BDE-209: Kinetic Studies and Effect of Humic Substances on Photodegradation in Water J. F. Leal, V. I. Esteves, and E. B. H. Santos* Department of Chemistry and CESAM, Centre for Environmental and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal * S Supporting Information ABSTRACT: BDE-209 is a brominated flame retardant and a priority contaminant, which has been found in several environmental matrices, namely, in water. To date, there are no quantum yield data for BDE-209 photodegradation by sunlight in water, to allow predicting half-life times in aquatic systems. In this work, the kinetics of BDE-209 photo- degradation in water was studied and the influence of different fractions of aquatic humic substances (HS) was evaluated. Aqueous solutions of BDE-209 exposed for different periods of time to simulated sunlight were analyzed by HPLC−UV after being concentrated using dispersive liquid−liquid micro- extraction (DLLME) or solid-phase extraction (SPE). The photodegradation of BDE-209 in aqueous solution followed pseudo-first-order kinetics. The average quantum yield obtained of 0.010 ± 0.001 (about 20-fold lower than the quantum yield determined in ethanol) allow to predict an outdoor half-life time of 3.5 h. The photodegradation percentage of BDE-209 was not significantly affected by the XAD-4 fraction of HS, but it decreased substantially in the presence of humic and fulvic acids. Light screening by the humic substances could not explain this delay, which is probably the result of the association of the compound with the hydrophobic sites of the humic material. ■ INTRODUCTION Flame retardants (FR) are chemicals added to combustible materials, such as plastics, textiles, and wood, to improve the resistance to fire by chemical or physical mechanisms. 1 There are two types of FR: reactive FR added during the polymerization process, becoming an integral part of the polymer, and additive FR, which are not covalently bound to the polymers. 2 Polybrominated diphenyl ethers (PBDEs) are additive flame retardants 3 easily blended and showing a great tendency for leaching compared to the reactive FR. 4 Bis(pentabromophenyl) ether (IUPAC name) is also known as 2,2′,3,3′,4,4′,5,5′,6,6′-decabromodiphenyl ether, decaBDE, BDE-209, or decabromodiphenyl oxide, it is the most brominated flame retardant, it stands out among the brominated FR for its wide commercial use and it has been recently considered a priority contaminant. 5 BDE-209 has been found in air, water, soil, and sediments, and there is a recent evidence of its presence in remote sites such as Canadian Lakes, North Pacific Ocean and Arctic. 6,7 Despite the low levels found in surface waters, 8,9 studies of BDE-209 in aquatic environ- ments are fully justified due to the bioaccumulation character- istics of this compound which were confirmed by several studies that refer significant levels of BDE-209 in organisms of aquatic origin, for instance fish or freshwater birds. 10,11 Furthermore, the toxicity associated with long-term chronic exposure to low doses of BDE-209 in solution (from 0.959 μg/ L) was demonstrated for zebra fish (vertebrate model organism). 12 Photodegradation of the environmental pollutants is especially relevant as a degradation pathway in surface water exposed to sunlight. Although the aerobic microbial decom- position of BDE-209 is also possible, this pathway is slow and inefficient whereas the photodegradation by sunlight may be the major pathway of BDE-209 decomposition in aerobic surface waters. 13,14 The photodegradation of BDE-209 has been studied in organic solvents and under distinct irradiation conditions. It is known that the photodegradation can occur through a sequential debromination of the compound, 15−17 giving rise to byproducts which are more toxic than the parent compound. 18 To our knowledge, to date, there are no data in the literature for the BDE-209 photodegradation quantum yield in aqueous solution. Those data are essential to predict half-life times in surface waters. Kuivikko et al. 14 predicted the photolytic half-life times in the mixing layer of the Baltic Sea and of the Atlantic Ocean using the photolytic quantum yield of BDE-209 in isooctane. However, it is known that the solvent can have a strong effect on the degradation kinetics. Received: April 17, 2013 Revised: November 18, 2013 Accepted: November 18, 2013 Published: November 18, 2013 Article pubs.acs.org/est © 2013 American Chemical Society 14010 dx.doi.org/10.1021/es4035254 | Environ. Sci. Technol. 2013, 47, 14010−14017