Unexpectedly high concentrations of 2,4-di-tert-butylphenol in human urine

Synthetic phenolic antioxidants (SPAs) have received increasing attention due to the reports of toxicity and environmental contamination. Nevertheless, limited information was available on human burdens of these SPAs, with the exception of 2,6-di-tert-butyl-4-methylphenol (BHT). In our study, BHT as well as six other SPAs were analyzed in human urine samples from United States donors. Three SPA congeners were detected in human urine: BHT, 2,4-di-tert-butylphenol (DBP), and 3-tert-butyl-4-hydroxyanisole (BHA). BHT, which is the congener received most concerns, was detected at low concentrations [geometric mean (GM): 0.06 ng/mL], whereas four of its metabolites were detected at relatively high concentrations (GM: 1.68 ng/mL). Surprisingly, DBP was detected at extremely high concentrations (GM: 18.3 ng/mL). The concentrations of DBP (GM: 25.8 ng/mL), BHT (0.853 ng/mL), and metabolites (GM: 10.5 ng/mL) increased significantly after the urine samples were hydrolyzed by β-glucuronidase (p < 0.01), indicating the prevalence of the conjugated forms of SPAs and their metabolites in human urine. DBP, which has previously received little attention, was the predominant congener, contributing 88.2% and 63.6% to total target concentrations in the urine samples before and after β-glucuronidase hydrolysis, respectively. Thus, previous studies have vastly underestimated the burdens of SPAs to humans. To our knowledge, this is the first study revealing the presence of DBP in human urine.