jesc.ac.cn Journal of Environmental Sciences 21(2009) 285–290 Abiotic degradation of four phthalic acid esters in aqueous phase under natural sunlight irradiation Ruttapol Lertsirisopon, Satoshi Soda, Kazunari Sei, Michihiko Ike ∗ Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Osaka, Japan. E-mail: ike@see.eng.osaka-u.ac.jp Received 24 April 2008; revised 02 June 2008; accepted 17 June 2008 Abstract Abiotic degradability of four phthalic acid esters (PAEs) in the aquatic phase was evaluated over a wide pH range 5–9. The PAE solutions in glass test tubes were placed either in the dark and under the natural sunlight irradiation for evaluating the degradation rate via hydrolysis or photolysis plus hydrolysis, respectively, at ambient temperature for 140 d from autumn to winter in Osaka, Japan. The efficiency of abiotic degradation of the PAEs with relatively short alkyl chains, such as butylbenzyl phthalate (BBP) and di-n- butyl phthalate (DBP), at neutral pH was significantly lower than that in the acidic or alkaline condition. Photolysis was considered to contribute mainly to the total abiotic degradation at all pH. Neither hydrolysis nor photolysis of di-ethylhexyl phthalate (DEHP) proceeded significantly at any pH, especially hydrolysis at neutral pH was negligible. On the other hand, the degradation rate of di- isononyl phthalate (DINP) catalyzed mainly by photolysis was much higher than those of the other PAEs, and was almost completely removed during the experimental period at pH 5 and 9. As a whole, according to the half-life (t 1/2 ) obtained in the experiments, the abiotic degradability of the PAEs was in the sequence: DINP (32–140 d) > DBP (50–360 d), BBP (58–480 d) > DEHP (390–1600 d) under sunlight irradiation (via photolysis plus hydrolysis). Although the abiotic degradation rates for BBP, DBP, and DEHP are much lower than the biodegradation rates reported, the photolysis rate for DINP is comparable to its biodegradation rate in the acidic or alkaline condition. Key words: phthalic acid esters; abiotic degradation; photolysis; hydrolysis; first-order kinetics DOI: 10.1016/S1001-0742(08)62265-2 Introduction In recent years, considerable attention has been paid to toxicity and degradability of phthalic acid esters (PAEs) (Staples et al., 1997), which have been frequently de- tected throughout aquatic environment (Fromme et al., 2002; Yuan et al., 2002). PAEs undergoing hydrolysis, photolysis, and aerobic/anaerobic biodegradation could be removed from aquatic environment. Among those different degradation processes, relatively abundant data are avail- able on biodegradation of PAEs (Chang et al., 2007; Li et al., 2005; Yuan et al., 2002; Wang et al., 1996, 2000). On the other hand, limited information has been known on the abiotic processes (hydrolysis and photolysis). There are several researchers who have focused on photolysis of PAEs using artificial irradiation sources, such as xenon arc lamps (Bajt et al., 2001), mercury lamps (Mailhot et al., 2002), and ultraviolet light (Lau et al., 2005), to clean up the PAEs-contaminated water. However, those irradi- ation sources had very different radiation intensities and wavelength distributions from natural sunlight irradiation. As a rare study for describing the abiotic degradation of * Corresponding author. E-mail: ike@see.eng.osaka-u.ac.jp PAEs under natural aquatic environment, Gledhill et al. (1980) have reported that butylbenzyl phthalate (BBP) exposing to sunlight irradiation for 28 d resulted in less than 5% degradation, but limited information is available to date. Wolfe et al. (1980) inferred that according to a mathematical model data the photolysis is the primary degradation process of PAEs in oligotrophic lakes. For better understanding of the fate of PAEs in aquatic envi- ronment, there is a need to conduct more realistic studies on abiotic degradation with natural solar intensity. The aim of this study was to assess the contribution of abiotic degradation of PAEs under the sunlight irra- diation at ambient temperature over a wide pH range that normally found in natural aquatic environments. Four commercial PAEs (BBP, di-n-butyl phthalate (DBP), di- ethylhexyl phthalate (DEHP), and di-isononyl phthalate (DINP)), were subjected to the abiotic degradation tests, and the half-lives of the PAEs by hydrolysis and photolysis were estimated by the first-order degradation kinetics. The role of abiotic degradation in the fate of the PAEs was discussed by comparing the estimated half-lives with those by aerobic/anaerobic biodegradation reported previously.