Toxicology 210 (2005) 123–133 Urinary metabolites of di-n-octyl phthalate in rats Manori J. Silva a, ∗ , Kayoko Kato a , Earl L. Gray b , Cynthia Wolf b , Larry L. Needham a , Antonia M. Calafat a a Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Mailstop F17, 4770 Buford Hwy NE, Atlanta, GA 30341, USA b Reproductive Toxicology Division, Endocrinology Branch, National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27705, USA Received 29 October 2004; received in revised form 20 January 2005; accepted 21 January 2005 Available online 24 February 2005 Abstract Di-n-octyl phthalate (DnOP) is a plasticizer used in polyvinyl chloride plastics, cellulose esters, and polystyrene resins. The metabolism of DnOP results in the hydrolysis of one ester linkage to produce mono-n-octyl phthalate (MnOP), which subsequently metabolizes to form oxidative metabolites. We investigated the toxicokinetics of DnOP in adult female Sprague–Dawley rats by monitoring the excretion of DnOP metabolites in urine after oral administration of DnOP (300 mg/kg). By using authentic standards, the presence of urinary phthalic acid (PA), MnOP, and the major DnOP metabolite, mono-(3-carboxypropyl) phthalate (MCPP) was clearly established. Furthermore, we identified five additional urinary DnOP oxidative metabolites based on their chromatographic behavior and mass spectrometric fragmentation pattern. These DnOP oxidative metabolites, are postulated to be mono-carboxymethyl phthalate (MCMP), mono-(5-carboxy-n-pentyl) phthalate (MCPeP), mono-(7-carboxy-n-heptyl) phthalate (MCHpP), and isomers of mono-hydroxy-n-octyl phthalate (MHOP) (e.g., mono-(7-hydroxy-n-octyl) phthalate) and of mono-oxo-n-octyl phthalate (MOOP) (e.g., mono-(7-oxo-n-octyl) phthalate). The urinary excretion of DnOP metabolites followed a biphasic excretion pattern. The metabolite levels decreased significantly after the first day of DnOP administration although MCPP, MCHpP, MHOP, and MOOP were detectable after 4 days. We also studied the in vitro metabolism of DnOP and MnOP by rat liver microsomes. DnOP produced MnOP, MHOP, and PA in vitro whereas, MnOP produced MHOP and PA in vitro at detectable levels. Published by Elsevier Ireland Ltd. Keywords: Di-n-octyl phthalate; Mono-n-octyl phthalate; Mono-3-carboxypropyl phthalate; Mono-(7-carboxy-n-heptyl) phthalate; Mono-(7- hydroxy-n-octyl) phthalate; Mono-(7-oxo-n-octyl) phthalate; Oxidative metabolism; Phthalates ∗ Corresponding author. Tel.: +1 770 488 7982; fax: +1 770 488 4609. E-mail address: zca2@cdc.gov (M.J. Silva). 1. Introduction Di-n-octyl phthalate (DnOP) is a plasticizer used in polyvinyl chloride plastics, and cellulose ester and polystyrene resins found in products such as carpet- 0300-483X/$ – see front matter. Published by Elsevier Ireland Ltd. doi:10.1016/j.tox.2005.01.012