometry. J. Chromatogr. A 2012, 1268 (0), 150−156. (24) Sanchez-Brunete, C.; Miguel, E.; Albero, B.; Tadeo, J. L. Determination of cyclic and linear siloxanes in soil samples by ultrasonic-assisted extraction and gas chromatography-mass spectrometry. J. Chromatogr. A 2010, 1217 (45), 7024−7030. (25) Brooke, D. N.; Crookes, M. J.; Gray, D.; Robertson, S. Environmental Risk Assessment Report: Dodecamethylcyclohexasiloxane; Environment Agency of England and Wales, Bristol, UK., 2009. (26) Brooke, D. N.; Crookes, M. J.; Gray, D.; Robertson, S. Environmental Risk Assessment Report: Octamethylcyclotetrasiloxane; Environment Agency of England and Wales, Bristol, UK., 2009. (27) Brooke, D. N.; Crookes, M. J.; Gray, D.; Robertson, S. Environmental Risk Assessment Report: Decamethylcyclopentasiloxane; Environment Agency of England and Wales: Bristol, UK., 2009. (28) Borgå, K.; Fjeld, E.; Kierkegaard, A.; McLachlan, M. S. Food web accumulation of cyclic siloxanes in Lake Mjøsa, Norway. Environ. Sci. Technol. 2012, 46 (11), 6347−6354. (29) Borgå, K.; Fjeld, E.; Kierkegaard, A.; McLachlan, M. S. Consistency in trophic magnification factors of cyclic methyl siloxanes in pelagic freshwater food webs leading to brown trout. Environ. Sci. Technol. 2013, 47 (24), 14394−14402. (30) Kierkegaard, A.; Bignert, A.; McLachlan, M. S. Cyclic volatile methylsiloxanes in fish from the Baltic Sea. Chemosphere 2013, 93 (5), 774−778.

background contamination owing to inadequate quality control and sample handling procedures. Re-evaluation of the data would be prudent to avoid potential misinterpretations of the environmental occurrence and behavior of VMS.

Nicholas A. Warner*,† Ingjerd S. Krogseth† Mick J. Whelan‡ †

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NILU-Norwegian Institute for Air Research, Fram Centre, P.O. Box 6606 Langnes, NO-9296 Tromsø Norway ‡ Department of Geography, University of Leicester, University Road, Leicester, LE17RH, United Kingdom

AUTHOR INFORMATION

Corresponding Author

*Phone: (+47) 777 503 88; fax: (+47) 777 503 76; e-mail: [email protected]. Author Contributions †‡

The manuscript was written through contributions from all authors. All authors have given approval to the final version of the manuscript.

Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Sanchís, J.; Cabrerizo, A.; Galban, C.; Barcelo, D.; Farré, M.; Dachs, J., Unexpected occurrence of volatile dimethylsiloxanes in Antarctic soils, vegetation, phytoplankton and krill. Environ. Sci. Technol. 2015. DOI: 10.1021/es503697t. (2) Wang, D. G.; Norwood, W.; Alaee, M.; Byer, J. D.; Brimble, S. Review of recent advances in research on the toxicity, detection, occurrence and fate of cyclic volatile methyl siloxanes in the environment. Chemosphere 2013, 93 (5), 711−725. (3) Wania, F. Assessing the potential of persistent organic chemicals for long-range transport and accumulation in polar regions. Environ. Sci. Technol. 2003, 37 (7), 1344−1351. (4) Xu, S.; Wania, F. Chemical fate, latitudinal distribution and longrange transport of cyclic volatile methylsiloxanes in the global environment: A modeling assessment. Chemosphere 2013, 93 (5), 835−843. (5) Atkinson, R. Kinetics of the gas-phase reactions of a series of organosilicon compounds with OH and NO3 radicals and O3 at 297 ± 2K. Environ. Sci. Technol. 1991, 25 (5), 863−866. (6) Markgraf, S. J.; Wells, J. R. The hydroxyl radical reaction rate constants and atmospheric reaction products of three siloxanes. Int. J. Chem. Kinet. 1997, 29 (6), 445−451. (7) Whelan, M. J.; Estrada, E.; van Egmond, R. A modelling assessment of the atmospheric fate of volatile methyl siloxanes and their reaction products. Chemosphere 2004, 57 (10), 1427−1437. (8) Kierkegaard, A.; Bignert, A.; McLachlan, M. S. Bioaccumulation of decamethylcyclopentasiloxane in perch in Swedish lakes. Chemosphere 2013, 93 (5), 789−793. (9) Warner, N. A.; Evenset, A.; Christensen, G.; Gabrielsen, G. W.; Borga, K.; Leknes, H. Volatile siloxanes in the European Arctic: Assessment of sources and spatial distribution. Environ. Sci. Technol. 2010, 44 (19), 7705−7710. (10) Geller, L. S.; Elkins, J. W.; Lobert, J. M.; Clarke, A. D.; Hurst, D. F.; Butler, J. H.; Myers, R. C. Tropospheric SF6: Observed latitudinal distribution and trends, derived emissions and interhemispheric exchange time. Geophys. Res. Lett. 1997, 24 (6), 675−678. (11) McLachlan, M. S.; Kierkegaard, A.; Hansen, K. M.; van Egmond, R.; Christensen, J. H.; Skjøth, C. A. Concentrations and fate of decamethylcyclopentasiloxane (D5) in the Atmosphere. Environ. Sci. Technol. 2010, 44 (14), 5365−5370. B

DOI: 10.1021/acs.est.5b01612 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

Environmental Science & Technology

Correspondence/Rebuttal

(31) Kierkegaard, A.; van Egmond, R.; McLachlan, M. S. Cyclic volatile methylsiloxane bioaccumulation in flounder and ragworm in the Humber Estuary. Environ. Sci. Technol. 2011, 45 (14), 5936−5942.

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DOI: 10.1021/acs.est.5b01612 Environ. Sci. Technol. XXXX, XXX, XXX−XXX