Environ. Sci. Technol. 2010, 44, 5365–5370
Concentrations and Fate of Decamethylcyclopentasiloxane (D5) in the Atmosphere M I C H A E L S . M C L A C H L A N , * ,† AMELIE KIERKEGAARD,† KAJ M. HANSEN,‡ ROGER VAN EGMOND,§ JESPER H. CHRISTENSEN,‡ AND CARSTEN A. SKJØTH‡ Department of Applied Environmental Science, Stockholm University, SE 106 91 Stockholm, Sweden, Department of Atmospheric Environment, National Environmental Research Institute, Aarhus University, 4000 Roskilde, Denmark, and Safety and Environmental Assurance Centre, Unilever Colworth Laboratory, Sharnbrook, Bedfordshire MK44 1LQ, U.K.
Received February 5, 2010. Revised manuscript received June 2, 2010. Accepted June 4, 2010.
Decamethylcyclopentasiloxane (D5) is a volatile compound used in personal care products that is released to the atmosphere in large quantities. Although D5 is currently under consideration for regulation, there have been no field investigations of its atmospheric fate. We employed a recently developed, quality assured method to measure D5 concentration in ambient air at a rural site in Sweden. The samples were collected with daily resolution between January and June 2009. The D5 concentration ranged from 0.3 to 9 ng m-3, which is 1-3 orders of magnitude lower than previous reports. The measured data were compared with D5 concentrations predicted using an atmospheric circulation model that included both OH radical and D5 chemistry. The model was parametrized using emissions estimates and physical chemical properties determined in laboratory experiments. There was good agreement between the measured and modeled D5 concentrations. The results show that D5 is clearly subject to long-range atmospheric transport, but that it is also effectively removed from the atmosphere viaphototransformation.Atmosphericdepositionhaslittleinfluence on the atmospheric fate. The good agreement between the model predictions and the field observations indicates that there is a good understanding of the major factors governing D5 concentrations in the atmosphere.
Introduction Decamethylcyclopentasiloxane (D5, Figure S1 in the Supporting Information) is a large volume production chemical that is widely used as a solvent or carrier in personal care products. It is currently being subjected to regulatory scrutiny; in the EU there is an ongoing risk assessment that has proposed classifying it as a very persistent, very bioaccumulative (vPvB) substance (1). D5 is emitted primarily to the air, largely during personal care product use. It is a volatile chemical, and multimedia fate and transport models indicate that in the environment a significant portion will be present * Corresponding author e-mail:
[email protected]; tel: +46 8 674 7228. † Stockholm University. ‡ Aarhus University. § Unilever Colworth Laboratory. 10.1021/es100411w
2010 American Chemical Society
Published on Web 06/22/2010
in the atmosphere (1). Hence, atmospheric fate of D5 plays a key role in determining its environmental fate and potential risk. The current understanding of the atmospheric fate of D5 is based largely on laboratory studies and modeling investigations. There are very few measurements of D5 concentrations in the atmosphere at locations not directly impacted by sources, and the available data range widely, from
