First Report on the Occurrence of <i>N</i>-(1,3-Dimethylbutyl)-<i>N</i>′-phenyl-<i>p</i>-phenylenediamine (6PPD) and 6PPD-Quinone as Pervasive Pollutants in Human Urine from South China

N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and its quinone derivative, 6PPD-quinone (6PPD-Q), have been found to be prevalent in the environment, but there are currently no data on their presence in humans. Herein, we conducted the first human biomonitoring study of 6PPD and 6PPD-Q by measuring 150 urine samples collected from three different populations (general adults, children, and pregnant women) in South China. Both 6PPD and 6PPD-Q were detected in the urine samples, with detection frequencies between 60% and 100%. Urinary 6PPD-Q concentrations were significantly higher than those of 6PPD and correlated well with those of 6PPD (p < 0.01), indicating coexposure to 6PPD and 6PPD-Q in humans. In vitro metabolic experiments demonstrated rapid depletion of 6PPD by human liver microsomes, which should be responsible for the lower concentrations of 6PPD in human urine. Additionally, pregnant women exhibited apparently higher concentrations of 6PPD and 6PPD-Q (median 0.068 and 2.91 ng/mL, respectively) than did adults (0.018 and 0.40 ng/mL) and children (0.015 and 0.076 ng/mL). The high daily urinary excretion of 6PPD-Q in pregnant women was estimated to be 273 (ng/kg bw)/day. Considering that 6PPD-Q was a lethal toxicant to multiple aquatic species, the potential human health risks posed by its long-term exposure require urgent attention.