Uptake and Biotransformation of the Tire Rubber-derived Contaminants 6‑PPD and 6‑PPD Quinone in the Zebrafish Embryo (Danio rerio)

N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD) is a
widely used antioxidant
in tire rubber known to enter the aquatic environment via road runoff.
The associated transformation product (TP) 6-PPD quinone (6-PPDQ)
causes extreme acute toxicity in some fish species (e.g., coho salmon).
To interpret the species-specific toxicity, information about biotransformation
products of 6-PPDQ would be relevant. This study investigated toxicokinetics
of 6-PPD and 6-PPDQ in the zebrafish embryo (ZFE) model. Over 96 h
of exposure, 6-PPD and 6-PPDQ accumulated in the ZFE with concentration
factors ranging from 140 to 2500 for 6-PPD and 70 to 220 for 6-PPDQ.
A total of 22 TPs of 6-PPD and 12 TPs of 6-PPDQ were tentatively identified
using liquid chromatography coupled to high-resolution mass spectrometry.
After 96 h of exposure to 6-PPD, the TPs of 6-PPD comprised 47% of
the total peak area (TPA), with 4-hydroxydiphenylamine being the most
prominent in the ZFE. Upon 6-PPDQ exposure, >95% of 6-PPDQ taken
up
in the ZFE was biotransformed, with 6-PPDQ + O + glucuronide dominating
(>80% of the TPA). Among other TPs of 6-PPD, a reactive N-phenyl-p-benzoquinone imine was found.
The knowledge
of TPs of 6-PPD and 6-PPDQ from this study may support biotransformation
studies in other organisms.